Operation Manual - Multicast
Quidway S3500 Series Ethernet Switches Chapter 1 IP Multicast Overview
Huawei Technologies Proprietary
1-2
Server
Unicast
Server
Multicast
Receiver
Receiver
Receiver
Receiver
Receiver
Receiver
Figure 1-1 Comparison between the unicast and multicast transmission
It should be noted that a multicast source does not necessarily belong to a multicast
group. It only sends data to the multicast group and it is not necessarily a receiver.
Multiple sources can send packets to a multicast group simultaneously.
A router that does not support multicast may exist on the network. A multicast router
can encapsulate the multicast packets in unicast IP packets with tunneling and send
them to the neighboring multicast router. The neighboring multicast router will remove
the unicast IP header and continue the multicast transmission. This avoids the network
architecture from changing greatly.
Multicast advantages:
z Enhanced efficiency: Reduce network traffic and relieve server and CPU loads.
z Optimized performance: Decrease traffic redundancy.
z Distributed applications: Make multipoint applications possible.
1.2 Multicast Addresses
1.2.1 IP Multicast Addresses
The destination addresses of multicast packets use Class D IP addresses ranging from
224.0.0.0 to 239.255.255.255. Class D addresses cannot appear in the source IP
address fields of IP packets.
During unicast data transmission, a packet is transmitted along a path from the source
address to the destination address with the "hop-by-hop" principle on the IP network.
However, in environments of IP multicast, a packet has more than one destination
address, i.e., a group of addresses. All the information receivers join a group. Once a
receiver joins the group, data flowing to the group is sent to the receiver immediately.
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