Methods for providing rendezvous point router redundancy in sparse mode multicast networks

#The present invention relates generally to Internet Protocol (IP) multicast-based communication networks and, more particularly, to sparse mode multicast networks incorporating Rendezvous Points (RPs).

#IP Multicast technology has become increasingly important in recent years. Generally, IP multicasting protocols provide one-to-many or many-to-many communication of packets representative of voice, video, data or control traffic between various endpoints (or “hosts” in IP terminology) of a packet network. Examples of hosts include, without limitation, base stations, consoles, zone controllers, mobile or portable radio units, computers, telephones, modems, fax machines, printers, personal digital assistants (PDA), cellular telephones, office and/or home appliances, and the like. Examples of packet networks include the Internet, Ethernet networks, local area networks (LANs), personal area networks (PANs), wide area networks (WANs) and mobile networks, alone or in combination. Node interconnections within or between packet networks may be provided by wired connections, such as telephone lines, T1 lines, coaxial cable, fiber optic cables, etc. and/or by wireless links.

#Multicast distribution of packets throughout the packet network is performed by various network routing devices (“routers”) that operate to define a spanning tree of router interfaces and necessary paths between those interfaces leading to members of the multicast group. The spanning tree of router interfaces and paths is frequently referred to as a multicast routing tree. Presently, there are two fundamental types of IP multicast routing protocols, commonly referred to as sparse mode and dense mode. Generally, in sparse mode, the routing tree for a particular multicast group is pre-configured to branch only to endpoints having joined an associated multicast address; whereas dense mode employs a “flood-and-prune” operation whereby the routing tree initially branches to all endpoints of the network and then is scaled back (or pruned) to eliminate unnecessary paths. As will be appreciated, the choice of sparse or dense mode is an implementation decision that depends on factors including, for example, the network topology and the number of source and recipient devices in the network.

#The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

#FIG. 1 shows a portion of a multicast network incorporating a plurality of candidate RPs, wherein a first one of the candidate RPs defines a designated candidate RP (DCRP), the DCRP having been elected as the active RP for a particular multicast group, and a second one of the candidate RPs defines a virtual candidate RP (VCRP) according to one embodiment of the present invention;

#FIG. 2 shows various messages sent from a sender, receiver and RP in the multicast network of FIG. 1;

#Turning now to the drawings and referring initially to FIG. 1, there is shown a portion of an IP multicast communication system (or “network”) 100. Generally, the network 100 comprises a plurality of router elements 102 interconnected by links 104, 106. The router elements 102 are functional elements that may be embodied in separate physical routers or combinations of routers. For convenience, the router elements will hereinafter be referred to as “routers.” The links 104, 106 comprise generally any commercial or proprietary medium (for example, Ethernet, Token Ring, Frame Relay, PPP or any commercial or proprietary LAN or WAN technology) operable to transport IP packets between and among the routers 102 and any attached hosts.

#For purposes of example and not limitation, FIG. 1 presumes that the communication network 100 is a part of a multicast-based radio communication system including mobile or portable wireless radio units (not shown) distributed among various radio frequency (RF) sites (not shown). To that end, there is shown a zone controller/server 108 of the type often used to manage and assign IP multicast addresses for payload (voice, data, video, etc.) and control messages between and among the various radio frequency (RF) sites. However, as will be appreciated, the network 100 may comprise virtually any type of multicast packet network with virtually any number and/or type of attached hosts.

#As shown, the routers 102 of the network 100 are denoted according to their function(s) relative to the presumed radio communication system. Routers “CR1” and “CR2” are control routers which pass control information between the zone controller 106 and the rest of the communication network 100. Routers “SR1” and “SR2” are local site routers associated with RF sites which, depending on call activity of participating devices at their respective sites, may comprise either senders or receivers of IP packets relative to the network 100.