GXcast: generalized explicit multicast routing protocol

Recently several multicast mechanisms were proposed that scale better with the number of multicast groups than traditional multicast. These proposals are known as small group multicast (SCM) or explicit multicast (Xcast). Explicit multicast protocols, such as the Xcast protocol, encode the list of group members in the Xcast header of every packet. If the number of members in a group increases, routers may need to fragment an Xcast packet. Fragmented packets may not be identified as Xcast packets by routers. In this paper, we show that the Xcast protocol does not support the IP fragmentation. We show also that avoiding fragmentation limits the group size that can be handled by the Xcast protocol. First, we describe the Xcast protocol, the Xcast+ protocol (which is an extension of Xcast) and we compare these two protocols with traditional multicast protocols. We propose then a generalized version of the Xcast protocol, called GXcast, intended to permit the Xcast packets fragmentation and to support the increasing number of members in a multicast group. The behavior of the GXcast protocol is analyzed according to several criteria. Finally, we present and evaluate with simulations an improvement to GXcast and we conclude that GXcast is a feasible and promising protocol.