There are two registration methods available with Skype Connect:
If your PBX is located on a private network behind a NAT firewall or router, you should use the SIP Registration method, which provides you with credentials for the SIP Profile that you use to configure your PBX.
If your PBX does not support SIP Registrations or you don’t want to use SIP Registrations (for example, because of your company’s security policy), you can use a static IP address as the registration method of authentication.
Skype Connect uses the SIP username for authentication, authorization and accounting. When using the SIP Registration method, each request is challenged. When using IP Authentication, there are no challenges to a request.