Question

A sender wants to transmit 16 frames in data link layer to a receiver, and every 4th transmission is lost. How many total transmissions are required if

A) Go-back-3 flow control is used?

B) Selective repeat is used?

C) Stop-and-wait is used?

Answer 1

Solution:

Given,

=>Number of frames to be transmitted = 16 frames

=>Every 4th transmission is lost

(a)

Given,

=>Go-back-3 flow control is used.

Explanation:

=>Let say frame numbers are 1 to 16.

=>Window size of GBN = 3 means atmax 3 frames can be sent from the sender side.

=>In case of GBN if a frame is lost inside the window then whole window is retransmitted.

Calculating total number of frames transmitted:

1 2 3 4 2 3 4 5 6 7 8 6 7 8 9 10 11 12 10 11 12 13 14 15 16 14 15 16

=>Hence total number of frames transmitted = 28

(b)

=>Selective repeat is used.

Explanation:

=>In selective repeat only lost frame is retransmitted.

Calculating total number of frames transmitted:

1 2 3 4 4 5 6 7 7 8 9 10 10 11 12 13 13 14 15 16 16

=>Total number of frames transmitted = 21

(c)

Given,

=>Stop and wait protocol is used.

Explanation:

=>In stop and wait protocol only lost frame is retransmitted.

Calculating total number of frames transmitted:

1 2 3 4 4 5 6 7 7 8 9 10 10 11 12 13 13 14 15 16 16

=>Total number of frames transmitted = 21

I have explained each and every part with the help of statements attached to it.