Calling number verification is a SIP feature where the calling number is verified by the ISP and the results of that verification is included with the incoming call. The aim of this is to help reduce call spoofing.
Support for and use of SIP calling number verification is mandated by law for US/Canadian locales. However, the feature can be enabled in any locale if supported by the local SIP ISP.
This feature only does calling number verification. The display name information supplied with calls is not verified.
Verification is done by the ITSP by looking at several factors:
Is the calling number associated with the subscriber making the call?
Is the call coming from a known customer?
Is the call originated by the known ITSP?
Was the call digitally signed and was the ITSP able to fetch the public certificate of the originating service provider in order to verify that the SIP INVITE has not be changed during transit.
The result of the verification process is then indicated in the call's headers using a verstat value:
TN-Validation-Passed plus an attestation level (see the table below). For example, TN-Validation-Passed-A.
TN-Validation-Failed plus an attestation level (see the table below). For example, TN-Validation-Failed-A.
No-TN-Validation -
The attestation levels are:
Attestation Level |
Description |
A |
Full Attestation |
The customer is known and the calling number is one associated with that customer.
|
B |
Partial Attestation |
The customer is known. However, the number not one associated with that customer. For example:
|
C |
Gateway Attestation |
The call has come via a trusted source, but the original customer and number are not known. |
When calling number verification is available, the IP Office system can use the results to determine how to handle calls.
Use of calling number verification is enabled on a per line basis.
On lines where it is enabled, the line can either use the system default settings or line specific settings
The settings determine whether a call should accepted or not.
If not accepted, the call is rejected by the system with a 666 response code.
If accepted, the call is routed as normal by features such as Incoming Call Route matching. However, if required, the specific result of the calling number verification can be used to vary the routing.
The attestation level is included in the call's SMDR record. That includes rejected calls.
