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

week 5 : Data Link Layer, Physical Layer cont.

Data Link Layer

- Data Link Layer moving data from node to node
- Control the way data are sent
- Major function of a data link layer
- Media Access Control

=(Point to point half duplex links - can't send and receive not the same time,

Multipoint configuration - only one computer that can send at the time)=

- Error Control (need to check that no data wrong)

- Message Delineation

Controlled Access

1 device that control point, to allow another device send data (Ex. token)

Polling

- Roll call polling (waste time, have to ask every client)

- Hub polling or token passing

Physical Layer

Pulse Amplitude Modulation (PAM) - technic that use for sampling

=More sampling, more better signal/data=

Nyquist : Sampling rate must be at least 2 times the highest frequency

If increase quantize, will get more data

Quantizing by using sign and magnitude

0 - positive value

1 - negative value

Calculate!!

Sampling rate must be twice the highest frequency

but if signal is low part (start from 0) use bandwidth to calculate

Bit rate = sampling rate x number of bits per sample

Parallel Transmission - can send data more than 1 bit at the same time

Serial Transmission - can send 1 bit at a time (1 wire)

Asynchronous transmission - send start bit(0) and stop bits(1), may have a gap between each byte

= each byte of the data doesn't need to be send in the same period of time, but each bit will send in the same period of time =

Isochronous - not acceptable in real time video and audio(slower frame)

Bit rate is the number of bits per second

Baud rate is the number of signal per second

ASK - bit rate and baud rate will be same, use just 2 amplitudes(normal)

N = log2L (L - number of amplitude, N - level)

Minimum bandwidth of ASK = Nbaud

Ex. If send data of 1000, minimum bandwidth is 1000 Hz

Half-duplex can send data and receive data at the same time, but if full duplex need to x2 cuz for each direction

FSK - same idea as ASK but use frequency instead amplitude

*bit rate = baud rate

BW = baud rate + fc1 - fc0

BW = bit rate + fc1 - fc0

baud rate never greater than bandwidth