There are two possibilities for the VLink TIF server to connect to a PBX. The first is via a “Registered” connection where we use a username and password to register a SIP Client to the PBX and then receive and initiate calls via SIP Invites from/to the PBX in the same manner as a SIP client. The second is via a “Direct IP” or non-registered connection in which we only use the user name to receive and initiate calls via the PBX. In this case there is no registration or authentication but rather simply SIP Invites from/to the PBX. At some customer installations, this second method is used to install a “SIP Trunk” between the VLink TIF server and an offsite 3rd Party provider for the phone line access.