Internet multicast provisioning issues for hierarchical architecture

Abstract

The ASM (any source multicast) have been proposed to forward IP multicast datagram. However, there remain unsolved deployment issues such as network management and address allocation of multicast sessions. To overcome the above issues, largely new three multicast mechanisms-SGM (Small Group Multicast), ALM (Application Level Multicast) and SSM (Source Specific Multicast)-have been proposed. While the SGM and ALM can support multicast service without constructing the multicast routing tree, SSM constructs the multicast routing tree rooted in the source. SGM is proposed to support a very large number of small multicast groups. However, since SGM needs an additional packet header to service multicast, modification of the legacy routers is inevitable. ALM provides multicast by means of a combination of unicast in WAN and multicast in LAN. Since the standard is not fixed, this mechanism has limited implementation conditions. SSM identifies the multicast session not by G but by (S, G) pair. This mechanism solves the multicast address allocation problem, which is the biggest issue in the ASM. However, all routers along the delivery path must maintain the state (S, G) in order to transmit multicast data. Though the three new mechanisms can solve the many of the problems, one feature of ASM, the scalability problem is not be removed at all. We propose a fast deployment mechanism, which is based on SSM as well as the use the Internet hierarchical architecture. This mechanism may help multicast deployment without any modification of the IP layer while the advantage of SSM is kept. A key feature of the new mechanism is the use of a different multicast service for macro level multicast and micro level multicast.