Ethernet's High-Wire Act

As ever-richer media burden data networks, a new IEEE standard is needed to ensure quality of service

4 min read

If there's a next killer application for the U.S. telecommunications industry, it's the triple play of voice, video, and data. Cable companies like Cablevision, Comcast, and Time Warner have been aggressively selling Internet and voice over Internet Protocol telephony services. Meanwhile, the three biggest regional U.S. phone companies, BellSouth, SCS, and Verizon, are gearing up to offer homeowners the same television content cable providers do. Each does so by piggybacking on the broadband data services they've been pushing for a few years now.

But voice and video services are very different from broadband data. No one much cares if it takes an extra half-second for an e-mail or Web page to show up onscreen. A half-second hitch in the middle of that championship football game or an important telephone call, though, would seem interminable. How, then, can carriers deliver these time-critical applications across the Internet?

It should come as no surprise that the IEEE 802.1 working group on internetworking has been much vexed by that question. So last November, its local-area and metropolitan-area networking committee formed a study group, IEEE 802.1ah, to develop a standard that could ensure the high quality of service needed to transmit streaming multimedia over a wide-area Ethernet network that covers an entire city.

Illustration: David Rodriguez

The new standard probably won't have a catchy name, like Wi-Fi. Nor will there be consumer products you can pick up at Best Buy and CompUSA. But 802.1ah, when it's completed in a couple of years, will make possible dramatic improvements in services such as Internet-based television. Indeed, an eventual transition from standard to high-definition TV across the Internet will be impossible without it, says John Hawkins, a member of the IEEE 802 LAN/MAN standards committee executive board.

"Besides the triple play, there's online gaming, which is incredibly popular," especially in Korea and Japan, says Hawkins, who is a senior marketing manager at Nortel Networks Corp. He spoke to IEEE Spectrum from his home in Atlanta, though the corporate headquarters, to which he telecommutes, is in Brampton, Ont., Canada, a suburb of Toronto. "Really, anything that's both multimedia and interactive will need this new standard," he says.

The need for the new standard is becoming acute, he says, in large part because Ethernet is being pushed into a new role that goes far beyond its local-area networking origins. In the last five years, it began to be used between buildings in a region, and even between regions. In these metropolitan-area networks, collections of connected Ethernet networks, dubbed clouds, are replacing the dedicated circuits that used to connect offices or buildings to one another or to the Internet.

"In the past," Hawkins explains, "you would call your local provider—here it's BellSouth—and order a circuit, if you needed to connect, say, Atlanta and Dallas. A T1 [1.5-megabit-per-second] or T3 [45-Mb/s] service is a dedicated circuit, one that's all yours."

"That's great from a quality-of-service point of view," he says, "but it's very expensive." It ties up a key resource—the bandwidth itself, which the buyer controls, even when the connection is largely idle. Since that bandwidth can't be used for anything else, the operator has to charge full value for it.

Going from a dedicated circuit to an Ethernet cloud saves money, but it comes at an operational cost. How do you guarantee quality of service if the cloud is suddenly swamped with data—say, kids logging into their online games when the school day ends? It's not just your Internet-based telephone calls getting those little auditory glitches. What if it's a clinic urgently transmitting a sonogram to obstetricians at the central hospital?

Hawkins explained that "traditionally, Ethernet has been a best-effort service," meaning it tries to send data packets as fast as possible, but some delays and congestion are a given. That's "fine in a local-area network," he says. "Now, though, you have to look at that and ask how you can guarantee service to an end user. That's what the new project is about."

Guaranteed service means that once a packet is passed to the network, it will reach its destination before a set amount of time has elapsed, so that an online gamer, for example, can shoot a missile at an enemy player before his opponent moves away.

An existing protocol, dubbed MPLS (for Multi Protocol Label Switching), is supposed to guarantee quality of service, but it, too, is problematic in an Ethernet network, says Hawkins. "For one thing, the basic model of Ethernet is that it's a connectionless medium. Unlike telephone circuit switching, for example, it's not based on setting up a call [through a dedicated circuit] and then breaking the circuit down afterward. Instead, packets make their way through the network autonomously, based on forwarding algorithms built into protocols like Ethernet's." MPLS tries to emulate the telephone circuit approach by creating a so-called tunnel—a digital version of a telephone connection—within a connectionless network.

This works fine but only goes so far in terms of scale. When thousands or even millions of tunnels are needed—as when serving an entire city—it becomes hard to manage. "It's fine to run MPLS for a Fortune 1000 company when you have an entire information technology department standing by to manage it," Hawkins says. "But for a residential service, such as BellSouth's, where there are millions of users and businesses, MPLS will quickly become unmanageable. It will still be useful in the core of the network but not at the edges." That's where 802.1ah will shine.

The task force will be receiving proposals for the details of just how 802.1ah will work through next month, and its schedule calls for another two years for a final draft standard to be approved in May 2007. In the meantime, telecommunications manufacturers such as Alcatel, Cisco, Fujitsu, Juniper, and Nortel will start shipping carrier-grade 802.1ah products as soon as they think they safely can—that is, when new products can be deployed that will need only software updates to bring them into line with any changes in the official specification. In fact, Hawkins says his company, Nortel, is already selling routers and switches that it calls, at least informally, "pre-802.1ah."

"It will take three to five years for the standard to make itself fully felt," says Hawkins. "And the benefits will be subtle. But our customers, for example, KPN Telecom in the Netherlands, already see the benefits from the prestandard." And once the standard is in place, costs will drop further for carriers, which can pass those savings on to the users of their high-speed services. That can only be good news for consumers, even if they never learn the phrase "IEEE 802.1ah."

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