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Analysis: Alternative WLAN Technologies: Page 7 of 16

Meru's Radio Switch multiradio line comes in four-, eight- and 12-radio AP models. Most deployments will likely operate two or three radios in the 2.4-GHz range for 802.11b/g service, with the remaining ones in the 5-GHz range for 802.11a service. Besides Meru's Air Traffic Control technology, which leverages its own MAC scheme to provide predictable service and QoS (quality of service), the Radio Switch load balances traffic across channels, going so far as to ignore probe requests from clients that should be on another channel.

Unlike Xirrus, which uses a separate directional antenna for each radio, the Meru system has just two omnidirectional antennas inside a shell. One antenna is dedicated to transmitting, the other to receiving. Each antenna is located at the other's "null," or dead, spot to assist in isolating RF, and RF output is actually combined in the AP and separated on the input. Without directionality, the antennas don't extend coverage as those in Xirrus' Array do, but co-channel interference isn't a problem for Meru because its deterministic approach coordinates AP transmission within the AP and across cells to other APs. Rather than overlay an area with second and third APs to increase capacity, the Radio Switch can be used to serve high user densities.

Detractors of wireless switch designs are quick to point out weaknesses, including increased cost per AP with a centralized versus a distributed investment, greater power draw and unproven real-world effectiveness.

It's true that the cost per AP will be higher; but the cost per radio will be correspondingly lower. And, as has been well-documented in our reader surveys, 802.11a sees very little usage, so most environments could start off with a three-channel 802.11b/g design with a single-channel overlay of 802.11a. Where serving a dense population is important, businesses will mandate--and educational institutions will gently encourage--users to take advantage of the 5-GHz range.

It's likewise true that additional radios draw more power, so poly-radio vendors offer three options: Use local AC, use a special adapter to draw power from multiple PoE (Power over Ethernet) ports or use a custom power injector from the vendor.