If you are operating in an environment where a more specialized 
standard/profile holds (such as 3gpp/IMS) then you should look there for 
guidance on what to do.

If not, then you will need to make up your own policies.

        Thanks,
        Paul

On 4/3/12 9:07 PM, Romel Khan wrote:
> ITU standards, such as, Q.1912.5, imply From header is used for caller id
> display.
>
> On Tue, Apr 3, 2012 at 3:46 PM, Brett Tate<[email protected]>  wrote:
>
>>> But this section 8 is written so generically (eg "However,
>>> any specific behavior is specific to implementations or
>>> services") that it is pretty much saying nothing on
>>> the usage of From header vs P-Asserted-ID.
>>
>> 8. User Agent Server Behavior
>>
>>    Typically, a user agent renders the value of a P-Asserted-Identity
>>    header field that it receives to its user.  It may consider the
>>    identity provided by a Trust Domain to be privileged, or
>>    intrinsically more trustworthy than the From header field of a
>>    request.  However, any specific behavior is specific to
>>    implementations or services.  This document also does not mandate any
>>    user agent handling for multiple P-Asserted-Identity header field
>>    values that happen to appear in a message (such as a SIP URI
>>    alongside a tel URL).
>>
>>    However, if a User Agent Server receives a message from a previous
>>    element that it does not trust, it MUST NOT use the P-Asserted-
>>    Identity header field in any way.
>>
>>    If a UA is part of the Trust Domain from which it received a message
>>    containing a P-Asserted-Identity header field, then it can use the
>>    value freely but it MUST ensure that it does not forward the
>>    information to any element that is not part of the Trust Domain, if
>>    the user has requested that asserted identity information be kept
>>    private.
>>
>>    If a UA is not part of the Trust Domain from which it received a
>>    message containing a P-Asserted-Identity header field, then it can
>>    assume this information does not need to be kept private.
>>
>>
>>> On a feature as simple as which header to use for caller
>>> ID display, so one carrier can try to enforce the From
>>> header while another could use the P-Asserted-ID?
>>
>> It is all about trust.  The trust issues were one of the reasons why RFC
>> 5876 is categorized as "Informational" instead of "Standards Track".
>>
>>
>>> Is there no standard pertaining to SIP in IETF and ITU
>>> which clarifies the proper usage?
>>
>> Concerning IETF, see Abstract.  3gpp may be more specific concerning the
>> topic.
>>
>> Abstract
>>
>>    This document describes private extensions to the Session Initiation
>>    Protocol (SIP) that enable a network of trusted SIP servers to assert
>>    the identity of authenticated users, and the application of existing
>>    privacy mechanisms to the identity problem.  The use of these
>>    extensions is only applicable inside an administrative domain with
>>    previously agreed-upon policies for generation, transport and usage
>>    of such information.  This document does NOT offer a general privacy
>>    or identity model suitable for use between different trust domains,
>>    or use in the Internet at large.
>>
>>
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