TCP Westwood and Easy RED to Improve Fairness in High-Speed Networks Luigi Alfredo Grieco, Saverio Mascolo Dipartimento di Elettrotecnica ed Elettronica, Politecnico di Bari, Italy To appear at Seventh International Workshop on Protocols For High-Speed Networks (PfHSN'2002), April 22 - 24, 2002 Berlin, Germany. Sponsored by IFIP TC6 WG6.2, IEEE Comsoc TC on Gigabit Networking Abstract. TCP Westwood (TCPW) is a sender-side only modification of TCP Reno congestion control, which exploits end-to-end bandwidth estimation to properly set the values of slow-start threshold and congestion window after a congestion episode. This paper aims at showing via both mathematical modeling and extensive simulations that TCPW significantly improves fair sharing of high-speed networks capacity and that TCPW is friendly to TCP Reno. Moreover, we propose EASY RED, which is a simple Active Queue management (AQM) scheme that improves fair sharing of network capacity especially over high-speed networks. Simulation results show that TCP Westwood provides a remarkable Jain’s fairness index increment up to 200% with respect to TCP Reno and confirm that TCPW is friendly to TCP Reno. Finally, simulations show that Easy RED improves fairness of Reno connections more than RED, whereas the improvement in the case of Westwood connections is much smaller since Westwood already exhibits a fairer behavior by itself. 1. Introduction Packet switching networks require sophisticated mechanism of flow and congestion control in order to share resources and avoid congestion phenomena. Congestion control functions were introduced into the TCP in 1988 and have been of crucial importance in preventing congestion collapse [1],[2],[9]. However, while end-to-end TCP congestion control [4],[5] can ensure that network capacity is not exceeded, it cannot insure fair sharing of that capacity [1]. In this paper we investigate via both mathematical analysis and computer simulations the issue of fairness in high-speed networks when Westwood TCP is implemented at the sender side. Moreover we propose a simpler version of RED, called EASY RED and we investigate how it interacts with Reno and Westwood TCP. TCP Westwood (TCPW) performs an end-to-end estimate of the bandwidth available along a TCP connection to adaptively set the control windows after congestion [3]. The rationale of TCPW is simple: in contrast with TCP Reno, which implements a multiplicative decrease algorithm after congestion, TCPW sets a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced.