A technology originally aimed at carrying different types of data traffic across an IP backbone has found a new application that’s not in the backbone. The technology, pseudowire, is now being deployed in Ethernet-based access networks to support a need we’ve been hearing a lot about lately—cellular backhaul.

As wireless network operators have begun to offer higher-speed data services, their bandwidth needs have increased dramatically, and so have their costs for the T-1 links used to connect cell sites or aggregation hubs to the terrestrial network. But as Eitan Schwartz, vice president for access equipment manufacturer RAD, explains, “The amount of revenue they get for the extra bandwidth for 3G and 4G networks is not proportional. They need a less expensive way to get to the towers.”

Ethernet is a much more economical access alternative, but wireless transmission equipment typically has T-1 interfaces. Pseudowire—which encompasses a broad set of standards for carrying a range of protocols including T-1, over IP, Ethernet or other packet network—enables network operators to connect their TDM-based equipment to a more efficient Ethernet access network. As Michael Howard, principal analyst of Infonetics, puts it, this solution “has the QoS characteristics of T-1 but not the capacity restraints.”

Howard estimates the cost of the pseudowire equipment to support a single cell site at about $3000 to $4000 for each end of the connection. Such a deployment can pay for itself within a few months based on T-1 savings, he says.

Alternatively, some wireless carriers may opt to lease pseudowires on a wholesale basis from Ethernet providers. In Houston, for example, Time Warner Cable has installed pseudowire equipment at the edge of its Ethernet access network to support a wireless network operator. The core network infrastructure is an MPLS-based network, which makes the Ethernet more efficient and scalable, Time Warner Cable regional vice president Chuck Sweeney explains.

The network was established several years ago to support Time Warner’s launch into the business Ethernet market. “We were so convinced the market would want Ethernet, we didn’t want to invest in any TDM ports into our network,” Sweeney says. Customers that want a T-1 connection—for example, to connect a PBX they don’t want to replace—are encouraged to install and manage a pseudowire access device, an investment that Sweeney says can easily be justified by the cost savings gained from a business Ethernet service.

When wireless operators began asking for T-1s, Time Warner offered them a similar solution, but in that case, the cable company was willing to “in essence, rent or manage the box at the edge of the network that does the conversion from T-1 to Ethernet,” says Sweeney. “This ensures that we’re keeping our long-term strategic vision intact, we remain consistent in our market strategy and avoid adding TDM services to our portfolio. We’re not hijacking our limited available resources to go to an application that may only provide us a significant long-term opportunity at cell tower sites.”

Sweeney is bullish about the cable company’s future prospects in using pseudowire to support cellular backhaul. “We’ve moved out of R&D and field trial and into the deployment and operation phase. Time Warner has five regions and there is cell tower activity to some degree in every region. The RBOCs have had a virtual monopoly on cellular backhaul. We’re the first alternative access provider that can truly address the majority of towers.”

To support its cellular backhaul deployment, Time Warner is using pseudowire equipment from RAD, which is one of several vendors—including Axerra, Overture and others—that are targeting this market. Some of these vendors have tweaked their offerings to make them particularly attractive for cellular backhaul applications, Howard says. For example, he notes that Axerra can detect the difference between 2G and 3G data and voice protocols, including protocols specific to GSM and CDMA.

Another advantage of pseudowire is that it can support upgrades to new types of protocols as backhaul connectivity evolves. Steve Byars, vice president of marketing for Axerra, notes that Ethernet interfaces are beginning to appear on wireless equipment for HSDPA networks. To use such equipment, Byars says, “It’s simply a matter of installing it to our access device and you have one unified backhaul strategy.”

If the interface is Ethernet and the access network is also Ethernet, why do network operators need pseudowire? “Mobile operators need to have very crisp, clear OAM capabilities,” Byars says. “They want visibility into their network operations, and often the Ethernet will be provided by a third party.” Byars adds that pseudowire also can be used with a range of access networks such as bonded copper and packet radio.

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