Building the Multicast Network Infrastructure


There are several ways to configure a network for multicasting, depending on the type of routing you plan to use. The method Fabrikam chose provides a high-quality end user experience and an efficient use of network resources. This method can be implemented with readily available equipment and has been tested and used successfully in enterprise environments.

There are a number of companies that manufacturer appropriate hardware and software for implementing multicast, including Cisco, Extreme, and Foundry. However, the basic concepts apply regardless of the hardware you choose. The following list summarizes the protocols and configurations that are used in the Fabrikam scenario, and describes alternatives for each:

IGMPv2 Client/Router Communication

Enables the client to initiate the routing of a multicast stream and leave the multicast. Supports PIM-SMv2.

IGMPv1 is less efficient because it does not support Leave Group messages. Without a Leave Group message, the only way that a router detects whether an end user has closed a Player is by sending query messages and waiting for a response. The path leading to the client is therefore filled with multicast packets until the process times out. IGMPv3 supports PIM-SSM, which is an improved multicast routing system that eliminates the need for an RP. IGMPv3 is supported by Windows Media 9 Series.

IGMP Snooping

Enables switches to restrict the forwarding of multicast packets to only those ports where an IGMP request has been received.

If you are using Cisco routers and switches, you can use the Cisco CGMP protocol, which requires less processing by switches. If a switch does not provide layer 3 snooping support, multicast streaming is still viable if it is restricted to small networks or network segments.

PIM-SMv2

Provides for efficient use of network resources and bandwidth by not forwarding multicast packets until a client request is received. With SPT switchover enabled, routers automatically create the shortest path between the source and clients.

In the future, Fabrikam may upgrade to PIM-SSM. PIM dense mode can be easier to set up than PIM sparse mode, but it is less efficient because it uses the flood-and-prune method. This mode and the original multicast routing protocol, Distance Vector Multicast Routing Protocol (DVMRP), are no longer preferred by most users because of their inefficient use of network resources and bandwidth.

Static RP

Multicast traffic is routed through an RP that has been assigned manually. Dynamic RP systems (such as Auto-RP) in which RPs are automatically and dynamically assigned can make multicast traffic handling easier on networks that carry many multicast groups. To implement dynamic RP, candidate RPs and BSRs are chosen. The BSRs will map multicast groups to RPs. In the Fabrikam scenario, one statically assigned RP can easily handle the predicted multicast traffic.




Microsoft Windows Media Resource Kit
Microsoft Windows Media Resource Kit (Pro-Resource Kit)
ISBN: 0735618070
EAN: 2147483647
Year: 2005
Pages: 258

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