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Debunking Multicast Urban Legends

Myth #1: Multicast Doesn’t Work, or is Too Complicated to Deploy
Native multicast works today. It is in use by over 400 separate Autonomous Systems on the Internet and, once set up, is no less reliable than the Internet in general. It is possible for a single network engineer to setup multicast routing on an enterprise network in a day. On-The-I.com, for example, has been conducting audio multicasts for over 3 years with very few problems and little technical support.

While Any Source Multicast (ASM) routing problems can be difficult to understand, most of that complexity has been removed in the Source Specific Multicasting (or SSM ) service model, and there is little doubt that SSM could be deployed everywhere.

Myth #2: Multicast is a Bandwidth Hog
This statement could be true for the old DVMRP MBone because of routing updates and the flood and prune model, but it is not true for native Protocol Independent Multicast-Sparse Mode multicast (see previous article).

Myth #3: My (OS, Router, Application) Does Not Support Multicast
Over the past ten years multicast has had great success in gaining support from Internet hardware and software manufacturers. The big three streaming players (Windows Media, Real, and QuickTime) all support ASM multicast, as do basically all operating systems (Windows, Mac OS, and Unix), and most routers (all Cisco routers, all Juniper routers, etc.). The big push now is to extend this support to include SSM (currently supported by Windows XP but not by many applications).

It is also true that the first generation of Digital Subscriber Line Access Multiplexers (DSLAMs) used to provide DSL service, generally does not support multicast well, but more modern DSLAM equipment can support multicast efficiently and this service is offered by, for example, Lava.Net in Hawaii.

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