ADTRAN manual IP Multicast Overview IP Multicast Stub Routing in AOS

IP Multicast Overview IP Multicast Stub Routing in AOS

Satellite Classroom Application on a Multicast-Enabled Network

In a multicast-enabled network, the media server sends specific content in a single stream to a specific multicast IP address, much like a local broadcast TV station sends its content on a specific broadcast frequency. The network has multicast intelligence and is able to make copies of the stream as necessary to reach all active receivers.

This provides two significant efficiencies:

1.At any given point in the network there is never more than one instance of a particular content stream.

2.The network will only copy and forward a stream to locations that have active receivers.

Referring to Figure 2 on page 5, PC1, PC2, PC4, and PC6 have subscribed to the same classroom broadcast. Using IGMP, these PCs have signaled to their local router that they wish to receive this multicast address. In multicast-speak, these PCs have joined the multicast group identified by that multicast address. The satellite routers use a multicast routing protocol (most likely PIM) to signal other routers in the backbone and the Central Router that they have receivers for that multicast group. Each router in the network then understands if it is in the path toward receivers for that group (this description is greatly simplified).

The Media Server is able to send a single copy of the stream to the multicast IP address (group address). The Central Router receives this stream and sends a copy out all interfaces that have receivers for that group. This is repeated at each router until the stream arrives at each segment that has receivers. Since there is never more than one copy of the stream on any given link, the possibility of a bottleneck is greatly reduced. Notice that PC1 and PC2 are on the same broadcast domain. Satellite Router 1 makes a single copy of the stream and transmits it into that broadcast domain, where it is received by both PCs. This solution is much more scalable.

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