Be sure to check out parts one and two of this series.

Part Three of this series assumes that you have your hardware in place, including your phones and PBX system. As I mentioned in part two, we chose to go with a Asterisk PBX system with Free PBX as the user interface.

The Network

VOIP Network Diagram

In part two I provided a network diagram that shows an overview of the hardware layout for a our VOIP installation. The main cause of much of my trouble understanding the network configuration for a VOIP system before this install came from never seeing a diagram like this. I assumed that the phones would need to interface directly with the PBX box with some type of hard connection and that I might need analog phone cards in the PBX system to make and receive calls outside of the office. It turns out that things are a lot simpler than that for a pure VOIP system.

PBX Hardware

As you can see in the diagram, the PBX computer merely sits on your network like any other device. The IP Phones, as long as they are on the same network, can use the SIP (Session Initiation Protocol) to discover and be discovered by the PBX system.

The PBX system needs only to be connected to your network via a standard network interface card (NIC) and be assigned a static IP address. Some guides that I read suggested that you install your entire VOIP network under a separate sub-net, but I decided to just leave the whole network on the same sub-net for ease of configuration.

IP Phones

I’m going to assume that the phones being used are SIP phones, if not, you’ll need to read the documentation on the particular protocol required for your devices. To connect your IP phone to the network, you only need to connect it via an Ethernet cable (some also require a power-over-Ethernet adapter) to the same network that the PBX is on. Once the phone has begun booting, it will attempt to locate a PBX system to pair with.

The Router

Your router will probably require some minor configuration in order to work properly with VOIP services. Some basic changes you’re likely to make are:

• Enable UPnP support
• Enable NAT
• Open Firewall port UDP:4569 to your PBX static IP
• Forward Ports 5060 – 5060 to your PBX static IP
• Forward Ports 10001 – 20000 to your PBX static IP
• Forward Ports 4569- 4569 to your PBX static IP

The Software

Hopefully now that you’re this far along in your install, the network and hardware setup are much less mysterious, or at least less difficult seeming. I say hopefully because the software configuration is probably going to leave you bewildered. I have by no means got it all figured out, I’ve basically reached a point where the phone system is working and I mostly understand how to make the basics happen.

I started to write the next steps for the software configuration and realized that it will take too much explaining to cram into this post. I’ll devote all of part 4 to the software configuration and aim to complete this series then.

Continue to Part IV…