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CHAPTER29 Analog Gateway

Mediant 1000 Gateway & E-SBC | User's Manual

Remote PBX Extension between FXO and FXS Devices

Remote PBX extension offers a company the capability of extending the "power" of its local PBX

by allowing remote phones (remote offices) to connect to the company's PBX over the IP network

(instead of via PSTN). This is as if the remote office is located in the head office (where the PBX is

installed). PBX extensions are connected through FXO ports to the IP network, instead of being

connected to individual telephone stations. At the remote office, FXS units connect analog phones

to the same IP network. To produce full transparency, each FXO port is mapped to an FXS port

(i.e., one-to-one mapping). This allows individual extensions to be extended to remote locations. To

call a remote office worker, a PBX user or a PSTN caller simply dials the PBX extension that is

mapped to the remote FXS port.

This section provides an example on how to implement a remote telephone extension through the

IP network, using FXO and FXS interfaces. In this configuration, the FXO device routes calls

received from the PBX to the ‘Remote PBX Extension’ connected to the FXS device. The routing is

transparent as if the telephone connected to the FXS device is directly connected to the PBX.

The following is required:

■ FXO interfaces with ports connected directly to the PBX lines (shown in the figure below)

■ FXS interfaces for the 'remote PBX extension'

■ Analog phones (POTS)

■ PBX (one or more PBX loop start lines)

■ LAN network

Dialing from Remote Extension (Phone at FXS)

The following procedure describes how to dial from the 'remote PBX extension' (i.e., phone

connected to the FXS interface).

➢ To make a call from the FXS interface:

1. Off-hook the phone and wait for the dial tone from the PBX. This is as if the phone is connected

directly to the PBX. The FXS and FXO interfaces establish a voice path connection from the

phone to the PBX immediately after the phone is off-hooked.

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AudioCodes E-SBC User Manual

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