Fair Sharing of MAC under TCP in Wireless Ad Hoc Networks Mario Gerla Computer Science Department...
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Transcript of Fair Sharing of MAC under TCP in Wireless Ad Hoc Networks Mario Gerla Computer Science Department...
Fair Sharing of MAC under TCP in Wireless Ad Hoc Networks
Mario Gerla
Computer Science Department
University of California, Los Angeles
Los Angeles, CA 90095
http://www.cs.ucla.edu/NRL/wireless
UCLA DARPA Domains Project
Outline
• Overview of CSMA, FAMA and IEEE 802.11.
• MAC performance with TCP. Variable Hop Length Experiments. Hidden Terminal Experiments. Ring Experiments. Grid Experiments.
• Static.• Mobility.
UCLA DARPA Domains Project
Simulation Using GloMoSim
• Detailed model of the protocol stack.• Allows investigation of TCP and MAC layer
interactions.• Capability to simulate large number of nodes.• GloMoSim web page.
http://pcl.cs.ucla.edu/projects/domains/glomosim.html
UCLA DARPA Domains Project
MAC Layer Protocols
• CSMA Requires carrier sensing before transmission. If the channel is free, the packet is transmitted immediately. Otherwise, it is rescheduled after a random timeout.
• FAMA Builds on CSMA. Uses the RTS (Request To Send) and CTS (Clear To Send) exchange
to prepare the floor for data transmission.
• 802.11 Uses carrier sensing and RTS/CTS, similar to FAMA. Utilizes link-level ACKs. Collision Avoidance scheme.
UCLA DARPA Domains Project
Variable Hop Length Experiments Configuration
0 1 2 543
• Each node is 10 meters apart from its neighbors.• Each node has a radio power range of 10 meters.• 2Mbps channel bandwidth.
• FTP traffic.• TCP window size varies from 1 to 16 packet size.• Variable number of hops (single connection).
i.e., FTP connection 0-1, 0-2, 0-3, 0-4, 0-5 (one at a time).
UCLA DARPA Domains Project
Variable Hop Length Experiments ResultsVariable Hop Length Experiments Results
Variable Number of Hops Experiment (CSMA)
0500000
100000015000002000000
1 2 3 4 5
Number of Hops
Thro
ughp
ut (b
ps)
W = 1
W = 2
W = 4
W = 8
W = 16
UCLA DARPA Domains Project
Variable Hop Length Experiments Results (Cont’d)
Variable Hop Length Experiments Results (Cont’d)
Variable Number of Hops Experiment (FAMA)
0500000
100000015000002000000
1 2 3 4 5
Number of Hops
Thro
ughp
ut (b
ps)
W = 1
W = 2
W = 4
W = 8
W = 16
UCLA DARPA Domains Project
Variable Hop Length Experiments Results (Cont’d)
Variable Hop Length Experiments Results (Cont’d)
• CSMA and FAMA degrades with window size > 1 pkt. Collisions between TCP data and ACKs.
• 802.11 performs the same no matter the window size. Link-level ACKs combat collisions.
Variable Number of Hops Experiment (802.11)
0500000
100000015000002000000
1 2 3 4 5
Number of Hops
Thro
ughp
ut (b
ps)
W = 1
W = 2
W = 4
W = 8
W = 16
UCLA DARPA Domains Project
Hidden Terminal Experiments Configuration
Hidden Terminal Experiments Configuration
• FTP traffic
• Connections from node 0 to node 1 and from node 2 to node 1.
• Node 0 and node 2 cannot hear each other.
0 1 2
UCLA DARPA Domains Project
Hidden Terminal Experiments Results
Hidden Terminal Experiments Results
• CSMA suffers from hidden terminal.
• FAMA and 802.11 performs well due to RTS/CTS exchange.
0
500000
1000000
1500000
2000000
Throughput (bps)
CSMA FAMA 802.11
MAC Protocol
Hidden Terminal Experiment
0-1
2-1
UCLA DARPA Domains Project
Ring Experiment Configuration
Ring Experiment Configuration
• FTP traffic
• Multiple single hop connections. i.e., 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-0 (at the same time).
0
1
6
5
4
3
2
7
UCLA DARPA Domains Project
Ring Experiment ResultsRing Experiment Results
• FAMA best in both fairness and aggregate throughput.
• 802.11 unfairness due to timers.
0
100
200
300
400
500
600
Th
rou
gh
pu
t (K
bp
s)
CSMA FAMA 802.11
MAC Protocol
0-1
1-2
2-3
3-4
4-5
5-6
6-7
7-0
UCLA DARPA Domains Project
802.11 Fairness802.11 Fairness
• Yield time. Time a node yields after transmitting a frame.
0100200300400500600
Th
rou
gh
pu
t (K
bp
s)
802.11 (Standard) 802.11 (YieldTime)
MAC Protocol
0-1
1-2
2-3
3-4
4-5
5-6
6-7
7-0
UCLA DARPA Domains Project
Grid Experiment Configuration
• Each node is 10 meters apart from its horizontal and vertical neighbors.• Each node has a radio power range of 30 meters.• FTP connections are established between node 18 to node 26, node 36 to node 44, node 54 to node 62, node 2 to node 74, node 4 to node
76 and node 6 to node 78.
0 1
109
8 2
19 18
17 11
20
74 7372
26
80
3 4
1312
5
22 21
14
23
777675
6
15
7
24
16
25
7978
27 28
3736
35 29
4438
30 31
4039
32
41
33
42
34
43
46 45 47 534948 50 51 52
54 55
6463
62 56
7165
57 58
6766
59
68
60
69
61
70
UCLA DARPA Domains Project
Grid Experiment Configuration (Cont’d)
Grid Experiment Configuration (Cont’d)
• 2Mbps channel bandwidth.
