Interference-Free WLAN Delivers Robust Mobile Telephony

By Ted Stevenson

April 25, 2005

Total centralized control allows Extricom to defy the known laws of wireless LAN operation.

While many vendors are trumpeting advances in voice over WLAN (also known as VoWiFi or wVoIP), they are nonetheless working against fundamental problems inherent in the IEEE 802.11 standard that underpins most wireless LAN technology—and therefore most wVoIP.

Extricom Ltd., an Israeli R&D company, claims to have overcome these problems while remaining compliant with all current flavors of 802.11—.11b, .11a, and .11g. The limited number of RF channels, interchannel interference from adjacent channels, and restricted range and capacity are all dragons Extricom technology has slain, according to CEO Gideon Rottem.

The result: a wireless LAN architecture highly friendly to voice traffic.

The Extricom system consists of a centralized switch (not an unusual feature in today's Wi-Fi world) "directing," in the company's parlance, groups of ultra-thin access points. "Ultra-thin" means there is a complete absence of "intelligence"—software or storage—on the units. They are just radio conduits linking clients (phones and computers) to the switch.

"There's a general consensus in the industry that centralized decision making is better [than distributed]," commented CEO Rottem. "Extricom has taken this to its logical conclusion," he said, "making all decisions at the center."

What this means is that the decision maker (switch) is aware of the state of the entire network for each packet that travels it, so each packet is routed to the optimum path, providing "dynamic, packet-by-packet diversity processing," as Rottem terms it.

In using the Extricom system, a client associates not with an access point, as in most other switch-based systems, but with the network—the switch. The APs are mere pipelines to which the switch dispatches packets.

If the stream is a phone call and the client is moving through the network, there is no need for the client to reassociate with new APs as the caller walks along. The switch just directs the packets to the most appropriate AP, based on actual conditions. Thus there is no latency or "handoff hiccup"—a key problem for mobile VoWiFi.

Furthermore, since adjacent channels are not broadcasting (due to optimized central management), there is no RF interference in the system. This makes for greatly increased channel use efficiency, and ultimately to increased network capacity.

The same goes for range. Cancel interference, and the access point serves a larger space.

Furthermore, each Extricom AP can support up to four radios, which can broadcast any flavor of 802.11 a, b, or g, and can be specified in any combination. Different kinds of traffic can be assigned to specific radios, with, say, 802.11b for voice (since most Wi-Fi telephone handsets currently use .11b), .11g for normal data, and .11a for video.

In a Yokahama, Japan-based trial, the Extricom product line has been deployed to support a telephone system on three floors of an office building, with users moving freely throughout the space. Extricom claims "wireline voice quality" for this pilot.

The Wireless Switch/Ultra-Thin Radio Points (the official product name) combination will be officially announced in early May, when it will be available in quantity. The system will be packaged as an eight-port switch bundled with eight APs, at a cost of between $8,000 and $14,000, depending on purchase volume. A 32-port system is planned for later in the year.



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