1. Overview Jaringan Komputer (2)
Kuliah 3
Overview Jaringan Komputer (2)

2. Data Link Layer Services Provided to the Network Layer Framing
Error Control
Flow Control

3. Functions of the Data Link Layer
Provide service interface to the network layer
Dealing with transmission errors
Regulating data flow
Slow receivers not swamped by fast senders

4. Functions of the Data Link Layer (2)

5. A character stream. (a) Without errors. (b) With one error.
Framing
A character stream. (a) Without errors. (b) With one error.

6. Framing (2) (a) A frame delimited by flag bytes.
(b) Four examples of byte sequences before and after stuffing.

7. Framing (3) Bit stuffing (a) The original data.
(b) The data as they appear on the line.
(c) The data as they are stored in receiver’s memory after destuffing.

8. Error Detection and Correction
Error-Correcting Codes
Error-Detecting Codes

9. Error-Correcting Codes
Use of a Hamming code to correct burst errors.

10. Error-Detecting Codes

11. Data Link Protocols Simplex Stop-and-Wait Protocol
One-Bit Sliding Window Protocol
Go Back N
Selective Repeat

12. Stop-and-Wait Simplest form of flow control.
How does it work? (assume error-free channel)
(1) Send 1 frame;
(2) Wait for ACK.
(3) Go to 1.

13. Noisy Channels

14. Stop-and-Wait in Noisy Channels
Need timers, retransmissions, and duplicate detection.
Use sequence numbers.
Why?
Distinguish frames.
How large (e.g., in number of bits) are sequence numbers?

15. ARQ Protocols Automatic Repeat Request.
Protocols that wait for ACK before sending more data.
ACKs now are used for flow AND error control.
What can happen?
At receiver: frame arrives correctly, frame arrives damaged, frame does not arrive.
At sender: ACK arrives correctly, ACK arrives damaged, ACK does not arrive.

16. ARQ Protocols Sender: Receiver: Send frame 0. Start timer.
If ACK 0, arrives, send frame 1.
If timeout, re-send frame 0.
Receiver:
**Waits for frame.
If frame arrives, check if correct sequence number.
Then send ACK for that frame.
Go to (**)

17. Sliding Window Protocols
Window: number of “outstanding” frames at any given point in time.
Every ACK received, window slides…

18. Sliding Window Protocols
A sliding window of size 1, with a 3-bit sequence number.
(a) Initially.
(b) After the first frame has been sent.
(c) After the first frame has been received.
(d) After the first acknowledgement has been received.

19. A One-Bit Sliding Window Protocol
Normal case. (b) Abnormal case.
The notation is (seq, ack, packet number). An asterisk indicates where a network layer accepts a packet.

20. A Protocol Using Go Back N
Pipelining and error recovery. Effect on an error when
(a) Receiver’s window size is 1.
(b) Receiver’s window size is large.

21. A Sliding Window Protocol Using Selective Repeat
(a) Initial situation with a window size seven.
(b) After seven frames sent and received, but not acknowledged.
(c) Initial situation with a window size of four.
(d) After four frames sent and received, but not acknowledged.