Transcript Document 7571674

CPET/ECET 355
10. Data Link Layer
Data Communications and Networking
Fall 2004
Professor Paul I-Hai Lin
Electrical and Computer Engineering Technology
Indiana University-Purdue University Fort Wayne
www.ecet.ipfw.edu/~lin
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Data Link Layer
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Packetizing
Flow Control
Media Access Control
Addressing
Error Control
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Data Link Layer
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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 Layer
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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 Layer
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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 Correction
10.1 Types of Errors
 Single-Bit Error
 Burst Error
10.2 Detection
 Redundancy
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Parity Check
Cyclic Redundancy Check (CRC)
Checksum
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Error Detection and Correction
10.3 Error Correction
 Retransmission
 Forward Error Correction
 Hamming Code
 Burst Error Correction
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10.1 Types of Errors
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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 Errors
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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 Detection
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Redundancy
From p. 245, Figure 10.3 of Data Communications and Networking, Forouzan, McGrawHill
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10.2 Detection
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Parity Checking (based on addition)
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Even parity
Odd parity
Performance
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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 Detection
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Even Parity Check
From p. 246, Figure 10.5 of Data Communications and Networking, Forouzan, McGrawHill
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10.2 Detection
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Two-Dimensional Parity Check
From p. 248, Figure 10.6 of Data Communications and Networking, Forouzan, McGrawHill
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Two-Dimensional Parity Check
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Method
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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
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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 Detection
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CRC Generator and Checker
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Based on binary division (remainder)
From p. 250, Figure 10.7 of Data Communications and Networking, Forouzan, McGrawHill
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CRC Generator
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Binary Division (modulo-2)
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C code, (VHDL)
Assembly language
From p. 251, Figure 10.8 of Data Communications and Networking, Forouzan, McGrawHill
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CRC Checker
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Binary Division – CRC Cheker
From p. 252, Figure 10.9 of Data Communications and Networking, Forouzan, McGrawHill
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CRC - Polynomial
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Polynomial selecting criteria
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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 Detection
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Standard Polynomials
Name
Polynomial
Application
CRC-8
x8 + x2 + x + 1
ATM header
CRC-10
x10 + x9 + x5 + x4 + x 2 + 1
ATM AAL
ITU-16
x16 + x12 + x5 + 1
HDLC
ITU-32
x32 + x26 + x23 + x22 + x16 + x12 + x11 + x10 +
x8 + x7 + x5 + x4 + x2 + x + 1
LANs
From p. 253, Table 10.1 of Data Communications and Networking, Forouzan, McGrawHill
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10.2 Detection
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Checksum
From p. 254, Figure 10.12 of Data Communications and Networking, Forouzan, McGrawHill
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Summary
Questions?
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