![NP 19 Future of the Brain [호환 모드] - khu.ac.kr](https://static.fdocuments.net/doc/165x107/6249c9f1dd91534fe20dc62f/np-19-future-of-the-brain-khuackr.jpg)
PHY and DLL Doug Young Suh [email protected] Last update : Aug 1, 2009 PHY MAC.
36
-
Upload
johnathan-conley -
Category
Documents
-
view
217 -
download
0
Transcript of PHY and DLL Doug Young Suh [email protected] Last update : Aug 1, 2009 PHY MAC.
PHY and DLL
Doug Young Suhsuhkhuackr
Last update Aug 1 2009
PHY MAC
PHY (Physical Layer)
Analog bandwidth W[Hz]digital [bps]Nyquist theorem with V levelssample
maximum data rate = 2W log2 V bitssec
Shannonrsquos theorem in noisy channel
maximum data rate = W log2 (1+SN) bitssec
ex) W=3kHz SN=30dB 30kbps
PHY MAC
Nyquist Criterion
A theoretically sufficient condition to allow an analog signal to be reconstructed completely from a set of uniformly spaced discrete-time samplesNyquist rate
Speech 8kHz sampling gt 2 X 32kHz Audio 441kHz sampling gt 2 X 20kHz
mS ff 2
Sampling (Cont)
Sampling (Cont)
2sf W
2sf W
2sf W
Aliasing
Spectrum
Symbol rate fs = 1Ts where Ts = symbol duration
ex) Binary 1Mbps fs = 106Hz Ts = 10-6sec
Spectrum with main lobe = 2fs
PHY MAC
0 fs 2fs
Fourier transform
===
-2fs -fs
Main lobe
side lobe-1 -1 1 -11 -11 -1 1 -11 -1 1
Ts
Quantization
L-level quantizer consists of L codewordsA codeword of L-level quantizer is represented by B-bit binary digits
Quantization error Δ = dynamic range2Lfs symbolssec Bfs bitssec = R [bps]
symbolbitsLLogB 2
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
PHY (Physical Layer)
Analog bandwidth W[Hz]digital [bps]Nyquist theorem with V levelssample
maximum data rate = 2W log2 V bitssec
Shannonrsquos theorem in noisy channel
maximum data rate = W log2 (1+SN) bitssec
ex) W=3kHz SN=30dB 30kbps
PHY MAC
Nyquist Criterion
A theoretically sufficient condition to allow an analog signal to be reconstructed completely from a set of uniformly spaced discrete-time samplesNyquist rate
Speech 8kHz sampling gt 2 X 32kHz Audio 441kHz sampling gt 2 X 20kHz
mS ff 2
Sampling (Cont)
Sampling (Cont)
2sf W
2sf W
2sf W
Aliasing
Spectrum
Symbol rate fs = 1Ts where Ts = symbol duration
ex) Binary 1Mbps fs = 106Hz Ts = 10-6sec
Spectrum with main lobe = 2fs
PHY MAC
0 fs 2fs
Fourier transform
===
-2fs -fs
Main lobe
side lobe-1 -1 1 -11 -11 -1 1 -11 -1 1
Ts
Quantization
L-level quantizer consists of L codewordsA codeword of L-level quantizer is represented by B-bit binary digits
Quantization error Δ = dynamic range2Lfs symbolssec Bfs bitssec = R [bps]
symbolbitsLLogB 2
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Nyquist Criterion
A theoretically sufficient condition to allow an analog signal to be reconstructed completely from a set of uniformly spaced discrete-time samplesNyquist rate
Speech 8kHz sampling gt 2 X 32kHz Audio 441kHz sampling gt 2 X 20kHz
mS ff 2
Sampling (Cont)
Sampling (Cont)
2sf W
2sf W
2sf W
Aliasing
Spectrum
Symbol rate fs = 1Ts where Ts = symbol duration
ex) Binary 1Mbps fs = 106Hz Ts = 10-6sec
Spectrum with main lobe = 2fs
PHY MAC
0 fs 2fs
Fourier transform
===
-2fs -fs
Main lobe
side lobe-1 -1 1 -11 -11 -1 1 -11 -1 1
Ts
Quantization
L-level quantizer consists of L codewordsA codeword of L-level quantizer is represented by B-bit binary digits
Quantization error Δ = dynamic range2Lfs symbolssec Bfs bitssec = R [bps]
symbolbitsLLogB 2
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Sampling (Cont)
Sampling (Cont)
2sf W
2sf W
2sf W
Aliasing
Spectrum
Symbol rate fs = 1Ts where Ts = symbol duration
ex) Binary 1Mbps fs = 106Hz Ts = 10-6sec
Spectrum with main lobe = 2fs
PHY MAC
0 fs 2fs
Fourier transform
===
-2fs -fs
Main lobe
side lobe-1 -1 1 -11 -11 -1 1 -11 -1 1
Ts
Quantization
