Last month Daniel Berninger wrote a guest column expressing the benefits of using high definition codec for voice communication. In that post, Dan argues that widespread use of compatible codecs is critical. Inexplicably I had missed it when it appeared and a tweet brought it to my attention. For a long time, I have argued in these pages that we should be using wideband codecs and more specifically, I have been a proponent of Speex. But I differ with Dan in some respects and this post captures some of my thoughts.
When we decided to use a wideband codec in EnThinnai, we also faced the problem of compatibility. More importantly, we decided that our users would like to communicate with people who are not yet users of EnThinnai. Our strategy is to dynamically download the codec. I think this simple technique effectively addresses the compatibility issue.
But this means that the codec we use must be freely distributable. This is the reason we decided to use Speex. Last week Skype announced that they will make their codec widely available. I am not sure whether this kind of use is allowed.
In his post, Dan also makes a point that is not really relevant. He suggests that supporting wideband codec in PSTN will require massive overhaul of the network and so is not practical. But that is not the case. It has gone into the folklore that PSTN is not a "stupid network" and no change can be introduced at the edges. But that is not really true. Data modems and fax machines are well known examples. STU III that is designed for encrypted communication is another. So if we really want to use wideband codec and both the parties have wideband codec enabled telephones, then they can switch over to this codec, just like STU III users switch to secure mode. So let us not perpetuate the myth that PSTN is not a stupid network.
But more importantly, we should recognize that if a VoIP end-point is based on ATA, then it is "PSTN" for all practical purposes. So let us try to guide the industry to use native end-points and not ATA based. This is more critical.
Posted by aswath at March 7, 2009 04:41 PM
Unfortunately many non-POTS VoIP devices do not support wideband codecs either. My Philips VOIP841 skypephone doesn't.
People still repeat that old chestnut about VoIP not matching POTS quality. My experience with Skype and SVOPC is that it is far superior to POTS, let alone cell phones, specially in communicating subtle nuances in timbre.
Posted by: Fazal Majid at March 9, 2009 12:21 PMIn fact, Polycom's very first wideband product was a conference phone called the VTX-1000. It's designed to connect to a POTS line, yet it truly is wideband capable.
When it dials the remote party it sends a few tones to try and determine if the far end is also a VTX-1000. If so, then it creates a data connection (v.32) and passes the call data as if it were a apri of modems connected.
Since the VTX uses a low bit rate codec (G.722.1)the call can be sustained in < 56 kbps and still have a wideband connection.
If the far end is NOT another VTX then the call is handled as a normal G.711 call, merely with superior hardware (transducer) capabilities.
So, wideband cann effectively tunnel through the existing PSTN. But is this a model that would work more widely? Or is this simply a way of making end-points more costly with little benefit in most cases?
Posted by: Michael Graves at May 18, 2009 01:00 PMMike, Yes as you sate here and have pointed out to me in another context that VTX-1000 uses the exact procedure I describe here. It just supports my claim that one can have HD voice in PSTN as well.
This is the only model that will work in a "stupid" network and PSTN is a stupid one. I am not sure that the phones will be expensive one. I think it can be added to DECT-class phones with not much appreciable cost. In my opinion this is better than trying to improve the network quality globally.
Posted by: Aswath at May 18, 2009 01:30 PM