Concepts Related to PBX

A logical PBX is an exchange office. When the calling and called parties are in the same exchange office, the call is an intra-office call.

When an exchange office communicates with another exchange office through a trunk line, the call is an inter-office call.

A trunk is a logical link between two exchange offices. Inter-office calls must be transmitted by trunks. To set up a connection channel with a remote office, a trunk is bound to the signaling and media addresses of the local office and signaling address of the remote office.

A trunk group is a set of trunks for inter-office calls with the same attributes.

A call prefix, an important attribute of the call service, defines a call number rule and describes the call number distribution and routing plans in an exchange office. A call prefix identifies the service attribute (basic service or supplementary service; intra-office call, national long-distance call, or international long-distance call) of a dialing plan and determines the range of dialed number length. Call prefixes can also be used to control call permissions. A PBX checks the validity of a dialed number and connects or rejects the call based on the call prefix. A call can be connected correctly only if the call matches the correct call prefix. Therefore, a correct call prefix configuration is the key to the call service. A call must match at least one call prefix.

A call route binds an inter-office call prefix to a trunk group so that calls with the specified call prefix are transmitted on the specified trunk line.

A PBX system is divided into multiple virtual PBX systems based on enterprise names. Users in an enterprise can directly call each other, while users in different enterprises cannot directly call each other.

A DN set is also called a dial plan. DN sets divide a physical network or a device into multiple logical networks.

A short number is an internal number of an enterprise, and a long number is allocated by the carrier to an enterprise. Internal users of an enterprise can dial the short numbers of each other. External users need to dial the long number of the enterprise.