CCM4010 - Revision

• Introduction, computer networks, standards, OSI, TCP/IP, LANs, MANs, WANs

• Wireless LANs• Data Compression• Error Detection/Correction• Routing• Network Management• Network Security

OSI Reference Model

• Seven layered structure– Application– Presentation– Session– Transport– Network– Data Link – Physical

OSIRM

• Functions of each layer• Relationships between various networking

standards and the OSIRM– LAN standards

• IEEE802.x

• FDDI

• DQDB

– ATM

– etc.

Protocols

Protocol is the set of rules that make communication more efficient.

LANs/MANs/WANs

• IEEE802.11 – wireless LAN• HiperLAN - wireless LAN (Europe)• IEEE802.x – LANs• 10Base2/10Base5/10Base T/100Base T etc.• ATM• DQDB• FDDI – SAS/DAS• SDH/SONET• Selection criteria

LANs/MANs/WANs

• Topologies– LAN

• Bus

• Token ring

• Star

• Extended star

Wireless LANs and Mobile Systems

• Infrastructure

• Ad-hoc

• WAP

• i-mode

• UMTS

• Location technology:– Global Positioning System (GPS)

Transmission Media and supporting technologies

• ISDN

• ADSL

• PSTN

• Satellite link

• Data link using mobile telephony

• Microwave

• The Internet

Delay calculations

• Propagation time = distance/speed

• Transmission time = Number of bits in a frame/bit rate

• Total time = outward propagation time + outward transmission time + inward propagation time + inward transmission time

Bridges/Routers

• Use of bridges

• Routing– Routing tables– Adaptive routing– Non-adaptive routing

Data Compression

• Packed decimal

• Relative encoding

• Character suppression

• Huffman coding– Static – dynamic

• Limpel-Zev coding

Huffman coding

• Statistical encoding

• Analyse the characters to be transmitted

• Determine character types and their relative frequency

• Create an unbalanced tree (Huffman code tree/ binary tree)

• Obtain codeword for each character

• Calculate the number of bits needed to transmit these characters

• Calculate the average number of bits per codeword needed to transmit these characters

Huffman coding

• Example:– “AGAIN AND AGAIN AND AGAIN”

• Determine character types and their relative frequencyA 8; N 5; Sp 4; G 3; I 3; D 2. Total 25

• Create an unbalanced tree (Huffman code tree/ binary tree)• Obtain codeword for each character

A 00; N 11; Sp 010; G 011; I 100; D 101

• Calculate the number of bits needed to transmit these charactersTotal bits 62

• Calculate the average number of bits per codeword needed to transmit these characters62/25 = 2.48 b/character

Limpel-Zev Coding

• Example:– “AGAIN AND AGAIN AND AGAIN”– Ad a space to make the number of characters even (26)– “AGAIN AND AGAIN AND AGAIN ”

• Take pair of characters together and determine their frequencyAG 3; AI 3; NSp 3; AN 2; DSp 2; Total 13

• Create binary tree• Obtain codeword for each character

AG 11; AI 00; NSp 01; AN 100; DSp 101

• Calculate the number of bits needed to transmit these charactersTotal bits 30

Compression

• A very simple stratagem applied to the string could reduce the number of bits needed for transmission of the string still further. Suggest and validate, a suitable stratagem

• AnswerPut the extra space at the beginning of the string. There

are now only four pairs and the total number of bits is 26.

SpA; GA; IN; ND;

Huffman - decoding

• A code table must be available

• Read data as received, compare to known codes, – if it is a match, identify code, – if not keep reading and concatenating bits

received

Huffman - decoding

• Example001101000000010110011010011010001

Character coding:

E = 1; T = 01; G = 001; C = 0000; A = 0001

001 1 01 0000 0001 01 1 001 1 01 001 1 01 0001

G E T C A T E G E T G E T A

Error control

• ASCII• Parity bit: additional bit added to each

character– Even parity

• Total number of bits (inclusive) in a digital word is even; e.g. 10110111

– Odd parity• Total number of bits (inclusive) in a digital word is

odd; e.g. 10110110

Error control

• Hamming distance: The Hamming distance of the code is the minimum number of bit positions in which two valid codewords differ.00000000

00000011

00000101

00000110

Hamming distance?

Odd/even parity?

Hamming Codes

• The parity bits are inserted into the positions which numerically are the powers of 2 (i.e. 1,2,4,8,16 etc.)

• Parity bit 1 covers bits 1,3,5,7,9,…• Parity bit 2 covers bits 2,3,6,7,10,11,14,15,..• Parity bit 4 covers bits

4,5,6,7,12,13,14,15,20,21,22,23,…• Parity bit 8 covers bits

8,9,10,11,12,13,14,15,24,25,26,27,28,29,30,31,…

Network Management

• Functions– Fault management– Performance management– Security– Accounting– etc.

• Characteristics of network managers• Other network management topics

Network Security

• Terminology/definitions

• Solutions