Among voice mail and email system vendors, the debate is on. Will the industry opt for a multiple message-store (client-based) solution or a single message-store (server-based) solution? As Figure 1 and Figure 2 illustrate, the architectural difference is in how many separate databases, directories, and message copies the integrated or unified messaging system must maintain.

With integrated messaging solutions, you must often store message objects on both the native message server and the email server. One reason for dual storage is to avoid the time-consuming process of having to convert files from your desktop message viewer on the fly. The conversion is necessary to change files from the native message format to the fastest format. For example, dual storage lets you quickly review a voice mail message in native format by making a telephone call into the voice mail server or by playing the message out in .wav format from your Web browser or desktop messaging program.

So, what happens if your email server goes down while you are calling into your voice mail system to delete two voice messages from your inbox? You now have a synchronization problem between the two message servers. Figuring out how to keep both message lists in synch is challenging. One vendor of integrated/unified messaging systems told me the company could never arrive at a satisfactory synchronization solution. Synchronization is tricky.

Unified messaging systems don't have this synchronization problem because only one copy of every message is on the system. However, vendors of unified messaging systems say this method of message management is much more difficult to implement. To work effectively, unified messaging relies on features that require close cooperation among email and operating system vendors.

Another unified messaging issue is message retrieval performance. With voice mail, for example, the unified messaging server has to retrieve the next voice mail message object so that the voice mail server can begin playing the message to a telephone caller very quickly. Although email users are conditioned to wait a bit before they read their email messages, telephone-based voice mail callers expect immediate response to their touch-tone commands. Not all messaging platforms today can meet this requirement.

Unified messaging vendors say the best possible path is a phased approach from today's integrated messaging to unified messaging systems, given the current state of messaging platforms and their APIs. The good news is that companies, including Octel, have already announced true unified solutions. Expect to see single-store unified messaging systems from major voice mail vendors in production by late this year.