Introduction
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As a business grows, it is necessary to open further offices, usually in separate locations, or due to geographic requirements, they need a warehouse or distribution center that is separate to the head office.

One of the issues that occurs is the isolation of the two or more offices, almost as though they are two separate businesses. This occurs due the geographic isolation, but also in many cases isolation as they are using separate systems. Even the necessity, when dialling the other office, to dial a full phone number, continues to enforce this isolation.

It is surprising, especially in an office culture, how a simple change of dialling other office extensions directly, makes a change to the mentality of how the other office(s) are perceived. Add a few other functions such as the receptionist console providing visibility of the other office extensions (and their visibility of yours), and even an internal Instant Messaging/Presence ability that works across the two offices, and the culture changes. Further add in the ability for any staff to call the person that they need direct, knowing that there is no cost for the call.

I have seen it on many occasions, and I have had discussions with company directors who will categorically state that it has had a huge impact on their business efficiency and co-operation between branches due to a more homogenous single business. They also know that calls between all their offices have no call costs, and even if they wish to, they could stretch it further to include video between the various offices, either in a single room at each site, or at key staff desktops.

This document is not going to cover how to implement instant messaging, or the receptionist console, or how to setup video as these are generally covered by other tutorials on this site. Like all good systems, it is best implemented one building block at a time, test, and then move to the next phase, unless you are very experienced in which case, you generally don’t require this tutorial .

So the purpose of this guide is to provide you with the step by step guide on how to connect two offices together utilising an Elastix system in both offices.

Planning
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Connecting two offices or sites with Elastix is relatively simple, but like all good things a bit of planning ahead of implementation is a good investment. I have seen many mistakes made, not from not understanding the concepts, but actually becoming confused with setup details and not putting the basic building blocks in place first. Some do start with the basic building blocks, but part way through they make a leap feeling confident, making changes on the fly, and then it ends up not working.

So it is important to write out what you are trying to do, it will make it easier in the long run. Even printing the configs from this tutorial, making changes to the names to suit your setup, will keep you on the right track.

This planning also extends to making sure that each site is using a separate set of Extension numbers e.g. 200 range in Sydney and the 500 range in Melbourne. This simplifies your routing rules. If you are setting up the two Elastix systems for the first time, then this is worth considering the particular numbering separation to make it easy for both yourself and the business. It may not always possible, especially if the two systems are already in existence and already using a common extension numbering scheme, and this is covered quickly at the end of this tutorial.

The Scenario
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This is scenario and configurations are taken from a production system, so you know that they work.

The company has two offices one in Sydney and one in Melbourne. The office in Sydney has 60 staff and the one Melbourne has 20 staff

The two offices have a Virtual Private Network (VPN) between them which will generally be the case with most businesses that need to share or access data between their offices.

Elastix IP Address & IP Ranges used by each office
The Sydney office has a 192.168.0.0/255.255.255.0 ip address range
The Sydney Elastix system has an ip address of 192.168.0.100
The Melbourne office as a 192.168.1.0/255.255.255.0 ip address range
The Melbourne Elastix system has an ip address of 192.168.1.100

Extensions setup on Elastix at each Office

Sydney : Extensions 201 – 260
Melbourne : Extensions 501 – 521
(more…)