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Reject Calls with a specific STIR/SHAKEN Attestation Level


If you are looking to reject calls with a STIR/SHAKEN Attestation level such as C or no Attestation level you can use our sample dialplan below. Requires a PJSIP trunk to Clearly IP trunking.

Requirements

  • ClearlyIP Trunks using PJSIP 
  • In the ClearlyIP trunking portal, ensure that inbound Verification is set to 'Enhanced Verification Status'
  • Tested on FreePBX 16/ Asterisk 20 and will work on later versions

Dialplan to Add

  • Add the following dialplan to /etc/asterisk/extensions_custom.conf
  1. [from-pstn-check-ss]
  2. exten => _.,1,Noop(Entering user defined context from-pstn-check-ss in extensions_custom.conf)

  4. ; get the value of P-Attestation-Indicator where CIP stores the s/s attestation and store in CDR
  5. exten => _.,n,Set(CALL_ATTESTATION=${PJSIP_HEADER(read,P-Attestation-Indicator)})
  6. exten => _.,n,NoOp(S/S Attestation Level: ${CALL_ATTESTATION})
  7. exten => _.,n,ExecIf($["${CALL_ATTESTATION}"!=""]?Set(CDR(userfield)=S/S Level ${CALL_ATTESTATION}):Set(CDR(userfield)=S/S Level Unsigned))

  9. ; Branch call based on s/s attestation value
  10. exten => _.,n,GotoIf($["${CALL_ATTESTATION}"="A" || "${CALL_ATTESTATION}"="a"]?inroute)
  11. exten => _.,n,GotoIf($["${CALL_ATTESTATION}"="B" || "${CALL_ATTESTATION}"="b"]?inroute)
  12. exten => _.,n,GotoIf($["${CALL_ATTESTATION}"="C" || "${CALL_ATTESTATION}"="c"]?intercept)
  13. exten => _.,n,GotoIf($["${CALL_ATTESTATION}"=""]?intercept)    ; unsigned call

  15. ; any other values go to inbound routes
  16. exten => _.,n(inroute),Goto(from-pstn,${EXTEN},1)

  18. ; automatically hangup
  19. exten => _.,n(intercept),NoOp(Call is being rejected)
  20. exten => _.,n,PJSIPHangup(404)        ; comment this line if you want to answer the call and play noservice
  21. exten => _.,n,Goto(app-blackhole,no-service,1)
  • If you only want to block calls signed as a C you can change line 10 from intercept to be inroute like lines 8 and 9 have.
  • On line 13 we are saying any Attestation level above that we have going to inroute will send the call to the inbound route and process like normal, in our example above that would be for calls signed with a A or B Attestation level.
  • On line 16 we are saying any Attestation level above that we have going to intercept will play message of the number you called is not in service and hangup, in our example above that would be for calls signed with a C or no Attestation level.

Update Trunks to use the special context above

  • Go into the Trunks that are created in FreePBX/PBXact for Clearly IP and modify the following GUI option
  • Under the Trunk navigate to the pjsip Settings tab and change the context line to be "from-pstn-check-ss" (without the quotes)


  • Save and Apply Config you the calls will now route through the dialplan above.


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