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Data Link Control
• Line Discipline• Flow Control• Error Control
Functions of Data Link Layer
Figure 10-1
Figure 10-2
Figure 10-3
ENQ/ACKFigure 10-4
Figure 10-5
ENQ/ACK
Multipoint DisciplineFigure 10-6
SelectFigure 10-7
PollFigure 10-8
Figure 10-9
Flow control – set of procedures that tells the sender how much data it can transmit before it must wait for an acknowledgement from the receiver
Stop and WaitFigure 10-10
Sliding Window
Figure 10-11
Figure 10-12
Sender Sliding Window
Figure 10-13
Receiver Sliding Window
Figure 10-14 Sliding Window Example
Figure 10-14-continued Sender
Figure 10-14-continued Receiver
Figure 10-15
Flow Diagram: Normal Operation
Time
Sender Receiver
Time
Frame 0
ACK 1Frame 1
ACK 0
S = 0
S = 1
R = 0
R = 1
R = 0
Deliver
Deliver
Damaged FrameFigure 10-16
Flow Diagram: Lost Frame
Time
Sender Receiver
Time
Frame 0
ACK 1
Frame 1
ACK 0
S = 0 R = 0
R = 1
R = 0
S = 1
Timeout
Frame 1
Deliver
Deliver
Flow Diagram: Lost ACK
Time
Sender Receiver
Time
Frame 0
ACK 1
Frame 1
ACK 0
S = 0 R = 0
R = 1
R = 0
Frame 1S = 1
TimeoutACK 0
S = 1
S = 0
R = 0Frame 0
expected; discard
Deliver
Deliver
Damaged FrameFigure 10-19
Lost FrameFigure 10-20
Lost ACKFigure 10-21
Selective RejectFigure 10-22
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