VPort 25 User’s Manual
System Configuration
4-17
y
Reduces the load on the source (for example, a server) because it does not need to produce
multiple copies of the same data.
y
Makes efficient use of network bandwidth and scales well as the number of participants or
collaborators expands.
y
Works with other IP protocols and services, such as Quality of Service (QoS).
y
There are situations where a multicast approach is more logical and efficient than a unicast
approach. A typical use of multicasts is in video-conferencing, in which high volumes of traffic
need to be sent to several end-stations simultaneously, but for which broadcasting that traffic to
all end-stations would seriously reduce network performance. Besides, several industrial
automation protocols, such as Allen-Bradley, EtherNet/IP, Siemens Profibus, and Foundation
Fieldbus HSE (High Speed Ethernet), use the multicast approach. These industrial Ethernet
protocols use publisher/subscriber communications models by multicasting packets that could
flood a network with heavy traffic. IGMP provides the ability to prune multicast traffic so that it
travels only to those end destinations that require the traffic, thus reducing the amount of traffic
on the Ethernet LAN.
The network WITHOUT Multicast
Group 2
Group 2
Group 1
Group 1
Video Stream Group 2
Video Stream Group 1
Group 2
Group 2
Group 1
Group 1
Group 2
Group 2
Group 2
Group 2
Group 1
Group 1
Group 1
Group 1
Video Stream Group 2
Video Stream Group 2
Video Stream Group 1
Video Stream Group 1
The network WITH Multicast
Group 1 Multicast Stream
Group 2 Multicast Stream
IGMP Group 2
IGMP Group 2
IGMP Group 1
IGMP Group 1
Group 1 Multicast Stream
Group 1 Multicast Stream
Group 2 Multicast Stream
Group 2 Multicast Stream
IGMP Group 2
IGMP Group 2
IGMP Group 2
IGMP Group 2
IGMP Group 1
IGMP Group 1
IGMP Group 1
IGMP Group 1
NOTE
The VPort 25 is the source that delivers the multicast video stream. To benefit from the
Multicast protocol, the gateway or network switch should support the multicast filtering function
(such as IGMP Snooping) so that the multicast stream is delivered correctly and precisely. To
learn more about IGMP Snooping, refer to the Moxa EtherDeviceTM series Industrial Ethernet
Switch user’s manual.
