InFocus: Pseudowires branch out

Pseudowire technology has so far been used mainly in business applications, allowing carriers to send frame relay, ATM and other legacy traffic over newer multiprotocol label switching (MPLS) networks while seemingly preserving the recognizable attributes of that traffic. But, by all accounts, pseudowires will spread increasingly to other applications it hasn't been applied to before, namely wireless backhaul and residential broadband.

Born early this century out of a standards document authored by influential Cisco Systems executive Luca Martini, pseudowires get their name from the way they essentially "pretend" to be certain kinds of circuits. As they transport legacy time-division traffic over more modern packet-based MPLS networks, they "emulate" the characteristics of those legacy services, such as frame relay or ATM, to keep them consistent and manageable.

Only a couple of years ago, there were only a few vendors of pseudowire equipment, but the number is growing as MPLS spreads and pseudowire standards develop within the Internet Engineering Task Force's Pseudowire Emulation Edge-to-Edge (PWE3) working group. In February several equipment vendors--including Alcatel, Ciena and Cisco Systems--participated in a multivendor pseudowire interoperability demonstration at the MPLS World Congress in Paris. Last year, they held a similar event at the Supercomm trade show.

As equipment vendors vie to win pieces of the multiservice edge and wireless backhaul equipment markets, they are increasingly proposing pseudowires as a powerful tool in both situations.

As carriers look to deploy advanced fiber access networks (fiber-to-the-node, fiber-to-the-premises, etc.), they are still growing already large installed bases of legacy DSL networks. Whereas those legacy DSL networks are based on ATM, the more advanced fiber networks rely heavily on gigabit Ethernet for big bandwidth, with IPTV as a competitive differentiator with which to fight the cable companies. Pseudowires offer a way for carriers to consolidate both old and new networks, bringing the legacy ATM-based networks into the fold as they deploy the IP stuff and combining it all for transport over the same MPLS network.

"In most of those fiber-to-the-X architectures, pseudowires show up," said David Parks, Ciena's senior product marketing manager. "They're not necessarily turning the pseudowires on right away. In some cases they are. It's not far behind. As [carriers] build out [fiber broadband networks], pseudowires are a part of that architecture. They optimize networks in transition."

Ciena built pseudowires into the DN 7000 multiservice edge platform the company obtained through its 2003 acquisition of Wavesmith Networks. That gear has been widely deployed, including by Verizon Communications, which uses it for business and broadband aggregation, and AT&T, which uses it strictly for broadband aggregation. Of the three main products in that family, the most popular so far is the 7100, which scales to 10 Gb/s, a sweet spot between the 7050's 5 Gb/s and the 7200's 40 Gb/s.

Ciena is also selling the 7000's pseudowire capabilities as a solution for wireless backhaul networks, as mobile operators are making a migration from time-division traffic to packets similar to the one occurring in residential broadband. With Release 99, wireless operators have already rolled out ATM-based wireless data networks. But in evolving to releases 5 and 6, and moving to a greater mix of voice and data traffic, they may use pseudowires to put it all over MPLS.

Mobile operators need to haul traffic from each wireless base station to a base station controller, a mobile switching center and finally to the public switched telephone network. To cross those bridges, operators typically have to lease landlines from incumbent carriers. Backhaul is, in fact, one of the most expensive parts of the wireless business, sucking up most of carriers' total operating expenses. Worldwide, operators spent about $22 billion leasing lines for backhaul last year, according to The Yankee Group.

Pseudowires could help reduce those costs by making backhaul networks more efficient, allowing operators to deploy just one network for multiple disparate traffic types. And the chameleon-like versatility of pseudowires allows mobile operators to choose from a variety of packet technologies to backhaul voice and data traffic, from carrier Ethernet to DSL to broadband wireless.

Opinions vary on how soon carriers might apply pseudowires to broadband aggregation or wireless backhaul. Some say wireless will come first, but on other continents. Some say it's already beginning here. Others say it will be applied first to wireline broadband.

"In all the wireless bids we see, support for pseudowires and MPLS is emerging as a standard requirement," said Ciena's Parks. "Not that it's getting deployed today, but any investment [mobile operators] make in Ethernet and MPLS can support pseudowires."

Parks predicts North American wireless carriers will deploy pseudowires for backhaul sometime in the next 12 to 18 months. Starhub, a wireless carrier in Singapore, has already deployed Ciena's DN 7000 for backhaul.

Axerra Networks, a pseudowire equipment vendor partnered with both Ericsson and Nortel Networks, claims several U.S. wireless operators are currently trialing its gear, including one using Axerra's gear to backhaul live, revenue-producing voice and data traffic over WiMAX. The vendor already has a few mobile customers in China.

"The latter part of 2006 will become the tipping point for [pseudowires in wireless backhaul]," said Steve Byars, Axerra's vice president of marketing. "3G services have tended to roll out faster in Asia than here, but look at what Cingular's planning to do with HSDPA, or what Sprint's talking about with EV-DO, or what's Verizon's already doing. Those kinds of things push the demand for this capability."

It's not for everyone, however. A spokesman for Alltel, which is deploying EV-DO, said, "We have looked at [pseudowire] technology, and it doesn't look like it would apply in the vast majority of our markets."

"Our research tells us the adoption of pseudowires in wireless backhaul in the U.S. will take several years," said Mark Bieberich, Yankee Group program manager. "They might not be available from some of the entrenched wireless [equipment] vendors. Other vendors have told us they're in trials, but actual deployments are few and far between today. The demand for pseudowires over the next three to five years in wireless backhaul networks is there, without question. But TDM backhaul will remain the de facto way of transporting wireless traffic in the radio access network for the next couple years."

Part of the reason wireless operators may be hesitant to deploy pseudowires in wireless backhaul, Bieberich said, is the operational complexity it entails. "Any time you introduce new elements in wireless backhaul networks, there's a process for integrating that element into the network's operations," he said. "That takes quite a bit of time."

In the near term at least, Bieberich believes pseudowires will appear in U.S. broadband aggregation networks before they appear in U.S. wireless networks, especially as competition heats up among vendors of multiservice edge gear. (Axerra has not targeted residential broadband with its gear because it doesn't have expertise there, Byars said.)

As AT&T rolls out fiber-to-the-node and fiber-to-the-premises broadband networks, Gene Edmon, executive director of SBC Labs (now part of AT&T), said he has so far not been asked to apply pseudowire technology to residential broadband.

"There's probably some potential in wireless backhaul, where you're trying to maintain some circuit functionality," Edmon said. "But to homes in general, I'm not seeing what the real need might be."

That will likely change, Bieberich said. "All of the largest service providers in the U.S. and some of the competitive carriers have embraced pseudowires in some way, shape or form. In the next two to three years, we'll see each of those service providers use pseudowires in more and more applications."

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