Transport of TCP/IP Traffic over Assured Forwarding IP Differentiated Services

The Internet is currently facing a twofold challenge: to increase network capacity in order to accommodate a steadily increasing number of users, and to guarantee the Quality of Service for existing applications as well as for new multimedia applications requiring real-time network response. In order to meet these requirements, the Internet Engineering Task Force is currently defining the Differentiated Service architecture, which should offer a simple and scalable platform to guarantee differentiated Quality of Service in the Internet. In the Differentiated Services domain, the Assured Forwarding service is designed to provide data applications with acceptable performance, overcoming the limits of the best-effort service currently offered by the Internet. Since data applications mostly rely on the TCP transport protocol, it is important to examine the interaction between the TCP and the assured forwarding congestion avoidance and control mechanisms. The main purpose of this article is to shed light on this interaction and to show that, in the current Differentiated Services framework, poor performance of TCP traffic flows can result from the existing mismatch between the assured forwarding traffic conditioning procedures and the TCP congestion management. We propose a new adaptive packet marking policy to deal with congestion situations that may occur in the network. We show that with this policy the provisioned rate for TCP flows can be achieved. Transport of TCP/IP Traffic over