CCM4010 - Revision

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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 frequency

A 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
characters

Total bits 62


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

62/25 = 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
frequency

AG 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
characters

Total 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


Answer

Put 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


Example

001101000000010110011010011010001

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. 1011011
1


Odd parity


Total number of bits (inclusive) in a digital word is
odd; e.g. 1011011
0

Error control


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

0000000
0

0000001
1

0000010
1

0000011
0

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