Subject: [Ecrit] Audio Codecs for 911 CALLS.

From: "Karihaloo, Ujjval" <[email-masked]>
Date: Mon, 7 Aug 2006 12:22:30 -0600

Hi All,

  Is there any draft/RFC around which Codec (G711, G729 etc) to use for
a 911 Call?

Thx,

Ujjval.

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From: Hannes Tschofenig <[email-masked]>
Date: Mon, 07 Aug 2006 20:27:47 +0200

Hi Ujjval,

our Phone BCP draft should give some guidance on the codecs to use for 
emergency calls. However, to some extend this is also a SPEERMINT issue.

The Phone BCP draft can be found here:
http://www.ietf-ecrit.org/cache/draft-rosen-ecrit-phonebcp-01.txt

Feedback for the draft is appreciated.

Ciao
Hannes

Karihaloo, Ujjval wrote:
> ------------------------------------------------------------------------
>

---

From: "James M. Polk" <[email-masked]>
Date: Mon, 07 Aug 2006 13:53:34 -0500

At 08:27 PM 8/7/2006 +0200, Hannes Tschofenig wrote:
>emergency calls.

I believe we state G.711 is the preferred codec. We don't want much 
compressed due to sounds in the background that are otherwise recognizable 
to a PSAP call-taker not being heard because the codec didn't reproduce 
them accurately.  A gunshot is one example that some codecs, I've been 
told, cannot reproduce because it happens so fast, and the sound doesn't last.

>However, to some extend this is also a SPEERMINT issue.

??

I don't get this comment.

SPEERMINT is an IP-NNI, and I don't believe should have much to do with 
endpoint codec description in an SDP offer/answer exchange.

Someone correct me if this is something SPEERMINT cares about, and I'll go 
smack Dave Meyer (WG chair).

---

From: "Stastny Richard" <[email-masked]>
Date: Mon, 7 Aug 2006 23:36:38 +0200

>smack Dave Meyer (WG chair).

Hi James,

you haven't been on the SPEERMINT list recently, have you? 

poor Dave ;-)

Richard

PS: OTOH, what are the codecs a PSAP MUST support?
or said the other way round, what are the coducs you must support in
a device to be sure to be able to contact a PSAP?

________________________________

Von: James M. Polk [mailto:[email-masked]]
Gesendet: Mo 07.08.2006 20:53
An: Hannes Tschofenig; Karihaloo, Ujjval
Cc: [email-masked]
Betreff: Re: [Ecrit] Audio Codecs for 911 CALLS.

??

---

From: Andrew Newton <[email-masked]>
Date: Mon, 7 Aug 2006 17:45:11 -0400

On Aug 7, 2006, at 2:53 PM, James M. Polk wrote:

>> our Phone BCP draft should give some guidance on the codecs to use  
>> for emergency calls.
>
> compressed due to sounds in the background that are otherwise  
> recognizable to a PSAP call-taker not being heard because the codec  
> didn't reproduce them accurately.  A gunshot is one example that  
> some codecs, I've been told, cannot reproduce because it happens so  
> fast, and the sound doesn't last.

G.711 is likely not a very good choice for wireless environments.     
I think the correct thing to do is have the phone-bcp list a small  
number of codecs (hopefully no more than 3) of which atleast one MUST  
be supported (though all would be good), and then advise PSAPs to  
support all of them.

> SPEERMINT is an IP-NNI, and I don't believe should have much to do  
> with endpoint codec description in an SDP offer/answer exchange.

I don't believe we should let SPEERMINT decide this at all.  While  
specifying codecs is a requirement for interoperability, that working  
group is split on the matter.  Plus, ECRIT is way, way ahead of  
SPEERMINT and we'd just be stalled waiting on them.

> I'll go smack Dave Meyer (WG chair).

I won't stop ya.

-andy

---

From: "James M. Polk" <[email-masked]>
Date: Mon, 07 Aug 2006 16:52:25 -0500

>you haven't been on the SPEERMINT list recently, have you?

there's a reason for that!!

hehe

>poor Dave ;-)

bigtime

>PS: OTOH, what are the codecs a PSAP MUST support?

NENA says G.711 at a minimum, video codecs haven't been identified yet

>a device to be sure to be able to contact a PSAP?

aha, that's what the phoneBCP ID is specifying to get to PSAPs, and I guess 
that means ECRIT, through the phoneBCP ID, or NENA directly, need(s) to 
bring a requirement into SPEERMINT - is that what I'm thinking you'll say next?

---

From: "Stastny Richard" <[email-masked]>
Date: Mon, 7 Aug 2006 23:59:07 +0200

>bring a requirement into SPEERMINT - is that what I'm thinking you'll say next?

The phonebcp requirement is simpler, because it is unidirectional:

The PSAP MUST support at least a set of codecs (e.g. G.711 and a mobile
codec), which can easily be achieved, a device may choose to support at least
one of them.
 
