Basic components II Basic components II (06.523)(06.523)

Basic components of

communication networks II

Lecture 2

Network layersNetwork layers

Application layer

Network layer

Data link layer

Physical layer

Application layerApplication layer

HTTP POP

Network layerNetwork layer

TCP IPX EBUI

Data link layerData link layer

802.3 PPP Z-Modem

Physical layerPhysical layer

RS-232C cables (serial) IEEE 802.3 category 5 V.34 Modem

Shannon’s lawShannon’s law

bits/sec =bandwidth log 2 (1 +S/N)bits/sec = 2600 Hz * log 2 (1 + 30dB)bits/sec = 26k

In Wellington you can get 28.8k, in Hawke’s Bay, 19.2k

33k assumes digital telephone network 56k assumes ISP physically at

telephone network -- no modem Higher rates through compression. I

have got 120k

Modem theoryModem theory

Three ways to encode information + baud rate

Amplitude modulationFrequency modulationPhase modulation

Data compressionData compression

Modems use v42 for data compression

v42 is the same compression standard as used in GIFsworks by sending 5*1, 2*0, etc.

LAN networkingLAN networking

802.3, 802.5, 802.1110baseT, 10base 2Appletalk, EthertalkIncompatible protocols