On Premise Telephone

Telephone System's make connections among the internal telephones of a private organization — usually a business — and also 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.

Functionally, the Telephone System performs:

• Establishing connections (circuits) between the telephone sets of two users (e.g. mapping a dialed number to a physical phone, ensuring the phone isn't already busy)
• Maintaining such connections as long as the users require them (i.e. channeling voice signals between the users)
• Disconnecting those connections as per the user's requirement
• Providing information for accounting purposes (e.g. metering calls)

In addition to these basic functions, telephone systems offer many other calling features and capabilities, with different manufacturers providing different features in an effort to differentiate their products. Common capabilities include (manufacturers may have a different name for each capability):