Re: [Sip] info-events and "in-order delivery"

[Paul Kyzivat <pkyzivat at cisco.com>]

Jeroen,

There may be some utility to overlapping info packages of the *same* 
package type. This can work if subsequent messages *supersede* the 
preceding one, so if a later one is processed first then the loss of the 
earlier one is irrelevant. But this is much less likely to be the case 
for packages of *different* types.

I think this simply needs to be highlighted as an issue - especially the 
cross-package-type issue. The details need to be addressed on a 
per-package-type basis.

	Thanks,
	Paul

Jeroen van Bemmel wrote:
>    The current info-events text says (section 5.6):
>
> "In addition, the INFO method does not define mechanisms for ensuring
>   in-order delivery.  While the UAC will increment the CSeq header upon
>   the transmission of new INFO messages, the UAS cannot use the CSeq to
>   determine the sequence of INFO information.  This is due to the fact
>   that there could be gaps in the INFO message CSeq count caused by a
>   user agent sending re-INVITES or other SIP messages."
>
>
> This is not entirely accurate: SIP guarantees that INFO messages are 
> never delivered out-of-sequence. Only in case of *overlapping INFO 
> requests* (i.e. sending a next one before having received a final 
> response for the previous one) it cannot be guaranteed that all are 
> received.
>
> The partial event mechanism (RFC5263) includes a 'version' attribute to 
> detect such gaps. In case of INFO events, I think it is better to simply 
> say: the UAC MUST NOT send an INFO request with a given event type when 
> a previous INFO request containing that event type has not yet received 
> a final response.
>
> Regards,
> Jeroen
>
>
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