Subject: Re: [Sipping] new draft-ietf-sipping-isup-05

From: [email-masked]
Date: Wed, 14 Aug 2002 10:57:35 EDT

In a message dated 8/14/02 4:34:46 AM Eastern Daylight Time, 
[email-masked] writes:

> The media clipping issue related to the
> what-about-if-media-is-received-before-the-answer problem I think it's 
> difficult
> for us to solve on a protocol level. I think the easiest way would be to 
> solve it
> on an applicatoin level. The server could for example send the answer a 
> little
> before it starts sending media, which would at least reduce the risk of the 
> media
> reaching the caller before the SIP message. Or something like that...
> 
> 

Media clipping (resulting in "speech clipping") occurs when the person 
answering the phone starts to speak ("Hello") before the protocol messages 
passing the answer gets to the other end and back. This can not be solved on 
an "application level", since the real "application" here is the human. You 
would have to train all humans to wait sufficient time after picking up the 
handset before saying "hello", that is, as you say, "send the answer a little 
before it starts sending media".

No, a solution must be found on the protocol level.

As William Marshall wrote:
A "solution" that results in clipping the initial conversation is so 
fundamentally broken that it doesn't deserve consideration at all.

Mike Pierce
Artel

---

From: Alan Johnston <[email-masked]>
Date: Wed, 14 Aug 2002 10:12:15 -0500

Reading this long, long thread, one might conclude that SIP/ISUP mapping is 
somehow a new and untested thing.  Actually, it has been out there and 
implemented for years now, and guess what - it works!  Some of us have 
commercial products that use it.

It is true that if you do three or four questionable things in a row, it is 
possible to get clipping.  However, these cases can be avoided.  If you 
want to know how, look at the call flows or talk to a vendor that 
understands SIP/ISUP interworking.

Lets get this document finished - Gonzalo and Jon have done an excellent 
job of fielding all these last minute questions and theoretical 
discussions, but we need to move on.

Thanks,
Alan Johnston
sip:[email-masked]

At 10:57 AM 8/14/2002 -0400, [email-masked] wrote:
>>before it starts sending media, which would at least reduce the risk of 
>>the media
>passing the answer gets to the other end and back. This can not be solved 
>on an "application level", since the real "application" here is the human. 
>You would have to train all humans to wait sufficient time after picking 
>up the handset before saying "hello", that is, as you say, "send the 
>answer a little before it starts sending media".
>

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---

From: Henry Sinnreich <[email-masked]>
Date: Wed, 14 Aug 2002 13:06:22 -0500

>> Lets get this document finished
>>but we need to move on.

Amen, and the discussions on the list as well.

Henry

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] 
> On Behalf Of Alan Johnston
> Sent: Wednesday, August 14, 2002 10:12 AM
> To: [email-masked]; [email-masked]; 
> [email-masked]
> Cc: [email-masked]; [email-masked]
> Subject: Re: [Sipping] new draft-ietf-sipping-isup-05
> 
> 
> >>difficult for us to solve on a protocol level. I think the 
> easiest way 
> >>would be to solve it
> Use [email-masked] for questions on current 
> sip Use [email-masked] for new developments of core SIP
>

---

From: Christer Holmberg <[email-masked]>
Date: Thu, 15 Aug 2002 08:14:14 +0300

Hi,

[email-masked] wrote:

>> what-about-if-media-is-received-before-the-answer problem I think
>> it's difficult
>> for us to solve on a protocol level. I think the easiest way would
>> be to solve it
>> on an applicatoin level. The server could for example send the
>> answer a little
>> before it starts sending media, which would at least reduce the risk
>> of the media
> answering the phone starts to speak ("Hello") before the protocol
> messages passing the answer gets to the other end and back. This can
> not be solved on an "application level", since the real "application"
> here is the human. You would have to train all humans to wait
> sufficient time after picking up the handset before saying "hello",
> that is, as you say, "send the answer a little before it starts
> sending media".
>

Perhaps. My comment, however, had nothing to do with the 200/UPDATE
issue we're discussing now, which I DO think will make the clipping even
worse (which is one of the reasons I don't think we should use it), but
the old general problem about receiving media before the signalling
message indicating we'll receive media. What I meant was that THAT is
something we will have to live with, and I'm not sure it's even going to
be a big problem (mostly does take some time to lift the hook, bring it
to the ear etc, before you say "Hello!" :). My concerns are the idea of
200/UPDATE, and also (which has been discussed before) the MUST of
buffering 200 before a PRACK has been received, and those things I DO
think shall be solved on a protocol level.

Regards,

Christer Holmberg
Ericsson Finland

---

From: Michael Hammer <[email-masked]>
Date: Thu, 15 Aug 2002 15:02:20 -0400

Alan,

Yes, but how?

Do you interpret 180 as pure call signaling indication to be propagated 
back, or as in implicit indicator that alerting should be inserted into the 
in-band backwards path?

Mike

At 10:12 AM 8/14/2002 -0500, Alan Johnston wrote:
>Reading this long, long thread, one might conclude that SIP/ISUP mapping 
>is somehow a new and untested thing.  Actually, it has been out there and 
>It is true that if you do three or four questionable things in a row, it 
>is possible to get clipping.  However, these cases can be avoided.  If you 
>>messages passing the answer gets to the other end and back. This can not 
>>be solved on an "application level", since the real "application" here is 
>>the human. You would have to train all humans to wait sufficient time 
>>after picking up the handset before saying "hello", that is, as you say, 
>>"send the answer a little before it starts sending media".
>>