A differentiated services implementation for high-performance TCP flows

The IETF's recent di erentiated services architecture, which speci es a scalable mechanism for treating packets di erently, o ers new opportunities for building endto-end quality of service (QoS) systems. However, it also introduces new challenges. In particular, it is not clear whether TCP's ow and congestion control mechanisms work well with the mechanisms used for end-to-end QoS. For that reason it is essential to analyze whether the existing di erentiated services mechanisms can be used with standard TCP implementations or whether it is necessary to wait for upcoming features introduced in future modi ed versions of TCP. The Globus Architecture for Reservation and Allocation (GARA) supports ow-speci c QoS speci cation, immediate and advance reservation, and online monitoring and control of both individual resources and heterogeneous resource ensembles. Using GARA, we evaluated actual di erentiated services mechanisms provided by Cisco routers. We present the results of this evaluation and discuss their impact on the performance of popular TCP implementations.