Transport Layer challenges in hybrid military satellite networks

Abstract

On 26th of March 2010, the Norwegian Parliament approved the Norwegian Armed Forces project of acquiring a communications satellite. Combined with the increasing use of civilian technology like the Transmission Control Protocol (TCP) in military networks, research on TCP in military and satellite environments are required.

This thesis provides a thorough description of TCP, satellite environments, and related challenges in military networks containing both satellite and radio links. Geostationary satellites introduce an added delay of around 550 ms, while radio links are prone to high bit error rates. In such environments, TCP performance may suffer severely - the penalty depends on several factors, including the TCP flavor utilized at the sender. For Windows 7, the default TCP flavor is TCP NewReno, while Compound TCP is available. A wide variety of flavors are available for Linux, including the satellite-tailored variant TCP Hybla - the default flavor is CUBIC.

Evaluation and analysis through emulation has shown the mentioned TCP flavors to exhibit significant different performances at the sender side. The flavors available to Windows 7 perform poorly in lossy networks when compared to CUBIC and especially Hybla which outperforms the other flavors in such environments. CUBIC and Hybla are also seen to be more aggressive than Windows 7 flavors. If competing on the same bottleneck, this results in an unfair division of bandwidth - at the cost of Windows 7 flavors. Possible solutions include tuning of the TCP flavors and avoiding mixed-OS/TCP environments.

Another approach is the use of a Performance Enhancing Proxy at the sender side. The proxy evaluated, PEPsal, will intercept all TCP flows and forward traffic along a new TCP flow towards the intended receiver. This new TCP flow utilizes a tailored TCP flavor (e.g. Hybla) in order to increase performance regardless of the original TCP flavor at the sender. Analysis shows significant improved performance of Windows 7 flows in lossy networks. The unfair division of bandwidth is also decreased, but performance issues where observed. In addition, PEPsal break the end-to-end principle of TCP, and depends on a plaintext TCP header - causing challenges in encrypted military networks.