Consider a reliable data transfer protocol that uses only negative acknowledment
ID: 3794602 • Letter: C
Question
Consider a reliable data transfer protocol that uses only negative acknowledments. Suppose the sender sends data only infrequently. Would a Nak-only protocol be preferable to a protocol that uses ACKs? Why? Now suppose the sender has a lot of data to send and the end-to-end connection experiences a few losees. In this second case, would a NAK-only protocol be preferable to a protocol that uses ACKs? Why?
Chapter 3
Jim Kurose and Keith Ross,”Computer Networking – A Top-Down Approach”, Addison-Wesley, Seventh Edition, 2017.
ISBN-13: 978-0-13-359414-0
Explanation / Answer
In a NAK only protocol, the loss of packet x is only detected by the receiver when packet x+1 is received. That is, the receiver receives x-1 and then x+1, only when x+1 is received does the receiver realizes that x was missed. If there is a long delay between the transmission of x and the transmission of x+1, then it will be a long time until x can be recovered, under a NAK only protocol. On the other hand, if data is being sent often, then recovery under a NAK-only scheme could happen quickly. Moreover, if errors are infrequent, then NAKs are only occasionally sent (when needed), and ACK are never sent – a significant reduction in feedback in the NAK-only case over the ACK-only case.