Worst-case performance limitation of TCP SACK and a feasible solution

In the present implementation of the transmission control protocol (TCP) selective acknowledgment (SACK), every SACK block needs 8 bytes to carry information about the received packets, back to the sender. Since TCP options field has a fixed length, there is a limit on the number of SACK block that can be carried by the acknowledgment packets. Under some error conditions, this limitation can force the TCP sender to retransmit packets that have already been received successfully by the receiver. This paper puts forward a proposal to modify the present SACK implementation, in order to prevent these unwanted retransmissions. We show that the proposed implementation of SACK mechanism increases the throughput of SACK enabled TCP connections.