Digital Networks North America DNswitch 800 - Manual (Page 47)

DNswitch 800 Configuring and Monitoring the Switch 37
IGMP Multicast Filtering
Multicasting is used to support real-time applications such as video
conferencing or streaming audio. A multicast server does not have to
establish a separate connection with each client. It merely broadcasts its
service to the network, and any hosts which want to receive the multicast
register with their local multicast switch/router. Although this approach
reduces the network overhead required by a multicast server, the
broadcast traffic must be carefully pruned at every multicast switch/router
it passes through to ensure that traffic is only passed on the hosts which
subscribed to this service.
This switch uses IGMP (Internet Group Management Protocol) to query
for any attached hosts who want to receive a specific multicast service.
The switch looks up the IP Multicast Group used for this service and adds
any port which received a similar request to that group. It then propagates
the service request on to any neighboring multicast switch/router to
ensure that it will continue to receive the multicast service. (For more
information, see “IP Multicast Filtering” in the DNswitch 800 Management
Guide.)
Configuring IGMP
This protocol allows a host to inform its local switch/router that it wants to
receive transmissions addressed to a specific multicast address group.
Use the IGMP Configuration screen to set key parameters for multicast
filtering as shown below.
Figure 3-30. IGMP Configuration
Parameter Description
IGMP Status If enabled, the switch will monitor network traffic to determine
which hosts want to receive multicast traffic.
Act as IGMP
Querier If enabled, the switch can serve as the “querier,” which is
responsible for asking hosts if they want to receive multicast
traffic. (Not available for the current firmware release.)
IGMP Query Count The maximum number of queries issued for which there has
been no response before the switch takes action to solicit
reports. (Range: 2 - 10.)
IGMP Report Delay The time (in seconds) between receiving an IGMP Report for an
IP multicast address on a port before the switch sends an IGMP
Query out that port and removes the entry from its list.
(Range: 5 - 30.)
Note: The default values are indicated in the sample screen.