Question

Problem 9:6 Points (why?) Most IP datagram reassembly algorithms have a timer to avoid having a lost fragment tie up reassembly buffers forever. Suppose that a datagram is fragmented into six fragments. The first and second fragments arrive, then the fifth and sixth ones arrive, but the third and fourth ones are delayed. Eventually, the timer goes off and the six fragments in the receiver's memory are discarded. A little later, the third and fourth fragments stumble in. What should be done with them?

Answer 1

in this situation re-transmission will get place because timer get expired as well as packets are discarded from memory so re-transmit packets with go-back-n protocol or by selective repeat protocol to recover data from packet and reassemble it on receiver side.

in selective repeat protocol only those packets are re-transmit which are lost and in go - back - n protocol all packets will get re-transmit

Thanks