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

Paul Kyzivat pkyzivat at alum.mit.edu
Mon Aug 17 15:49:26 UTC 2015

On 8/16/15 2:28 AM, pendyala syam 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.

The callee should not even *see* P-Preferred-Identity!

The callee may get P-Asserted-Identity. Depending on the envirnment in 
which it operates, it may choose to display that rather than the 
contents of From.

P-Preferred-Identity and P-Asserted-Identity are used in some some 
networks (e.g. 3gpp IMS) based on a trusted core network.

In some cases a device wishes to register and authenticate once to the 
core network but then have multiple identities enabled by that 
registration. In that case, P-Preferred-Identity is a way for the device 
to indicate which of those identities is to be used on a particular 
call. The core network can then verify if the caller is authorized to 
use that identity. If so, it removes the P-Preferred-Identity and adds a 

The recipient depends on the core network having authenticated the 
caller and having only added P-Asserted-Identity when authorized.

This is all used because the From header is not supposed to be altered 
between caller and callee.

Hope this helps.


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