MultiGRIP: Quality of Service Aware Multicasting over DiffServ
University of
Efficient delivery of real-time multicast traffic imposes on the underlying network infrastructure the burden of supporting Quality of Service (QoS). This can be quite a complex issue in a Differentiated Services (DiffServ) IP network, especially if multicast users are allowed to dynamically join and leave the multicast tree. In fact, since DiffServ lacks of explicit reservation states, i) a replicating node cannot test whether a corresponding reservation exists on an output link, and ii) upon a dynamic join of a QoS multicast user, the DiffServ network lacks of control functions to verify whether resources are available along the new path. In this document, we present a solution to support dynamic multicast with QoS over a DiffServ network. Our solution combines two ideas. First, resource availability along a new QoS path is verified via a probe-based approach. Second, QoS is maintained by marking replicated packets with a special DSCP value, before forwarding them on the QoS path. We are fully aware that the possible application of the principles described in this draft in the Internet raises many issues, which we do not address. Our aim, then, is not proposing a fully-fledged solution, but contributing to the on-going discussions in the international arena on these matters, by means of what we may see also as a problem statement document.