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Establishing a private wireless WAN with microwave wireless backhaul

Wireless backhaul offers an alternative that goes the distance for organizations that can't trench their own fiber or add T1 lines, or want to avoid doing so.

This may sound like networking blasphemy, but fiber isn't always king when an organization needs to build a private...

wide area network (WAN). The cost, construction time and red tape involved in trenching your own fiber to remote sites can deter some utilities, governments and other organizations. Sometimes a private wireless WAN is a better alternative. Some organizations are using microwave wireless backhaul technology as an alternative to adding expensive T1 lines or trenching fiber into the ground.

The government of Sioux Falls, S.D., where temperatures can plummet to -30 degrees Fahrenheit in the winter, has a private fiber network connecting many of its agencies and offices. But the freezing temperatures make the fiber less reliable in the winter, according to Kim Hansen, network administrator for the city. When freezing weather sets in and heavy snowfall saturates the ground, he said, the city's fiber is likely to freeze, morph or snap.

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"Unfortunately, around here in Sioux Falls, there's a lot of granite in the ground -- especially in the downtown area -- so there's a lot of places where we can't get fiber below the frost line very easily. We've got places where the conduit is just below the sidewalks," Hansen said. "It doesn't take much -- utility work or the dead of winter -- for these conduits, especially if they're not sealed correctly and get full of water, to freeze by Christmastime. The first Christmas present I get every year is my fiber freezes up."

As the city's WAN began to shoulder more bandwidth-heavy and critical applications such as voice over IP (VoIP), Hansen realized that Sioux Falls' 25 branch sites needed redundant links. Looking to avoid being at the mercy of a service provider or construction lead times, he plunged into microwave wireless backhaul to build a private wireless WAN.

"T1 lines were costing too much. Their speeds weren't the greatest and we wanted to get voice out," Hansen said. "Sioux Falls has been growing really quickly, so to try to get any type of network communications further out toward the edge of the city, wireless has been our best option -- and our only option. We can expand faster with our wireless infrastructure than with our fiber."

Microwave radios sit atop remote sites outside the fiber backbone's reach, such as a library or fire station, and transmit data to nearby water towers that function as aggregation points on the private wireless WAN, Hansen said. From there, more powerful radios backhaul the traffic to radios that offer a 1 Gbps fiber connection back into the WAN.

The savings on operational and capital expenses for organizations that embrace a private wireless WAN as an alternative to trenched fiber or leased links can be "pretty dramatic," offering a one-year return on investment, according to Esme Vos, founder of, a niche publisher covering municipal wireless projects.

"[CIOs] are sitting there going, 'So, we have to dig up fiber. It's going to take 10 months because we have to get permission, and it's going to cost so much money,'" Vos said. "But there's this little bird whispering in their ears, 'If you set up point-to-point microwave links, you can do it in five days and you can do it for one-fiftieth of the cost' … [because] the equipment just gets better and better, and cheaper and cheaper."

A private wireless WAN goes where fiber can't

Hansen started the Sioux Falls' private wireless WAN about five years ago by relying entirely on point-to-multipoint radios that operated at high frequencies -- between 75 and 85 GHz -- and could only reach one to three miles between hops. Although they operated at Gigabit speeds, the region's wild weather often interfered with their delicate signals.

To me, [our wireless WAN] is as reliable as the copper the phone company brings in.
Kim Hansen
Network AdministratorCity of Sioux Falls, S.D.

Working with his local systems integrator, Calhoun Communications, Hansen ripped out the millimeter wave radios and deployed a combination of one Proxim Wireless point-to-multipoint 802.11a radio for each branch's rooftop and five Exalt Communications' point-to-point radios for the wireless backhaul from the edge.

Because the Proxim Wi-Fi radios operate on unlicensed spectrum at 5 GHz, they have fallen prey to interference, making them an unlikely choice to handle wireless backhaul, Hansen said. The city worked with a third-party company to obtain a license from the Federal Communications Commission (FCC) to build a private wireless WAN backbone with Exalt radios operating interference-free at 18 GHz.

Unlike the city's fiber backbone, its wireless backhaul system has yet to succumb to the elements, offering a more reliable connection at 100 Mbps back into the WAN during the harsh winter months, Hansen said.


"We don't bat an eye anymore when someone says, 'We want to take wireless to a facility here,'" he said. "To me, it's as reliable as the copper the phone company brings in."

Connecting traffic cameras via private wireless WAN

Engineers at the Colorado Department of Transportation (CDOT) last year weren't sure whether they could afford to backhaul live, high-definition video feeds from US Highway 36, which runs between Denver and Boulder, according to Jill Scott, a project engineer within the department's Intelligent Transportation System team.

The highway is heavily used by people driving between the two cities, but the state didn't have fiber in the ground there, Scott said. With an $800,000 budget to get US 36's camera feeds backhauled to CDOT headquarters, it was not feasible to spend millions of dollars trenching fiber for the 22-mile stretch.

One vendor, which Scott declined to identify, told the state's contractor that the live video feeds would have to hop between 18 microwave radios to cover the distance, she said. Although Exalt's microwave radios were more expensive, the state's contractor learned they could cover the same stretch in nine hops, saving money and packets.

"I did learn a lesson -- don't be cheap with your radios," said Scott, who added that the radios' performance hasn't suffered from the 125 mph winds in the US 36 corridor but needed some retuning after experiencing interference from a nearby airport.

Microwave wireless backhaul management: Easier than Wi-Fi?

Because Exalt's radios support Simple Network Management Protocol (SNMP), Hansen can monitor their signal strength, throughput and status throughout Sioux Falls using his existing network monitoring tool, WhatsUp Gold from Ipswitch.

Although not identical to 802.11 wireless networking, microwave wireless backhaul is similar enough. Hansen said that his experience with radio frequency (RF) management and relative signal levels has helped him understand and manage wireless backhaul.

Smaller organizations and municipalities with limited IT resources that are trying wireless backhaul for the first time are likely to outsource management, Vos said. Larger enterprises usually have networking pros, well trained in wireless LANs and WANs, who can navigate wireless backhaul on their own, she added.

Wireless backhaul is different from -- sometimes easier than -- deploying a Wi-Fi-based private wireless WAN. It often requires about a dozen devices to configure and manage, Vos said.

"The way they put it up is quite methodical…. You do it in phases and you tweak it until it works," she said. "It's not like setting up these giant Wi-Fi networks where there are so many variables coming into play."

Let us know what you think about the story; email: Jessica Scarpati, News Writer

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