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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 13

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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Introduction to IP Multicast

Introduction to IP Multicast

This section describes the definition, purpose, and benefits of IP multicast.


IP multicast transmission is a mode in which packets are transmitted from a source to a group of receivers. Compared with unicast and broadcast transmission, IP multicast transmission saves network bandwidth and reduces loads on networks. IP multicast is widely used in IPTV, real-time data transmission, and multimedia conferencing services.


Traditional IP communication supports two transmission modes: unicast and broadcast.

  • In unicast transmission, a source sends an independent data packet to each host that requiring its data.
  • In broadcast transmission, a source sends data to all the hosts on the local network segment, regardless whether the hosts require its data.

To transmit data to multiple destination hosts but not all hosts, a source host uses the broadcast mode or sends multiple copies of data in unicast mode to the destination hosts one by one, as shown in Figure 8-1.

Figure 8-1 Point-to-multipoint data transmission in unicast and broadcast modes

  • In unicast mode, the amount of data transmitted on the network is proportional to the number of users that require the data. If a large number of users require the same data, the source host must send many copies of data to these users, consuming high bandwidth on the source host and network. Therefore, the unicast mode is not suitable for batch data transmission and is applicable only to networks with a small number of users.
  • In broadcast mode, data is sent to all hosts on a network segment regardless of whether they require the data. This threatens information security and causes storms on the network segment. Therefore, the broadcast mode is not suitable for data transmission from a source to specified destinations and it also wastes network bandwidth.

In a summary, traditional unicast and broadcast modes cannot effectively implement point-to-multipoint data transmission.

Multicast is a solution to point-to-multipoint data transmission. As shown in Figure 8-2, the source sends only one copy of data, and all the hosts that require the data (HostA and HostC) can receive the same data copy. HostB cannot receive the data.

Figure 8-2 Point-to-multipoint data transmission in multicast mode

Multicast has the following advantages over unicast and broadcast:
  • Compared with the unicast mode, the multicast mode starts to copy data and distribute data copies on the network node as far from the source as possible. Therefore, the amount of data and network resource consumption will not increase greatly when the number of receivers increases.
  • Compared with the broadcast mode, the multicast mode transmits data only to receivers that require the data. This saves network resources and enhances data transmission security.


IP multicast applies in any point-to-multipoint data transmission scenarios, including:

  • Multimedia and streaming media applications
  • Remote training and collaboration
  • Data warehouse and financial applications (stocks and securities)

Internet service providers (ISP) have been using IP multicast technology to provide Internet services, such as online live broadcasting, web TV, tele-education, telemedicine, web radio, and video/audio conferencing.

Updated: 2019-12-13

Document ID: EDOC1000041694

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