User manual

Global Data (Publish/ Subscribe)
192
33002479 06 07/2008
Multicast Filtering
Overview Your NOE may offer the multicast filtering functionality.
The global data service synchronizes several stations located in a distribution group.
A distribution group is a set of stations identified by using the same IP multicast
address for all stations in the group. By using the same IP address for multiple
devices, multicast exchanges can be used to distribute global data. Several
independent distribution groups can coexist on the same sub-network. Each
distribution group possesses its own unique IP multicast address.
Early versions of switches treat multicast packets as a broadcast, thereby
broadcasting to all nodes and suppressing all benefits of both switching and
multicasting. Newer versions of switches provide automatic multicast filtering, and
consequently only forward multicast traffic to ports that are connected to registered
end stations.
Multicast filtering uses the GARP Multicast Registration Protocol (GMRP) to inform
a switch which IP multicast addresses are of interest to the attached device
GMRP is defined in the IEEE 802.1D-1998 Standard, which is available as a free
download at: http://IEEE802.org.
In order to use Multicast filtering, you need to:
1. Ensure that your switch supports IEEE 802.1D - 1998
2. Click the Multicast filtering check box (see Illustration, p. 284) on the Global Data
Configuration area on the NOE 771 x1 web page.
Reducing Traffic Multicast filtering helps to reduce the traffic on a network, because broadcasts are
sent only to interested, or subscribed, devices.
For distributed applications and one to many communications, multicast affords
advantages over unicast because it:
z utilizes the network bandwidth more efficiently
z sends a single transmission instead of multiple transmissions.
z reduces collisions
z optimizes the performance of Ethernet module processing
Using Multicast
Filtering
These ConneXium switches support multicast filtering. Other switches from
alternate vendors also support multicast filtering.
Switch Description
499NES17100 Managed Switch with 7 ports 10/100 BASE-TX
499NOS17100 Managed Switch with 5 ports 10/100 BASE-TX and 2 ports 100 BASE-FX