In a telephony network, a Private Branch Extension (PBX) or IP-PBX can be configured to have a single hunt group or multiple hunt groups. Each hunt group that is created on a PBX or IP-PBX must have an associated pilot number. The PBX or IP-PBX uses the pilot number to locate the hunt group and in turn to locate the telephone extension number on which the incoming call was received. Without a defined pilot number, the PBX or IP-PBX cannot locate where the incoming call was received.
A pilot number is the address or location of the hunt group inside the PBX or IP-PBX. A pilot number is generally defined as a "blank" extension number or one extension number from a hunt group of extension numbers that does not have a person or telephone associated with it. For example, you configure a hunt group on a PBX or IP-PBX to contain extension numbers 4100, 4101, 4102, 4103, 4104, and 4105. The pilot number for the hunt group is configured as extension 4100. When a call is received on the extension number 4100, the PBX or IP-PBX looks for the next available extension number to determine where to deliver the call. In this case, the PBX or IP-PBX looks at the extension numbers 4101, 4102, 4103, 4104, and 4105. Using a pilot number helps eliminate busy signals and helps route incoming calls to the circuits that are available.
The PBX or IP-PBX pilot number, when it is used with Exchange Server 2007 Unified Messaging, is used as the target. When an incoming call is unanswered or the line is busy, the call is correctly routed to an Exchange Server 2007 Unified Messaging server. For more information about telephony concepts, see Overview of Telephony Concepts and Components.