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4G backhaul--an opportunity and a dilemma
|10 июня 2009|
There are no easy answers to the hard questions bandwidth-intensive 3G and 4G backhaul pose for wireless carriers. There are, however, enough possibilities--from packetized bonded copper to cable-proffered fiber links--that mobile carriers should be able to determine an economically and structurally efficient way to move ahead before data traffic congestion causes gridlock.
"There are no absolute statements you could can make about mobile backhaul because every operator has built the network differently, had a different migration strategy, different requirements," said Taylor Salman, director of solutions market for Ciena. "There's no consistency across it."
Keeping costs in check
There may not be network consistency, but there is a common message: Backhaul must be upgraded even though this is a lousy time to spend money.
"If you want to offer a fairly high-bandwidth pipe and you want to be able to make some money on it, the only way to do that and be cost-effective is to have a very efficient infrastructure," said Glenn Hunt, principal analyst at Current Analysis.
"All the newer systems are all-IP, so there are no circuit-switched voice or SMS applications," said Salman. "That being said, there's a lot invested in the current infrastructure, which is TDM-based, and they'll use that equipment until it falls apart."
Legacy backhaul has generally consisted of leased TDM T1 lines that work fine for low bandwidth voice traffic but are too narrow to handle wideband video and other Internet-type applications now running over cell networks.
"It needs to be packets," said Steve Dyck, director of mobile backhaul solutions for Alcatel-Lucent. "The mobile operator has to be able to manage growth on the network while staying on a TDM-based infrastructure. Packet can be over fiber, it can be over copper for some short distances, and it can be over microwave."
Pseudowire, which blends legacy TDM while moving to a cellular Ethernet architecture, also has potential.
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.