This paper illustrates comparative analysis of TCP-SACK against three different TCP variants namely TCP-Reno, TCP-New Reno, and TCP-Tahoe. The comparison is conducted with the help of simulations, which corroborate the reliability of TCP-SACK as a stream-based, connection-oriented, and most reliable end-to-end data transfer protocol amongst other TCP variants. The performances of TCP variants have been evaluated against constant rate assignment for the values of 2500bps and 4500bps. The selected parameter provides different results in terms of TCP throughput for all of the TCP variants. In each case, the values of the congestion window (cwnd) are recorded and plotted against regular intervals of time. The behaviour of TCP variants is studied by observing the simulated graph results provided for each case. The results prove TCP-SACK to be efficient wireless, heterogeneous networks.