Question

In Go-back-N protocol with m=6, the sending machine is in the ready state with Sf=10 and Sn=15, An ACK with ACKNo =13 arrives, what are the next values of Sf, Sn and Rn?

Answer 1

Sf==>First Outstanding bytes in sender window.So before the Sf Byte all bytes are already acknowledged.

Sn==>Next Byte to be sent in sender window

Rn==>Next Byte to be received in receiving window

Ack no 13 has arrived means till the 12 byte all have received by receiver and expecting Byte No 13

So Sf variable will move and point to the 13th Byte

Sn will Still remain  the same.it might happened that from 13 to 14 still not reached to the receiver till the time of acknowledgment

Rn will point to the 13^th Byte.