Which SIP headers in CUCM are used to identify the calling party?

[voip7372]

I'm trying to work out some SIP profiles in CUBE to change the calling party number behind the scenes just so our phone company will accept the call (authorized to call out) but I don't want the number people see (caller-id) to be changed.  

Anyway, I know our phone company uses this order to ID a valid caller (they will accept the call if at least ONE of these has one of their numbers we own in the header and they're processed in this order):

1.  Diversion
2.  P-Asserted-Identity

3.  From or Remote-Party-ID

What SIP headers will CUCM use (11.5.1) and in what order, if it can/will use more than one header to determine the calling party (for the caller-id)?  I know it uses P-Asserted-Identity for sure because I changed a SIP profile in CUBE and for that header for calls going to CUCM and I saw that number I put in the P-Asserted-Identity header showed up as the calling party number in CUCM (that's what appeared on the phone's display).  

[Anthony Holloway]

Good question! I would like to know this as well.

I have used the Contact P-Asserted-Identity header to manipulate the caller ID via SIP Profiles, as I found the From address was not being used by CUCM to display the caller ID on the phone.

Edit: corrected the header name

[voip7372]

Yeah. I know what our service provider expects and uses as their priority to identify the calling party and for billing/CDR purposes so now I just need to know what headers CUCM cares about and what priority it uses (related to the calling party).

[Anthony Holloway]

I looked in the SIP Trunk messaging guide:
https://developer.cisco.com/site/uc-manager-sip/documents/sip_trunk/

As well as in the SIP Line side guide:
https://developer.cisco.com/site/uc-manager-sip/documents/sip_line/

Neither are conclusive, and neither confirm my experience with the Contact header.

[voip7372]

Thanks.  I suppose if I don't get the answer here I can just do it the hard way and edit my SIP profile for the incoming calls in CUBE to see if changing any of the headers used to ID the caller has the affect I want in CUCM.  I have a tricky situation I'm trying to work out with our service provider and some of our employees related to a call center that's hosted by the provider (in the 'cloud' I guess you could say).  Ultimately what I'm trying to do I think SHOULD be done by the call center before the call hits the CUBE and then CUCM, but just in case, I'd like to have a trick up my sleeve in case they say they can't do what we need.  Anyway, it would be useful to know the answer to this regardless of my current challenge. 

Oh and I could also ask TAC...if it comes to that.  

[voip7372 · Accepted solution]

I opened a ticket with Cisco to get the answer and this is what they said: 

A calling user’s name and number can be sent over Unified CM SIP trunks in the following SIP message headers:

From : The From header field indicates contact information of the initiator of the SIP INVITE request.
The From and To message headers sent in SIP Requests and Responses indicate the direction of the call. (The From header represents the calling user and the To header represents the called user.) The From and To headers remain the same in all SIP Requests and Responses for the call

P-Asserted-Identity : The P-Asserted-Identity header field is an important SIP header used among trusted SIP entities (typically intermediaries) to carry the identity of the user sending a SIP message as it was verified by authentication. This header is commonly used in call centers who need to present the calling number of its customer, rather than it actual telephone number.

Cisco Collaboration System 11.x Solution Reference Network Designs (SRND)
Section: User Identity and SIP Trunks
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab11/collab11/trunks.html

I also asked if there are different numbers in the From header and the P-Asserted-Identity header, which one of those would take precedence for the caller-id (the number the called party sees). This was the answer:

In that scenario P-Asserted-Identity will be preference.

[Anthony Holloway]

Awesome! Thanks for checking and reporting the findings!