For what purpose?
An Invite and a register request are two unrelated requests. An INVITE is used to set-up a call whereas a register request is used to let the provider know how to "contact" (where) an authenticated device/PBX. The register will have an expiry period associated to it whereby once reached, the PBX will send a new register request. If this is not received by the provider, the provider may then start to initiate their pre-programmed disaster recovery mode whereby incoming calls will be re-routed to a fail-over number or IP so as to maintain some form of call continuity. Once the register requests are resumed, calls will revert to normal handling.
When you send an INVITE, the provider will challenge same and the PBX will respond with the needed authentications to prove that the INVITE is valid and should be accepted and acted upon.
