Sliding Window:
In sliding window method, Sender can sent multiple frames at a time before needing an acknowledgment from receiver’s side.
The maximum window size for data transmission using the selective reject protocol with n-bit frame sequence numbers is 2^(n-1)
The maximum window size for data transmission using the SR protocol with n-bit frame sequence numbers is (N+1)/2
The maximum window size for both sender and receiver with n-bit frame sequence numbers is N/2.
Numerical question based on sliding window protocol
This question asked in JAN 2017 Paper 3 in CBSE NET
Question no 26:
Station A uses 32 byte packets to transmit messages to station B using sliding window protocol. The round trip delay between A and B is 40 milliseconds and the bottleneck bandwidth on the path between A and B is 64 kbps. The optimal window size of A is
(A) 20
(B) 10
(C) 30
(D) 40
(A) 20
(B) 10
(C) 30
(D) 40
Explanation:
Always write given data in question
Round Trip propagation delay = 40ms
Frame size = 32 bytes=32*8 bits ( because 1 byte = 8 bits)
Bandwidth = 64 kbps
Transmission Time = Frame size/Bandwidth = 32*8/(64) ms = 4 ms
Let n be the window size.
Utilization = n/(1+2a)
where a = Propagation time / transmission time = n/(1+40/4)
For maximum utilization: n = 11
Ans: (B)