Features of multicast – H3C Technologies H3C SecPath F1000-E User Manual
Page 4
3
Figure 3 Multicast transmission
Assume that only Host B, Host D, and Host E need the information. The multicast source (Source in the
figure) sends only one copy of the information to a multicast group. Host B, Host D and Host E, which are
receivers of the information, must join the multicast group. The routers on the network duplicate and
forward the information based on the distribution of the group members. Finally, the information is
correctly delivered to Host B, Host D, and Host E.
To sum up, the advantages of multicast are summarized as follows:
•
Over unicast: Because multicast traffic flows to the node the farthest possible from the source before
it is replicated and distributed, an increase of the number of hosts will not increase the load of the
source and will not remarkably add to network resource usage.
•
Over broadcast: Because multicast data is sent only to the receivers that need it, multicast uses the
network bandwidth reasonably and enhances network security. In addition, data broadcast is
confined to the same subnet, while multicast is not.
Features of Multicast
Multicast has the following features:
•
A multicast group is a multicast receiver set identified by an IP multicast address. Hosts join a
multicast group to become members of the multicast group, before they can receive the multicast
data addressed to that multicast group. Typically, a multicast source does not need to join a
multicast group.
•
An information sender is referred to as a multicast source (Source in
). A multicast source
can send data to multiple multicast groups at the same time, and multiple multicast sources can send
data to the same multicast group at the same time.
•
All hosts that have joined a multicast group become members of the multicast group (Receiver in
). The group memberships are dynamic. Hosts can join or leave multicast groups at any
time. Multicast groups are not subject to geographic restrictions.