1. Field of the Invention
This invention relates to a star local-area network system, and more particularly to improvement of the central switching unit installed in a star local-area network.
2. Description of the Related Art
In star local-area network systems, communication between data stations is generally achieved by the central switching unit, which changes the connection between stations.
A typical central switching unit is a PBX, which has a plurality of input/output ports individually connected to separate data stations. When a data station requests a circuit connection, the PBX receives the circuit number of the called data station from the calling data station. The circuit number indicates the number of the input/output port of the PBX to which the called data station is connected. The PBX connects the input/output port connected to the calling data station to that connected to the called data station to establish a telecommunication circuit between the two data stations.
In a star local-area network system using a PBX as the central switching unit, each data station specifies the called data station, using the latter's circuit number.
The circuit number of the called data station, however, is determined on the basis of the input/output port to which the called data station is connected, so that when the connection of the called data station is changed to another input/output port, its circuit number is also changed. Therefore, to call a station whose input/output port has been changed, the calling station must recognize the new circuit number of the called station in advance.
As noted above, the calling data station always recognizes the numbers of the PBX physical input/output ports to which other data stations are actually connected. For this reason, it is necessary for the supervisor of the network system to inform the operator at each data station of the new numbers of other data stations.
With this situation in mind, a PBX is now available which contains an address table showing which input/output port numbers correspond to which data station names. By referring to the address table, the PBX recognizes which input/output port is connected to the data station whose name is specified by the calling data station. Therefore, the calling data station can specify the called data station by name without taking into account the number of the PBX physical input/output port connected to the called data station.
The information relating to the state of connection between data stations is entered in the address table by the supervisor beforehand. In this case, however, changes in the connection of data stations require the network supervisor to update the contents of the address table according to each new state of connection of the stations.