Wireless backhaul's intelligence injection

EXPENSE IS JUST ONE OF THE PROBLEMS with TDM-based backhaul. Aside from the cost, TDM solutions are not terribly flexible and do not present many options for intelligently dealing with increasingly common bandwidth-rich mobile applications. They also don't offer options for intelligently managing the complex array of traffic types presented by these applications.

The problem with that is that some applications, like voice and video, are very sensitive to latency, and if leased-line TDM solutions can't tell the difference between traffic types, then they cannot prioritize that service traffic over applications that are less sensitive to latency. That leaves mobile carriers with no way to guarantee — or even confidently market — the reliability of their broadband services.

Ethernet backhaul, which can be delivered over fiber, copper or wireless facilities, offers a potentially less expensive, higher-bandwidth, more easily upgradable alternative to traditional TDM methods. As the wireline network operators providing the backhaul infrastructure migrate their networks to IP, Ethernet can provide a basis for pseudowires that could carry T-1 based backhaul more cost-effectively and efficiently. Ethernet doesn't require truck-roll installation and has generally lower operations and maintenance costs. Meanwhile, it offers far greater bandwidth than any TDM alternatives, starting at 10 Mb/s all the way up to 10 Gb/s.

3G and future-generation mobile networks, as well as other types of wireless broadband networks, support a natural evolution to IP-based Ethernet backhaul because many elements in broadband radio access networks already are IP-based — or are heading there. “IP/Ethernet interfaces are already being added to some of the base stations and other equipment in the radio access network,” Schwartz said.

Converting ATM cells traffic into IP or MPLS frames allows traffic optimization that TDM can't perform, eliminating idle bandwidth that occurs between ATM cells, he said. “Doing this kind of optimization, maybe you can go from eight T-1s at a cell site down to five, which can be a huge savings,” Schwartz said.

Having IP/Ethernet-based access and backhaul transport also allows for more rapid provisioning and upgrades in bandwidth that are more incremental than the wholesale build-outs of TDM infrastructure were. “With Ethernet, you can build on backhaul bandwidth incrementally,” said Peter Allen, president and CEO of Dragonwave, a vendor of point-to-point broadband wireless systems that can be used to provide Ethernet-based backhaul. “In the old days with TDM, you had to build out a ring and hope that somebody would come and fill up that capacity.”