L-level quantizer consists of L codewordsA codeword of L-level quantizer is represented by B-bit binary digits
Quantization error Δ = dynamic range2Lfs symbolssec Bfs bitssec = R [bps]
symbolbitsLLogB 2
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Sampling (Cont)
2sf W
2sf W
2sf W
Aliasing
Spectrum
Symbol rate fs = 1Ts where Ts = symbol duration
ex) Binary 1Mbps fs = 106Hz Ts = 10-6sec
Spectrum with main lobe = 2fs
PHY MAC
0 fs 2fs
Fourier transform
===
-2fs -fs
Main lobe
side lobe-1 -1 1 -11 -11 -1 1 -11 -1 1
Ts
Quantization
L-level quantizer consists of L codewordsA codeword of L-level quantizer is represented by B-bit binary digits
Quantization error Δ = dynamic range2Lfs symbolssec Bfs bitssec = R [bps]
symbolbitsLLogB 2
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Spectrum
Symbol rate fs = 1Ts where Ts = symbol duration
ex) Binary 1Mbps fs = 106Hz Ts = 10-6sec
Spectrum with main lobe = 2fs
PHY MAC
0 fs 2fs
Fourier transform
===
-2fs -fs
Main lobe
side lobe-1 -1 1 -11 -11 -1 1 -11 -1 1
Ts
Quantization
L-level quantizer consists of L codewordsA codeword of L-level quantizer is represented by B-bit binary digits
Quantization error Δ = dynamic range2Lfs symbolssec Bfs bitssec = R [bps]
symbolbitsLLogB 2
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Quantization
L-level quantizer consists of L codewordsA codeword of L-level quantizer is represented by B-bit binary digits
Quantization error Δ = dynamic range2Lfs symbolssec Bfs bitssec = R [bps]
symbolbitsLLogB 2
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Entropy and transmission rate
Information Theory
Shannonrsquos coding theory
ldquoNo loss of information if R(X)gtH(X)rdquo
Entropy average of information amount of symbols uncertainty
][)1
(log
)(
)]([)(
1
02
1
0
symbolbitsp
p
XIp
XIEXH
N
k kk
X
kkk
j
Ex) Dice ][3582)
61
1(log
6
1)(
6
12 symbolbitsXH
k
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Noise and Detection of signals Noise and Detection of signals
PHY MAC
Two conditional pdfs likelihood of s1(s2)
2
0
1
0
1 2
1exp
2
1)|(
az
szp
2
0
2
0
2 2
1exp
2
1)|(
az
szp
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Digital modulation
ModulationHigh-frequency carrier Binary M-ary for narrower baseband
Ex) M-ary PSK EbN0 vs BER (bit error rate)
PHY MAC
M=2
M=4
M=16
fb
fb2
fb4
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Packing problem
ldquoHow many balls can you pack in a jarrdquo
Dependent on size of the jarDependent on size of each ball
PHY MAC
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Error Probability PlaneCoherently Detected M-ary Signaling
2kM =
MFSK MPSK
What happens in PB if the bandwidth efficiency RbW increases
① tradeoff between PB and EbN0 with fixed W
③ tradeoff between W and EbN0 with fixed PB
② tradeoff between PB and W with fixed EbN0
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Bandwidth Efficiency of M-ary Signaling
Bandwidth Efficiency RW bitssHzMeasure of how much data can be communicated in a specified bandwidth within a given time reflecting how efficiently the bandwidth resources is utilized
M-ary Signaling
Data rate
Bit duration
Bandwidth efficiency
Digital Communications 2 -13-
22 or log bits symbolkM k M= =
2log bits s ( symbol duration)s
s s
MkR T
T T= =
2
1 1 ( symbol rate)
logs
b ss
T RT R
R k kR M= = = =
2log 1 bits s Hz
s b
MRW WT WT
= =
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Shannon Capacity Theorem
Digital Communications 2 -14-
[bps]
Shannon Capacity C = W log2(1+SN)
W Bandwidth S Average received signal power
N Average noise power
Limited by the signal power and bandwidth 3dB increase in SNR 1 bpsHz increase in
capacityAnalog TV digital TV
Cable TV (CW=6~7) satellite TV(~3)
terrestrial TV(1~2)
