During a conference call, the CTO of a company adds an external user to the call. The CTO leaves at the end of the call, but the external user stays on and dials out to a premium rate number…

The "Drop Ad Hoc Conference" parameter (often found in the service parameter settings for Cisco UCM's Conference Bridge or Call Manager service) is designed to control what happens to an ad hoc conference when the initiator leaves. By enabling or configuring this parameter, an administrator can ensure that the entire ad hoc conference is terminated when the original initiator disconnects, thereby preventing external participants from remaining on the conference and potentially incurring unauthorized charges.

Limit Ad Hoc Conference would typically refer to setting a maximum number of participants for an ad hoc conference, not controlling what happens when the initiator leaves.

Restrict Ad Hoc Conference is a general term and doesn't point to a specific UCM parameter that would solve this problem; restrictions usually involve who can initiate or join conferences.

Monitor Ad Hoc Conference would involve observing or logging conference activity, not actively preventing the scenario described.