Question

When you write an email to your family, the email is sent over the Internet. Before the message is sent, it is broken into many data packets. These data packets are numbered consecutively, but they are out of order while transferred over the network. The packets need to be sequenced when they reach the destination computer so your family can read your message. Discuss how you would sort these packets with two kinds of sort algorithms.

Answer 1

1. Stop-n-Wait protocol :

This aims at sending an acknowledgement for each packets received and the order has to be maintained. If any packet is not received, no acknowledgement is sent to the sender. Hence the sender understands that the packet was not sent and hence re--transmits the packet. If any packet out of sequence reaches the receiver and the previous packets has not arrives, it send a NACK for negative acknowledgement hence telling the sender to send again.

2. Go back n protocol:

When ever any sequence reaches out of order or any previous packet is faulty, the receiver sends a NACK to the sender and sender sends all the packets sent there after from the negatively acknowledged packet.