Moxa Technologies PT-7728 user manual Benefits of Multicast, Multicast Filtering

PT-7728 User’s Manual Featured Functions

Benefits of Multicast

The benefits of using IP multicast are that it:

yUses the most efficient, sensible method to deliver the same information to many receivers with only one transmission.

yReduces the load on the source (for example, a server) since it will not need to produce several copies of the same data.

yMakes efficient use of network bandwidth and scales well as the number of multicast group members increases.

yWorks with other IP protocols and services, such as Quality of Service (QoS).

Multicast transmission makes more sense and is more efficient than unicast transmission for some applications. For example, multicasts are often used for video-conferencing, since high volumes of traffic must be sent to several end-stations at the same time, but where broadcasting the traffic to all end-stations would cause a substantial reduction in network performance. Furthermore, several industrial automation protocols, such as Allen-Bradley, EtherNet/IP, Siemens Profibus, and Foundation Fieldbus HSE (High Speed Ethernet), use multicast. These industrial Ethernet protocols use publisher/subscriber communications models by multicasting packets that could flood a network with heavy traffic. IGMP Snooping is used to prune multicast traffic so that it travels only to those end destinations that require the traffic, reducing the amount of traffic on the Ethernet LAN.

Multicast Filtering

Multicast filtering ensures that only end-stations that have joined certain groups receive multicast traffic. With multicast filtering, network devices only forward multicast traffic to the ports that are connected to registered end-stations. The following two figures illustrate how a network behaves without multicast filtering, and with multicast filtering.

Network without multicast filtering

M1 M2 M3 M4 PT-7728

All hosts receive the multicast traffic, even if they don’t need it.

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