วันอังคารที่ 21 กรกฎาคม พ.ศ. 2552

week 6 : Physical Layer cont.

ADSL is an asymmetric communication (asymmetric - not equal, download rate and upload rate is not equal)
Bitrate = N x baud rate

Splitter - if don't use splitter, can't use phone and internet at the same time

Multiplexer - to share link to many devices very high bandwidth channel
FDM - Analog multiplexing technique that combine analog signal
channel x bandwidth(kHz) + guard band x kHz for guard band = minimum bandwidth of the link

Guard band - if don't have it, will be cause a problem between channel
Ex. 5 channels use 4 guard band
For FDM can't use the all frequency, need to provide the gap that is Guard band
TDM don't need guard band (each slot reserve for 1 machine if machine don't want to send data, no-one can use it)

Complexities of STDM
- additional address
- reaponse time delay
Inverse Multiplexing(IMUX) - want to combine multiplex together to get a high bandwidth

Circuit - Switched networks(FDM, TDM)
- need to setup link first
- no-one can share link
Packet - switched networks(Network with VCs, Datagram Networks)
- if want to send data, can use slot
- will get the delay if slot is not enough, system have to wait
- will loss data cuz it doesn't have own link

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