Video Streams

Video applications generally fall into two types—bidirectional and unidirectional. Videoconferencing between remote sites is an example of a point-to-point video application. Traffic flow is bidirectional in videoconferencing. The flow of a video stream from one source to many users on the network is an example of unidirectional flow.

Multicasting can help reduce the total amount of bandwidth used on the network (see Figure 311). In Figure 3-11, traffic flows through the network, and the video stream is sent to only those networks with registered clients. Note that the video stream is sent once from the server; there are no duplicate unicasts being sent. The video stream is sent to a multicast address.

Figure 3-11 Video Stream Traffic Flow Using Multicast Routing

Figure 3-11 Video Stream Traffic Flow Using Multicast Routing

In multicast environments, a multicast server registers with its local router as a multicast group number. Clients register with the local router, requesting a multicast group. Using a multicast routing protocol, the routers determine the paths to forward the video stream through the network to only those segments that have a client that requested the multicast group. Client and server registration is done using the Internet Group Management Protocol (IGMP). More information on IGMP can be found in RFC 1112. The most current multicast routing protocol is Protocol Independent Multicast (PIM). For more information on PIM go to http://

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