Abstract: Communication units organized into user groups are divided into user groups that distinguish whether a member of the user group may or may not interrupt active calls. Communications will not be interrupted (303) by units that are not allowed to interrupt active calls. Communications are interrupted (304) only by units that are allowed to interrupt active calls.

Abstract: A method for a non-registered communication unit to access a communication system consists of sending a service request. Upon receiving a service request, the communication resource allocator assigns an entry in the communication system database to the non-registered unit and assigns system default features to the entry such that the unit has default access to the communication system. Thus allowing a communication unit that has subscribed to system services and has not been recognized by the system manager to access the system utilizing default parameters until the system manages properly registers the unit.

Abstract: In a wide area communication system that includes a central controller, a plurality of sites, and a plurality of subscriber units, a requesting subscriber unit can locate a neighboring subscriber unit in the following manner. Each of the plurality of subscriber units registers with the central controller. The central controller stores registration information in a database. When the requesting subscriber unit transmits a request for a subscriber identification of a neighboring subscriber unit, the central controller determines whether the neighboring subscriber unit exists. When the neighboring subscriber unit exists, the central controller transmits the subscriber identification of the neighboring subscriber unit to the requesting subscriber unit.

Abstract: A quad linked data structure that provides bidirectional search capability for multiple related fields within a single record. The data base is searched by providing sets of pointers at intervals of N data entries to accommodate a binary search of the pointers followed by a linear search of the resultant range to locate an item of interest and its related field.