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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