Which conference types can occur at anytime without the need for the conference to be scheduled, and can be created as permanent conferences?

Ad hoc conferences are spontaneously created on-the-fly when a call is initiated, but they are temporary and terminate when participants disconnect, making them non-permanent.

Auto-dialed participants is a participant configuration feature that defines how specific endpoints are called into a conference, not a conference type itself.

Multiway conferences are initiated directly from a compatible video endpoint using the Multiway feature and are temporary, lasting only for the duration of that call.

Scheduled conferences by definition require advance booking through Cisco TMS and are not available at arbitrary times without that scheduling step.

Rendezvous conferences are designed to exist as standing, permanent conference rooms that participants can join at any time without requiring an administrator or organizer to schedule them in advance. Unlike ad hoc or scheduled conferences, rendezvous conferences persist indefinitely and can be configured in Cisco TMS to always be available on a specific MCU resource.