3. Computer Networks Unit-II Part 1

7/27/2019 3. Computer Networks Unit-II Part 1

1/42

7/27/2019 3. Computer Networks Unit-II Part 1

2/42

7/27/2019 3. Computer Networks Unit-II Part 1

3/42

7/27/2019 3. Computer Networks Unit-II Part 1

4/42

7/27/2019 3. Computer Networks Unit-II Part 1

5/42

7/27/2019 3. Computer Networks Unit-II Part 1

6/42

7/27/2019 3. Computer Networks Unit-II Part 1

7/42

7/27/2019 3. Computer Networks Unit-II Part 1

8/42

Character count.Flag bytes with byte stuffing.

Starting and ending flags, with bit stuffing.

Physical layer coding violations.

7/27/2019 3. Computer Networks Unit-II Part 1

9/42

7/27/2019 3. Computer Networks Unit-II Part 1

10/42

7/27/2019 3. Computer Networks Unit-II Part 1

11/42

7/27/2019 3. Computer Networks Unit-II Part 1

12/42

7/27/2019 3. Computer Networks Unit-II Part 1

13/42

7/27/2019 3. Computer Networks Unit-II Part 1

14/42

7/27/2019 3. Computer Networks Unit-II Part 1

15/42

7/27/2019 3. Computer Networks Unit-II Part 1

16/42

7/27/2019 3. Computer Networks Unit-II Part 1

17/42

7/27/2019 3. Computer Networks Unit-II Part 1

18/42

1. The network layer on A gives packet 1 to its data link layer. The

packet is correctly received at B and passed to the network layer on

B. B sends an acknowledgement frame back to A.

2. The acknowledgement frame gets lost completely. It just never arrives

at all.

3. The data link layer on A eventually times out. Not having received an,

lost or damaged and sends the frame containing packet 1 again.

4. The duplicate frame also arrives at the data link layer on B perfectly

and is unwittingly passed to the network layer there. If A is sending a

file to B, part of the file will be duplicated (i.e., the copy of the file

made by B will be incorrect and the error will not have been detected).In other words, the protocol will fail.

7/27/2019 3. Computer Networks Unit-II Part 1

19/42

7/27/2019 3. Computer Networks Unit-II Part 1

20/42

7/27/2019 3. Computer Networks Unit-II Part 1

21/42

In the previous protocols, data frames were transmitted in one directiononly.

In most practical situations, there is a need for transmitting data in both

directions. One way of achieving full-duplex data transmission is to

have two separate communication channels and use each one for

simplex data traffic.

7/27/2019 3. Computer Networks Unit-II Part 1

22/42

7/27/2019 3. Computer Networks Unit-II Part 1

23/42

7/27/2019 3. Computer Networks Unit-II Part 1

24/42

7/27/2019 3. Computer Networks Unit-II Part 1

25/42

7/27/2019 3. Computer Networks Unit-II Part 1

26/42

7/27/2019 3. Computer Networks Unit-II Part 1

27/42

7/27/2019 3. Computer Networks Unit-II Part 1

28/42

7/27/2019 3. Computer Networks Unit-II Part 1

29/42

7/27/2019 3. Computer Networks Unit-II Part 1

30/42

7/27/2019 3. Computer Networks Unit-II Part 1

31/42

7/27/2019 3. Computer Networks Unit-II Part 1

32/42

7/27/2019 3. Computer Networks Unit-II Part 1

33/42

7/27/2019 3. Computer Networks Unit-II Part 1

34/42

7/27/2019 3. Computer Networks Unit-II Part 1

35/42

7/27/2019 3. Computer Networks Unit-II Part 1

36/42

7/27/2019 3. Computer Networks Unit-II Part 1

37/42

7/27/2019 3. Computer Networks Unit-II Part 1

38/42

TheAddress fieldis primarily of importance on lines with multiple terminals,

where it is used to identify one of the terminals.

The Control fieldis used for sequence numbers, acknowledgements, and

other purposesThe Data fieldmay contain any information

The Checksum fieldis a cyclic redundancy code

The minimum frame contains three fields and totals 32 bits

7/27/2019 3. Computer Networks Unit-II Part 1

39/42

7/27/2019 3. Computer Networks Unit-II Part 1

40/42

A supervisory frame.

Type 0 is an acknowledgement frame (RECEIVE READY) used toindicate the next frame expected

Type 1 is a negative acknowledgement frame (REJECT). It is used to

indicate that a transmission error has been detected

Type 2 is RECEIVE NOT READY. It acknowledges all frames up to but

not including Next, just as RECEIVE READY does, but it tells the sender to

stop sendingType 3 is the SELECTIVE REJECT. It calls for retransmission of only the

frame specified

An Unnumbered frame

It is sometimes used for control purposes but can also carry data when

unreliable connectionless service is called for.

7/27/2019 3. Computer Networks Unit-II Part 1

41/42

7/27/2019 3. Computer Networks Unit-II Part 1

42/42