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 VoFi Gets a Boost By Ted Stevenson
July 27, 2005
That we can run phone calls over IP networks at all is a minor miracle. It goes against the grain of IP's "connectionless" architecture, and is achieved only by making the network jump through many protocol hoops. Wireless LANs, such as 802.11 (aka Wi-Fi), compound the basic IP-related problem, adding uncertainties that stem from their architecture. In brief, voice apps over Wi-Fi work only if they essentially hog the bandwidth—get priority. As such, there's a finite limit to the number of calls that any base station ("access point" or AP) can handle before the quality of all the packet streams (voice calls) falls below the acceptable level. Wi-Fi infrastructure vendor Meru Networks yesterday announced a software add-on for System Director, the operating system for Meru Controller, its central command hardware. The Voice Services Module (VSM) is designed to reduce those uncertainties and otherwise tweak the performance of voice over Wi-Fi to some semblance of wire-line quality and reliability and to make it robust enough for large deployments. VSM constitutes a four-pronged attack on the weaknesses of VoWi-Fi. The first of these is so sensible it's startling that no one has sought to implement it before: Limit the number of calls transmitted over an AP. Call Admission Control, as the feature is dubbed, lets managers set a ceiling on the number of calls to be processed at one time, presumably well below the threshold of degradation. Incoming or outgoing calls that exceed the limit get a busy signal—pretty much what happens when the PSTN gets overloaded. Mind you, this is handled by the network control infrastructure, not the IP PBX. Next on the agenda is balancing the call density over the network as a whole, which, like controlling call admission, reduces contention. Meru's central network controller monitors and manages many aspects of traffic flow over theLAN, and it can dynamically re-route calls from one AP to another as calls set up and are terminated, keeping the traffic evenly distributed. Factoring in Meru's proprietary "virtual cell" technology allows the overlaying of channels in a given area, thus increasing the available call density. Also included in VSM is an "Enhanced Call Flow Detection" feature, which efficiently figures out what protocol a client handset requires for setting up the call (and includes support for a broad range of protocols in common use, including SIP and H.323) and other details of enabling a connection The final piece of VSM addresses packet loss, which is pretty much inevitable in VoIP, regardless of the transmission medium, technological intervention notwithstanding. Lost or "dropped" packets—chunks of the digitized sound stream that don't reach their intended destination, for whatever reason—create disconcerting gaps in the sound transmission. VSM's "Dynamic Error Correction" (which might more accurately be called "Error Compensation") detects packet loss and inserts a "predictive sample" into the voice flow to keep the signal continuous. Predictive sample essentially means duplicating the packet preceding the missing one and resending it. While obviously not recreating the original stream, the feature improves comprehension significantly. VSM, though only announced this week, has been under trials for some time. "Our solution has been widely received in Japan where enterprises are aggressively adopting and deploying wireless VoIP," said Meru's president and CEO Ihab Abu-Hakima in a statement. Joel Vincent, Meru director of product marketing points told EnterpriseVoIPplanet that "VSM—and our entire Air Traffic Control technology—was definitely a significant factor in getting the nod to deploy wireless VoIP to the 50 offices of Osaka Gas" (also announced this week). Craig Mathias, principal at the Massachusetts-based consultancy Farpoint Group, told EnterpriseVoIPplanet that this new technology is building on the company's existing strengths. "Meru, from the outset, has touted their products as tuned for voice," Mathias said. "These are very logical developments that can only make their infrastructure more robust for VoFi. When VoFi really begins to drive the industry—when the cellular carriers get into the game—Meru is going to be very well positioned," Mathias concluded. The Voice Services Module is available immediately. Pricing has been set at $20 per client, with volume discounts.
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Measuring Infrastructure Value
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