Wireless backhaul's intelligence injection

AS THE MOBILE BACKHAUL environment continues to change, copper and fiber won't be the only infrastructures gradually becoming the foundation for Ethernet-based backhaul. Fixed wireless technology also will increasingly enter the mix. Point-to-point solutions for licensed spectrum already are offered by companies such as FiberTower and Nextlink and vendors like Stratex Networks and Dragonwave, and both WiMAX and wireless mesh architectures are expected to have an impact on how different types of wireless broadband networks are backhauled in the years to come.

EarthLink, which is building municipal wireless networks in several cities nationwide, recently picked Dragonwave to provide a point-to-point-based Ethernet backhaul solution that will aggregate broadband traffic at tower tops in dense urban environments.

“The benefit to using Ethernet there is that it can give us flexibility up to 500 Mb/s,” said Jeb Linton, chief network architect for EarthLink's municipal wireless networks. “We wanted that type of aggregation capability and didn't want to install a solution that required TDM scheduling. The main reason we didn't want that is because [a point-to-point Ethernet solution] is less expensive and easier to manage. TDM didn't quite fill the sweet spot for us.”

Meanwhile, the wireless mesh architecture used to provide access coverage in most of the municipal wireless networks being built also offers some of its own Ethernet-based backhaul capability. In a mesh network, traffic can be intelligently routed through the mesh over multiple hops to a backhaul aggregation point. The network's capability to do so increases if the mesh uses dual-radio, rather than single-radio configurations, said Kirby Russell, director of product marketing for Strix Systems, a vendor of Ethernet wireless mesh solutions.

“Using a single radio is like having an Ethernet switch,” Russell. “You have to wait for what goes in to come out. But you want a cell site you're are using for backhaul to be able to do more than just backhaul. You want it to function for access, too, and that's where the dual-radio solution comes in.”

Russell and other proponents of Ethernet-based backhaul over wireless feeder infrastructure — rather than copper or fiber — know there are some carriers that won't want to deploy wireless for backhaul transport because of perceived concerns about reliability. Shields, of GeoResults, said wireless will remain the backhaul infrastructure of choice mostly for certain cell towers that are hard to reach with fiber or copper, while fiber-fed backhaul likely will be the basis for about 45% of the backhaul market by 2010.

But Russell said that according to one unimpeachable source, Ethernet and wireless are destined for one another. “You know [Ethernet inventor] Bob Mecalfe? Well even he says Ethernet is going wireless,” Russell said. “He ought to know.”