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CCM4010 - Revision

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

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CCM4010 - Revision

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  1. CCM4010 - Revision • Introduction, computer networks, standards, OSI, TCP/IP, LANs, MANs, WANs • Wireless LANs • Data Compression • Error Detection/Correction • Routing • Network Management • Network Security

  2. OSI Reference Model • Seven layered structure • Application • Presentation • Session • Transport • Network • Data Link • Physical

  3. OSIRM • Functions of each layer • Relationships between various networking standards and the OSIRM • LAN standards • IEEE802.x • FDDI • DQDB • ATM • etc.

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

  5. 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

  6. LANs/MANs/WANs • Topologies • LAN • Bus • Token ring • Star • Extended star

  7. Wireless LANs and Mobile Systems • Infrastructure • Ad-hoc • WAP • i-mode • UMTS • Location technology: • Global Positioning System (GPS)

  8. Transmission Media and supporting technologies • ISDN • ADSL • PSTN • Satellite link • Data link using mobile telephony • Microwave • The Internet

  9. 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

  10. Bridges/Routers • Use of bridges • Routing • Routing tables • Adaptive routing • Non-adaptive routing

  11. Data Compression • Packed decimal • Relative encoding • Character suppression • Huffman coding • Static • dynamic • Limpel-Zev coding

  12. 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

  13. 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

  14. 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

  15. 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;

  16. 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

  17. 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

  18. 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

  19. 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?

  20. 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,…

  21. Network Management • Functions • Fault management • Performance management • Security • Accounting • etc. • Characteristics of network managers • Other network management topics

  22. Network Security • Terminology/definitions • Solutions

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