IP Multicast Still Waiting for Takeoff

During the 1980s and early 1990s, cellular telephone technology had limited reach and use. Fast forward to 2000, and it seems everyone owns a cell phone. IP Multicast today is the same as early cell phone technology -- useful and available, but not ubiquitous.

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 -- such as streaming media, stock quotes or inventory updates -- simultaneously from one-to-many or many-to-many sources, be it server to client or application to 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.

Despite its advantages, there are a number of obstacles preventing IP Multicast from 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.

"A lot of these enterprises are a mixed bag in terms of what they have for equipment," says Stan Schatt, research director at Giga Group. "There is still something like 6 percent of companies with token ring. A lot of networks still have hubs, not switches."

Most of the new high-end Layer 3 switches from 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, not just a check-off item," says Esmeralda Silva, a research manager at International Data Corp. in Framingham, Massachusetts. "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.

"People are looking at the kind of management tools available in the enterprise. We have a couple, but there is no HP OpenView for multicast," says Christine Falsedti, product line manager for multicast and quality of service at Cisco. "People want to know how they're going to manage multicast once they deploy it."

A bigger problem is IP Multicast over the Internet, where no single entity controls the entire infrastructure. Backbone service providers such as UUNET, Qwest and Sprint offer multicast in their networks, but smaller ISPs have been slower to implement the technology.

Part of the problem is technological. Protocols such as Multicast Border Gateway Protocol have been developed to help ease the transmission of IP Multicast traffic between two ISP networks but are still relatively immature.

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.

As happens with many "standards" however, PIM's implementation may vary from vendor to vendor, observers say.

"Some PIM implementations will not talk to other versions of PIM," says Jeremy Hall, an engineer at UUNET and an IETF member. "It's complex trying to get everyone to agree on how to implement the technology."

IP Multicast is also designed as an any-to-any model, which further complicates its implementation, says Rob Coltun, co-routing area director at the IETF.

Currently, there are no real security measures that protect multicast traffic.

"How do you ensure that any one sender is allowed to send to a given group?"

Coltun asks. This is especially problematic for a user on one ISP who wants to broadcast information to a group on another ISP, with a third ISP standing in the middle.

Also, because IP Multicast is broadcast over a reserved Class D IP address, there is some worry about its scalability. Multicast uses "routing trees" to determine its path through the network. Because Class D addresses are limited, Coltun fears there won't be enough addresses available if the technology becomes extremely popular.

But this is not to say IP Multicast isn't finding some roots.

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

Novell uses RealNetworks' RealSystem G2 to multicast company addresses made by CEO Eric Schmidt to every desktop in the company. "IP Multicast gives us bandwidth advantages during large-scale events," says Benjamin Brimhall, manager of streaming media services. "The experience for the end user seems to be better reliability as well. When we go to view video, we don't have the lag, dropped packets, buffering ... you don't run into the network congestion problems."

Brimhall says each broadcast runs between 80K and 200K bit/sec, depending on the event. The company streams audio and video at this rate over a WAN to its Provo, Utah, headquarters and offices in San Jose, which are connected by a T-3. Novell upgraded its network infrastructure 18 months ago to ensure everything is multicast-enabled.

"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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