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Consider a reliable data transfer protocol that uses only negative acknowledgments. 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 few losses. In this second case, would a NAK-only protocol be preferable to a protocol that uses ACKs? Why?

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A NAK-only protocol is not preferable to a protocol that uses ACKs especially when the sender sends data only infrequently.

• A NAK-only protocol will be able to detect that a packet has been lost only when the receiver receives the subsequent packet.

• As the sender sends data only infrequently, NAK-only protocol will take a long time to realize that a packet has been lost.

• NAK-only protocol will realize that the packet is lost only when the receiver will receive the packet with the sequence number, which is out of order.

• The receiver will then send a NAK to lost packet to the sender.

• Then the sender has to retransmit both the lost packet as well as the subsequent packet.

When the sender sends data frequently and the data loss rate is very less, then a NAK-only protocol is preferable to a protocol that uses ACKs.

• As the sender sends data frequently, NAK-only protocol will realize quickly when a packet has been lost.

• In NAK-only protocol, the receiver need not have to send acknowledgment for every packet the receiver receives.

• As the data loss rate is very less, so the receiver will rarely send NAK for the lost packet to the sender.


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