Dense multicast
Encyclopedia
Dense 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
.
The basic assumption behind dense mode is that the multicast packet stream has receivers at most locations. Sparse mode assumes relatively fewer receivers. Dense mode is ideal for groups where many of the nodes will subscribe to receive the multicast packets, so that most of the routers must receive and forward these packets (groups of a high density).
This difference shows up in the initial behavior and mechanisms of the two protocols. Dense Mode uses a fairly simple approach to handle IP multicast routing. The source initially broadcast
s to every router, and thus every node
. Then each node that does not wish to receive packets destined for that group will send a prune message to its router. Upon receiving a prune message, the router will modify its state so that it will not forward those packets out that interface
. If every interface on a router is pruned, the router will also be pruned.
Additionally, the routers will use reverse-path forwarding to ensure that there are no loops for packet forwarding among routers that wish to receive multicast packets.
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...
can use to construct a tree
Tree (data structure)
In computer science, a tree is a widely-used data structure that emulates a hierarchical tree structure with a set of linked nodes.Mathematically, it is an ordered directed tree, more specifically an arborescence: an acyclic connected graph where each node has zero or more children nodes and at...
for sending packets to the multicast subscribers. It is the opposite of sparse multicast
Sparse multicast
Protocol Independent Multicast - Sparse-Mode is a protocol for efficiently routing Internet Protocol packets to multicast groups that may span wide-area and inter-domain internets...
.
The basic assumption behind dense mode is that the multicast packet stream has receivers at most locations. Sparse mode assumes relatively fewer receivers. Dense mode is ideal for groups where many of the nodes will subscribe to receive the multicast packets, so that most of the routers must receive and forward these packets (groups of a high density).
This difference shows up in the initial behavior and mechanisms of the two protocols. Dense Mode uses a fairly simple approach to handle IP multicast routing. The source initially broadcast
Broadcasting (networks)
right|250pxIn telecommunication and information theory, broadcasting refers to a method of transferring a message to all recipients simultaneously...
s to every router, and thus every node
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
. Then each node that does not wish to receive packets destined for that group will send a prune message to its router. Upon receiving a prune message, the router will modify its state so that it will not forward those packets out that interface
Interface (computer science)
In the field of computer science, an interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software...
. If every interface on a router is pruned, the router will also be pruned.
Additionally, the routers will use reverse-path forwarding to ensure that there are no loops for packet forwarding among routers that wish to receive multicast packets.