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What is Source Specific Multicast ?

April 26, 2017Multicast source

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What is Source Specific Multicast ?

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Source Specific Multicasting (SSM) uses the capabilities of IGMP v3 to tune PIM-SM to the needs of large scale, one-to-many, webcasting. IGMP v3 allows a source to explicitly request traffic from a particular (S,G) pair, through an INCLUDE report. In SSM edge routers must be modified to generate a PIM-SM SPT (S,G) join directly from a IGMP v3 INCLUDE report, joining directly to the source without using a Rendezvous Point at all. In SSM, routers in the interior of the network do not have to be modified at all, and could run standard PIM-SM. Knowledge of the source and group pair is assumed to come from “out-of-band”, such as from a web-page. Since the Internet address of the source is given explicitly, there is no need to run MSDP. SSM is now included as part of the PIM-SM v. 2 draft. More SSM implementation details can be obtained from my presentation at NANOG 21. The address range 232/8 has been reserved for SSM.