Wireless Mesh Networks/How many radios?

= How many radios? = Meshes can be built with nodes that have a single radio, two radios and multiple radios. The number of radios in mesh nodes depends on the throughput and latency demands of the mesh network.

One
Single radio wireless mesh nodes are low cost, but are limited by latency and scalability. The single radio node has take turns providing client access and transport to the network. The node is forced to store and forward and thus introduces latency.

Two
Dual-radio wireless mesh nodes enhance the scalability and capacity of the wireless mesh network. One radio is used for client access and the other radio provides transport. Since the radios operate independently on two different frequencies, one radio can send while the other one is receiving. This reduces the latency from the access link to the transport link. However, when one node is relaying from one node to the next, a two radio node still needs to store and forward, which introduces latency.

Three or More
A multi-radio wireless mesh node solves the latency problem for both the access link and the transport link. Multi-radio wireless nodes perform with very low latency and work well with real-time applications such as multimedia, voice and video applications. Because the throughput is related to throughput, multi-radio nodes address high density coverage areas, and can be used to aggregate traffic from single- and dual-radio wireless mesh nodes.

Sample Deployments
Colgate University <!--- Colgate University in New York state is broadening its Wi-Fi horizons by launching a campus-wide outdoor network using Tropos Networks' MetroMesh equipment— but none of the units are meshing, reports Wi-Fi Planet

The university decided that it needed to expand its reach after a student survey found that students had as many as three to four IP-based devices—everything from PCs to game consoles to handheld devices used primarily for text messaging.

"We just wanted maximum throughput," says Rich Grant, the associate director of technology planning for the liberal arts school. "We have backhaul on all the Tropos access points. That's an unusual implementation, but we wanted to maximize the number of users. It wasn't about geographical area — we wanted to service a large volume [of users]."

"To be competitive, any campus needs to support some kind of Wi-Fi," says Grant. The network was installed for Colgate by Integral Wireless Solutions, an integrator based in Atlanta.

There have been some technological hurdles in implement in wider Wi-Fi system, however.

It was hoped that the Tropos hardware would provide a very strong signal strong, which worked fine on the lower part of campus where most of the buildings are wood-frame construction. The upper campus, however has stone buildings and needed interior APs. For that, Colgate turned to Cisco products supporting 802.11a/b/g.

The network is free to the college community of 2,750 undergraduates plus faculty and staff, plus it's open to visitors for Internet access.

==== When is a mesh network not a mesh network?

http://www.colgate.edu/ in central New York State knows. It recently completed the rollout of a campus wide outdoor network using http://www.tropos.com/ MetroMesh equipment but none of the units are meshing.

“We just wanted maximum throughput,” says Rich Grant, the associate director of technology planning for the liberal arts school. “We have backhaul on all the Tropos access points. That’s an unusual implementation, but we wanted to maximize the number of users. It wasn’t about geographical area we wanted to service a large volume [of users].”

Colgate’s foray into wireless started after the school’s Student Services group performed a survey of the student body, the vast majority of whom live on campus. Most reported owning as many as three to four IP-based devices. That includes everything from PCs to game consoles to handheld devices used primarily for instant messaging.

“To be competitive, any campus needs to support some kind of Wi-Fi,” says Grant. The network was installed for Colgate by http://www.integralwireless.net/, an integrator based in Atlanta.

Originally, Grant hoped the Tropos hardware would provide a signal strong enough to punch through walls and give students, faculty, and staff access to the network indoors. That worked fine on the lower part of campus where most of the buildings are wood-frame construction. However, on the upper campus filled with big stone buildings, it required interior APs. For that, Colgate turned to http://www.cisco.com/ products supporting 802.11a/b/g.

For now, the 5GHz 11a aspect is unused. It could come into play in the future for wireless VoIP. “It wasn’t that much more expensive to have a/b/g than b/g,” says Grant. “We’re hoping it’ll be upgradeable to 11n.”

Colgate uses http://www.bluesocket.com/ controllers to manage both the indoor and outdoor networks.

The outdoor Tropos-based network also extends into downtown http://www.hamiltonny.com/, Colgate’s hometown not far from Syracuse. The downtown hotspots are limited to areas around the http://www.colgateinn.com/ (owned by the college) and a centralized park. “It’s not an attempt at a pervasive metro network in town,” says Grant.

The network is free to the college community of 2,750 undergraduates plus faculty and staff, plus it’s open to visitors for Internet access.

-->