Companies wanting to get the most use of voice over IP (VOIP) need to know the steps involved in hardening their network and Internet infrastructure to get the best results out of their digital voice deployment projects.

VOIP for businesses is on the rise, so even if you don't deploy VOIP now, you most likely will at some time. "The overall business adoption of VOIP in North America will increase more than twofold by 2010," according to Infonetics Research. And the Dell'Oro Group estimates that IP PBX sales are expected to reach $US2 billion by that time.

Here are some questions and issues to resolve before you take the plunge.

What is your present Internet connection and how much bandwidth will you need for voice?

Just like you can't be too rich or too thin, you can never have enough Internet bandwidth, especially if you're moving to VOIP. A good place to start is a free service with TestYourVOIP.com, which places a test VOIP call using your current Internet connection and reports on the results.

But you also want to examine your existing Internet service provider contracts. "You need a rigorous service-level agreement. We have been doing this for five years and have the requirements nailed and understand the kinds of edge devices that our networks need," says Henry Kaestner, founder and CEO of Bandwidth.com, a VOIP supplier. Make sure you work with providers that understand these SLAs and have performance guarantees in their contracts, too.

You may be interested in upgrading your existing ISP connection because you have maxxed it out. You probably need a dedicated T1 or better if you are going to have more than a dozen VOIP users, so it might be worthwhile to investigate having a separate ISP connection just for voice. "Companies are going to need a voice-optimized SDSL line at a minimum for VOIP," says Kaestner. "A better rule of thumb should be to only consider using business VOIP applications with at least a T1." Bandwidth.com and Cbeyond Inc. have packages that combine connectivity with VOIP services, so it's worth checking these out first.

What kind of wiring is in your walls?

Leftover Category 3 wiring from the days when Ethernet was 10Mbit/sec. isn't going to support VOIP. And you might also think about having a separate wire plant for just your phones, depending on how much of your existing data wiring you need to replace. "Typically, cable plant is an issue for many installations. Places that have been using Category 3 wiring for 10 Megabit Ethernet do not realize that voice is going to need better wiring, like Cat 5e or Cat 6," says Chat Agate, CEO of NeoPhonetics, a national VOIP integrator in the Chicago area. Cat 5e and 6 will handle higher throughput for the best voice quality.

"The vast majority of VOIP problems that we see have to do with using the wrong cabling or problems in other parts of the local network," says Kaestner.