Process control system for PBX - simplifies call-back connections using existing storage space with address stores

摘要

The process control system allows the original caller and the original called party to be accessed separately whilst the call is being held. The address of the called party or of the selected line group assigned to the called party is stored when call-back occurs from an authorised extension irrespective of whether the call-back is due to an engaged extension or an engaged line in a line group. The condition of the called extension is checked periodically and when found to be free all other incoming or outgoing calls to and from the extension are disabled.