This page covers EPABX or PBX basics for the beginners and also mention link to EPABX/PBX manufacturers. EPABX stands for Electronic Private Automatic Branch Exchange.

As shown in the figure EPABX/PBX facilitates use of one external telephone line by many internal users in the office premises. In the office each employee is provided one telephone set and all the telephones are connected with PBX. All the employees within the office premises can communicate using 3-digit or 4-digit number programmed in EPABX/PBX without any charge.


EPABX/PBX is connected to PSTN (Public switched Telephone network) via trunk lines; hence all can use one external voice line in time shared basis. PSTN is connected with MSC (Mobile switching centre) of cellular networks such as GSM/CDMA/UMTS. By this mobile cell phone user can connect to any telephone set in the office premises using extension number.

Similar to voice line EPABX/PBX can be used for Data applications. As shown in figure Data port of PBX is connected to LAN where so many PCs are connected and are using same external internet connection line from ISP via Modem/router. The same facility of PBX can be extended for WLAN users too.

EPABX specifications/features

Following typical specifications need to be considered while purchasing EPABX system from manufacturers or any installation service providers.

•  It should support voice over IP to provide voice communication over IP network
•  It should support IP extensions, IP trunk in addition to PCM/TDM capacity. •  It should have following interfaces supported on EPABX system:
-Analog Public Network (P&T lines)
-ISDN Public Network (BRI /PRI/E1R2/T1)
-Private Network of E&M
-LD Trunk as well Lease Line
•  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
•  It should provide CLIP feature in all the extensions & analog trunks
•  It should support DECT handset as well as WiFi handsets
•  It should have VAD (voice activity detection) and AGC (automatic gain control).
•  It should support voice mail
•  It should support G711 and G729 compression standards
•  It should support multi party conference
•  It should support secure conversations i.e. should support sRTP, SIPs with TLS (Transport Layer security) protocols


For EPABX manufacturers pl. visit our page in vendors section.

For signaling-types which include Start Dial signaling, Ground start signaling, E & M signaling used on trunk of exchange, READ MORE.

RF and Wireless Terminologies