Subject: [Sip] question on draft-ietf-sip-asserted-identity-02.txt

From: [email-masked]
Date: Thu, 31 Oct 2002 20:33:56 -0500

Hi,

On page 8, in Table 2 for the P-Asserted-Identity header, the header is not
allowed in SIP INFO method. Is there any special reason?

The scenario i have is the case where a UAC (gateway) sends an initial
INVITE to a UAS without a calling name as the name information is not yet
available and then sends a calling name in a subsequent INFO method before
the UAS answers, assuming an early call leg is established. In this case,
couldn't the P-Asserted-Identity header be sent in the INFO carrying the
calling name? The UAC can wait until the calling name is available before
sending the initial INVITE, but this scenario may be considered to minimize
call setup delay.

Thanks,
YoungSun

                    "Mark Watson"                                                               
                    <mwatson@nortelnet        To:     "[email-masked]'"                  
                    works.com>                <[email-masked]>                            
                                              cc:     [email-masked], (bcc: Youngsun              
                    10/31/2002 08:06          Song/Telcordia)                                   
                    AM                        Subject:     RE: [Sip]                            
                                              draft-ietf-sip-asserted-identity-02.txt: ppi from 
                                              trust    ed entity                                

Harsh,

See comments inline...

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> Sent: 31 October 2002 03:58
> To: Watson, Mark [MOP:EP10:EXCH]
> Cc: [email-masked]; [email-masked]
> Subject: RE: [Sip] draft-ietf-sip-asserted-identity-02.txt: ppi from
> trust ed entity
>
>
>
>
> Mark,
>
> I understand the point that you've made and that  how a proxy uses the
> P-Preferred-Identity headers
> received from a user agent is a policy decision.
>
> I got confused because of the first statement in Section 6
> which reads:
> 'If a P-Preferred-Identity header field is present in the message that
>    a proxy receives from an entity that it does not trust.....'.
>
> Is this statement then equivalent to the following?
> 'If a P-Preferred-Identity header field is present in the message that
>    a proxy receives from a user agent.....'.
>

No, in this draft 'an entity that [the proxy] does not trust' formally
means
'an entity outside the Trust Domain for Asserted Identity of which the
proxy
is a member'.

Normal User Agents will usually be outside the Trust Domain. But a User
Agent such as a PSTN gateway may be inside the Trust Domain.

Another proxy could be either inside or outside the Trust Domain. The
requirements that have to be met for another proxy to be considered inside
the Trust Domain are defined in the definition of a particular Trust Domain
(called Spec(T)). The minimum things that Spec(T) has to include to make
the
mechanism work are described in the drafts.

> I was also trying to understand why the P-Preferred-Identity MUST be
> removed
> by a proxy from any message that it forwards.Would it be
> correct to say
> that the reason lies in
> requirments themselves, as put forward in
> draft-ietf-sipping-nai-reqs-02.txt , section 3 of which reads
>
> 'It shall be possible for a UA to provide a preferred identity to the
>    network intermediary, which MAY be used to inform the generation of
>    the Network Asserted Identity according to the policies of
> the Trust
>    Domain.'.
>
> And therefore the significance of P-Preferred-Identity exists
> only between
> a UA and the proxy that performs its authentication.
>

Yes.

>
> thanks
> harsh
>
>
>
>
>
>
>
> "Mark Watson" <[email-masked]> on 10/30/2002 07:13:39 PM
>
> To:   Harsh Bhondwe/HSSBLR, [email-masked]
> cc:
>
> Subject:  RE: [Sip] draft-ietf-sip-asserted-identity-02.txt:
> ppi from trust
>       ed entity
>
>
>
>
> Harsh,
>
> From memory, a proxy should not expect to receive
> P-Preferred-Identity from
> another member of the Trust Domain for Asserted Identity.
>
> You may be right that the behaviour if it is received is not
> specified. If
> a
> P-Asserted-Identity is present, then I would expect the
> P-Preferred-Identity
> to be discarded (they should not coexist). If there is no
> P-Asserted-Identity, then I suppose the Proxy could behave as if the
> message
> were received from outside the Trust Domain...
>
> If P-Preferred-Identity is received from outside the Trust Domain, the
> proxy
> attempts to authenticate the originator of the message.
>
> You ask whether the proxy MAY or MUST use the
> P-Preferred-Identity, but I'm
> not sure the question makes sense. If it were a MAY, then
> whether to use it
> or not must be a matter of local policy for the proxy. If it
> were a MUST,
> then as long as the P-Preferred-Identity is 'a valid identity for that
> user'
> then it MUST use it. But the list of 'valid identities for
> that user' is a
> matter of local policy too. So there is no difference.
>
> For example, if the proxy NEVER uses P-Preferred-Identity,
> then this is
> equivalent to saying that there is only one valid identity
> for the user.
>
> Regards,
>
> Mark Watson
>
>
> > -----Original Message-----
> > From: [email-masked] [mailto:[email-masked]]
> > Sent: 29 October 2002 05:30
> > To: [email-masked]
> > Cc: [email-masked]
> > Subject: [Sip] draft-ietf-sip-asserted-identity-02.txt: ppi
> > from trusted
> > entity
> >
> >
> >
> >
> > Hi,
> >
> > Section 6 does not seem to explicitely specify proxy's
> behaviour when
> > p-preferred-identity header is received by a proxy from a
> > trusted entity:
> >
> > a)preferred identity corresponds to a valid identify known to
> > the proxy for
> > that user.
> > -MUST the proxy use this identity or  MAY it ? I assume it MUST.
> > b)preferred identity does not correspond to a valid identity
> > known to the
> > proxy for that user.
> > -Should the proxy behaviour be same as when the entity from
> which the
> > header was received is not trusted.
> >
> >
> > thanks
> > harsh
> >
> >
> >
> >
> >
> >
> >
> >
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