SIP trunking between Asterisk and Telcos with SIP-I

Hi guys !
I’m not sure if SIP trunking will work with a Telco which has SIP-I. The scenario meant is that asterisk will only accept incoming calls ,that is a subscriber of Telco can only make calls towards Asterisk and not the reverse. Maybe the figure below explain better the scenario :

telco user -->ISUP— Telco Exchange ----SIP-I —Asterisk —> SIP phone

It is possible that SIP protocol that Asterisk has can inter-work with SIP-I of that Telco ?

Thanks in advance for your thoughts and suggestions !


According to … and-sip-t/, it is not valid to use SIP-I unless both the entry and exit interfaces to the SIP network are ISDN, so your configuration is not valid, no matter the PABX type.

Asterisk is a back to back user agent, and will not pass SIP bodies, except in limited contexts, SDP, to the other party.

I would expect it to complain and ignore the unknown body type, but process the rest of the information, but it is possible that it will get more confused than that.

Thanks a lot for your answer !
According to Tekelec documentation looks that the only way is that Telco should have a pure SIP gateway mapping there all isup messages to sip ones and not like SIP-I which according Tekelec transits “ISUP parameters through a SIP network is by attaching a literal copy of the original ISUP message to the SIP message at the ingress PSTN gateway; this ISUP message appears as another body on the SIP message (typically, a peer to an SDP body)”
Is that correct ?

Thanks !