Turning A Wireless LAN Into A Mesh

Last year, the Wi-Fi network built by the University of Georgia that covers downtown Athens, Georgia was very literally deteriorating.

The access points forming the network had been cobbled together by students who made up an interdisciplinary group at the university called the Mobile Media Consortium. The network was being used by the group to study applications delivered over a wireless network and usage by the community.

But Athens has very humid weather and the access points, designed by Cisco for indoor use, couldn't withstand the environment.

"I found that you can teach a music student how to solder antennas but caulking is beyond them," joked Scott Shamp, director of the New Media Institute at the university as well as director of the Mobile Media Consortium. He said that moisture leaking into the home-made access point enclosures was quickly rusting the contents.

This was just one of the problems the group faced in keeping the wireless network running. To the rescue: mesh networking. This technology has received the most attention for its use in large city-wide networks. However, smaller municipal networks such as the one in Athens, as well as enterprises and other large organizations, are increasingly turning to mesh to make sure that large, disparate areas are covered.A Network Mess

The network in Athens consisted of nine Cisco 350 access points that the students had specially rigged to accommodate for the challenges of the environment and a limited budget.

"Cisco didn't really make enclosures that were reasonably priced. They cost as much as the AP," Shamp said.

Joe Colapietro, an engineer with mesh equipment vendor BelAir Networks who later worked on replacing the network described the student-made access points like this: "They took an indoor repeater, put it in a Tupperware box with a power supply and mounted an external antenna."

Environment and budget weren't the only challenges facing the students. They worked with the city of Athens to secure permission to hang the access points on telephone poles and use city electricity to power them. The city was cooperative, but couldn't help put together all the pieces of the puzzle."It was impossible to get backhaul to each one of these," Shamp said. "They were going to allow us to put boxes on poles and use power, but as far as running wires, no."

Other municipal networks in the country have worked around the backhaul issue by soliciting volunteers in strategically placed offices to donate a DSL line and place an AP in their window. But Shamp and his group viewed this as a short term approach because the volunteers might move or change their minds.

Instead, the group took advantage of what Shamp calls a glitch in the older Cisco APs. They were able to configure the APs to pass traffic from one to the next until reaching the AP in the Mobile Media Consortium's facility which had a data line for backhaul. Later iterations of the line of Cisco APs don't have this capability.

The network worked well for over a year but by early 2004, one by one, the access points were starting to fail due to the affects of moisture.

Moving To Mesh

Shamp and his group shopped around for access points to replace the Cisco network and settled on equipment from BelAir."It's a truly robust mesh network," Shamp said. Mesh networks pass traffic along the access points until reaching one that has a wired backhaul connection to the Internet. The networks are ideal for situations where it's difficult to provide a wired connection to each access point.

The BelAir access points used in Athens include multiple radios. The 802.11b radio serves users and the 802.11g radios pass traffic along the network until reaching the access point at the consortium's office that is connected to backhaul. A local ISP has donated the use of a T1 connection to link the AP in the office to the Internet.

The process of replacing the network went off without a hitch.

"It was a very elegant replacement," said BelAir's Colapietro. "There was little or no downtime." The BelAir engineers were able to remove each Cisco AP one at a time, immediately replacing each with the BelAir AP while the rest of the network continued to serve users.

The Mobile Media Consortium immediately realized benefits by using the BelAir system. Instead of nine Cisco APs, the new network only uses five BelAir APs. The BelAir product uses a higher power radio and an integrated antenna, allowing each AP to cover a larger area. The network covers an area of about 30 square blocks.In addition, the BelAir APs were made specifically for outdoor use. The individual components were designed to withstand a broad range of temperatures and the enclosure is completely sealed.

Shamp was also looking for a very robust network that was unlikely to require many repairs. This is especially important because the consortium must rely on the city if they need to access one of the devices.

"They city has to come out and go up on the pole and get the device and bring it down for us to fix it," Shamp said. "The city does this for us out of the goodness of their heart and as soon as we become a real pain we won't be able to do this any more." Since the network was deployed in December 2004, it hasn't had any problems, he said.

How It's Used

The network has always been free to use for anyone who visits downtown Athens. Since about a year ago, users are required to register to access it and 3,500 people have done so.The Mobile Media Consortium is a group within the University of Georgia's New Media Institute and it is dedicated to studying and promoting mobile media. So far, the group has delivered a variety of applications over the network, including streaming video, a video walking tour of Athens, an event guide and a guide to the town's historic districts.

The network also includes a security appliance from Bluesocket that provides a firewall, encryption and network monitoring tools.

Mesh networks like those available from BelAir are increasingly being used and considered for municipal deployments as well as commercial networks in places like hotels and convention centers where wired backhaul may be difficult to access. Mesh is also being used by manufacturing facilities and is expected to be used increasingly on corporate campuses.

The 802.11 development groups are also working on standardizing the mesh technology so that customers could buy access points from multiple vendors and they would interoperate. However, the mesh standard will employ just one radio per access point to form lower cost products that can be used in networks that won't be required to support a very large number of users. BelAir offers both multi-radio and single radio network gear.

While BelAir is supportive of the standardization process, it doesn't feel that the development of a mesh standard will significantly increase its market, said Phil Belanger, vice president of marketing for BelAir.Shamp said he's happy with the BelAir equipment and that buying from multiple vendors would probably only add complexity in handling potential problems with the network.