Data link control
Automatic Repeat Request (ARQ)
- Stop and Wait ARQ(after sender send 1 frame of data then wait for receiver check it correct or not)
- Continuous ARQ (sender can send more than 1 frame, don't have to wait)
Stop and Wait ARQ
ACK - Acknowleadge (tell that data is correct and send the number of next frame)
NAK - Negative Acknowleage (tell that data is incorrect and tell the number of frame that sender need to send again)
If receiver lost data when it reply to sender and sender doesn't receive anything, it have to wait until time out and send data to receiver again.
In case delayed ACK, receiver can't reach sender before time out and sender send data again.
If receiver want to send data too, have to reply first then send it own data, use Piggybacking to fix it.
Go-Back-N ARQ
sender will send more than 1 frame at the time (1 2 3 4). If receiver tell sender that frame #2 error, sender have to send frame 2 3 4 again.
Can send just frame in window If no respond from receiver, it have to wait(can't send more frame) but receiver doesn't have to reply every frame
Size of the sender window must less than 2 power n (2 power n - 1), Size of the reciever window is always 1.
Data link protocol
- Message delineation (start of frame and end of frame)
- Frame length
- Frame field structure (How many field we use in frame?)
Synchronous Transmission photocols
- Bit oriented protocol (bit by bit)
- Byte count protocol (sender and receiver count number of byte)
- Byte oriented protocol (special character)
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