A system uses the GobackN ARQ protocol with a window size of

A system uses the Go-back-N ARQ protocol with a window size of 7. If each packet carries 1000 bits of data, how long does it take to send 1 million bits of data if the distance between the sender and receiver is 5000 Km and the propagation speed of the signal is 2x10^8 meters per second? Ignore transmission, waiting, and processing delays. Assume no errors in the link.

Solution

We consider a size 7 and then wait for the result of the whole window. We need to send 1000/7 143

windows.

Data frame trip time = 5000 km / 200,000 km = 25 ms

ACK transmission time = 0 negligible

ACK trip time = 5000 km / 200,000 km = 25 ms

Delay for 1 window = 25 + 25 = 50 ms.

Total delay = 143 × 50 ms = 7.150 s