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

Pritam SE prachipritam at gmail.com
Mon Aug 17 16:30:01 UTC 2015

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


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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