1. DATA COMMUNICATION
Lecture-38

2. Recap of Lecture 37
Line Discipline
ENQ/ACK
POLL/SELECT
Flow Control

3. Overview of Lecture 38 Flow Control -Stop-and-Wait -Sliding Window
Error Control

4. Flow Control
A set of procedures used to restrict the amount of data the sender can send before waiting for acknowledgment
Each receiving device has a buffer

5. Flow Control

6. Stop-and-Wait
Sender sends one frame and waits for an acknowledgment before sending the next frame
Simple, but inefficient

7. Stop-and-Wait

8. Sliding Window Sliding window is an imaginary box
At both sender and the receiver
Frames are numbered modulo-n, window size is n-1
An ACK includes the number of next frame it expects

9. Sliding Window
The sender can transmit several frames before needing an acknowledgment

10. Sender Window Sliding window of the sender
Shrink from the left when frames are sent
Expands to the right when ACKs are received

11. Sender Window

12. Receiver Window Sliding window of the receiver
Shrink from the left when frames are received
Expands to the right when ACKs are sent

13. Receiver Window

15. Error Control
Error control in the data link layer is based on ARQ (Automatic Repeat Request)
Retransmission in three cases
Damaged frame, lost frame, and lost ACK

16. Error Control

17. Stop-and-Wait ARQ: Damaged Frame

18. Stop-and-Wait ARQ: Lost Frame

19. Stop-and-Wait ARQ: Lost ACK

20. Summary
Flow Control
-Stop-and-Wait-
-Sliding Window
Error Control

21. Suggested Reading
Section 10.2,10.3 “Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan