User`s manual

IKS-6726 Featured Functions

3-46

Benefits of Multicast

The benefits of using IP multicast are that it:

• Uses the most efficient, sensible method to deliver the same information to many receivers with only one

transmission.

• Reduces the load on the source (for example, a server) since it will not need to produce several copies of the

same data.

• Makes efficient use of network bandwidth and scales well as the number of multicast group members

increases.

• Works 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

TX RX

IKS-6726

TX RX

STAT

FAULT

PWR1

MASTER

PWR2

COUPLER

LNK/ACT SPEED FDX/HDX

RING PORT

COMUPLER 

PORT

MODE

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