ZyXEL Communications IP PBX X6004 - Manual (Page 41)

X6004 User’s Guide
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H A P T E R
1
Introduction
This chapter introduces the main features and applications of the X6004.
1.1 Overview
An IP PBX is a telephone exchange device located at a company site which allows
an organization to set up and control calls. IP stands for Internet Protocol, and
PBX stands for Private Branch Exchange. A regular company telephone
switchboard is an example of a PBX. The company’s telephones are connected to
the IP PBX. The IP PBX is then connected to the outside world via connections to
any combination of the following networks:
• A traditional Public Switched Telephone Network (PSTN)
• A broadband Internet connection to an Internet Telephony Service Provider
(ITSP)
• An Integrated Services Digital Network/Basic Rate Interface Network (ISDN
BRI)
• An Integrated Services Digital Network/Primary Rate Interface Network (ISDN
PRI T1/E1)
Each telephone connected to an IP PBX has an extension assigned to it. An
extension is a unique telephone number within an organization typically consisting
of only a few digits. People inside the company can call each other by dialing
extensions. Calls to the outside world go through the IP PBX to the PSTN, ITSP or
ISDN.