Can you have different values in From and PAI?

Asterisk Asterisk SIP
1

Hello,

When Asterisk 20 is sending an outbound call using PJSIP, with send_pai and trust_id_outbound both set to yes, and when your dialplan don’t add any custom P-Asserted-Identity header, is it possible to observe different values in From and P-Asserted-Identity headers (beside Privacy: id or Privacy: none presence in P-Asserted-Identity) within outbound INVITE messages ?

If positive, how can this happen ?

Best regards

2

If the from_user / from_domain options were set then From would be different. PAI can also be updated throughout the lifetime of a call, while From can not.

3

You mean:

  • From is set according from_user and from_domain settings in pjsip.conf
  • while PAI would be set by the dialplan through Set(CALLERID()=) calls ?
4

From CAN be set using from_user / from_domain for cases where it is needed. P-Asserted-Identity and Remote-Party-ID can be set using CALLERID() or CONNECTEDLINE() depending on the channel (caller vs called) and situation.

5

What I have in mind is Stir/Shaken compliance for outbound calling.

I read one frequent source of non-compliance calls, arise when From/PAI values are different and Attestation/Verification are done on different headers.

I somehow took for granted that, as I don’t customize my SIP trunks from_user / from_domain settings and don’t use PJSIP_HEADER to build any P-Asserted-Identity header, I should be immune to verification issues by the receiving Telco, even for anonymous calls or for forwarded calls.

My reasoning is:

  • even if the inbound call I have to forward to the PSTN, features different or missing values in from/PAI/whatever headers, Asterisk selects a single value the one being returned by ${CALLERID(num)},
  • as I explicitly normalize this value (to +E164 format) with a Set(CALLERID(num)=)
  • then I should be assured that my outbound call to the PSTN will have identical values in From and PAI headers
  • when Asterisk implicitly builds the Identity header for Stir/Shaken using From value (if I’m not mistaken), then this Identity will also “match” the PAI
  • receiving telco that is required to verify Identity should be happy.

Is this reasoning correct ?

6

The reasoning is correct, but I won’t comment on receiving telco providers.

7

I won’t comment either ;-))))

8

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