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Bandwidth-Efficiency Plane
Digital Communications 2 -15-
① tradeoff between PB and EbN0 with fixed RW
③ tradeoff between RW and EbN0 with fixed PB
② tradeoff between PB and RW with fixed EbN0
well-designed
( )0
2 1C WbE WN C
= -
M
M
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Data Link LayerError controlFlow controlMAC (Medium Access Control)
Doug Young Suhsuhkhuackr
Last updated Aug 1 2009
PHY MAC
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
IEEE 8022 Logical Link Control
(a) Position of LLC (b) Protocol formats
PHY MAC
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Error control
EDARQError Detection and Automatic Repeat RequestCRC (Cyclic Redundancy Check)
FEC (Forward Error Correction)Bit error correction BCH convolution codeByte error correction Reed Solomon LDPCPacket loss recovery Reed Solomon Raptor
23年 4月 21日 MediaLab Kyunghee University
18
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Bit error and transmission rate
Digital Communications 2 -19-
Binary Symmetric Channel (BSC)
For an error-free channel (p=0) (no uncertainty in X with the
knowledge of Y)
( ) ( )0 1 1 2P X P X= = = =
0
1
0
1
-1 p
pp
-1 p
X Y
( ) ( )0 1 1 2P Y P Y= = = =
BP p=
( ) 0X Y =H
])[1(log)1(log)|( 22 mbolreceivedSybitsppppYXH
p=0
05 1
H(X|Y)
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Effective Transmission Rate
-20-
Digital Communications 2
Bit error loss of information
For a BSC channel with PB=001
If Rs=1000 symbolss (1000-919=81 for channel coding)
What happens if PB=05
( )H X Y
( )XHX Y
( ) ( )eff X X Y= -H H H
( )
( ) ( )
eff
1 bit symbol
001 0081 bit received symbol
1 0081 0919 bit received symbol
X
X Y
=
= =
= - =
H
H H
H
bpsHRR effseff 91991901000
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Error detection
Checksum with CRC (Cyclic Redundancy Code) Example with generator G(X)=X4+X+1
All XOR operation Send C(X)=S(X)middotX4 + [S(X)middotX4 G(X)] Let S(X)= 1101011011 then C(X)= 11010110111110 Note that C(X)G(X)=0cf) For any integer n [n - (n3)]3 = 0
PHY MAC
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Error correctionExample with Hamming (74) code
generator G(X)=X3+X+1 Send C(X)=M(X)middotX3 + [M(X)middotX3 G(X)]Let M(X)= 1110 then C(X)= 1110100 (C(X)G(X)=0)
If error E(X) = 0010000 then receive R(X) = 1100100S(X) = R(X)G(X) = E(X)G(X)Unique syndrome 1 bit error correction
PHY MAC
E(X) Syndrome
0000 001 001
0000 010 010
0000 100 100
0001 000 011
0010 000 110
0100 000 111
1000 000 101
Error prone
channel
E(X)
C(X) R(X) Mrsquo(X
)M(X)
Channel
Decode
Channel
Encode
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Flow control
Different capacity of the both partiesAvailable bitrateBuffer size
Tools ACK Seq_Num timer piggy-back
Protocols Stop-and-wait protocol simple amp slow (satellite)Sliding-window protocol over noisy channel
Sliding window limited window sizeGo-back-N protocol Selective repeat protocol
PHY MAC
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Sliding window (size 1 seq c3 bits)
PHY MAC
(a) initially (b) after Packet 0 sent (c) after Packet 0 received (d) after ACK1 received
Ready to receive Pkt0
Ready to receive Pkt1
Ready to retransmit Pkt0
Ready to send Pkt1
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Go-back-N vs selective repeat
PHY MAC
0 1 2 3 4 5 6 7 8
0 1 E D D D D D D
0 1 2 3 4 5 6 7 8 2 9 10 11 12 13 14
0 1
2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8
Ack
0Ac
k 1
Ack
2Ac
k 3
Ack
4Ac
k 5
Ack
6Ac
k 7
Timeout interval
3 4 5 6 7 8E 2
Ack
0Ac
k 1
Ack
2Ac
k 8
Ack
9Ac
k 10
Ack
11
Timeout interval
Ack
1Ac
k 1
Ack
1Ac
k 1
Ack
1Ac
k 1
9 10 11 12
Discarded by datalink layerError
Error buffered by datalink layer Packets 2-8 passed to network layer
