Multicasting makes sense

For years, engineers have been talking about how improvements in network performance could be achieved with a simple fix by allowing routers to copy packets to more than one path at a time, resulting in a continuous data stream that could make networks cheaper and stronger.

Multicasting, where a single server could simultaneously send a consistent data stream to tens of millions of desktops with no delay, is proving them right, providing a significant change in contemporary networks.

The three basic methods of transmitting data are unicast, broadcast and multicast.

Unicast is what lets you connect your browser to your favourite Web sites, download files and do most of what gets done on the Internet. But it tends to be limiting -- you can communicate with only one host at a time.

Every packet that leaves a server goes to one client only. The cost of this is felt by workers in the time wasted waiting for responses from overburdened servers, as well as by managers forced to buy unnecessary hardware and extra bandwidth to assure a given service level.

Using the broadcast transmission method to transmit voice and video seems to be a good solution, since your packets get sent out only once and could, in theory, be delivered to every host on the Internet. In practice, however, broadcast solutions are generally frowned upon because they tend to crowd out other kinds of traffic, even when they`re used only on a single network.

A major problem with broadcast transmissions is that if only 100 members of the network of 200 participate in the conference call, all devices, even those that are not participating, will receive the broadcast. This robs systems of valuable processing time and can cause a dramatic drop in performance on older systems.

This inability to control the broadcast effectively restricts its use in QOS network environments.

With the first two options having various drawbacks, the answer to transmitting data seems to be a multicast-enabled network that allows routers to copy packets to several paths at once using a single data stream.

As transmitting voice and video over a network requires an enormous amount of bandwidth, the use of multicasting for those transmissions has many benefits over other traditional transmission methods.

The idea of multicasting is to minimise bandwidth waste due to duplication of packets. And unlike broadcast packets, only those people that are participating in the multicast group receive the data stream -- a feat accomplished by using special multicast addresses. Multicasting also reduces some of the overhead associated with voice and video conferencing across the Web.

While multicasting has in the past traversed mainly research networks at universities and network providers it has, over the past few years, evolved into a valuable tool that allows companies to transmit voice, video, interactive training, and software updates. It allows companies to do real-time streaming video multicasts of company and management communications meetings and training events without flooding the network with traffic.

Actual users of multicasting are still rare, but they are growing in number. As multicast applications continue to grow in popularity and as businesses begin using their data networks to replace telephones and video conferencing equipment, and as they become aware of the benefits, the amount of multicast traffic on corporate networks is bound to increase.