It is tempting to assume that you can simply implement VoIP on your existing network, as most vendors claim, and everything will just work, this is not the case.

For VoIP to be successful you have to have a certain level of service in place. Unlike data packets, voice packets must make it to their destination, if a packet is lost, it cannot be resent without repercussions.

So before you start planning your VoIP roll-out, do some home work, you might have to upgrade your network switches to prioritize voice traffic, you may have to upgrade your routers or even network wiring.

Here is an interesting article from Network World about VoIP analysis tools that will help you along the way.

Remember, not all switches/routers are the same; There is a difference between a high dollar (HP Procurve, Cisco, etc.) switch and a low cost (Linksys, D-Link, Netgear, etc.) switch. I know both might say they support 10/100 MBPS, both might be managed but if you test both side by side in a lab, you will see the difference.

Always have some sort of network traffic sniffer/analyzer in your toolkit, sooner or later, you will need it. Ethereal is a good opensource network packet analyzer to have in your arsenal. Ethereal will let you see the traffic flowing back and forth on your network so you’re not running blind when problems arise with voice quality and end node connectivity.

Know what codec your VoIP devices are using, all codecs are not the same and voice quality along with bandwidth usage is heavily dependent on codec used.