Private branch exchange (PBX):
PBXsystem for small office and small business is a private or leased telephone switching system that connects telephone extension in-house. (A switched line is a communication line that connects through a switching system to a variety of destinations.)A PBX also connects users to outside telephone system.
A public telephone system consists of “public branch exchanges” thousands of switching stations that direct calls to different “branches” of the network. A branch exchange is essentially the old- fashioned company switchboard you call in form of the outside.
New PBXs can handle not only analog telephones but also digital equipments, including computer. however, because older PBXs use existing telephone lines, they many lots be able to handle the volume of electronic messages found in some of the today’s organization. These companies may be better served by LANs.