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CPET/ECET 355CPET/ECET 35510. Data Link Layer

Data Communications and NetworkingFall 2004

Professor Paul I-Hai LinElectrical and Computer Engineering TechnologyIndiana University-Purdue University Fort Wayne

www.ecet.ipfw.edu/~lin

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Data Link LayerData Link Layer

Packetizing Flow Control Media Access Control Addressing Error Control

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Data Link LayerData Link Layer

IEEE LAN Standards 802.3 CSMA/CD 802.4 Token Bus 802.5 Token Ring 802.6 DQDB 802.11 Wireless

Data Link Layer (Internet Model) Medium Access Layer Logical Link Control

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Data Link LayerData Link Layer

Ch 10 – Error Detection and Correction

Ch 11 – Data Link Control and Protocols

Ch 12 – Point-to-Point Access: PPP

Ch 13 – Multiple Access Ch 14 – Local Area Networks:

Ethernet Ch 15 – Wireless LANs

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Data Link LayerData Link Layer

Ch 16 – Connecting LANs, Backbone Networks, and Virtual LANs

Ch 17 – Cellular Telephone and Satellite Networks

Ch 18 – Virtual Circuit Switching: Frame Relay and ATM

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Error Detection and CorrectionError Detection and Correction

10.1 Types of Errors Single-Bit Error Burst Error

10.2 Detection Redundancy

Parity Check Cyclic Redundancy Check (CRC) Checksum

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Error Detection and CorrectionError Detection and Correction

10.3 Error Correction Retransmission Forward Error Correction Hamming Code Burst Error Correction

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10.1 Types of Errors10.1 Types of Errors Single-Bit Error

One bit error Happen often in parallel

communications

From p. 244, Figure 10.1 of Data Communications and Networking, Forouzan, McGrawHill

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10.1 Types of Errors10.1 Types of Errors Burst Error

2 or more bits affected by noise Not necessarily in consecutive bits

From p. 244, Figure 10.2 of Data Communications and Networking, Forouzan, McGrawHill

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10.2 Detection10.2 Detection Redundancy

From p. 245, Figure 10.3 of Data Communications and Networking, Forouzan, McGrawHill

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10.2 Detection10.2 Detection Parity Checking (based on addition)

Even parity Odd parity

Performance Check all single bit errors Detect burst errors with a total number

of bits changed is ODD (1, 3, 5, etc)

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10.2 Detection10.2 Detection Even Parity Check

From p. 246, Figure 10.5 of Data Communications and Networking, Forouzan, McGrawHill

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10.2 Detection10.2 Detection Two-Dimensional Parity Check

From p. 248, Figure 10.6 of Data Communications and Networking, Forouzan, McGrawHill

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Two-Dimensional Parity CheckTwo-Dimensional Parity Check Method

Calculate parity bit for each data unit (row)

Calculate parity bit for each column to create a new parity row

Add parity row to the end of the data stream for transmitting

Performance Can detect a burst errors of n bits Cannot detect one pattern of errors: 2 bit

in one data unit is damaged and another 2 bit in exactly the same positions in another data unit is also damaged

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10.2 Detection10.2 Detection CRC Generator and Checker

Based on binary division (remainder)

From p. 250, Figure 10.7 of Data Communications and Networking, Forouzan, McGrawHill

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CRC CRC GeneratorGenerator Binary Division (modulo-2)

C code, (VHDL) Assembly language

From p. 251, Figure 10.8 of Data Communications and Networking, Forouzan, McGrawHill

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CRC CheckerCRC Checker Binary Division – CRC Cheker

From p. 252, Figure 10.9 of Data Communications and Networking, Forouzan, McGrawHill

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CRC - PolynomialCRC - Polynomial Polynomial selecting criteria

It should not be divisible by x -> all burst errors of a length equal to the degree of the polynomial are detected

It should be divisible by x + 1 -> all burst errors affecting an ODD number of bits are detected

From p. 252, Figure 10.11 of Data Communications and Networking, Forouzan, McGrawHill

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10.2 Detection10.2 Detection Standard Polynomials

From p. 253, Table 10.1 of Data Communications and Networking, Forouzan, McGrawHill

Name Polynomial Application

CRC-8CRC-8 x8 + x2 + x + 1 ATM header

CRC-10CRC-10 x10 + x9 + x5 + x4 + x 2 + 1 ATM AAL

ITU-16ITU-16 x16 + x12 + x5 + 1 HDLC

ITU-32ITU-32 x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 + x8 + x7 + x5 + x4 + x2 + x + 1 LANs

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10.2 Detection10.2 Detection Checksum

From p. 254, Figure 10.12 of Data Communications and Networking, Forouzan, McGrawHill

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SummarySummary

Questions?