VoIP--do it right

If you're planning to take the plunge and swap out your old PBX for a VoIP system, you need to keep your eye on what's critical--and know the pitfalls to avoid.

Do it right:

• Make sure your network can handle the load. Analyze your data network configuration, monitoring current usage levels of key components. Thoroughly assess your current call usage and desired quality level in order to predict the load on your network. You need to measure a number of factors, such as call usage (including volume, duration, and so on) and quality, because there is no such thing as simply a "clear" call--you choose the quality level you want and use that to help determine system needs. To help do this, Infotel Systems Corp. offers VoIP-Calc, an Excel tool for calculating bandwidth required for VoIP. (Download VoIP-Calc tutorial here.)
• Select a VoIP vendor. Use a vendor's specs to evaluate your network infrastructure's ability to support a specific VoIP system. Look at such issues as hardware reliability, network link and carrier reliability, and network design.
• Use a testing algorithm. The current state-of-the-art methods for evaluating VoIP call quality are perceptual analysis measurement system (PAMS) and perceptual evaluation of speech quality (PESQ), the latter of which implements the International Telecommunication Union P.862 standard. Consider using test equipment with PESQ installed when you measure the speech quality of VoIP systems. There is specific equipment available that does the actual measurement. The vendor should install a small test system before the entire system is implemented.
• Establish call setup protocol. Know which call setup protocol the system uses. H.323, which was established by the ITU, is the most-used today. However, because it was developed as a telephony-based standard for multimedia, it has a high overhead. Many consider SIP (Session Information Protocol), introduced by the IETF (Internet Engineering Task Force), to be its successor. SIP reduces VoIP complexity and enables a number of new features (such as simultaneously ringing, instant messaging, and easier integration of e-mail and voice).]. SIP is just coming into wide distribution. For example, Microsoft's latest release of Messenger for Windows supports SIP for Windows XP and Windows 2000.
• Get high-quality codecs. The type of codec (coder/decoder or compression/decompression) you choose to convert analog speech to digital code (and compress it) can affect the quality of your transmissions and the amount of bandwith you use. The codec is the algorithm that is built into either the hardware or software. A hardware codec would most likely be a chip built into a board. While high-speed codecs consume more bandwidth, low-speed codecs impair the quality of the audio signal. It's recommended that you get higher-quality codecs, up to 64kbps.
• Watch for tricky VoIP apps. Typically, VoIP systems offer more communications-related applications than traditional PBXs. When selecting applications, be aware of accounting issues, such as the need to track usage and allocate costs. Tracking specific VoIP calls can be trickier than tracking calls over a traditional PBX system.
• Carefully monitor voice quality. Problems with latency and echo can still trouble IP PBX users, although these issues have become less common with improved systems and testing. Don't accept problems with voice quality as a "byproduct" of IP PBX--make sure your vendor helps you bring quality up to par.

• Don't have unrealistic expectations. Don't expect immediate cost savings. Enterprises are finding that it costs as much (or more) to implement a new IP PBX system as to install a traditional circuit-switched PBX. Make sure you evaluate all the costs of the system, including adding servers, switches, and desksets.
• Don't neglect training. Convergence means that you will be training telecom people to work with data, and IT people to work with telephones, so prepare them to work together on the project, and plan for cross-training.

• Protect it like it's a computer network. If your VoIP system connects to the outside world, it is just as vulnerable as your data network (although it is not any more vulnerable). Like their data-carrying counterparts, IP PBXs need to be placed behind firewalls, and protected against hackers and viruses. One simple solution is to put all phones and servers on separate virtual LAN (VLAN), so data and voice are not on the same VLAN.
• Check your firewalls. Be aware that if you're using SIP, your firewalls may not be able to accommodate SIP's dynamically assigned ports. Vendors provide a number of solutions for this. Some vendors that already support H.323-aware firewalls are working on a SIP version.