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 wit ...
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
The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships. IGMP is an integral part of IP multicast and allows the network to direct mu ...
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. 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 daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
. 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 d ...
. For
IPv6
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. I ...
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