In SPEERMINT we ar etalking about two endpoints

Richard

Von: James M. Polk [mailto:[email-masked]]
Gesendet: Mo 07.08.2006 23:52
An: Stastny Richard
Cc: [email-masked]
Betreff: Re: [Ecrit] Audio Codecs for 911 CALLS.

hehe

bigtime

---

From: "James M. Polk" <[email-masked]>
Date: Mon, 07 Aug 2006 17:22:09 -0500

>G.711 is likely not a very good choice for wireless environments.

does this mean that my wired IP-phone, like the majority of all others, 
will not have any chance at communicating with anyone else's IP 
cellphone?  I think the reverse will have the same problem...

>>I'll go smack Dave Meyer (WG chair).

I'll tell him you said that  ;-)

---

From: Andrew Newton <[email-masked]>
Date: Mon, 7 Aug 2006 18:44:09 -0400

On Aug 7, 2006, at 6:22 PM, James M. Polk wrote:

> does this mean that my wired IP-phone, like the majority of all  
> others, will not have any chance at communicating with anyone  
> else's IP cellphone?  I think the reverse will have the same  
> problem...

That's my non-expert understanding.  Fortunately, we aren't concerned  
with getting a call through between any two UAs: we are concerned  
about getting a call through from any UA to a PSAP.

-andy

---

From: "James M. Polk" <[email-masked]>
Date: Mon, 07 Aug 2006 17:47:44 -0500

At 06:44 PM 8/7/2006 -0400, Andrew Newton wrote:

>That's my non-expert understanding.  Fortunately, we aren't concerned with 
>getting a call through between any two UAs: we are concerned about getting 
>a call through from any UA to a PSAP.

err, what do you think will be answering the call in the PSAP?

(hint: it'll be a UA)

---

From: "Brian Rosen" <[email-masked]>
Date: Mon, 7 Aug 2006 20:20:09 -0400

I believe that the minimum codec is G.711.  Every PSAP will support it,
every call must be able to support it.

I think we will recommend that every PSAP support the codecs applicable to
the wireless networks that are in their service boundaries, as well as
wideband codecs that may be supported in their service area, so that
transcoding is not required.  From the emergency service vantage point, the
lack of standardization in this area (and I do mean "the wonderful thing
about standards is there are so many to choose from") is glaringly,
painfully stupid.

It is unwise to support the compressed codecs (G.723, G.729, ...).  Some of
the adaptable codecs might be supported in their better-than-toll-quality
modes.

We might want to recommend support for straight linear 16 bit audio, so that
transcoding can be minimal loss, although since no transcoders can do this
now, that might be a futile gesture.

Every PSAP will support the text codec, of course, and I hope, one or two IM
streams.  Every PSAP will probably (maybe eventually) support H.264, and
some will support H.263.

But in the end, I think these have to be recommendations (SHOULD) and thus
the MUST, for everyone, is G.711.

AND NO VOICE ACTIVITY DETECTION.

And I don't think this is SPEERMINT territory, even if the subject matter
overlaps some.  Peering is not assumed to be able to place an emergency
call.

Brian

> -----Original Message-----
> From: James M. Polk [mailto:[email-masked]]
> Sent: Monday, August 07, 2006 6:48 PM
> To: Andrew Newton
> Cc: [email-masked]; Karihaloo, Ujjval
> Subject: Re: [Ecrit] Audio Codecs for 911 CALLS.
> 
> with

---

From: Andrew Newton <[email-masked]>
Date: Mon, 7 Aug 2006 20:49:16 -0400

> err, what do you think will be answering the call in the PSAP?

Upgrade every PSAP UA, or upgrade every UA everywhere?  Which do you  
believe to be the harder problem?

-andy

---

From: "James M. Polk" <[email-masked]>
Date: Mon, 07 Aug 2006 19:51:51 -0500

Brian

I agree completely.

And I have a comment about SPEERMINT: though peering shouldn't have 
anything to do with endpoint codec support, peering in SIP will likely 
involve an SBC, which, by definition is a B2BUA - meaning it can change the 
SDP, meaning it can change the codecs to whatever it wants.

That said, we don't want peering (meaning SPEERMINT) to *NOT* have a 
requirement from this WG to support our minimal specifications in ECRIT to 
establish SIP calls as if the peering point wasn't there.

We/someone needs to make that WG aware of this situation - and have them 
incorporate, if appropriate, whatever we reasonably require of a peering 
specification from them.

---

From: Andrew Newton <[email-masked]>
Date: Mon, 7 Aug 2006 20:56:47 -0400

> about standards is there are so many to choose from") is glaringly,

What about WiFi SIP phones and DECT phones?

> overlaps some.  Peering is not assumed to be able to place an  

I'm glad we can agree on this.

-andy

---

From: Gunnar Hellstrom <[email-masked]>
Date: Tue, 8 Aug 2006 06:51:57 +0100

Brian,
I am glad to see this statement:
"Every PSAP will support the text codec, of course,"

Regards
Gunnar

[email-masked]

-----Original Message-----
From: Brian Rosen [mailto:[email-masked]]
Sent: Tuesday, August 08, 2006 1:20 AM
To: 'James M. Polk'; 'Andrew Newton'
Cc: 'Karihaloo, Ujjval'; [email-masked]
Subject: RE: [Ecrit] Audio Codecs for 911 CALLS.

