Using flow control to improve performance of Demand-Assignment Multiple Access systems with performance enhancing proxies

Abstract

It is widely known that TCP's congestion control algorithm can cause it to under-perform when round trip times and error rates are high. Performance Enhancing Proxies (PEPs) can improve performance by breaking end-to-end TCP connections and using a separate, tuned transport protocol to transit ‘stressed’ links. While PEPs can be tuned to work well when a single pair of PEPs bracket a fixed-rate link, these systems can be difficult to tune when the stressed link has variable bandwidth as in a Demand Assigned Multiple Access (DAMA) scheme, when multiple encrypted enclaves must share the outgoing bandwidth, or when the round trip times vary widely. Previous efforts have shown the effect of using a modified version of the TCP Vegas congestion control algorithm in Time Division Multiple Access (TDMA) DAMA systems where bandwidth is allocated based on current queue length and where multiple enclaves must share the outgoing bandwidth. This paper examines the performance of a DAMA based system when the TCP PEP uses flow control between the PEP and the DAMA access terminal. This improves performance by removing an adverse interaction between PEP congestion control and DAMA channel access protocols. We show the effects of employing proxies when the modem provides direct feedback about the amount of data it is willing to consume.