Last week's column on Exchange 2007's unified messaging (UM) feature (“Digging In to Exchange UM” InstantDoc ID 50363) drew a lot of reader email, which is interesting for two reasons. First is that it showed how many unanswered questions people have about how Exchange will implement UM, and second is that it helps prove my suspicion from my column two weeks earlier (“What Do You Do Daily?” InstantDoc ID 50322). You might remember that in that column, I cited a Ferris Research report that claimed that Exchange administrators need better tools for performing daily and weekly maintenance. Then I asked whether anyone out there was actually doing daily or weekly scheduled maintenance on their Exchange servers and, if so, what exactly they were doing. The overwhelming response: the sound of crickets chirping.

Because so many people wrote to ask about Exchange UM, I concluded that the lack of response about scheduled maintenance wasn't because some kind of bizarre worldwide email failure was preventing you from writing to me. Rather, I take it as evidence that there really aren't any significant daily tasks you need to perform on your Exchange servers, apart from the obvious ones, such as checking backup results, that you'd have to do with any backup system.

So, on to answer a few of your questions about UM.

The biggest group of questions concerned whether UM would work with a particular PBX. Last week, I mentioned that some PBX systems natively support the two protocols that Exchange UM uses: the Session Initiation Protocol (SIP; used for call set-up and tear-down) and the Real Time Protocol (RTP; used for moving audio data from the PBX to the UM server). Some PBXs require the use of a separate gateway. If you want to know whether a Brand X PBX can be used with Exchange UM, the answer is "it depends." If your PBX natively supports SIP and RTP over TCP, then it might be supported. (Microsoft hasn't yet released results of its interoperability tests.) If your PBX doesn't support those protocols, then it might be supported if it works a third-party PBX gateway product for Exchange 2007 UM. Both Intel and AudioCodes have such products.

I got a few questions about Asterisk, the popular Linux-based software PBX. I'm a big Asterisk fan, since I have several friends who work for Digium, acompany that provides Asterisk installation support. Unfortunately, you can't use Exchange 2007 UM with Asterisk. Why? Asterisk supports only SIP over UDP, and Exchange supports only SIP over TCP. According to Exchange Technical Product Manager Michael Khalili, Microsoft made the decision to use SIP over TCP for two reasons: security and interoperability. The broad market is clearly moving toward using TCP as the preferred SIP transport. For whatever reason, however, the Asterisk community never quite got around to adding TCP support to its product. Until it does so, you can't use the two together (although you might be able to cobble something together using a SIP gateway product).

As I expected, a few readers wrote to ask about small-business implementations of Exchange and how they might be affected by the UM server role. The Exchange UM role doesn’t have to be installed on its own server, so if you have only one Exchange server now, you can continue to use a single server after you upgrade. Michael told me that the current implementation of the UM server can handle 50 to 100 concurrent telephone calls--closer to 100 if you have a dedicated machine, and fewer if the server is shared with other roles. Microsoft's sizing guidance is thus simple: if you have fewer than 100 calls arriving at a time, you can handle them with a single server; if you have a higher arriving-call volume, you'll probably need multiple servers.

Having a robust, well-integrated UM feature would give Microsoft an outstanding competitive advantage because, as things stand now, full-fledged UM systems that work with Exchange or Lotus Notes tend to be too expensive and complicated for most small-to-midsized businesses (SMBs). Enterprises can afford to deploy Cisco CallManager, Adomo Voice Messaging, or the like, but small organizations often can't afford or support such products. Exchange UM also includes some features, such as the built-in speech recognition engine and the ability to access calendar data over the telephone, that no other competing product has.

Being able to provide voicemail and fax integration at a low incremental cost will help push Exchange 2007 into organizations that want more communication flexibility without having to deploy their own set of Scary Phone Guys. And that's a compelling prospect indeed.