Unified Messaging Server role

The following section was originally published at http://nickgillott.blogspot.com/2006/04/unified-messaging-ramble.html


http://www.microsoft.com/exchange/preview/unified_messaging.mspx tells you all about what UM actually does.

First lets work out about concurrent users. Your average working day is 8 hours or 480 working minutes. Time spent leaving voicemails for internal staff and picking up your own voicemail messages per day: 10 minutes. As a ratio that is 2%. Build in a 100% additional usage and say 4% ratio.

A UM Server of decent specification (dual processor, dual core, 4GB RAM running Windows Server 2003 SP1 and a set of 15,000rpm Ultra320 SCSI disks configured appropriately) should cope adequately with at least 100 concurrent connections. Doing the maths (or math if you hail from the west side of the pond), 100 concurrent connections on a ratio of 4% user usage means one UM per 2,500 employees. It is possible that this is under estimated but safe however any company with more than 1,000 employees would be well placed to implement at least 2 UM servers for redundancy / fault tolerance.

Can you put UM and other services on the same box? Well if SBS can combine Exchange, SQL and ISA on one piece of hardware, you can stick UM on a box with other services. But think logically - if that box goes down, you lose voicemail and any other service installed on it.

With a VoIP connection to your PBX this puts voicemail into your Inbox and fax ability into your Inbox. Yeah, so what. Voicemail over OWA anyone? Anywhere in the world.

To expand on that, this is a fairly big step on the convergence road. Ignoring the back office parts, the users will see Exchange Server 2007 as their primary source of information û emails, voicemails and faxes. Obviously there will be a knock on effect of increasing mailbox sizes but with the drop in IO requirements, the increase in disk sizes available and the increased uptime of hardware and software, the users will love this.

So how does Unified Messaging work (technical jargon)?

Text extracted from Mark Arnolds Blog entry about UM, Monday June 12th 2006 from http://markarnold.blogspot.com/2006/06/exchange-2007-and-unified-messaging.html reproduced with kind permission and some editing.

This is the 30,000 feet view of getting a call into UM.
1. Caller dials your normal DDI and it hits your inbound line.

2. The switch asks itself what it's going to do with the call.

3. If you are not available (calls set to go to voicemail) then the switch will then ask itself what the route is to your voicemail (it will ask because you will have told it that the called party has voicemail and what the voicemail extension is)

4. It's worth quickly pointing out here that only the phone system knows this voicemail number; it's seamless to the calling or the called parties.

5. The call has to vector off to the right voicemail system. This is where we get a fork in the road.

6.
a. If your switch is IP enabled and also SIP active (http://en.wikipedia.org/wiki/Session_Initiation_Protocol) then you (or your phone boys) will have configured the switch to send calls for this voicemail channel down to the IP address of the Exchange server (it's part of the switch configuration which will have been set up during the switch config day by your external consultant).

b. If your switch isn't IP enabled then you'll be needing a H323 to SIP converter. This is a pretty standard box these days costing not-much-cash. This takes QSIG (http://en.wikipedia.org/wiki/QSIG) or Q931 (http://searchvoip.techtarget.com/sDefinition/0,290660,sid66_gci1047017,00.html) from a DPNSS (http://en.wikipedia.org/wiki/DPNSS) feed out of the switch and into the "box". Then the "box" makes it into SIP/RTP and pushes it to the right IP device on your network. You may already have LCS on the network so will need to throw traffic for the voicemail destination at a different IP address. For this the key word for you is URI. (http://en.wikipedia.org/wiki/Uniform_Resource_Identifier) It's just routing really, if you know routing, you will already understand this part.

7. So, the call has just arrived at the Exchange server. Now what? Exchange will take the call and look up who it is for. It will do this because you will have put the users extension number into AD (Yes, Active Directory) and yes, it is the users extension - not the users voicemail number (that nobody need know) because the presented number will be the called number, not the diverted number.

8. As part of the Exchange 2007 UM call handling process the server will also do a lookup of the display name and the TTS (Text to Speech) engine will say that "Fred Bloggs" then the standard dictionary will kick in and say "is not available to answer your call at this timeö.

9. Calling party leaves a message and the UM server wraps up a nice WAV file and throws it into the users mailbox.

What is missing?

A) How the call arrives in the inbox and what it looks like.
B) How the mailbox owner gets the message (no, fools, not the Outlook bit) via Outlook Voice Access.
C) A chunk of other stuff.