Network Operations & administration CS 4592 Lecture 13
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Transcript of Network Operations & administration CS 4592 Lecture 13
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Network Operations & administration CS 4592
Lecture 13
Instructor: Ibrahim Tariq
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Data Link Layer
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Error Correction
1. By retransmission– flow and error control protocols
2. Forward Error Correction (FEC)– require more redundancy bits– should locate the invalid bit or bits– n-bit code word contains m data bits + r
redundancy bitsn=m+r
– m+r+1 bits discoverable by r bits– 2r>=m+r+1
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Data and redundancy bits
Number ofdata bits
m
Number of redundancy bits
r
Total bits
m + r
1 2 3
2 3 5
3 3 6
4 3 7
5 4 9
6 4 10
7 4 11
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Hamming Code
• Hamming codes provide for FEC using a “Block Parity”– i.e, instead of one parity bit send a block of parity
bits• Allows correction of single bit errors• This is accomplished by using more than one
parity bit• Each computed on different combination of
bits in the data
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Positions of Redundancy Bits
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Redundancy Bits Calculation
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Example
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Error Correction using Hamming Code
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Revision
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1.11
Categories of topology
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1.12
A fully connected mesh topology (five devices)
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1.13
A star topology connecting four stations
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1.14
A bus topology connecting three stations
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1.15
A ring topology connecting six stations
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1.16
A hybrid topology: a star backbone with three bus networks
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2.17
Figure 2.2 Seven layers of the OSI model
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2.18
Figure 2.3 The interaction between layers in the OSI model
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Four Level of Addresses
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Relationship of Layers & Addresses in TCP/IP
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Communication NetworkCommunication networks
Broadcast networksEnd nodes share a common channel (TV,
radio…)
Switched networks End nodes send to one (or more) end nodes
Packet switchingData sent in discrete portions
(the Internet)
Circuit switchingDedicated circuit per call
(telephone, ISDN)(physical)
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6.22
Figure 6.2 Categories of multiplexing
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6.23
Figure 6.13 Synchronous time-division multiplexing
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6.24
Figure 6.26 TDM slot comparison
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Transmission Impairments
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Bit Rate & Bit Interval (contd.)
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Noiseless Channel: Nyquist Bit Rate
• Defines theoretical maximum bit rate for Noiseless Channel:
• Bit Rate=2 X Bandwidth X log2L
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ExampleWe have a channel with a 1 MHz bandwidth. The SNR for this channel is 63; what is the appropriate bit rate and signal level?
Solution
C = B log2 (1 + SNR) = 106 log2 (1 + 63) = 106 log2 (64) = 6 Mbps
Then we use the Nyquist formula to find the number of signal levels.
6 Mbps = 2 1 MHz log2 L L = 8
First, we use the Shannon formula to find our upper limit.
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Noisy Channel: Shannon Capacity
• Defines theoretical maximum bit rate for Noisy Channel:
• Capacity=Bandwidth X log2(1+SNR)
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Data Communication & Networks, Summer 2009
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Line Coding Schemes
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Unipolar Encoding
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Data Communication & Networks, Summer 2009
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Polar: NRZ-L and NRZ-I Encoding
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Polar: RZ Encoding
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Polar: Manchester Encoding
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Polar: Differential Manchester Encoding
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4.36
Figure 4.6 Polar NRZ-L and NRZ-I schemes
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4.37
Figure 4.9 Bipolar schemes: AMI and pseudoternary
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4.39
ANALOG-TO-DIGITAL CONVERSION
Digital signal is superior to an analog signal. The tendency today is to change an analog signal to digital data. pulse code modulation
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4.40
Components of PCM encoder
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5.41
Types of digital-to-analog conversion
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5.42
Concept of a constellation diagram
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5.43
Figure 5.13 Three constellation diagrams
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5.44
Types of analog-to-analog modulation
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Circuit Switching
• There are three phases in circuit switching:– Establish– Transfer– Disconnect
• The telephone message is sent in one go, it is not broken up. The message arrives in the same order that it was originally sent.
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Packet Switching
• In packet-based networks, the message gets broken into small data packets.
• These packets seek out the most efficient route to travel as circuits become available.
• Each packet may go a different route from the others.
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9.47
Figure 9.11 Bandwidth division in ADSL
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9.48
ADSL modem
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9.49
DSLAM
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9.50
Summary of DSL technologies