Patent ID: 8023448

Claim:
A relay apparatus for performing multicast communications in PIM-SM (Protocol Independent Multicast Sparse-Mode), the relay apparatus being connected to at least one RP (Rendezvous-Point) via a network and accommodating a transmission terminal of a multicast packet, comprising: a line for receiving a multicast packet from said transmission terminal; a multicast packet relay processor for searching a route of said multicast packet in accordance with a multicast address of said received multicast packet; a memory for storing an RP management table storing a correspondence between a multicast address and an RP address; an RP reachability monitor for monitoring reachability by transmitting a ping packet to said RP and storing monitor results RP in said RP management table in said memory; and a PIM-SM route calculator for searching from said RP management table an RP address corresponding to the multicast address of said multicast packet received at said line, judging a monitor result of reachability of the searched RP address, and in accordance with the judgement, encapsulating said multicast packet into a unicast packet and transmitting said unicast packet to said RP having said searched RP address, wherein said RP reachability monitor transmits periodically said ping packet.