Multicasting the ITU MCS: integrating point-to-point and multicast transport

Many designs for multicast transport protocols presume a homogeneous view of the network environment they are operating in, the latter hiding the various networks´ features from the transport layer. However, knowing its underlying network characteristics enables a multicast transport protocol to adjust itself to particular networks. This can be important for providing a scalable, reliable multicast transport. A multicast group often is faced with different topologies (point-to-point links vs. broadcast capable networks) and different network service qualities (e.g. packet loss probability, throughput, and delay). For some parts of the group, network connectivity allows multicasting and the usage of negative acknowledgment schemes, for others, point-to-point connections with positive ACKs are required. Trying to unite both service types within a single type of transport is inefficient and often not possible at all. We present a hybrid approach to a multicast transport that extends a standardized multicast service based on point-to-point connections to be efficiently applicable in multicast capable networks as well. A typical teleconferencing scenario we have in mind consists of several sites, interconnected via WANs, each of which may involve several participants via LANs