Re: [codec] #1: Application: 2.1. Point to point calls supporting transcoding?

James Rafferty <> Wed, 24 March 2010 21:46 UTC

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From: James Rafferty <>
To: stephen botzko <>
Date: Wed, 24 Mar 2010 17:46:24 -0400
Thread-Topic: [codec] #1: Application: 2.1. Point to point calls supporting transcoding?
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Subject: Re: [codec] #1: Application: 2.1. Point to point calls supporting transcoding?
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The "two gateway" or back-to-back gateway case will inevitably degrade quality to be G.711 level or worse.  The IP - IP case where there is no PSTN codec conversion  is the much more interesting one for the marketplace.  I'd agree picking a limited set of HD codecs (for example, G.722 and G.722.2) for these tandeming purposes is the practical approach.

James Rafferty
Product Line Director, Integrated Media Gateways
Dialogic, Inc.
15 Crawford Street
Needham, MA 02494

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From: stephen botzko []
Sent: Wednesday, March 24, 2010 2:22 PM
To: James Rafferty
Cc: Christian Hoene;
Subject: Re: [codec] #1: Application: 2.1. Point to point calls supporting transcoding?

Seems to me that there are two cases here - single gateway, and double gateway.:In the double gateway case, Endpoint A connects to Endpoint B via a gateway pair using PSTN.  The audio is converted to G.711 narrowband by the first gateway, and back to the internet codec by the second.  The best quality that can result is G.711, and the acoustic bandwidth is also limited to narrowband, even though both endpoints can not see the G.711 hop.  Users may have other expectations, but they cannot be met.

In any event, measuring the tandeming quality performance of this codec with all other standard or popular) codecs would be a very tedious exercise, and IMHO not practical.   We'd have to pick one or two codecs and let it go at that.

Stephen Botzko

On Wed, Mar 24, 2010 at 1:59 PM, James Rafferty <<>> wrote:
Hi Christian,

See below (JR).


-----Original Message-----
From: Christian Hoene [<>]
Sent: Wednesday, March 24, 2010 9:23 PM
To: James Rafferty;<>
Subject: RE: [codec] #1: Application: 2.1. Point to point calls supporting transcoding?
Hi James,

>-----Original Message-----
>From: James Rafferty [<>]
>Vendors of products on these network edges will take the steps needed to get endpoints to communicate
>(as driven by their service provider customers), even if it requires a codec change to complete the

So, the main requirement in these cases is the interoperability. Conversational quality is of lesser importance.
Thus, we need not particular quality requirements beside that it works OK?
JR - An ability to interop is the first consideration and quality is still important; the customer will expect (whether reasonable or not) better than PSTN quality if wideband codecs are being used by both endpoints.


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