Casting a vote for multicasting

The live Victoria's Secret fashion show on Feb. 3 will go down as an important campaign in the battle to get video onto the Internet. About 1.5 million surfers logged on, making the sight of Naomi Campbell slinking down the runway the Shot Seen 'Round the World.

The problem was, it wasn't. Seen, that is, by an estimated 75,000 others who could not get onto the site.

Those results may be acceptable for supermodels in skivvies but not for stockholder meetings, marketing presentations or training demos. The answer may be Internet protocol multicasting, one of a trinity of transmission paradigms.

Unicasting sends a separate data stream to the desktop of everyone who requests it-simple, but a terrifically inefficient use of bandwidth. Broadcasting sends the data stream to a list of routers whether or not the desktops they serve have asked for it.

Multicasting uses a special distribution protocol and dedicated routers to send out one copy of that data and circulate it selectively among routers serving only users that ask for it. No matter how many users request the data, only one packet is sent.

Though multicasting has existed for more than a decade and most router vendors support it, service providers have been slow to roll it out. But UUNet, the Internet services arm of MCI WorldCom, has had its UUcast offering in place for a year and a half, permitting content providers to multicast throughout the company's dial-up network. Starting in June, the next phase will permit businesses to send content to domestic end users connected with dedicated lines and create private multicast networks.

In dial-up multicasting, the modem port serves as a proxy, keeping track of what the user is watching and telling the router to stop porting the stream when the user stops watching. "A high-speed receiver has no modem port but a direct connection into a hub," said Kelly King, a product manager with UUNet. "So we had to write some multicast protocols and code that allow the routers to keep track of the comings and goings of multicast groups."

The content provider selects a stream size and encodes the data. UUNet configures a multicast tunnel from the router on the provider's LAN, over the Internet, to another tunnel ending in a UUNet T-1 (1.54 Mb/s) on the receiver side. "We don't charge for the receiver tunnel," King said. "Our product is focused at the content source."

UUcast's first phase offered streams from 5 to 128 kb/s. Phase Two will offer six new stream sizes ranging from 200 kb/s to 1.5 Mb/s. Prices vary from a $900 flat monthly fee for the dial-up streams to $20,000 a month for the highest speed.

King acknowledged that UUcast is not for videoconferencing 10 people. Low-end customers that don't need high production quality can buy equipment off the shelf and do IP multicasting over Mbone, an experimental infrastructure designed by the Internet Engineering Task Force and maintained by thousands of private ISPs as a multicasting proving ground.

Mbone symbolizes both what's good and bad about multicasting today, said Dan Pico, an analyst with Reed Staley Partners. "Most multicasting happens on a specially designed network because unicast routers can't read multicast packets," he said. UUNet sends multicast over a 52-router overlay separate from the company's core unicast network.

Pico believes multicast won't come into its own until providers feel more confident that the applications it enables won't overwhelm their networks, and until corporate customers decide they need the streaming video it provides. The latter will happen as video spreads out into the Internet at large, he said.

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