PBX History
Posted By AVAD Business Editor on 2009-06-12
The term PBX was first applied when switchboard operators ran company switchboards by hand. As automated electromechanical and then electronic switching systems gradually began to replace the manual systems, the terms PABX (Private Automatic Branch eXchange) and PMBX (Private Manual Branch eXchange) were used to differentiate them. Solid state digital systems were sometimes referred to as EPABXs (Electronic Private Automatic Branch eXchange). Now, the term PBX is by far the most widely recognized.
The acronym is now applied to all types of complex, in-house telephony switching systems, even if they are not Private, Branches, or eXchanging anything.
PBX's are distinguished from smaller "key systems" by the fact that external lines are not normally indicated or selectable at an individual extension. From a user's point of view, calls on a key system are made by selecting a specific outgoing line and dialing the external number.
A PBX, in contrast, has a Dial plan. Users dial an escape code (usually a single digit; often the same as the first digit of the local emergency telephone number) that connects them to an outside line (DDCO or Direct Dial Central Office in Bell System jargon), followed by the external number. Some modern number analysis systems allow users to dial internal and external numbers without escape codes.
