Connecting Asterisk to a Topex VoIP/E1 GSM Gateway

This document presents the main configuration steps for interconnecting Asterisk IP PBX to the Topex VoiBridge VoIP/E1 GSM Gateway.

What is Topex Voibridge?


The Topex Voibridge VoIP/E1 GSM Gateway is an ideal complementary product to any IP PBX. It’s suitable for small and medium companies with IP infrastructure and for companies with international affiliates. With Voibridge you gain significant savings on outgoing and incoming calls between IP and GSM networks.

What is Asterisk

Asterisk is the most used open source IP PBX software, can be downloaded from, installed and used without any limitations. For more information on the Asterisk software solution see

Main Scenario


The above scenario consists of:
• Topex Voibridge VoIP/E1 GSM Gateway – IP Address :
• Asterisk IP PBX – IP Address :
• IP phones registered to Asterisk IP PBX – Extensions 70x

Topex Voibridge Configuration

For ease of configuration, we presume we have 2 SIM cards from Operator1 on GSM-Ports 1 and 2, and 2 SIM cards from Operator2 on GSM-Ports 3 and 4.
We assume Operator1 is identified by 072 prefix and Operator2 is identified by 074 prefix.

Step 1 : Port Config – GSM Settings

Configure the GSM ports so all incoming calls will be automatically directed to a PBX user(most likely the secretary's extension).


Step 2 : Routing – VoIP to GSM

Accept incoming calls from Asterisk's IP, filter them based on Operator prefix(in order to accomplish LCR) and send them out on the corresponding GSM ports.

Asterisk PBX Configuration

The following lines need to be added to the Asterisk configuration, in order to acomplish proper routing of incoming and outgoing calls to and from Topex Voibridge.

Outgoing calls:

Edit /etc/asterisk/extensions.conf file

exten => _70X,1,Dial(SIP/${EXTEN})
exten => _70X,1,Dial(SIP/${EXTEN})
exten => _072.,1,Dial(SIP/${EXTEN}@
exten => _074.,1,Dial(SIP/${EXTEN}@

Save the file and restart asterisk. All calls starting with 072 and 074 will be routed to the Topex Voibridge Gateway.

Incoming calls:

Edit /etc/asterisk/sip.conf file and add the following:


Save the file and restart asterisk. Now you will receive calls from Topex Voibridge VoIP/E1 GSM Gateway.

Additional information can be found on this webpage : Topex Voibridge


Created by: mircea, Last modification: Tue 19 of Jun, 2012 (06:31 UTC) by admin
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