HDVoice: On The Cheap & Analog RJ-11 Style

HDVoice RJ-11 Wall Plate A short while back I addressed the question of how DECT & CAT-iq may foster the broad deployment of HDVoice. At that time I described one possible scenario where carriers would deploy customer premises equipment (CPE) with an on-board cordless base station. Although a frontrunner, and the basis of Comcast’s (decidedly non-HD) HomePoint service, this is not the only approach afoot. There’s another possibility arising that involves conveying HDVoice over a plain old analog RJ-11 connection.

At first glance HDVoice and analog lines would certainly seem to be mutually exclusive. The common wisdom is that wideband telephony requires the use of an all-IP call path. This is in fact a generalization, and not absolutely true.

Firstly, it has long been possible to pass wideband audio, in the form of G.722 encoded media, over the PSTN by way of ISDN connections. Also known as BRI interfaces, an ISDN connection supports  up to two 64 kbps channels (bearer channels) and one D channel for the purposes of call setup & teardown signaling. High-quality voice using G.722 was one of the selling points of ISDN in the 1980s.

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Considering Wideband Audio Over The Traditional PSTN

polycomlogoQuestion: What was the first HDVoice product that Polycom offered?

Answer: The Polycom VTX 1000 conference phone.

The thing that makes this fact so curious is not immediately obvious. The VTX 1000 is not a SIP device, nor even IP capable. Like it’s closest relative the Polycom SoundStation 2, it’s designed to connect to a plain old analog phone line (a.k.a. POTS, the PSTN).

Of course, the common wisdom is that you just can’t have wideband telephony over the PSTN. Yet the VTX 1000, circa 2003, delivers wideband conference calls so it seems that assertion is not strictly true. Understanding this is in a little more depth would seem like a good thing. Happily, Polycom published a white paper describing the internals of the VTX 1000.

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