Using Performance Enhancing Proxies with Demand Assigned Multiple Access systems

TCPpsilas congestion control algorithm can cause it to under-perform when round trip times and error rates are high. Performance Enhancing Proxies (PEPs) improve performance by breaking end-to-end TCP connections and tuning the transport protocol used over the inter-PEP portion of the path. While PEPs can be tuned to work well when a single pair of PEPs bracket a fixed-rate satellite link, these systems can be difficult to tune when the SATCOM link has variable bandwidth, when multiple encrypted enclaves must share the outgoing bandwidth as in a demand assigned multiple access (DAMA) scheme, or when the round trip times vary widely. Complicating matters further, congestion control in the PEPs may interact with the DAMA allocation scheme, degrading performance. This paper examines system performance in a model of a medium-data-rate channel access protocol (MCAP) time division multiple access (TDMA) DAMA system where bandwidth is allocated based on current queue length and where multiple enclaves must share the outgoing bandwidth. We show the effects of employing proxies that use a modified version of the TCP Vegas congestion control algorithm and flow control between the layer-2 channel access scheme and the proxy. We examine the case where proxies are placed only next to the DAMA modems.