My company needs a new voicemail and PBX system. We want to tie the selected system to four office sites. We've narrowed down the search to Avaya's Unified Messenger for Microsoft Exchange and DEFINITY Business Communication Systems (BCS) or Cisco Systems' Cisco Unity and Cisco Architecture for Voice, Video, and Integrated Data (AVVID). What are your thoughts about these systems?

Unified Messenger and Cisco Unity both are heavily dependent on Windows 2000 and Microsoft Exchange Server and represent the next step in corporate telecommunications: Voice over IP (VoIP), which provides centralized solutions for both voice and data. (I don't have room in this column for more than an overview of these systems, so you need to look closely at both sets of products to find out which will work best for your company. For general information about VoIP and VoIP products, you can read Tao Zhou, "Valuable VoIP," July 2001, InstantDoc ID 21130, and David Chernicoff, Buyer's Guide, "Voice over IP," December 2000, InstantDoc ID 16005.)

DEFINITY BCS and Unified Messenger. Few vendors can compete with Avaya's user base and reliability, and DEFINITY BCS is a tried-and-true product. That said, the system has a few limitations.

You can connect a BCS system to other BCS systems through a shared pipe for voice and data or through dedicated lines for voice. To share a voice and data line, you can connect two BCS systems over an IP trunk.

The first BCS system can determine whether a call destination is local or on the remote BCS system, then can compress communications as necessary. This compression can result in a bandwidth requirement of as little as 8KB per call, with little loss in voice quality. Because BCS allocates bandwidth on the fly, it can support more concurrent calls and dedicate more bandwidth to data traffic, as needed. You can prioritize voice and data traffic on your LAN or WAN.

However, at the time of this writing, BCS contains a bug that won't let you use centralized voicemail when connecting BCS systems over an IP trunk. Therefore, if you want to support voicemail for all your locations from one central site, you need to devote a set number of channels to voice-only traffic.

The problem with setting aside channels in this way is that you can't use dedicated voice channels for data, even when you aren't using them for voice communications. But if you set aside too few channels, you'll need to borrow more bandwidth from the data pipe. And under this setup, each call between BCS systems uses 64KB. (If you plan to maintain a Unified Messenger server at each office, this bug won't affect you and you can use a shared pipe. Also, Avaya might have resolved the bug by the time you read this article, so I suggest you discuss the situation with your vendor.)

Unified Messenger is an interesting voicemail product because it stores voicemail on an Exchange system. One advantage to this method is that users have ready access to voicemail through Microsoft Outlook or Outlook Web Access (OWA). You also get neat features such as text-to-voice conversion (i.e., the system can read email over the telephone to users) and fax capabilities. One of the product's most impressive aspects is that you can administer it through Win2K Active Directory (AD)—a capability that vastly simplifies voicemail administration. When you open a user's Properties dialog box through the Win2K Microsoft Management Console (MMC) Active Directory Users and Computers snap-in, you'll see a Unified Messenger tab through which you can configure various voicemail options.

Cisco AVVID and Cisco Unity. Cisco AVVID pushes the envelope of corporate communications. This product is a pure VoIP solution, but you can dedicate leased lines for voice-only traffic between offices. (I've seen reasonably large organizations roll out the product with both unified and distributed Voicemail capabilities.)

Of all the VoIP systems I've seen, Cisco's is by far the most mature, but its quality and reliability depend strongly on your network. If you choose this package, I suggest you use Cisco gear at the sites to which you might send voice traffic. The system's remote office requirements are simple: a router and a switch. The switch must support inline power, and you should add a backup gateway to the router. Also, all the Cisco equipment you use needs to support Quality of Service (QoS).

You should configure Cisco's IP phones on a separate Virtual LAN (VLAN) so that broadcast traffic is limited to voice traffic. To increase reliability, you can use additional Cisco CallCenter systems, which emulate PBX functions. (These systems are usually Compaq servers running Win2K.)

Cisco Unity is similar to Unified Messenger in that both products use Exchange to store voicemail and both products provide the same bells and whistles, including text-to-voice translation. Unlike Unified Messenger, however, Cisco Unity doesn't integrate with AD (you administer the Cisco product over HTTP) and doesn't include fax capabilities. The product does offer several features that Avaya's system doesn't offer (e.g., phone-display access to the entire company directory and Outlook Contacts, remote phone access through Cisco IP SoftPhone).