Indian Journal of Science and Technology
Year: 2015, Volume: 8, Issue: 17, Pages: 1-14
K. Sindhu Raj 1* , B. Thanudas2 , N. Radhika1 and V. S. Smitha3
1 Amrita Vishwa Vidyapeetham, Amrita Nagar PO, Coimbatore – 641 112, Tamil Nadu, India; [email protected], [email protected]
2 CNG, VSSC, ISRO, Thiruvananthapuram – 695022, Kerala, India; [email protected]
3 VSSC, ISRO, Thiruvananthapuram – 695022, Kerala, India; [email protected]
Objective: In this world of advanced technology, satellite communication is the basis for all data communications. TCP was designed to be flexible and robust but it cannot perform efficiently over the satellite links with long delay. The major objective of our work is to propose a novel flow control algorithm for satellite network to prevent the heavy degradation in the network performance due to long propagation delay, high bit error rate and bandwidth asymmetry. Methods: A strong flow control mechanism is necessary to eliminate the network performance degradation due to the satellite link characteristics like long propagation delay, high bit error rate and bandwidth asymmetry. Satellite-TCP is a flow control mechanism based on the negative acknowledgement strategy and connection splitting. The satellite link utilization is monitored and the active connections are assigned with the window values. The window values were considered as it can easily reflect the available bandwidth in the satellite links. Findings: The major problems affecting the performance in satellite links are long propagation delay, high bit error rate and bandwidth asymmetry. The proposed Flow Control Algorithm called Satellite-TCP is based on controlling the flow of Negative Acknowledgement packets (NACK), according to the level of congestion at the network. The two main modules in the proposed system include an enhanced TCP flow control mechanism and a data loss recovery mechanism. Among this the flow control is based on link utilization measurements and throughput calculation techniques. Data loss recovery strategy is based on Negative Acknowledgements coming from the receiver side. In this way, we can decrease the amount of packet loss in the network and even eliminate the packet loss, sometimes. Satellite-TCP adopts a window growth strategy to accelerate the speed of increase in the size of congestion window. The flow control mechanism not only enhanced the throughput of forward link but also greatly reduced the bandwidth occupancy rate in back-ward link in the satellite network. This in turn increases the overall performance of the satellite link. Improvements: If we add a priority based strategy to the new flow control mechanism, it can judge the network performance according to the data loss. Moreover we are expecting that, if we add a priority bit based strategy to the new flow control mechanism, it will help to distinguish the specific reasons for data loss and can take corresponding flow control strategies. While considering the throughput and loss rate, Satellite –TCP is showing excellent performance in the case of forward link but it performs poor in the case of backward link. So we are planning to extend our work in such a way that it will perform well in the case of backward link also.
Keywords: Bandwidth Asymmetry, Bit Error Rate, Flow Control Mechanism, Loss Recovery System, Propagation Delay, Satellite –TCP
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