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
10. Data Link Layer - Lin
1
10/27/2004
Data Link Layer





Packetizing
Flow Control
Media Access Control
Addressing
Error Control
10. Data Link Layer - Lin
2
10/27/2004
Data 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
10. Data Link Layer - Lin
3
10/27/2004
Data 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
10. Data Link Layer - Lin
4
10/27/2004
Data 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
10. Data Link Layer - Lin
5
10/27/2004
Error Detection and Correction
10.1 Types of Errors
 Single-Bit Error
 Burst Error
10.2 Detection
 Redundancy



Parity Check
Cyclic Redundancy Check (CRC)
Checksum
10. Data Link Layer - Lin
6
10/27/2004
Error Detection and Correction
10.3 Error Correction
 Retransmission
 Forward Error Correction
 Hamming Code
 Burst Error Correction
10. Data Link Layer - Lin
7
10/27/2004
10.1 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
10. Data Link Layer - Lin
8
10/27/2004
10.1 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
10. Data Link Layer - Lin
9
10/27/2004
10.2 Detection

Redundancy
From p. 245, Figure 10.3 of Data Communications and Networking, Forouzan, McGrawHill
10. Data Link Layer - Lin
10
10/27/2004
10.2 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)
10. Data Link Layer - Lin
11
10/27/2004
10.2 Detection

Even Parity Check
From p. 246, Figure 10.5 of Data Communications and Networking, Forouzan, McGrawHill
10. Data Link Layer - Lin
12
10/27/2004
10.2 Detection

Two-Dimensional Parity Check
From p. 248, Figure 10.6 of Data Communications and Networking, Forouzan, McGrawHill
10. Data Link Layer - Lin
13
10/27/2004
Two-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
10. Data Link Layer - Lin
14
10/27/2004
10.2 Detection

CRC Generator and Checker

Based on binary division (remainder)
From p. 250, Figure 10.7 of Data Communications and Networking, Forouzan, McGrawHill
10. Data Link Layer - Lin
15
10/27/2004
CRC Generator

Binary Division (modulo-2)


C code, (VHDL)
Assembly language
From p. 251, Figure 10.8 of Data Communications and Networking, Forouzan, McGrawHill
10. Data Link Layer - Lin
16
10/27/2004
CRC Checker

Binary Division – CRC Cheker
From p. 252, Figure 10.9 of Data Communications and Networking, Forouzan, McGrawHill
10. Data Link Layer - Lin
17
10/27/2004
CRC - 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
10. Data Link Layer - Lin
18
10/27/2004
10.2 Detection

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
10. Data Link Layer - Lin
19
10/27/2004
10.2 Detection

Checksum
From p. 254, Figure 10.12 of Data Communications and Networking, Forouzan, McGrawHill
10. Data Link Layer - Lin
20
10/27/2004
Summary
Questions?
10. Data Link Layer - Lin
21
10/27/2004