Re: draft-ietf-sip-info-events-00: package negotiation

I would offer the likelihood of a UAC only half implementing Info  
Packages is about 00.000% (five zeros, anyone?).  I cannot imagine  
anyone expending the effort to implement Info Packages but not use them.

If the UAS is a legacy device, the UAC will detect it from the absence  
of Send/Recv-Info headers.

If the UAC is a legacy device, the UAS will detect it from the absence  
of Send/Recv-Info headers.

Since I will soon make it clear a conforming UAC can send a legacy  
INFO, half negotiation is a non-issue.

For example, let's say it's two weeks from now and I've published the  
update to RFC 3398 to use Info Packages. Either the implementor will  
implement the full ISUP package, or not. It just does not make sense  
to do half the job, since 90% of the job gets done when one does the  
first half. If one side does not do Info Packages, then presumably, in  
the interests of legacy interoperability (and often because the code  
is already written), the device falls back to legacy INFO/RFC 3398.

3pcc? By the time you can list one header (Send or Recv), you can list  
both.

Therefore, I would offer it is an implementation failure to list only  
a Send-Info or Recv-Info header.

On Oct 22, 2008, at 5:36 AM, Christer Holmberg wrote:

>
> Hi,
>
>> General issues with the negotiation mechanism:
>>
>> What happens if the initial INVITE by a UAC includes only Send-Info  
>> or
> Recv-Info? Does that indicate a "half-legacy" device??? Or does it  
> delay
> negotiation for one but not the other? Or does
>> the presence of one mean the absence of the other is equivalent to an
> empty one?
>>
>> As I think about it, I don't think its really necessary to treat the
> absence of these headers as meaning "legacy". Treating the absence of
> these headers as equivalent to their presence without
>> any packages is sufficient to get the proper legacy behavior. The
> tricky part is figuring out out when their absence *doesn't* mean  
> that,
> which is significant only in the non-legacy case. In
>> particular, when they aren't present in INVITE it means deferral of  
>> the
> "offer" to the UAS. And possibly absence in an UPDATE means "don't
> renegotiate"???
>
> I don't think the presence, or absence, of the S/R-Info headers should
> in any way be connected to legacy in any way. A UA can be legacy no
> matter if the headers are present, or not present, but that is all  
> done
> based on "configuration", as described in the draft.
>
> So, if a UAC only included Send-Info, it means that it only supports
> sending of Info packages. Then, it may, or may not, also support  
> legacy
> INFO usages, but that is completely separated.
>
>
>> I'm confused by the three way negotiation of info packages in
> INVITE/2xx/ACK. Its allowed when the Send-Info/Recv-Info are in the
> INVITE, but not when they are deferred to the INVITE response,
>> or when they are conveyed in UPDATE and its response. If the three  
>> way
> handshake is needed to seal the deal, then those other options  
> should be
> off the table. But the "deferred offer" of these
>> is really needed, so it can't be off the table. Or is this just an
> extra benefit that can be exploited when possible?
>>
>> Also, I don't see any provision for additional round(s) of  
>> negotiation
> before 2xx via PRACK and UPDATE, though there is provision for
> additional "half-negotiations" via provisional responses
>> and the final response. Given the parallels with O/A, I'd prefer to  
>> see
> them more aligned in this regard, though I can be talked out of that
> with a good argument.
>
> I agree (I think :). The negotiation whould be 2-way. Then, based on
> what the UAC gets from the UAS, it may send a PRACK/UPDATE/re-INVITE
> with a new set of supported Info packages, but that is a new 2-way
> negotiation transaction.
>
>
>> I'd also like to take advantage of the lessons that have been learned
> with O/A and nail down more of the semantics now. One issue that leaps
> to mind in that regard is what happens if we start
>> to negotiate info packages in a reINVITE and then the reINVITE fails?
>
> That's a good point.
>
> I think we should use the same rule as for offer/answer. Because,  
> assume
> I send you a new set of packages in a re-INVITE, and you send me  
> back a
> set in a 18x. Then we may start using info packages based on that
> negotiation long before the re-INVITE is rejected.
>
>> IMO what is needed is a state model for this stuff, added to the  
>> state
> for an invite-dialog-usage. This state should determine which packages
> may be sent, and which should be received without
>> error. We should be very clear about exactly which events cause  
>> changes
> to this state.
>>
>> Even then there are race conditions that need to be clarified. For
>> instance: Suppose, as a result of an INVITE/1xx exchange between  
>> Alice
> and Bob, that packages P & Q are allowed to be sent from Alice to Bob.
>> Alice then sends an INFO with package Q, and at the same time Bob  
>> sends
> a 2xx that only allows the receipt of package P. Then Bob receives the
> INFO with package Q. What should happen?
>>
>> Another issue is that if the Send-Info/Recv-Info contents change in
> subsequent 1xx responses to the same INVITE, the UAS has no guarantee
> that they are received. So any reduction in what can be
>> received cannot be counted upon until the 2xx/ACK.
>
> True. But, I wonder whether this will really be a real-life problem.
>
> And, we could a response code (4xx Info package not supported),  
> which is
> used by the UAS if it receives an info package which it doesn't  
> support.
> Then the UAC knows.
>
> Regards.
>
> Christer
>
> _______________________________________________
> Sip mailing list  https://www.ietf.org/mailman/listinfo/sip
> This list is for NEW development of the core SIP Protocol
> Use [email protected] for questions on current sip
> Use [email protected] for new developments on the application of sip

_______________________________________________
Sip mailing list  https://www.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [email protected] for questions on current sip
Use [email protected] for new developments on the application of sip