Data Link Control

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