答复: Re: PRACK: Change MUST requirement to include SDP offer in first reliable provisional response

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More points of view to this question:

By RFC3262:
1. "Retransmissions of the reliable provisional response cease when a matching PRACK is received by the UA core."

2. "If the PRACK does match an unacknowledged reliable provisional response, it MUST be responded to
   with a 2xx response."

So, when UAs receive a matching PRACK, it will stop re-transmit the reliable provisional response(18x). And the response
to PRACK MUST be 2xx.

It is simple and clear. And when UAs receive non-2xx response to PRACK, it is clear that the other side do not receive the
PRACK. It can send a new PRACK(CSeq++, the same RAck).

And now, we can use PRACK to send "precondition notification" and "codec refine". When we need to issue session modification like adding codec,
adding/removing media streams, we MUST using Re-INVITE/UPDATE.

I think we should not re-write RFC3262 to allow the UA to reject the PRACK.





Paul Kyzivat <pkyzivat@xxxxxxxxx>
发件人:  sipping-bounces@xxxxxxxx

2009-04-06 20:16

收件人
"Rockson Li (zhengyli)" <zhengyli@xxxxxxxxx>
抄送
sipping@xxxxxxxx, Christer Holmberg <christer.holmberg@xxxxxxxxxxxx>
主题
Re: [Sipping] PRACK: Change MUST requirement to include SDP offer in        first reliable provisional response





I think I also agree. There are a lot of things that in hindsight we
probably would have done differently. But that is water over the dam. We
are where we are.

                Paul

Rockson Li (zhengyli) wrote:
> I totally agree with Hadriel's insight here.
>
> It should have been avoided to put too many jobs into PRACK,
>
> I miss KISS(Keep It Simple and Stupid) principle
>
>  
>
> Regards,
>
> -Rockson
>
> ------------------------------------------------------------------------
> *From:* sipping-bounces@xxxxxxxx [mailto:sipping-bounces@xxxxxxxx] *On
> Behalf Of *Hadriel Kaplan
> *Sent:* Tuesday, March 31, 2009 9:50 PM
> *To:* Christer Holmberg; sipping@xxxxxxxx
> *Subject:* Re: [Sipping] PRACK: Change MUST requirement to include SDP
> offer in first reliable provisional response
>
>  
>
>  
>
> In hindsight I’m thinking we probably also shouldn’t have made the SDP
> answer (or another offer) required or even possible in the PRACK
> either.  I think it should have been for one and only one purpose: to
> acknowledge receipt of the provisional response.
>
>  
>
> -hadriel
>
>  
>
>  
>
>
> ------------------------------------------------------------------------
>
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> This list is for NEW development of the application of SIP
> Use sip-implementors@xxxxxxxxxxxxxxx for questions on current sip
> Use sip@xxxxxxxx for new developments of core SIP
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Use sip@xxxxxxxx for new developments of core SIP


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