Protocol Independent Multicast
Encyclopedia
Protocol-Independent Multicast (PIM) is a family of multicast
routing protocol
s for Internet Protocol
(IP) networks that provide one-to-many and many-to-many distribution of data over a LAN
, WAN
or the Internet
. It is termed protocol-independent because PIM does not include its own topology discovery
mechanism, but instead uses routing information supplied by other traditional routing protocol
s such as the Border Gateway Protocol
(BGP).
There are four variants of PIM:
Of the four, PIM-SM has the widest deployment.
PIM-SM is commonly used in IPTV
systems for routing multicast streams between VLANs, Subnet
s or local area networks.
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
routing protocol
Routing protocol
A routing protocol is a protocol that specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network, the choice of the route being done by routing algorithms. Each router has a priori knowledge only of...
s for Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
(IP) networks that provide one-to-many and many-to-many distribution of data over a LAN
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....
, WAN
WAN
WAN may refer to:* Wide area network * World Association of Newspapers* Wanborough railway station in England, which has the station code WAN...
or the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
. It is termed protocol-independent because PIM does not include its own topology discovery
Network topology
Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....
mechanism, but instead uses routing information supplied by other traditional routing protocol
Routing protocol
A routing protocol is a protocol that specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network, the choice of the route being done by routing algorithms. Each router has a priori knowledge only of...
s such as the Border Gateway Protocol
Border Gateway Protocol
The Border Gateway Protocol is the protocol backing the core routing decisions on the Internet. It maintains a table of IP networks or 'prefixes' which designate network reachability among autonomous systems . It is described as a path vector protocol...
(BGP).
There are four variants of PIM:
- PIM Sparse Mode (PIM-SM) explicitly builds unidirectional shared trees rooted at a rendezvous point (RP) per group, and optionally creates shortest-path trees per source. PIM-SM generally scales fairly well for wide-area usage. See the PIM Internet Standard RFC 4601.
- PIM Dense ModePIM Dense ModePIM dense mode is the mode of Protocol Independent Multicast which assumes that almost all receivers receive this packet stream....
(PIM-DM) uses dense multicastDense multicastDense mode multicast is one mode that multicast can use to construct a tree for sending packets to the multicast subscribers. It is the opposite of sparse multicast....
routing. It implicitly builds shortest-path trees by flooding multicastMulticastIn computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
traffic domain wide, and then pruning back branches of the tree where no receivers are present. PIM-DM is straightforward to implement but generally has poor scaling properties. The first multicast routing protocol, DVMRP used dense-mode multicast routing. See the PIM Internet Standard RFC 3973. - Bidirectional PIM explicitly builds shared bi-directional trees. It never builds a shortest path tree, so may have longer end-to-end delays than PIM-SM, but scales well because it needs no source-specific state. See Bidirectional PIM Internet Standard RFC 5015.
- PIM source-specific multicastSource-specific multicastSource-specific multicast is a method of delivering multicast packets in which the only packets that are delivered to a receiver are those originating from a specific source address requested by the receiver...
(PIM-SSM) builds trees that are rooted in just one source, offering a more secure and scalable model for a limited amount of applications (mostly broadcasting of content). In SSM, an IP datagram is transmitted by a source S to an SSM destination address G, and receivers can receive this datagram by subscribing to channel (S,G). See informational RFC 3569.
Of the four, PIM-SM has the widest deployment.
PIM-SM is commonly used in IPTV
IPTV
Internet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...
systems for routing multicast streams between VLANs, Subnet
Subnet
The word subnet may refer to:* In computer networks, an abbreviation for subnetwork.* In mathematics, a subnet of a net in a topological space....
s or local area networks.
External links
- PIM Routing (PDF)