HOME

TheInfoList



OR:

Source-specific multicast (SSM) is a method of delivering
multicast In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with ...
packets in which the only packets that are delivered to a receiver are those originating from a specific source address requested by the receiver. By so limiting the source, SSM reduces demands on the network and improves security. SSM requires that the receiver specify the source address and explicitly excludes the use of the (*,G) join for all multicast groups in RFC 3376, which is possible only in IPv4's IGMPv3 and IPv6's MLDv2.


Any-source multicast (as counterexample)

Source-specific multicast is best understood in contrast to any-source multicast (ASM). In the ASM service model a receiver expresses interest in traffic ''to'' a
multicast address A multicast address is a logical identifier for a group of hosts in a computer network that are available to process datagrams or frames intended to be multicast for a designated network service. Multicast addressing can be used in the link laye ...
. The multicast network must # discover all multicast sources sending to that address, and # route data from all sources to all interested receivers. This behavior is particularly well suited to groupware applications where # all participants in the group want to be aware of all other participants, and # the list of participants is not known in advance. The source discovery burden on the network can become significant when the number of sources is large.


Operation

In the SSM service model, in addition to the receiver expressing interest in traffic ''to'' a multicast address, the receiver expresses interest in receiving traffic ''from'' only one specific source sending to that multicast address. This relieves the network of discovering many multicast sources and reduces the amount of multicast routing information that the network must maintain. SSM requires support in last-hop routers and in the receiver's
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
. SSM support is not required in other network components, including routers and even the sending host. Interest in multicast traffic from a specific source is conveyed from hosts to routers using IGMPv3 as specified in RFC 4607. SSM destination addresses must be in the ranges 232.0.0.0/8 for
IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...
. For
IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...
current allowed SSM destination addresses are specified by ff3x::/96, where the hexadecimal digit x represents the scope. Note however that the allocation may be extended in the future so receivers and network equipment should treat any ff3x::/32 address as SSM.


References

* * {{cite web , author=H. Holbrook, B. Cain , date=August 2006 , title=RFC 4607: Source-Specific Multicast for IP , url=http://tools.ietf.org/html/rfc4607


External links


JAVA Source-specific multicast support library
Internet broadcasting Internet Protocol Network protocols