Block CallerID on Individual Calls

Hi Guys,

we’re running FreePBX distro, trying to build an option to block the outbound CallerID on specific calls.

Our SIP carrier has advised that we need to use the P‐Asserted‐Identity tag to achieve this, which is about where my comprehension of the situation has failed.

Their guide says the following.

Connected party Information
The P‐Asserted Identity is also used for carrying the connected Identity information in scenarios
involving call Transfer. The P‐Asserted Identity can be supported with the SIP 200 OK Answer
SIP PBX Interoperability Guide (CVM13) Version 4.0 Page 26 of 41
message to support handling and sending of the connected party information after the transferred
call terminates and answered.
It is imperative that the privacy indications that may be applied to calling party information (be it
numeric, name or alias) be preserved across differing nodes involved in a call as well as across any
gateway function to a non‐SIP protocol. These indications are typically carried within TDM based
protocols as optional octets with a CallingPartyNumber IE or equivalent.
Where the desire is that presentation is restricted then a Privacy header is added thus:
Privacy: id
Where the desire is that presentation is allowed then a Privacy header is added thus:
Privacy: none
Should a display name have been included and privacy is required for the name (that is its
presentation is restricted) then a Privacy header is added thus:
Privacy: user,
Note that non‐inclusion of a Privacy header is taken to mean the same as if a Privacy header had
been included with a value of ‘none’.
Note also that the AAPT soft switch has a network based privacy service and so may present Privacy
headers to a trusted endpoint; in such cases the tag ‘critical’ is included. Meaning that if the endpoint
cannot honour the privacy level requested the call MUST be failed with a 500 response.

Does anyone has any advice on how we could implement this with the least amount of custom stuff?

Any advice appreciated,


Anyone have any suggestions on this?