An EPABX System handles voice signals under Internet protocol, bringing benefits for computer telephony integration (CTI). An IP-PBX can exist as physical hardware, or can carry out its functions virtually, performing the call-routing activities of the traditional PBX or key system as a software system. The virtual version is also called a “Soft PBX". PBXs 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. PBXs are differentiated from "key systems" in that users of key systems manually select their own outgoing lines, while PBXs select the outgoing line automatically. Hybrid systems combine features of both. PBX functions Functionally, the PBX performs four main call processing duties

• 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, PBXs 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)

• Auto attendant
• Auto dialing
• Automatic call distributor
• Automated directory services (where callers can be routed to a given employee by keying or speaking the letters of the employee's name)
• Automatic ring back
• Call accounting
• Call blocking
• Call forwarding on busy or absence
• Call park
• Call pick-up
• Call transfer
• Call waiting
• Camp-on
• Conference call
• Custom greetings
• Customized Abbreviated dialing (Speed Dialing)
• Busy Override
• Direct Inward Dialing
• Direct Inward System Access (DISA) (the ability to access internal features from an outside telephone line)
• Do not disturb (DND)
• Follow-me, also known as find-me: Determines the routing of incoming calls. The exchange is configured with a list of numbers for a person. When a call is received for that person, the exchange routes it to each number on the list in turn until either the call is answered or the list is exhausted (at which point the call may be routed to a voice mail system).
• Interactive voice response
• Music on hold
• Night service
• Public address voice paging
• Shared message boxes (where a department can have a shared voicemail box)
• Voice mail
• Voice message broadcasting
• Welcome Message

An EPABX System handles voice signals under Internet protocol, bringing benefits for computer telephony integration (CTI). An IP-PBX can exist as physical hardware, or can carry out its functions virtually, performing the call-routing activities of the traditional PBX or key system as a software system. The virtual version is also called a “Soft PBX". PBXs 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. PBXs are differentiated from "key systems" in that users of key systems manually select their own outgoing lines, while PBXs select the outgoing line automatically. Hybrid systems combine features of both. PBX functions Functionally, the PBX performs four main call processing duties

• 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, PBXs 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)

• Auto attendant
• Auto dialing
• Automatic call distributor
• Automated directory services (where callers can be routed to a given employee by keying or speaking the letters of the employee's name)
• Automatic ring back
• Call accounting
• Call blocking
• Call forwarding on busy or absence
• Call park
• Call pick-up
• Call transfer
• Call waiting
• Camp-on
• Conference call
• Custom greetings
• Customized Abbreviated dialing (Speed Dialing)
• Busy Override
• Direct Inward Dialing
• Direct Inward System Access (DISA) (the ability to access internal features from an outside telephone line)
• Do not disturb (DND)
• Follow-me, also known as find-me: Determines the routing of incoming calls. The exchange is configured with a list of numbers for a person. When a call is received for that person, the exchange routes it to each number on the list in turn until either the call is answered or the list is exhausted (at which point the call may be routed to a voice mail system).
• Interactive voice response
• Music on hold
• Night service
• Public address voice paging
• Shared message boxes (where a department can have a shared voicemail box)
• Voice mail
• Voice message broadcasting
• Welcome Message