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

[pendyala syam]

Dear Tim,

Thanks for providing valuable info on "user asserted" and "network
asserted" identities. From 3GPP specs, UE should use the first one of
P-Associated-Uris in From header. So when UE has already set From header to
the value that is already identified by network, why should UE add
P-Preferred-Identity again?  I am doubting this From header can be changed
during transmission(Please correct me if I am wrong). If so, Can you please
answer me in this perspective, why would network change From header?  Thank
you
On Aug 17, 2015 6:40 AM, "Dwight, Timothy M (Tim)" <
timothy.dwight at verizon.com> wrote:

> Pendyala,
>
>
>
> There is in some SIP implementations a distinction made between “user
> asserted identity” (the caller ID signaled by the originating UE) and
> “network asserted identity” (the network’s assertion of the caller’s
> identity).  Usually they are the same, but they can be different.
>
>
>
> The From header carries “user asserted caller identity”.
>
>
>
> The P-Asserted-Identity header carries “network asserted caller
> identity”.
>
>
>
> P-Preferred-Identity is not intended to be presented to the UAS, it is
> only meant to communicate between the UA and the network to which it
> subscribes.  I suppose there could be corner cases where it finds its way
> to the UAS, but if so I think the UAS would ignore it.
>
>
>
> See RFC-3325 and 5876 for additional information.
>
>
>
> The purpose of the P-Preferred-Identity header is to allow the UA to
> influence the network’s assignment of P-Asserted-Identity.  Sometimes the
> UA has multiple identities.  The UE can when it originates a call, indicate
> in P-Preferred-Identity header field which of these it wishes the network
> to assert to the called party as its “network asserted identity”.  The
> network will typically validate that the identity in the
> P-Preferred-Identity header field is one that was previously assigned to
> the UA by the network (in 3GPP SIP networks this assignment happens during
> SIP registration).  If it matches, the network will use it derive the value
> of the P-Asserted-Identity header.  That derivation could be to simply copy
> the contents of P-Preferred-Identity into P-Asserted-Identity, or there
> might be some additional processing involved.  If the value signaled by the
> UA in P-Preferred-Identity doesn’t match any of the identities the network
> considers valid for use by the UA, the network will assign an identity it
> considers valid for use by the UA and place this in the P-Asserted-Identity
> header field.
>
>
>
> It is possible that a SIP message received by the UAS will have both a
> From and a P-Asserted-Identity header field.  Either could in theory be
> rendered by the UAS to its user, as the “caller ID”.  In theory the
> decision is up to the device.  In practice there may be specifications to
> which the device is obliged to comply (e.g., if it’s a mobile device
> operating in a 3GPP network) that will dictate its behavior.  A common
> implementation is to render the caller ID presented to the user based on
> P-Asserted-Identity, if present;  and based on From, if P-Asserted-Identity
> is not present.
>
>
>
> tim
>
>
>
> *From:* discussion-bounces at sipforum.org [mailto:
> discussion-bounces at sipforum.org] *On Behalf Of *pendyala syam
> *Sent:* Sunday, August 16, 2015 1:28 AM
> *To:* discussion at sipforum.org
> *Subject:* [SIPForum-discussion] What are the uses of
> P-Preferred-Identity??
>
>
>
> 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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