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An in-depth analysis of error control and reliable transmission techniques, focusing on acknowledgements (acks) and timeouts. Topics include automatic repeat request (arq), frame transmission, sender and receiver processes, and stop and wait protocol. Discover how these mechanisms ensure reliable data transfer and handle lost frames.
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Frame ack
Timeout
sender
Receiver
Services
-^ Sender Process •^
-^
Idle DLL send / start Tx
Sender process:
Idle
Receiving End Rx / return
DLL Recv / start Rx Receiver Process:
Sending End Tx / return
Solution
Stop and Wait Protocol
Frame 0 ack 0
Timeout
Sender
Receiver
Sender
Receiver Frame 0ack 0 Frame 0ack 0
Timeout Frame 0^ Frame 0ack 0
Timeout
Sender
Receiver
Frame 0ack 0
Timeout
Sender
Receiver Frame 0ack 0
Basically require that the sender and receiver take care of all thesesituation.Sequence number:
Header includes sequence number^ modulo 2 counters
at receiver and sender
delay * BW = volumeHow many bits fit in the pipe? Suppose frame size is
maximum sending rate: (bits / frame) / (time / frame)
182 kbps
182 of l
ink cap
acit
y
What does delay * BW tell us?
67.5 kbps
can be transmit until an ack is expected.
Program as an FSM:
FSM = { states, events, actions}
DLL Send / start TxIdle
sending Ackawait
end of Tx
TimeoutstartTx Y / return
Sender Process: What if spurious ----reply
DLL Send / start Tx^ Idle
sending
Y / return
Ack await
End Tx
TimeoutstartTx
MakeAFrame(buffer, s)SendToPhysLayer(s)DLLState
Sending
else
error endif Sending: if event = EndTx then
DLLState
AwaitAck
endif
AwaitAck: if event = TimeOut then
increment numTriesif numTries > MaxTries then
DLLState
Idle
DLLReturn
Fail
else
SendToPhysLayer(s)DLLState
Sendif
endifelse if event = EndRcv then
if isAck and SegNo = ExpectedNo then
DLLState
Idle
send Success to upper layer else
discard ackDLLstate
AwaitAck
endif
Problem with Duplicate frame:^ - if ack lost, sender sends frame again.- Positive Acknowledgement with Retransmission- required sequence number on frame
DLL Recv / start Rx^ Idle
Awaitframe
End Rx / start Tx (ack)
Timeout /Fail
Y
Send frame to NWL and goto Idle
new N
pmodule Sender(event – eventType)
s – framebuffer – packetDLLStack – state of DLLwhile (event) docase DLLState if:
Idle : if event = DLLSend then
getFrame from NWL (buffer)MakeAFrame(buffer, s)DLLState
sending
SendTophysLayer(s)