• Nodes move at a rate of 10 meters per second in a random direction with a probability of 0.5.
• When mobility is not considered, static routing is used.
• When mobility is introduced, Bellman-Ford routing is utilized with routing table updates occurring once every second.
UCLA DARPA Domains Project
Grid Experiments Results (No Mobility)
• Without mobility CSMA performs poorly due to interference by neighboring streams and by intersecting streams. FAMA fair due to RTS/CTS and less aggressive yield time. 802.11 exhibits capture.
050000
100000150000200000250000
Th
rou
gh
pu
t (b
ps)
CSMA FAMA 802.11
MAC Protocol
No Mobility
18-26
36-44
54-62
2-74
4-76
6-78
UCLA DARPA Domains Project
Grid Experiments Results (With Mobility)
CSMA and FAMA collapse with mobility due to lack of fast loss recovery facilities. 802.11 still operational.
• Link level ACKs help recover from loss caused by transient nodes.• Capture exists.
0
50000
100000
150000
200000T
hro
ug
hp
ut
(bp
s)
CSMA FAMA 802.11
MAC Protocol
With Mobility
18-26
36-44
54-62
2-74
4-76
6-78
UCLA DARPA Domains Project
Bluetooth Experiments Gerla, M et al, Tyrrenia Conf,
sept 2000
Bluetooth Experiments Gerla, M et al, Tyrrenia Conf,
sept 2000• Experiment #!: TCP throughput in a single piconet.
Throughput versus the no. of TCP connections. Each TCP connection starts from a different slave on the common piconet, and goes through the access point (BT master).
• Experiment #2: TCP throughput when multiple piconets are used in parallel. Each piconet here supports a separate TCP connection.
• Experiment #3: TCP and IP Telephony in a multiple piconet configuration. IP Telephony uses ACL channel. Question: can TCP and Telephony coexist?
UCLA DARPA Domains Project
S
LAN
IP backbone
M1
IP router
M2 M3
LAN
IP backbone
IP router
M1 M2 M3
S 1
S 2
S 3
M3
IP backbone
M2
M1
LAN
IP router
S
(a) (b) (c)Fig. 4.
UCLA DARPA Domains Project
Exp # 1:TCP throughput in Bluetooth (single piconet)Exp # 1:TCP throughput in Bluetooth (single piconet)
Bluetooth - Single Piconet
0.687
0.688
0.689
0.69
0.691
0.692
0.693
0.694
1 2 3 4 5 6 7
No. Of TCP Connections
To
tal
TC
P T
hro
ug
hp
ut
(Mb
ps)
Bluetooth
UCLA DARPA Domains Project
Exp #2:TCP Throughput in WaveLAN vs BT (multiple
piconets)
Exp #2:TCP Throughput in WaveLAN vs BT (multiple
piconets)Bluetooth vs WaveLan
0
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8 9 10
No. of TCP connections
To
tal
TC
P T
hro
ug
hp
ut
(Mb
ps) Bluetooth
WaveLan
UCLA DARPA Domains Project
Exp #2 (cont): Throughput of TCP flows
Exp #2 (cont): Throughput of TCP flows
Throughput of Individual TCP flows
0
0.2
0.4
0.6
0.8
1
1.2
1 2 3 4 5 6 7 8 9 10
Flow Number --->
Th
rou
gh
pu
t (M
bp
s) -
-->
WaveLan
Bluetooth
UCLA DARPA Domains Project
TCP and IP TelephonyTCP and IP Telephony
• Voice carried on the ACL channel (ie, VoIP)
• Four piconets
• In each piconet: 1 TCP and 6 Voice connections
• TCP connections “always on” (file transfers)
• Voice: ON-OFF model; 8Kbps coding rate
• Voice packets: 20ms packetization -> 20 bytes
• With header overhead: voice pkt = 30 bytes
UCLA DARPA Domains Project
Exp #3: Bluetooth; TCP + VoIP
Exp #3: Bluetooth; TCP + VoIP
IP Telephony Delay Distribution
0
0.02
0.04
0.06
0.08
0.1
Delay (ms)--->
Fra
ctio
n o
f P
kts-
-->
Exp #3: Bluetooth; TCP + VoIP
Exp #3: Bluetooth; TCP + VoIP
IP Telephony Complementary Cumulative Distribution
00.10.20.30.40.50.60.70.80.9
1
2 6 10 14 18 22 24 28 32 36 40 60
Delay (ms) --->
Fra
ctio
n o
f P
kts
--->
UCLA DARPA Domains Project
Exp #3: WaveLan : TCP + VoIP
Exp #3: WaveLan : TCP + VoIP
IP Telephony Delay Distribution
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Delay (ms) --->
Fra
cti
on
of
Pk
ts -
-->
UCLA DARPA Domains Project
Exp #3: WaveLan : TCP + VoIP
Exp #3: WaveLan : TCP + VoIP
IP Telephony Complementary Cumulative Delay Distribution
00.10.20.30.40.5
0.60.70.80.9
1
Delay (ms) --->
Frac
tion
of P
kts
--->
With 750 ms playout buffer, still 5% packets lost!
UCLA DARPA Domains Project
Simulation: what have we learned?
Simulation: what have we learned?
• Fair sharing in BT across TCP connections (IEEE 802.11 is unfair, “capture”- prone)
• BT aggregate throughput exceeds IEEE 802.11
• BT supports voice well even in heavy TCP load (IEEE 802.11 cannot deliver voice with TCP load)