Microwave Journal

Sprint Bulks Up on Backhaul

Finds utility emerging IP/Ethernet and microwave approaches

April 16, 2008

Sprint Nextel may be one of the largest wireless network providers, but the growth of new unlimited plans, including its own Sprint Everything plan—not to mention its WiMAX network—is putting continuous constraint on its backhaul network.

Like its wireless brethren, Sprint Nextel’s default backhaul strategy has been to rent T1 circuits from the local ILEC. Sprint realizes, however, that T1s, despite their reliability, are limited in terms of scale and quite expensive to maintain.

“What we’re seeing with the Simply Everything product from Sprint and with the rest of the industry is that the increase in unlimited data and voice plans exponentially increases the backhaul requirements of 2G and 3G networks,” said Craig Cowden, Sprint’s vice president of cable/VoIP and access strategy, at the recent Converging 2G/3G and UMTS/CDMA on Common Backhaul Infrastructure panel at CTIA Wireless 2008 in Las Vegas. “There’s a challenge where we can’t just scale with LEC T1 because one, it’s expensive and two, it does not scale operationally or financially.” (See: Breaking the backhaul bottleneck)

Cowden added he’s keen on leveraging new alternatives that offset having to pay Sprint’s nearest competitor—the ILEC—any more money than it has to. To break free of the T1 bottleneck, Sprint is using a number of new approaches including everything from pseudowires and optical to HFC.

Even with all the options, Cowden said, “There’s no one silver bullet solution” for wireless backhaul.

Multi-purpose platforms

While fiber-based solutions are Sprint’s preferred method for wireless backhaul, the operator increasingly has been leveraging the cable MSO’s fiber and, in some cases, its coax.

Working with cable operators makes sense. In recent years, cable operators have been breaking out of their video-centric shells to offer business and even wholesale services. In terms of wireless backhaul, cable operators often have fiber and coax passing cell sites, so extending these facilities into a tower would be as easy as extending a fiber drop to the site.

In addition, Sprint already supplies many cable operators with turnkey VoIP solutions, besides working with major MSOs (i.e., Comcast, Cox and Time Warner Cable) on joint wireless initiatives.

“We’re spending a lot of time working with the MSOs, some more aggressively than others, to develop a DOCSIS-over-Ethernet standard,” Cowden said. “We’re working with them to develop not just the technology but also the systems interface because we want to use their coax for Ethernet.”

Cowden added that coax can be leveraged by other Sprint divisions. “It’s not just for cell site backhaul,” he said. “It’s also a huge driver for our enterprise last-mile access requirements.”

To expand its Ethernet service set to a broader audience, Sprint launched Sprint Provided Ethernet Access Service late last year. With this initiative, Sprint’s business division will leverage traditional copper, DSL, wireless and coax to deliver Ethernet to business customers. (See: Sprint steps out with Ethernet)

“By combining cell site backhaul needs and our business service requirements, it really creates a scale that makes it attractive for them,” Cowden said. “Strategically, Sprint is very interested in pursuing solutions that reduce access costs, but [also] redirect it from AT&T and Verizon.”

Along with cable, Sprint is trialing Ethernet-over-copper solutions with an unnamed access service provider that can bond potentially multiple T1 circuits to expand available bandwidth over existing copper for 3G backhaul.

It’s currently trialing one unnamed operator’s solution and, despite some of the distance limitations of copper, Cowden likes what he sees. “For all 3G cell site backhaul, we think there’s an interim niche, and an interim could be a long time,” Cowden said. “We are working with providers right now, and we think we’ll be able to test the viability of a 10-meg, Ethernet-over-copper solution. We’re very interested in it as an interim technology, and we will go to fiber as a long-term solution, but long term can be just that.” (See: Bonding with copper)

Two-tier WiMAX solution

Of course, 2G/3G wireless is only one part of the Sprint backhaul network equation.

Despite naysayers, Sprint’s new CEO Dan Hesse emphasized recently that the operator’s XOHM WiMAX service being offered up as a total package gives it a two-year start over others making a migration to long term evolution. Keeping the spirit of using common wireless technologies for its networks, Sprint is looking at various alternatives for its XOHM WiMAX service.

Because it’s a greenfield 4G wireless network, Sprint’s backhaul mode for WiMAX includes a mixture of fiber and microwave from alternative providers such as Fiber Tower.

Sprint has taken a two-tier approach to WiMAX backhaul:

• Wireless aggregation converged backhaul uses a mixture of traditional microwave, LMDS and/or BRS (2.5 GHz spectrum);
• Backhaul hub to Sprint facilities uses a mixture of Ethernet over DWDM, Ethernet over SONET, or a third-party provider’s facilities. (see Figure 1).

Sprint sees potential in LMDS, for example, for other wireless backhaul needs.

“We’re looking at LMDS aggressively,” Cowden said. “LMDS has some technical limitations that I think we can work through, but we’re more concerned about the economics right now.”

Bridging TDM to IP

For all Ethernet’s promised capabilities, the reality for wireless operators is there’s still a lot of TDM in their networks. The question then becomes how they can effectively bridge the gap between their current TDM- based investments and the IP road.

While some operators (mainly in Europe) have opted for a split deployment, placing all voice traffic on traditional TDM-based circuits then running data over Ethernet, Sprint is not chasing such an approach. Instead, Sprint is using two converged access methods to accommodate TDM and IP/Ethernet.

At the cell site, Sprint will deploy equipment that includes both an Ethernet interface and a traditional T1 interface. The egress port coming out of that equipment would be fiber. Within the fiber itself, Sprint will allocate T1 and Ethernet. Depending on the type of service, it would either ride the Ethernet or T1 pipe within that fiber.

In addition, Sprint is looking at pseudowire solutions that would emulate the T1 across a larger 1 GigE pipe.

As it deploys its WiMAX backhaul capabilities, Sprint will leverage the same solution for its existing 2G/3G wireless needs where necessary.

“With some of our AAV and MSO alternatives, they are producing fiber- based solutions for 4G backhaul, but the equipment they deploy allows for the muxing on a T1 interface and the output is across fiber,” Cowden said. “Where we have that type of solution and where a WiMAX tower is collocated with a 3G tower, we would take advantage of that same capability.”

Whatever technology strategy it pursues, depending on what the particular situation, Sprint is high on the possibilities of Ethernet.

“I want to send a message to vendors, potential vendors and access providers that we are motivated to move toward the economics of Ethernet-based solutions and the bandwidth upgrade flexibility of Ethernet solutions,” Cowden said. “We’re also motivated strategically to redirect our access spend away from AT&T and Verizon.”