Proxy-Assisted TCP Maximum Receive Window Control in Split-TCP Capable GEO Satellite Networks
Merkourios Karaliopoulos, Rahim Tafazolli, B.G. Evans · 2004
In this paper we focus on proxy-aware split-capable satellite networks. In addition to the well-reported performance enhancement, the split connection mechanism provides additional flexibility with respect to the treatment of TCP traffic. Having as a starting point an analytical framework drawing on fixed-point approximations, we introduce an algorithm for the active control of the TCP maximum receive window of the satellite component of the split-TCP connection. The algorithm accelerates transfers over the satellite network at low load without overloading unnecessarily the MAC buffers at high load. The utility of the algorithm is evaluated against simulations. I. Introduction CP Performance Enhancing Proxies (TCPPEPs) are among the favorite methods of enhancing TCP performance over satellite links. These solutions are viewed with skepticism within the Internet community, since their deployment within the Internet may contrast on a number of occasions with the end-to-end design principle dominating the latter 1 . The main arguments against their use reflect reliability and security concerns 2 . Nevertheless, satellite operators have deployed and still deploy these mechanisms, while they are exploring solutions for the aforementioned concerns 3 . The split-TCP mechanism is only one of the potential features of TCPPEPs. The potential of split-TCP connections to enhance the TCP performance over the satellite links has been well reported, mostly under simple assumptions for the satellite link model 4,5 , and to a lesser extent taking into account the impact of lower layers of the satellite radio interface 6 . Once the connection is split, the possible action of the proxy agent can vary in a wide range. The proxy can exploit the TCP-specific state that is maintained locally and use it for different purposes, effectively providing the network with information that in the standard case is not easily available. The trade-off is then between the level of support the proxy provides to TCP and the respective complexity. In this paper we investigate more closely a specific TCPPEP feature that can improve the TCP performance, the dynamic control of the maximum send window size, hereafter interchangeably called maximum receive window, of the TCP connections over the satellite link. We focus our attention on Medium Access Control (MAC)-shared satellite links, where the TCP connections are subject to bandwidth on demand mechanisms. The paper evolves as follows. Section II provides an analytical study of the impact of the TCP maximum receive window variable on the protocol performance, when multiple TCP connections share the satellite link under the control of packet-level demand assignment procedures. This analysis is the starting point for the derivation of the heuristic algorithm for the control of this variable in section III. The algorithm is then evaluated via ns2 simulations in section IV. We conclude our paper in section V. II. The impact of the maximum receive window variable of the split-TCP connection on the protocol performance