TCP throughput guarantee in the DiffServ Assured Forwarding service: what about the results?

Since the proposition of quality of service (QoS) architectures by the Internet Engineering Task Force (IETF), the interaction between TCP and the QoS services has been intensively studied. This paper proposes to look forward to the results obtained in terms of TCP throughput guarantee in the DiffServ assured forwarding (DiffServ/AF) service and to present an overview of the different proposals to solve the problem. It has been demonstrated that the standardized IETF DiffServ conditioners such as the token bucket color marker and the time sliding window color maker were not good TCP traffic descriptors. Starting with this point, several propositions have been made, and most of them present new marking schemes in order to replace or improve the traditional token bucket color marker. The main problem is that TCP congestion control is not designed to work with the AF service. Indeed, both mechanisms are antagonists. TCP has the property to share in a fair manner the bottleneck bandwidth between flows while DiffServ network provides a level of service that is controllable and predictable. In this paper, we build a classification of all the propositions made during the past few years and compare them. As a result, we will see that these conditioning schemes can be separated into three sets of action levels and that the conditioning at the network edge level is the most accepted one. We conclude that the problem is still unsolved and that TCP, conditioned or not conditioned, remains inappropriate for the DiffServ/AF service.