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EPABX Explained: A Beginner's Guide

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This page introduces the basics of EPABX (Electronic Private Automatic Branch Exchange) or PBX systems and provides links to EPABX/PBX manufacturers.

What is an EPABX?

EPABX stands for Electronic Private Automatic Branch Exchange. As the figure illustrates, an EPABX/PBX allows multiple internal users within an office to share a single external telephone line. Each employee in the office has their own telephone, and all these phones are connected to the PBX. Employees can communicate with each other internally using a 3 or 4-digit extension number programmed into the EPABX/PBX, without incurring any charges.

EPABX-PBX

The EPABX/PBX connects to the PSTN (Public Switched Telephone Network) via trunk lines, enabling everyone to share one external voice line on a time-shared basis. The PSTN is connected to the MSC (Mobile Switching Centre) of cellular networks like GSM/CDMA/UMTS. This allows mobile cell phone users to connect to any telephone within the office premises using the appropriate extension number.

Beyond voice calls, EPABX/PBX systems can also be used for data applications.

As the figure indicates, the data port of the PBX connects to a LAN where numerous PCs are connected and share the same external internet connection line from an ISP via a modem/router. This PBX functionality can also be extended to WLAN users.

Key EPABX Specifications and Features

When considering the purchase of an EPABX system from manufacturers or installation service providers, the following specifications are crucial:

  • Voice over IP (VoIP) Support: It should support voice over IP to enable voice communication over an IP network.
  • IP and Legacy Support: It should support IP extensions and IP trunks in addition to PCM/TDM capacity.
  • Interface Compatibility: The EPABX system should support the following interfaces:
    • Analog Public Network (P&T lines)
    • ISDN Public Network (BRI/PRI/E1R2/T1)
    • Private Network of E&M
    • LD Trunk as well Lease Line
    • Optical
  • Signaling Protocols:
    • Loop Start DP and DTMF Signaling with Pulse detection
    • Euro ISDN compatibility
    • E & M (Type-1 to Type-5) and 2 Wire & 4 Wire interface
  • Caller ID: It should provide CLIP (Calling Line Identification Presentation) feature in all extensions & analog trunks.
  • Handset Compatibility: It should support DECT handsets as well as WiFi handsets.
  • Voice Quality Enhancements: It should have VAD (voice activity detection) and AGC (automatic gain control).
  • Voice Mail: It should support voice mail functionality.
  • Audio Codecs: It should support G711 and G729 compression standards.
  • Conferencing: It should support multi-party conference calls.
  • Security: It should support secure conversations, i.e., support sRTP, SIPs with TLS (Transport Layer Security) protocols.