The future of enterprise telephony is clearer than ever. Circuit-switched PBXs are nearing obsolescence. IP technology is increasingly becoming the standard for corporate voice communications.

A recent report by Allied Business Intelligence predicted that premise-based (IP PBX) voice over IP (VoIP) gateways will grow from 4.3 million ports in 2001 to 47.6 ports in 2007 (See chart). VoIP uses a TCP/IP network for the transmission of audio signals, enabling an enterprise to use an existing network for its telephone system rather than a separate PBX.

"To go out and buy a new circuit-switched PBX now is investing in a dead-end technology," says Raymond D. Keneipp, Vice President of Networks & Telecom Strategies for the Burton Group. "I think that everybody has accepted the fact that we will end up with a converged infrastructure. It's only a question of are you going to do it sooner or later."

As with many establishing technologies, a realistic approach to VoIP's advantages and disadvantages is beginning to replace the initial--and sometimes irrational--enthusiasm of the early adopters. For example, one of the highly publicized selling points of VoIP has been the promise of significant savings on the cost of long distance using toll bypass. However, while some savings are possible, the true cost advantages are difficult to assess, especially for enterprises, whose long distance charges have already shrunk through dropping rates, calling plans, and existing PBX toll bypass.

A more realistic benefit is the consolidation of your current network infrastructure to support both data network and PBX functionality, which can result in operational savings, especially in offices where relocating employees and reshuffling facilities is commonplace. Rather than having to install a new phone and possibly even rewire for adds, moves, and changes, employees can just plug a phone into a network jack, or just log on from their PCs using specialised software at the new location.

Consolidation, however, can also mean a strain on bandwidth, depending on your organisation's current setup. Companies that add an IP PBX can expect that some upgrades will probably be necessary. For example, you may need to upgrade your routers and/or router software, add more servers, or upgrade your protocols.

Bandwidth and flexibility

In addition, the installation of a solid Quality of Service system, which prioritises the packets passing through a network, can handle performance problems due to increased network traffic, although it cannot make up for insufficient bandwidth. If necessary, many enterprise VoIP gateways can fall back automatically to existing public switched telephone network (PSTN) connections, instead of routing calls through the Internet, when the system is temporarily stressed.

The greatest return on investment from VoIP is the most difficult to quantify: Increased worker productivity through a variety of new applications and services that are only now becoming available on VoIP systems.

An IP PBX system offers consolidation of your data/voice/video, providing a means for users to assert more control over their use of phone features using a desktop GUI. Although some of these applications are already in place on circuit-switched PBX systems (albeit in a less friendly format), they can only be used with a dedicated call centre, whereas VoIP systems allow any user to access these features. Some VoIP systems, for example, let employees log on to the system anywhere on the network, and immediately route incoming calls to their station, along with appropriate data. Unified messaging combines and tracks email and voicemail on the same Windows screen, allowing users to keep call journals, record/cache calls, identify callers, easily set up scripts for filtering and call routing.

So while Keneipp advises enterprises not to do a forklift upgrade, gut their old system and put in a new one, he does suggest they investigate VoIP if they are installing telecom gear at a new site or have outgrown their old PBX. Enterprises that aren't ready to switch yet, but are planning network upgrades, should keep in mind that the odds are that their networks will need to accommodate an IP PBX sometime in the future.

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. Analyse 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 offers VoIP-Calc, an Excel tool for calculating bandwidth required for VoIP.
• 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 email 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.