Brian

---

From: "Brian Rosen" <[email-masked]>
Date: Tue, 8 Aug 2006 09:18:30 -0400

Every spec for a WiFi SIP phone I've ever seen supported G.711 from the
handset.  I don't know much about DECT phones, especially what codecs they
support in the handset, but they clearly support G.711 coming out of the
"base station", because they usually have ISDN connection options.

Do we not agree that forcing every PSAP to support every codec that every
carrier in its service area chooses makes no sense?  I'm assuming we can't
just pick one ourselves and demand the carriers support that one, right :)

Do we not agree that supporting compressed codecs other than the native
wireless codecs is a bad idea (they all do g.711 also)?

Brian

> From: Andrew Newton [mailto:[email-masked]]
> Sent: Monday, August 07, 2006 8:57 PM
> To: Brian Rosen
> Cc: 'James M. Polk'; [email-masked]; 'Karihaloo, Ujjval'

---

From: Andrew Newton <[email-masked]>
Date: Tue, 8 Aug 2006 10:31:53 -0400

> just pick one ourselves and demand the carriers support that one,  

A lot of "nots" in the sentence.  Yes, PSAPs ought to be encouraged  
to support the codecs of the wireless carriers in the service area.

> wireless codecs is a bad idea (they all do g.711 also)?

I really don't know about this.  I believe Barbara has a point.

Also, I've been told that 3GPP2 has settled on a codec that MUST be  
supported.

-andy

---

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 08 Aug 2006 12:40:26 -0400

Practically speaking, we're likely to have two classes of IP end systems:

(1) residential and enterprise, all of which speak G.711 mu-law today;

(2) 3GPP and 3GPP2, which all support AMR (although I'm not sure which 
of the set of codecs in the AMR family are mandatory to support)

Thus, I don't see this as particularly hard. I see no need to support 
A-law, unless somebody can show that there's a VoIP device out there 
that only speaks A-law.

Also, it is not necessarily true that G.711 is more resilient against 
packet loss than compressed codecs.

See http://www.globalipsound.com/datasheets/EG711.pdf for some comparisons.

Clearly, we're using compressed codecs (G.729 and GSM-FR, primarily, 
although I'm not sure what Sprint's CDMA network uses) today for 
emergency calls, given that roughly half originate from cell phones.

Henning

Andrew Newton wrote:
> A lot of "nots" in the sentence.  Yes, PSAPs ought to be encouraged to 
> support the codecs of the wireless carriers in the service area.
>

---

From: "Brian Rosen" <[email-masked]>
Date: Tue, 8 Aug 2006 13:13:29 -0400

I don't really know enough about A law issues.  I believe, as you suggest,
that the phones all support mu law.  That doesn't mean it's supported
through the carrier.  I'd be hesitant to say that, for emergency case only,
mu Law was required, if they weren't already doing that, or at least willing
to do that.  Plenty of VoIP systems "groom" codec lists with SBCs.

I don't think any cellular network uses G.729.  GSM systems will support
AMR, which will be nice, but doesn't cover all the cases.  There will be a
lot of EvRC out there I think.  There ARE a lot of other codecs out there
now.  Of course, they are all now transcoded to G.711. 

Can someone tell us where the transcode is done?  Is it at the MSC itself?
It may not be worth worrying about older systems because you may not be able
to get the compressed voice stream packetized any reasonable way.  If you
think about replacing the connection to the PSTN emergency call system now
with a gateway, it may already G.711 by that point.  If the transcode is
already done on some kind of PSTN gateway, maybe we could replace that
gateway with a VoIP gateway, and then you would have to deal with all the
old codecs.

Brian

> From: Henning Schulzrinne [mailto:[email-masked]]
> Sent: Tuesday, August 08, 2006 12:40 PM
> To: Andrew Newton
> Cc: Brian Rosen; 'Karihaloo, Ujjval'; [email-masked]

---

From: "Brian Rosen" <[email-masked]>
Date: Tue, 8 Aug 2006 14:04:37 -0400

SBCs routinely prune codec lists in the SDP.  An endpoint may offer it but
that offer may not get to you.

Brian

> Sent: Tuesday, August 08, 2006 1:50 PM
> To: Brian Rosen
> Cc: 'Andrew Newton'; 'Karihaloo, Ujjval'; [email-masked]
> Brian Rosen wrote:
> I don't know what you mean by "through the carrier". SDP negotiation is
> end-to-end.

---

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 08 Aug 2006 13:50:12 -0400

---

From: Andrew Newton <[email-masked]>
Date: Tue, 8 Aug 2006 19:00:55 -0400

On Aug 8, 2006, at 12:40 PM, Henning Schulzrinne wrote:

> (2) 3GPP and 3GPP2, which all support AMR (although I'm not sure  
> which of the set of codecs in the AMR family are mandatory to support)

Well, we shouldn't really guess about this.  Perhaps the co-chairs  
can make an official inquiry via the IETF 3GPP and 3GPP2 liaisons.

-andy