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March 2009 | Volume 12/ Number 3
Packet Voice over Wireless

Better Sounding Calls

According to Jean-Marc Valin, the lead programmer for Speex, “Wideband is basically the only way that VoIP can ever say that it’s better than the PSTN.” Several factors can make a VoIP call sound worse than a PSTN one, like aggressive compression, packet loss and latency. Fixing all these can get the sound quality of VoIP up to near parity with PTSN, but as Valin says, only wideband can make it sound better.

Polycom is beating the drum for wideband with its “HDvoice” logoed phones, and Skype (News - Alert) has been wideband since day one, but if you call a Polycom phone from a Skype phone the call will be narrowband. So we have islands of wideband. There is great value in joining these islands together. Metcalfe’s Law says that the value of a network node increases with the size of the network. This is also known as “the fax machine effect:” The more people you can send a fax to, the more useful your fax machine is. A textbook example of Metcalfe’s law is inter-carrier SMS. According to Billing and OSS World, “Within months of launching inter-carrier SMS services, AT&T (News - Alert) Wireless saw a 50 percent increase in SMS traffic”.

There are several barriers to joining up the islands of wideband voice. One of the most pernicious is that they are already joined, to an extent, through the PSTN. The problem is that calls get downgraded to narrowband as they pass through the PSTN. As VoIP trunking and VoIP peering gain in the market, calls will increasingly be able to bypass the PSTN. Then the barrier to wideband calls will become wideband codec incompatibility.

There are two simple solutions to codec incompatibility: transcoding in the network and negotiating a shared codec. Transcoding is intrinsically bad, because it introduces latency, it degrades the sound quality and it wastes computation. A shared codec is a far better solution.

There are now three high quality wideband voice codecs that phone vendors can use without paying royalties: Speex and two from Polycom. There is no reason why any phone or soft phone should ship without all three of them. IT

Michael Stanford (News - Alert) has been an entrepreneur and strategist in Voice-over-IP for over a decade. Visit his blog at

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