Sitecom ADSL2+ Modem DC-227
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6.4 IGMP
Multicasting is useful when the same data needs to be sent to more than one hosts. Using
multicasting as opposed to sending the same data to the individual hosts uses less network
bandwidth. The multicast feature also enables you to receive multicast video stream from
multicast servers.
IP hosts use Internet Group Management Protocol (IGMP) to report their multicast group
memberships to neighboring routers. Similarly, multicast routers use IGMP to discover which
of their hosts belong to multicast groups. This device supports IGMP proxy that handles IGMP
messages. When enabled, this device acts as a proxy for a LAN host making requests to join
and leave multicast groups, or a multicast router sending multicast packets to multicast
group on the WAN side.
When a host wishes to join a multicast group, it sends IGMP REPORT message to the device’s
IGMP downstream interface. The proxy sets up a multicast route for the interface and host
requesting the video content. It then forwards the Join to the upstream multicast router. The
multicast IP traffic will then be forwarded to the requesting host. On a leave, the proxy
removes the route and then forwards the leave to the upstream multicast router.
The IGMP Proxy page allows you to enable multicast on WAN and LAN interfaces. The LAN
interface is always served as downstream IGMP proxy, and you can configure one of the
available WAN interfaces as the upstream IGMP proxy.
Upstream: The interface that IGMP requests from hosts are sent to the
multicast router.
Downstream: The interface data from the multicast router are sent to hosts in
the multicast group database.
