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
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