Effects of TCP Transfer Buffers and Congestion Avoidance Algorithms on the End-to-End Throughput of TCP-over-TCP Tunnels

Tunneling is a networking approach to virtually encapsulate some channel of private communication within another channel, which is usually public, through means of encryption. Tunneling protocols allow for the establishment of Virtual Private Networks (VPNs) which are useful for anonymity and access to private networks behind firewalls. The many tunneling protocols generally take the form of one networking protocol being transmitted over another, or even over the same protocol. One noticeably less represented variation is TCP-over-TCP due to the overall degradation of performance which is observable as a distinct loss of overall end-to-end throughput of application data, called the goodput. This known loss of performance is a product of the multiple, nested congestion control algorithms inherent to Transmission Control Protocol (TCP) and has been coined the TCP meltdown problem. In this research, we have investigated the contributions that multiple factors play in degrading the goodput of TCP-over-TCP tunnels. Through ns-3 simulation we have studied the performance of the tunnel as we vary transfer buffer size, congestion avoidance algorithm, bandwidth of inner and outer channels, and drop rate. Our simulation is built with the ability to vary those parameters plus more for future cases. Through this analysis, we were able to find the performance of 448 different configurations, not counting experimental control cases.