Subject: [Sip] P-Asserted-Identity and Called Party Name Delivery

From: "Venkatesh Venkataramanan" <[email-masked]>
Date: Sat, 7 Jun 2003 19:56:05 -0700

Hi:

There has been some discussion in the mailing list about using the
P-Asserted-Identity header in requests like UPDATE to enable updating the
identity of the caller mid-call. I was thinking anyone has considered
enabling this header in SIP response messages as well? There are a few
features that would need updating the calling party, the identity of the
target while the called target is still being alerted. While 3261 allows the
UAS to use the Contact header, there are a couple scenarios that need
something more than the contact, a header a proxy in the middle can update
in responses. 

1) In the case of calls to numbers like hunt-groups and/or ACD, every UAS
that receives the INVITE will place its local contact information in the
response to this request. All that may be expected for these calls is that
the calling party see information they called a name corresponding to the
hunt group or ACD number they called; like "United Airlines" and not "Agent
John Doe". Arguably this may be achieved by local configuration of some sort
at the UAS that is a part of the ACD group; but there can be call flows
where the UAS receiving an INVITE might not even be aware that it is being
reached as a part of some application. For example an implementation might
choose to store hunt group information in a proxy and have the proxy fork
sequentially or round-robin or whatever, and not having the UAS know about
it. Another example might be a find me-follow me type service where the
calling party may not need to know the list of targets that is being looked
up or which of these targets answered the call.

2) A proxy providing called name lookup services for a user community
whereby it looks up a centralized directory database of some sort and update
the calling UA of the called party's name; this is useful if the called
number is a PSTN number. 

3) An UAS might not even place it's display name in a SIP response. Enabling
a proxy to add this information gurantees a end user of this feature
regardless of the capabilities and/or preferences of the UAS.

4) Display language preferences: A end user might have preferences to
display called names in English. The UAS called might have preferences that
makes it send the called display name in different language. A proxy might
want to provide a directory look up service based on the called number and
provide the information to the end user in a language preferred by the
calling UA. 

Is it worth considering enabling proxies to insert the P-Asserted-Identity
header in SIP response message for the same?? 

regards,
Venkatesh

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