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Considering Wideband Audio Over The Traditional PSTN

The idea that we might be able to achieve wideband over the PSTN is more than a little heretical in some circles. I was reminded of it by long time VoIP blogger Aswath Rao. he asserted in a tweet not long ago that;

“As you well know SIP URI and IP are not necessary for WBCodec. It can be done in PSTN without involving the carriers”

and further

“…by deploying new devices just like fax caught on, if the market feels the need.”

What Aswath is getting at is the idea that wideband calling doesn’t necessarily require wholly bypassing the PSTN. The very existence of the VTX 1000 supports this belief.

His assertion is also supported by the historical existence of the STU-III secure phones which he referenced in a blog post on March 7, 2009. Developed by the NSA in the late 1980s these phones employ strong encryption to secure calls made over the PSTN. When both end-points are encryption capable the callers can “go secure” and know that the content of their call is traveling over a secure channel.

So in pursuing wideband telephony using SIP over IP networks, essentially bypassing the PSTN, are we throwing out the baby with the bath water?

David Frankel points out that there is more to be learned by examining the typical end-users experience with the VTX 1000. A long-time veteran of the telecom industry David has been promoting wideband for longer than most people. He asserts that while the VTX 1000 was wideband capable most users rarely, and some possibly never experienced wideband calling because of the typical manner of its use.


Lets presume that a company of a significant size buys a number of VTX 1000 systems so that there’s one installed in each of its conference rooms at various locations. If any two offices are going to have a conference call they can make a point-to-point call between the two conference rooms and a wideband call will result. Happy times.

However, if there is a requirement for additional parties on the call they’ll need to use a conference bridge of some sort. Even though the VTX 1000 has been available for six years extremely few conference bridges* support the proprietary VTX 1000 protocol. Because of this fact it’s  most likely that everyone on that call would have a narrowband conference experience. The investment in the wideband-capable conference phones will yield the best possible G.711 conference calls, but not necessarily wideband calls.


In fact, in many cases people use a conference bridge even when only connecting two locations. Being able to circulate just one phone number, that of the conference bridge, makes organizing the call easier. So everyone calls the bridge rather than establishing a point-to-point call between conference rooms. In any such competition convenience wins over wideband calling.

There are several lessons in this that I can see. The first is that wideband telephony can be delivered over the PSTN. It’s effectively tunneling through the PSTN. Many possible issues make it less than ideal, but it can be done.

The second is that for any new telephony technology to survive it needs to have an ecosystem developed around it. It needs to be supported by a diversity of devices and services. The lack of that ecosystem dooms it be a short-lived or niche solution. This puts proprietary systems at a significant disadvantage.

The last and perhaps larger lesson is that convenience trumps quality, every time. If we want to deliver the superior call quality of wideband calling,  or any other new telephony service, we need to focus on making it just as convenient as dialing a desk phone. It needs to be transparent to the end-user.

Many thanks to Aswath Rao for inspiration through questioning my assumptions, and David Frankel for openly answering the questions of an inquisitive blogger.

This Post Has 5 Comments
  1. Thanks for exploring my point at this detail. I would like to extend your line of thinking to make a couple of points:

    1. There is no need to stimulate the carriers (wirelines, at least) as advocated by HDConnectNow. Consumer Electronics industry can build interoperable products as you suggest and stimulate the market. After all the market adopted faxes without any government incentives.

    2. More fundamentally, it is time to question the fundamental premise of the famous “Stupid Network” paper and conclude that PSTN IS a stupid network. It is long time that the so called thought leaders of telcom have claimed and been echoing the false assertion.

    1. Aswath,

      While I take a certain part of your points as being sound, I think what the VTX 1000 actually proves is that the approach of tunneling through the PSTN is technically possible, but ineffective. The very fact that many VTX 1000 users never actually realize the benefits of wideband significantly defeats it’s ability to deliver a compelling case for the capability. I think that the VTX 1000 is the test case that proves that this approach won’t ever achieve significant market penetration.

      Wideband audio is in some regards better compared to the STU-III secure phones. To start out it’s a compelling capability to a certain target market based upon their specific needs. But unlike secure phones it has the potential to be more widespread as public experience teaches people to expect more from the telephone.

      The fax machine is a completely different case, delivering a wholly new functionality if it works at all.

      As to whether the PSTN is or isn’t a stupid network, that I cannot say. I’m more inclined to consider such things on the basis of the actions of the carriers than the fundamental nature of the network 😉

  2. Since this was posted we have also learned that the ZipDX bridge supports the Polycom VTX-1000 conference phone. AFIAK, it’s the only service of its kind that does.

    1. I’m not pitching HDVoice. This post was merely to underscore the fact that wideband audio can and has been delivered through the legacy PSTN. That’s without reliance upon IP networking or the SIP protocol.

      It’s also true that to do so has drawbacks.

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