[SIPForum-discussion] What are the uses of P-Preferred-Identity??

[Pritam SE]

Hi Pendyala,


< Based on RFC 3325 >



The P-Preferred-Identity header field is used from a user agent to a
trusted proxy to carry the identity. The user sending the SIP message
wishes to be used for the P-Asserted-Header field value that the
trusted element will insert.

A P-Preferred-Identity header field value MUST consist of exactly one
name-addr or addr-spec.  There may be one or two P-Preferred-Identity
values.  If there is one value, it MUST be a sip, sips, or tel URI.



If there are two values, one value MUST be a sip or sips URI and the
other MUST be a tel URI.  It is worth noting that proxies can (and
will) remove this header field.



If a P-Preferred-Identity header field is present in the message that
a proxy receives from an entity that it does not trust, the proxy MAY
use this information as a hint suggesting which of multiple valid
identities for the authenticated user should be asserted.



A user agent only sends a P-Preferred-Identity header field to proxy
servers in a Trust Domain; user agents MUST NOT populate the
P-Preferred-Identity header field in a message that is not sent
directly to a proxy that is trusted by the user agent.






< Based on 3GPP 24.229 5.1.2A.1.1 General >



The UE may insert a P-Preferred-Identity header field in any initial
request for a dialog or request for a standalone transaction as a hint
for creation of an asserted identity (contained in the
P-Asserted-Identity header field) within the IM CN subsystem.



The UE shall determine the public user identity to be used for this
request as follows:

1) if a P-Preferred-Identity was included, then use that as the public
user identity for this request; or

2) if no P-Preferred-Identity was included, then use the default
public user identity for the security association or TLS session and
the associated contact address as the public user identity for this
request;


Thanks,
Prachi

On Sun, Aug 16, 2015 at 11:58 AM, pendyala syam <psyam545 at gmail.com> wrote:
> Hi All,
>
> As far I understand, P-Preferred-Identity will be shown as caller display
> name in callee UI. When SIP already have From header which carriers the
> caller identity, why is this P-Preferred-Identity header required? Why can't
> we use From header to show caller display name at callee UI?. Is there any
> added advantage of this header. Some body please explain. Thanks in advance.
>
> Regards,
> Pendyala
>
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