Computer-Networks

Question 48

Station A uses 32 byte packets to transmit messages to Station B using a sliding window protocol. The round trip delay between A and B is 80 milliseconds and the bottleneck bandwidth on the path between A and B is 128 kbps. What is the optimal window size that A should use?

A	20
B	40
C	160
D	320

Computer-NetworksSliding-Window-ProtocolGATE 2006

Question 48 Explanation:

T_t = L / B = 32 bytes/ 128 kbps = 32*8/128 ms = 2 ms
Round trip delay = 2 * T_p = 80 ms (given)
Optimal window size is = (T_t + 2*T_p) / T_t = 82 / 2 = 41
Option is not given, closest option is 40.

Correct Answer: B

Question 48 Explanation:

T_t = L / B = 32 bytes/ 128 kbps = 32*8/128 ms = 2 ms
Round trip delay = 2 * T_p = 80 ms (given)
Optimal window size is = (T_t + 2*T_p) / T_t = 82 / 2 = 41
Option is not given, closest option is 40.