IP is the answer
While most agree that IP is the ultimate answer, carriers still face questions about who provides what type of infrastructure. Traditional wireline carriers, many of which own mobile carriers, generally provide the leased TDM lines and could deliver packets over new fiber infrastructure built to the cell towers. The problem, economically speaking, is that mobile carriers are hesitant to give business to wireline competitors when operating outside their footprint.
"I've heard the phrase ‘no checks for LECs' said about this marketplace," said Salman. "The options outside the footprint are limited, but I'd have to say I think they consider the ILEC more of a mortal enemy than the [local] cable guy."
Cable is targeting mobile backhaul by pulling fiber from a residential hybrid/fiber coax (HFC) node directly to a cell site. The traffic is then backhauled over that fiber to the node and back to the cable headend. The cable infrastructure runs fiber deep into a neighborhood and close to a cell tower.
"They have a pretty good point-of-presence, obviously. They can run a lot of fiber out to cell towers or fairly close proximity so it's a good adjunct to their businesses," Hunt said.
Copper-based packets over existing infrastructure are more problematic, but can work if the copper is bonded, said Dyck, who proposed bonding as "a transition step so you can start off with some backhaul infrastructure and then swing over to the Ethernet port on the backhaul."
Dyck also likes using bonded DSL because "the reliability of the (DSL) network for residential services is just as high if not higher than a business service. In some cases they're primed for mobile backhaul service as well."
Wireless in the mix
Finally, there's wireless--which can range from conventional microwave, which is wildly popular in Europe and sparse in the U.S., to licensed and unlicensed wireless spectrum, to millimeter wave systems.
"There's a lot of work and a lot of innovation in terms of packet-based microwave to run native packet as well as TDM traffic and beef up the bandwidth," said Hunt, pointing to microwave links of 800 megabits to a gigabit and moving up to 3-plus gigs. "You're definitely going to see a lot of microwave backhaul."
In fact, as the cell backhaul space expands and demand grows, "you're going to see all four (wireless and wireline options) playing together," Hunt said.
In the end, a combination of economics and network needs will probably provide the best answer.
"There's going to be such a rush to turn up these systems that in the end whoever gets them fiber at the cheapest price is what makes the business model work," concluded Salman.