goBackN1.1

Question

MY QUESTION IS:
In Go BACK-N:

N is? window size or Sender window size?




A 1 Mbps satellite link connects two ground stations. The altitude of the satellite is 6000 km and speed of the signal is 3 × 10⁸ m/s. What should be the packet size for a channel utilization of 50% for a satellite link using go-back-63 sliding window protocol?

Assume that the acknowledgment packets are negligible in size and that there are no errors during communication.

Comments

I think in standard Go Back N receiver window size is 1 unless provided... So N must be sender window size

Answer 1

Since it Satellite Channel, if we calculate Tp (Propagation Delay = (2*d) / v), we will get 40ms.

efficiency is given as 50%. So in GBN efficiency formula is w / (1 + 2a)  = 1 / 2

after substituting all the values and after simplifying the expression, at the end we will get packet size as 640 bits (or) 80 Bytes.

So answer is 80 Bytes (or) 640 bits.

Answer 2

In GBN, N means Sender Window Size only and not receiver.