Subject: Re: [AVT] When and where to specify dtxmin for ERVC per RFC 4788

From: "Kapoor, Rohit" <[email-masked]>
Date: Sun, 8 Feb 2009 19:52:34 -0800

Hi Bing,

The whole idea behind dtxmin is so that voice capacity gains are still maintained. So, even if background noise changed, the sender should not send a 1/8th rate frame with new silence parameters more frequent than dtxmin.

Thanks,
Rohit
________________________________________
From: HE Bing [[email-masked]]
Sent: Sunday, February 08, 2009 6:45 PM
To: [email-masked]; Kapoor, Rohit; [email-masked]
Cc: Chen (China CIV), Wei; XU Hui N
Subject: When and where to specify dtxmin for ERVC per RFC 4788

Hello Mr Xie, Mr Kapoor and other AVT expert,

I feel hard in understanding the use of parameter dtxmin registered for media type EVRC, EVRC0, EVRC1, EVRCB, EVRCB0 and EVRCB1.

>From perspective of codec, whenever the characteristics of background noise changed during silence period, an SID frame should be sent out to make peer end adjust the regenerate comfort noise accordingly.

But RFC 4788 states in 6.1.
      dtxmin:  Permissible values are from 0 to 255.  Indicates the
         minimum DTX update interval in number of frames.  The RTP
         receiver may use 'dtxmin' to indicate to the RTP sender the
         minimal interval (in number of frames) between any two DTX
         updates it expects to receive from the RTP sender.

         If this parameter is not present, the default value 12, as
         specified in [8] MUST be assumed.  This parameter MUST be
         ignored if silence suppression using DTX is not used for the
         session.

Does it make real sense? If yes, could you share any valid use case?

Thanks!
He Bing

---

From: "Kapoor, Rohit" <[email-masked]>
Date: Sun, 8 Feb 2009 21:15:35 -0800

________________________________________
From: HE Bing [[email-masked]]
Sent: Sunday, February 08, 2009 9:11 PM
To: Kapoor, Rohit; [email-masked]; [email-masked]
Cc: Chen (China CIV), Wei; XU Hui N
Subject: RE: When and where to specify dtxmin for ERVC per RFC 4788

Hello Rohit,

Thanks for your quick response!

What does voice capacity gains mean? I guess the purpose is that over a
aggregated transmission channel, in order to support N EVRC streams,
upper limits of bandwidth of individual stream should be controlled via
dtxmin.

<Rohit> Voice capacity gains would be lost if too many 1/8th rate frames are sent. So, one would like to control the rate of 1/8th rate transmission.

Is it right?
If yes, then EVRC codec implementation shall be aware of it and support
it or this requirement should be supported by other entity like radio
sub-system in mobile station?

<Rohit> I don't think this requirement needs to be supported by radio sub-system. Rather, it needs to be supported by end points of the call, i.e., VoIP terminals.

Thanks,
Rohit

Best regards!
He Bing

-----Original Message-----
From: Kapoor, Rohit [mailto:[email-masked]]
Sent: Monday, February 09, 2009 11:53 AM
To: HE Bing; [email-masked]; [email-masked]
Cc: Chen (China CIV), Wei; XU Hui N
Subject: RE: When and where to specify dtxmin for ERVC per RFC 4788

Hi Bing,

The whole idea behind dtxmin is so that voice capacity gains are still
maintained. So, even if background noise changed, the sender should not
send a 1/8th rate frame with new silence parameters more frequent than
dtxmin.

Thanks,
Rohit

I feel hard in understanding the use of parameter dtxmin registered for
media type EVRC, EVRC0, EVRC1, EVRCB, EVRCB0 and EVRCB1.

>From perspective of codec, whenever the characteristics of background
noise changed during silence period, an SID frame should be sent out to
make peer end adjust the regenerate comfort noise accordingly.

Thanks!
He Bing