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¡ôIP Multicast today

Though it has distinct bandwidth-saving advantages over other modes of transmission, IP Multicast has not taken off like many had predicted when the technology was first introduced in Steve Deering¡¯s doctoral dissertation in 1988.

Multicast technology can be used to send data¡ªsuch as streaming media, stock quotes or inventory

updates¡ªsimultaneously form one-to-many or many-to-many sources, be it server to client or application .Unlike the more widely used unicast technology, which employs a separate connection for each user,  multicast has a single connection for every user.

The technology can reduce traffic on the corporate network by eliminating redundant access to the same content. Multicast can also reduce the load placed on network servers. With multicast, a single stream can be picked up by each client, saving bandwidth.

Despite its advantages, there are a number of obstacles preventing IP Multicast form becoming a dominant means of data delivery. For multicast to work, every router and switch between the source (usually a server) and the destination (typically as desktop) must be multicast-enabled.

That fact can be a problem for companies that have lots of older network gear.

Most of the new high-end Layer 3 switches form the likes of Cisco, 3Com and Nortel Networks come with multicast support; it¡¯s just a matter of turning it on .IP Multicast is a very important feature. When deploying any switch or router in a network that is going to distribute different types of data, you¡¯ve got to support multicast.

Even for companies with multicast-enabled networks, there is a lack of management tools to ensure smooth operation.

To help spur the deployment of multicast, Cisco helped author Protocol Independent Multicast (PIM), which is currently an IETF Internet Draft. The primary benefits of PIM are that it does not rely on any routing protocol to work and is ideal for large or small enterprise networks. Other IP Multicast protocols rely on certain routing protocols, such as Routing Information protocol or Open Shortest Path First.

Cisco, one of the leading proponents of IP Multicast, claims that 50% of Fortune 500 companies are using the technology for some form of content distribution. Any device that runs the company¡¯s routing software, ISO Version 10.2 and later, is multicast-enabled, though the feature is not turned on by default.

¡°Multicast is still moving forward,¡± says the IETF¡¯s Coltun, who sees a combination of servers and services that combine unicast and multicast technologies to deliver data as efficiently as possible. Under this scenario, corporations can multicast data as far out on the network as possible, and then use unicast technology to reach those in areas that are not multicast-enabled.

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