Mixing UDP and TCP in a Diffserv assured forwarding PHB - a programmable networks scenario

The Differentiated Services assured forwarding PHB is attractive from the network management perspective because it signals congestion by selective, random packet drops. End systems are expected to adapt their transmission rate in response permitting a level of fuzziness in resource allocation. While TCP-based applications are an obvious target of assured forwarding, streams using RTP over UDP are potentially adaptable using the packet loss indication in the return RTCP packets. We report results from a testbed system we have constructed around a simple implementation of assured forwarding in a rudimentary IntServ over DiffServ scenario. We demonstrate that, with suitably chosen RED parameters, two TCP and two UDP streams can be held to approximately their policed rates. The UDP-based DVD video stream is controlled by dropping the MPEG B frames using appropriate filters in a router. We use this to illustrate the type of application-oriented service that could be implemented by a service provider in a programmable networks scenario.