Re: 答复: Re: PRACK: Change MUST req uirement to include SDP offer in first reliab le provisional response

We could write in an RFC that lead must be turned into gold, but when it
came time to implement that it would be discovered that it wasn't
feasible to always follow the RFC.

The quotes below reflect a similar degree of naivety in 3262, at least
regarding the responses to PRACK. Plenty of examples have been given of
cases where it is inappropriate to return a 200 response.

The statement that retransmissions shall cease when the matching PRACK
is received is, IMO, predicated on the assumption that a 200 will always
be returned. Once you reverse that assumption, then you must also
reconsider this statement.

	Thanks,
	Paul


[email protected] wrote:
> 
> 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 <[email protected]>*
> 发件人:  [email protected]
> 
> 2009-04-06 20:16
> 
> 	
> 收件人
> 	"Rockson Li (zhengyli)" <[email protected]>
> 抄送
> 	[email protected], Christer Holmberg <[email protected]>
> 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:* [email protected] [mailto:[email protected]] *On
>  > Behalf Of *Hadriel Kaplan
>  > *Sent:* Tuesday, March 31, 2009 9:50 PM
>  > *To:* Christer Holmberg; [email protected]
>  > *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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