This document discusses functions and techniques of the data link layer, including line discipline, flow control, and error control. It describes flow control as procedures that tell a sender how much data it can transmit before waiting for an acknowledgement. It also explains stop-and-wait and sliding window protocols for flow control and includes diagrams of normal operation and scenarios involving damaged frames, lost frames, and lost acknowledgements.

2. Data Link Control
• Line Discipline
• Flow Control
• Error Control

3. Functions of
Data Link Layer
Functions of
Data Link Layer
Figure 10-1

4. Figure 10-2

5. Figure 10-3

6. ENQ/ACKENQ/ACK
Figure 10-4

7. Figure 10-5
ENQ/ACKENQ/ACK

8. Multipoint DisciplineMultipoint Discipline
Figure 10-6

9. SelectSelect
Figure 10-7

10. PollPoll
Figure 10-8

11. 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
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

12. Stop and WaitStop and Wait
Figure 10-10

13. Sliding WindowSliding Window
Figure 10-11

14. Figure 10-12
Sender Sliding WindowSender Sliding Window

15. Figure 10-13
Receiver Sliding WindowReceiver Sliding Window

16. Figure 10-14
Sliding Window ExampleSliding Window Example

17. Figure 10-14-continued
SenderSender

18. Figure 10-14-continued
ReceiverReceiver

19. Figure 10-15

20. Flow Diagram: Normal
Operation
Time
Sender Receiver
Time
Frame 0
ACK 1
Frame 1
ACK 0
S = 0
S = 1
R = 0
R = 1
R = 0
Deliver
Deliver

21. Damaged FrameDamaged Frame
Figure 10-16

22. 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

23. 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 1
S = 1
Timeout
ACK 0
S = 1
S = 0
R = 0
Frame 0
expected; discard
Deliver
Deliver

24. Damaged FrameDamaged Frame
Figure 10-19

25. Lost FrameLost Frame
Figure 10-20

26. Lost ACKLost ACK
Figure 10-21

27. Selective RejectSelective Reject
Figure 10-22