IP multicast implementation based on the multicast extensions to OSPF protocol

This paper describes an IP multicast implementation based on multicast extensions to open shortest path first (MOSPF) protocol. The MOSPF forwarding model presented in this study is used to forward multicast datagrams. The forwarding model has focused on interaction between MOSPF and OSPF in terms of group-membership link state advertisement (type-6 LSA) as well as developing a multicast routing table (MRT) and multicast forwarding cache (MFC). The MRT has been organised as a Patricia-based tree while the MFC has been maintained as hash-table data structures. The MFC entries are built from the local group database and the shortest path first (SPF) tree calculation. Since MOSPF protocol can only be deployed in networks running OSPF protocol, routing functionalities, such as flooding process, forming adjacencies, election of the designated router (DR) and the backup designated router (BDR), will be provided by the OSPF protocol. Implementation of MOSPF is required since MOSPF is the only multicasting routing protocol that can be configured for hierarchical multicast routing and also support for IP multicast's expanding ring search. In addition to that, MOSPF, like the other dense mode multicast routing protocols-distance vector multicast routing protocol (DVMRP) and protocol independent multicast (PIM) dense mode-is effective in commercial Internets.