الفهرس 
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Abstract
This thesis describes proposed modifications to TCP/IP protocol over satellite links in order to avoid performance drop in rates that are caused by communication errors rather than network congestion. On satellite.links, performance is limited by the delay inherent in geosynchronous systems and the probability of bit errors, hence achieving high efficiency requires some modifications to the TCP protocol.
TCP/IP has many parameters that control its performance. In this thesis, the focus is on modifying the existing TCP/IP congestion control scheme, which is implemented using the four interrelated algorithms: slow starts, congestion avoidance, fast transmit and fast recovery algorithms [1, 2, 3, 4]. The proposed modifications improve the performance of TCP over satellite links by eliminating the unneeded restart of slow start when TCP is still in slow start or congestion avoidance phases [5]. Entering slow start again is accompanied by the reduction of the size of the threshold value leading to poor performance on a high capacity link. Our proposed protocol (TCP SAT) tries to eliminate this unneeded drop in TCP performance over satellite links.
To validate the new protocol and test its performance, network simulator version 2 (ns2) was used. Simulation scenarios were performed in order to compare the performance of the new proposed protocol TCP SAT and three variants of TCP protocol: TCP Tahoe, TCP SACK and TCP Reno.
The results showed that there is an improvement in the slow start phase of TCP SAT where the new protocol was able to overcome link errors. Therefore, the number of packets reaching the receiver’s end increased.