Window size 1 ldquoGo-back-Nrdquo
Sufficient window size ldquoselective repeatrdquo
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Simple queueing theory
Delay T = 1(α-λ)Exponential distribution p(t)= λ e-λt
Poission distribution p[k] = (λT)k e-λT k
PHY MAC
Queue(eg router station AP)
λ framessec α framessec
For an AP 1(μC ndash λ) Departure 1u[bitsframe] C [bps]
Arrival λ[framessec]
Frame length
bandwidth
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Channel Allocation(Static divided by N) vs (Dynamic allocation)
Delay TFDM =1(μCN-λN) gtgt T=1(μC-λ) =TFDMN
Static TDM FDM
Dynamic Allocation IssuesStation model
generation period transmission periodSingle channel sharing with the same rightCollision assumptionContinuousslotted timeCarrier sense or not
PHY MAC
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
ALOHA (1970s)
Contention system contention-free
No carrier senseG attemptsframetime throughput S = G P0
Where P0 is probability of no collision
Pure ALOHA S=Ge-2G
No collision when no frame during 2t
Slotted ALOHA S=Ge-G
PHY MAC
Collision with the start of the shaded
frame
Collision with the end of the shaded
framet
t t+t0 t+2t0 t+3t0
vulnerable
S
(thro
ughput)
Load G
02
04
05 10
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
CSMACDCarrier Sense Multiple Access Persistent( 고집하는 ) and non-persistent
Non-persistent Send as soon as no carrier is sensed
p-persistentSend with a probability of p Optimal when pN=1
Collision Detection∵ propagation delayStop as soon as collision
is detected 2τ=10μs1km
PHY MAC
S
(thro
ughput)
Load G
02
04
05 10
Pure ALOHA
Slotted ALOHA
Nonpersistent CSMA
001 persistent CSMA
01
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Persistent and Nonpersistent CSMA
Comparison of the channel utilization versus load for various random access
protocols
PHY MAC
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
CSMACD 3 states
At t0 a station begins transmittingAt τ-ε the frame arrives at the most distant station which begins transmittingAt τ-ε the original station detects collision and stops transmitting
PHY MAC
Frame
t0
Frame Frame
contention slots
Transmission
period
contention
period
Idle period
time
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Ethernet MAC Protocol
PHY MAC
Collision detection can take as long as 2
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Gigabit Ethernet (switched)
(a)A two-station Ethernet (b)A multistation Ethernet
PHY MAC
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Collision-Free Protocols
Bit-map protocolOptimal grouping when Nmiddotp asymp 1
PHY MAC
N1P1 asymp 1 N2P2 asymp 1 N3P3 asymp 1
Collision-free protocol
Contention protocolin each group
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Bit-map protocol
reservation protocol
delay =N(d+1)2 maximum efficiency d(N+d)
Limited-contention protocol Two important performance measures
Delay at low load channel efficiency at high load
Bit-map for groups then contentionOptimal when pN=1
PHY MAC
1 1 1 1 3 7 1 1 2 5 1 1
framesN=8 contention slots
frames8 contention slots
d1
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
Conclusions MAC protocol
Load and protocolContention protocol at low load Contention-free protocol at high load
Two important performance measuresDelay at low loadchannel efficiency at high load
PHY MAC
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Slide 9
- Slide 10
- Slide 11
- Slide 12
- Slide 13
- Slide 14
- Slide 15
- Slide 16
- Slide 17
- Slide 18
- Slide 19
- Slide 20
- Slide 21
- Slide 22
- Slide 23
- Slide 24
- Slide 25
- Slide 26
- Slide 27
- Slide 28
- Slide 29
- Slide 30
- Slide 31
- Slide 32
- Slide 33
- Slide 34
- Slide 35
- Slide 36
-
