Investigation of TCP Protocols in Dynamically Varying Bandwidth Conditions

Cognitive radio (CR) networks experience fluctuating spectrum availability that impacts the end to end bandwidth of a connection. In this paper, we conduct an extensive simulation study of three different window-based TCP flavorsNewReno, Westwood+, and Compound, each of which has unique methods to determine the available bandwidth and scale the congestion window appropriately. These protocols also differ in their respective sensitivities to the metrics of round trip time, loss rate, residual buffer space, among others. These metrics exhibit divergent behavior in CR networks, as compared to classical wireless networks, owing to the frequent channel switching and spectrum sensing functions, and this influences the choice of the TCP protocol. Our ns3 based simulation study reveals which specific rate control mechanism in these various TCP protocols are best suited for quickly adapting to varying spectrum and bandwidth conditions, and ensuring the maximum possible throughput for the connection.