Interconnecting Asterisk IP PBX

Hi all,

It has been a long time since I had published any item on this blog. There have just been distractions but I am back now. The period of absence does not mean that nothing has been happening in the IP PBX world or that I have not been doing things. I will share with you a scenario where I was involved in the design of a voice network that spans Nigeria and Ghana.

This scenario will make us understand practical situations where we can use an IP PBX and how we can configure the PBX to achieve so much.

Scenario: An international organisation requires Asterisk PBX in Lagos, Nigeria and Accra, Ghana offices.  The organisation has a VPN link in place between the offices in the two countries. As such, a computer in Nigeria can ping an IP in Ghana and vice versa.


Requirement:  The PBX should do the following:
  1. Users in Lagos should dial the extension number of the Accra users directly without a leading number and vice versa.
  2. The users in both countries to make calls on their respective PSTN lines
  3. Nigerian users can make PSTN calls on Ghanaian Asterisk and vice versa.





Assumptions and Requirements:

·         All configuration to be done via FreePBX 2.8.1.4
·         Flavour of Asterisk is Elastix (Asterisk 1.8.12.0) running on CentOS Linux
·         The asterisk has been properly installed and working correctly
·         Extensions have been created on respective PBXs.
·         PSTN cards have been installed on PCI ports and necessary drivers installed

 PSTN Cards that can be used include the following



On the Nigerian Asterisk
1.       An IAX trunk was created to connect to the Ghanaian Asterisk box.
2.       A route was defined that ensures that upon dialling a 3 digit number starting with 3 (i.e 3XX), the call is transferred to the Ghanaian Asterisk via the IAX trunk earlier created.
3.       A PSTN card was installed on the Asterisk and configured with DAHDI
4.        A Route was configured that ensures that upon dialling a leading “9….”, the PBX will select the DAHDI trunk. The Extension 20X in Nigeria will dial 9xxxxx to call via the PSTN.

On the Ghanaian Asterisk
1.       An IAX trunk was created to connect to the Asterisk box in Lagos.
2.       A route was defined that ensures that upon dialling a 3 digit number starting with 2 (i.e 2XX), the call is transferred to the Asterisk in Lagos via the IAX trunk earlier created.
3.       A PSTN card was installed on the Asterisk and configured with DAHDI
4.       A Route was configured that ensures that upon dialling a leading “8….”, the PBX selects the DAHDI trunk. The Extension 30X in Ghana will dial 8xxxxx to call via the PSTN.

The above configuration achieves the first two requirements but not Nigerian users making calls via Ghanaian PSTN and vice versa.

The third requirement can be interpreted as such:
Lagos user (2XX) dials 8XXXXXXX to call PSTN in Ghana.
For example, 201 in Lagos wants to call +233 30 238 4000 in Ghana. Instead of making an international call via its own PSTN trunk by dialling 9 009 233 30 238 4000, he should dial 8 238 4000 just like a 3XX can in Ghana.

Ghanaian user (3XX) dials 9XXXXX to call PSTN in Nigeria
An example of this is, 301 in Accra calls +234 1 271 2400 in Lagos. Instead of making an international call via its own PSTN trunk by dialling 8 009 234 1 271 2400, he should dial 9 271 2400 just like a 2XX can in Lagos.

Configuration Solution:
Since an IAX trunk exists already, therefore, only new routes are to be configured.
On Lagos PBX, configure a route using a leading number 8 to simply use the predefined IAX trunk to take the call to the Ghanaian PBX which upon translation will route such a call to the DAHDI trunk.

Similar configuration will be done for the Accra PBX but for a leading number 9.

Note:
Despite the configuration looking so simple, if the organisation is to route VOIP calls between Nigeria and Ghana, the same set up can be used and it will work effectively. The only difference may be that the hardware will be scaled to accommodate more calls simultaneously.

Next:
We shall be looking at a setup that integrates two different flavours of Asterisk: Elastix (Palo Santo) and SwitchVox (Digium).



Comments

Post a Comment

Popular posts from this blog

Asterisk PBX System: Introduction

Hi all, Open source PBX solutions have been in existence for quite sometime. However, the adoption is still low in this side of the world. A majority of organisations in Nigeria have deployed analog PBX systems with Panasonic systems leading the pack. This is because the cost of implementing the analog solution was lower than the alternatives, then. However, the market started asking for more than what the conventional analog system offers. This led to some organisations deploying digital telephone systems. Asides functionality, certain organisations went digital for aesthetics of the phones (and/or "effizy"). Most IP phones are nice looking with brightly lit screens. The few organisations that adopted digital PBX technology used proprietary solutions like Alcatel Lucent, Avaya, Ericsson and Cisco Unified Communication System. Certain other organisations have deployed hybrid systems which are mixtures of analog and digital PBX systems. Open source PBX syste...
Read more