3.12 Calling

A call is initiated by sending an INVITE request. For user to user calls the request line URI will contain the SIP login of the user associated with the called contact item. The contact item can be a phone number or a username (service ID) both of which are public IDs of a called RCS user but not necessarily they are equal to the user’s SIP login. RCS users can sign up with username or phone number and therefore their logins can be either. Also in non-generic RCS mode the SIP logins are different from both the username and phone number as they are sequential numbers.

When the INVITE is composed the user part of the URI is the login, not public ID.

When the call is sent to PSTN numbers the user part of the URI will be the phone number.