(Editor’s note: The following is an excerpt from our latest report, Inside Clearwire: A Network Report, which looks specifically at Clearwire’s use of microwave backhaul for its nascent national WiMAX broadband network. The full report can be downloaded FREE by clicking on this link.)
BACKHAUL: THE BACKBONE OF THE NEW NETWORK
Though its funding comes in chunks of billions of dollars, in the world of telecom Clearwire is a scrappy startup — an underfunded underdog that is forced to improvise and invent new rules to play against the telecom titans whose advertising budgets alone dwarf Clearwire’s yearly captial expenses. On Clearwire’s side, however, is an impressive swath of wireless spectrum, and the power of using open, standards-based Internet Protocol (IP) technology at its base to produce economies of scale and to promote competition among its suppliers.
“When you have no money, and you’re a small company, and you are desperate to differentiate yourself, you’d be amazed at what you can come up with,” said Dr. John Saw, Clearwire’s Chief Technical Officer who has been with the company since its inception — his bio notes that he was the company’s second employee hired. “The nice thing about Clearwire is that the first day on the job, I had no legacy network to worry about,” said Saw, a veteran of AT&T’s wireless operations before joining Clearwire. “Craig [McCaw] told me let’s not make the same mistakes that were made before.”
One of the places Saw and Clearwire started innovating right away — and this was starting when the company was launched in 2004 — was to figure out a better way to do “backhaul,” the term associated with bringing bandwidth from the Internet to the radio towers.
“From the first day we built the company we started asking what we were going to do with backhaul,” Saw said. In the buildout of previous cellular infrastructures, most carriers used a pair of T-1 lines — about 1.5 Mbps of bandwidth in each — to provide connectivity to their towers.
“That’s enough [backhaul] to carry narrowband voice traffic, but we know that a couple of T-1s is insufficient when you have a lot of bandwidth needs,” Saw said. “If your iPhone is slow, it might be the fact that AT&T’s backhaul is completely full.” Indeed, AT&T announced in January of 2010 that it had spent the past year putting in an additional 13,500 T-1 lines into just San Francisco and New York — among the most congested of its 3G markets — along with 238 new optical backhaul lines as well.
Clearwire’s early calculations on user demand, Saw said, led the company to believe that it would need conservatively to provide 30 Mbps to 50 Mbps bandwidth to each of its towers — “That’s 20 T-1s, or else you are going to need to bring optical fiber to the sites,” Saw said.
While optical fiber connections could certainly support such bandwidth needs, Clearwire had two expensive problems in the way of using that approach: The cost of trenching the physical fiber to each tower location (which typically involves digging up streets) and the cost of metro fiber facilities and fiber-based services. Instead, the newest wireless broadband provider looked to the air when it came to its own backhaul needs — using technologies based on microwaves, which have long been used to transmit television programs, long-distance phone calls and other communications traffic.
“We didn’t do this because we wanted to be different, we did it because we had to,” Saw said. “Clearwire does not own any fiber facilities, so we put a strong and heavy emphasis on microwave backhaul.”
A big problem, especially in 2004 when Clearwire started its initial buildout, was that there were no vendors in sight with the equipment Saw wanted — a microwave radio that spoke Ethernet, so that the company could keep its flat, IP-based architecture intact.
“When we asked for an Ethernet-based microwave radio, 5 years ago nobody even knew how to spell that,” Saw said. After many frustrating meetings, Saw and Clearwire finally found the Canadian firm Dragonwave, whose Ethernet microwave radios fit the bill. Saw and Clearwire used those radios to build what he describes as a “flat Layer 2 mesh network,” where cheap Ethernet switches at each tower site help establish a network that doesn’t have a single point of failure.
“What we do is basically switch those microwave packets around, so that every cell site has more than one path back to the data center,” Saw said. “They are very low cost Layer 2 Ethernet switches, but they are very intelligent and will automatically switch traffic around with intelligent failover. It’s far cheaper than any cell site switches used for 3G today.”
Though Clearwire hasn’t yet launched enough networks or attracted enough users to know how the microwave setup will really perform under strain, Saw said its implementation seems to be a harbinger of the future, since now many vendors are offering Ethernet microwave radios.
“What nobody knows is that by being a wholesale backhaul service provider to ourselves, we’re probably one the the largest in the world on microwave,” Saw said.
For more on Clearwire’s network, download our latest report, Inside Clearwire: A Network Report, for free by clicking here.
