Providing feature transparency between a plurality of pbxs

Abstract

An arrangement for according station and attendant feature transparency between independently operational PBXs of a PBX network. Each PBX includes a switch processor, station lines and tie-trunks extending to other PBXs. Each PBX also has a Direct Memory Data Controller (DMDC) for transmitting service or feature related data messages associated with tie-trunk calls to other PBXs over data links. On an interPBX call, the DMDC in a calling PBX transmits a data message to a DMDC in the called PBX over a direct link between the calling and called PBXs. In the event there is no direct link between the calling and called PBXs, the DMDC in the calling PBX transmits a message over a data link to a DMDC at a tandem PBX which, in turn, sends the message over a link to a DMDC in the called PBX. The DMDC in the called PBX processes the received data message and, by direct memory access, sends the message to its switch processor which provides the specified feature or other service required on the call above and beyond the establishment of a voice path connection between the calling and called stations. This arrangement allows interPBX calls to appear to the customers as if they are served by a single large PBX.