PBX vs. Keyswitch

• A key system or key telephone system is a multiline telephone system typically used in small office environments. Key systems can be noted for their expandablity and having individual line selection buttons for each connected phone line.
• A private branch exchange (PBX) is a telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company for many business or for the general public.
  1. PBX make connections among the internal telephones of a private organization - usually a business - and aslo connect them to the public switched telephone network (PSTN) via trunk lines. Because they incorporate telephones, fax machines, modems, and more, the general term "extension" is used to refer to any end point on the branch.
  2. PBXs are differentiated from "key systems" in that users of key systems manually select their own outgoing lines, while PABXs select the outgoing line automatically. Hybrid systems combine features of both.
  3. Initially, the primary advantage of PBXs was cost savings on internal phone calls: handling the circuit switching locally reduced charges for local phone services. As PBXs gained popularity, they started offering services that were not available in the operator network, such as hunt groups, call forwarding, and extension dialing. In the 1960x a simulated PBX known as Centrex provided similar features from the central telephone exchange.
  4. PBXs offer any other callig features and capabilities:
  Auto attendant 自動服務
  Auto dialing 自動撥號
  Automatic directory services 自動目錄服務 (when callers can be routed to a given employee bye keying or speaking the letters of the employee's name)
  Call accounting 通話統計
  Call forwarding on busy or absence 呼叫轉接