• United States
by Steve Taylor and Joanie Wexler

Wireless as a substitute for metro fiber

Aug 07, 20032 mins
Cellular NetworksNetworkingWi-Fi

* 802.11a-based outdoor bridges hold appeal

A scant few commercial business sites in the U.S. have access to fiber in the local loop. Enterprises that can’t wait for the arrival of high-capacity fiber-optic Ethernet last-mile services might consider wireless LAN bridging as a multimegabit-speed option.

Devices that analysts say have become much simpler to install and use are emerging based on the 802.11 suite of WLAN standards. Most notable are newer products based on the 802.11a standard for 54M bit/sec networking in the unlicensed 5 GHz range. For super-high throughput, some vendors will allow you to link two of these bridges together for an aggregate 108M bit/sec with load-balancing.

The Cisco 802.11a-based Aironet 1400 Series Bridge, announced in June, for example, allows this capability. Meanwhile, as you read this, wireless networking veteran Proxim is announcing an 802.11a version of its MP.11 WLAN bridge. Both vendors also offer 802.11b-based bridges.

Wireless bridges are quick to install and require just a one-time capital investment of a few thousand dollars per site with no recurring service charges. You can set the devices up in point-to-point or point-to-multipoint configurations. You’ll select your antennas based on the radius and distance across which each bridge must communicate. The narrower and more concentrated the beam (an effect of the antenna) the farther the distance the bridge can transmit. The range is up to about 20 miles, depending on vendor.

Analysts say that the 802.11 protocol is robust in the face of interference; for example, a connection speed might degrade, but would generally not be dropped. And for now, anyway, the 5 GHz range is much less cluttered than 802.11b’s 2.4 GHz range; in addition, it has many more channels available to avoid interference.

Note that there are all types of bridges that run in various frequencies based on a slew of technologies. Older ones have more traditional telco WAN connections (e.g., T-1 WAN links) that can, for example, support TDM voice in a wireless circuit. If you want to support TDM voice using an 802.11-based bridge, you’ll probably need a voice gateway at participating sites to convert TDM voice to voice over IP (VoIP) voice (you might be running one anyway). And, for now, VoIP might only be supported across point-to-point links due to latency issues associated with point-to-multipoint connections.