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The
sending of a packet from one sender to multiple receivers with a single
"transmit" operation is known as multicast routing. Teleconferencing
is an example which requires multicast routing.
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The
goal of multicast routing is to find a tree of links that connects all of the
routers that have attached hosts belonging to the multicast group. Multicast
packets will then be routed along this tree from the sender to all of the hosts
belonging to the multicast tree.
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There
are many ways to generate multicast tree, MBONE is also one approach to generate
multicast tree. The Internet Multicast Backbone (MBone) is an interconnected set
of subnetworks and routers that support the delivery of IP multicast traffic.
v An
IP multicast group is identified by a Class D address.
Figure:
Multicast tree routed at source S
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In
the above figure, the source S wants to transmit to destinations with multicast
group G1.
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The
source can send each copy of the packet separately to each destination by using
conventional unicast routing or else a more efficient method which will reduce
the number of copies
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For
example, when router 1 receives a packet from the source, router 1 copies the
packet to router 2 and router 5 simultaneously. Upon receipt of these packets,
router 2 forwards the packet to its local network, and router 5 copies the
packet to router 7 and router 8. The packet will be received by each intended
destinations.
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