Influence of the discarding the out-of-profile packets policy on TCP traffic

In the recent year a variety of approaches for QoS support in the Internet such as Integrated Services [1], Differentiated Services [2], Bandwidth Distribution Scheme (BDS) [3], and others have been proposed. Most of the proposed approaches rely on the traffic policing unit, which may mark, delay, or drop packets that arrive above their reserved rate. The packets that arrive above their reserved rate are often referred to as out-of-profile packets. Often the policer limits the transmission rate of the flows that enter the network by dropping all out-of-profile packets. The Transport Control Protocol (TCP) [4] treats packet loss as an indication of congestion and reduces the flow's congestion window. Reducing the flow's congestion window effectively reduces the transmission rate of that flow. Thus, dropping out-of-profile packet may have a double effect on the transmission rate of the flow: the flow's rate is reduced by the traffic policer and by the congestion control mechanism of TCP. In this paper we examine the influence of the traffic policer that drops out-of-profile packets on the TCP traffic. We examine the performance of the traffic policer within the BDS framework using the OPNET Modeler network simulator [5].