Powering VoIP over Wimax

18 Aug 2008

'Disaster.' 'Miserable failure.' These are just a couple of the terms Garth Freeman, CEO of Buzz Broadband, used to describe his experience with Wimax at a conference in Bangkok last March.

Freeman warned the audience that Wimax 'may not work' and that it was still 'mired in opportunistic hype'. The source for Freeman's frustrations was Buzz Broadband's own experience with its fixed Wimax network. Freeman said that the network's non-line-of-sight performance was 'non-existent' beyond just 2 km from the base station and that the indoor performance decayed at just 400 meters. He also said that the latency rates reached as high as 1000 milliseconds - values that make services like VoIP virtually useless.

Airspan, Buzz Broadband's equipment provider, was quick to respond. CMO Declan Byrne released a statement saying that Buzz Broadband had deployed Airspan equipment that is also installed in over 100 other fixed Wimax networks, but that Buzz had traded off range for cost by using less-expensive microcell base stations. As for VoIP QoS, wrote Byrne, '[AirSpan's] MicroMAX certainly offers appropriate QoS for wire-line quality voice support, but, as an access technology, can only do so for the portion of the link between the user device and the base station. In the case of Buzz Broadband, we know that there were significant under-provisioning issues in the core network which connected the Airspan equipment to the Internet.'

Sprint was quick to separate itself from Buzz Broadband, pointing out that while Buzz Broadband was operating a fixed Wimax (802.16d) service at 3.5-GHz - which requires line of sight - Sprint was using mobile Wimax (802.16e) in the 2.5-GHz band, 'which does not require LOS and has better building penetration.'

Still, the Buzz Broadband flap raises a legitimate challenge that Wimax players face in offering VoIP services. And by many accounts, it's becoming increasingly imperative that they do offer VoIP. At every major and minor Wimax conference in the last year, operator licensees, vendors and analysts alike have maintained that, in many markets, a voice service is essential to Wimax's success. In July, ROA Group analyst Ku Kang said in a report that one reason KT's WiBro service in Korea has seen sluggish take-up to date is that it lacks a killer app, and that app may well be VoIP, which WiBro (and Wimax) needs if it wants to compete against HSDPA and LTE.

Whatever one makes of Buzz Broadband's technology decisions, the fact of the matter is that VoIP over Wimax is a real challenge, says Tom Flak, senior operations VP and chief marketing officer for SOMA Networks - but it's a mistake to focus just on the air interface.

'Getting voice to work over the interface is the tricky part of the problem but it's not the whole problem,' Flak says. 'The technical challenges are very much the same in doing voice over Wimax as they have been for the last ten years in doing voice over broadband wireless in general. Wimax does provide some built-in quality-of-service channels to carry voice. But voice quality requires an end-to-end solution. In general delivering an access system on an end-to-end basis is still a technically challenging task.'

Some of the challenges are relatively easy to overcome. Sprint's Polivka alluded to one when he stated that Buzz Broadband's network was operating at 3.5 GHz, while Sprint is operating at 2.5 GHz. A network can not defy the laws of physics: signal loss is not only a function of the distance between the handset and the base station, but also a function of the frequency of the system - actually the square of the frequency.


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