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Deploying Unified Messaging servers on Exchange Server 2007

Unified Messaging can be installed as a standalone server role or with any of the other server roles that are not clustered. However, a good installation requires knowledge of the minimum configurations, along with the recommended steps offered by Microsoft. In this excerpt from "Microsoft Exchange Server 2007: The Complete Reference," find out how to deploy your Unified Messaging server role, including the necessary hardware requirements and your migration staging options.

Deploying Unified Messaging servers

The Unified Messaging role can be installed as a standalone server role. It can also be installed with the Hub Transport, Client Access Server, and/or Mailbox server roles, but not clustered Mailbox server roles.

This is part #4 from "Microsoft Exchange Server 2007 Unified Messaging for administrators," excerpted from Chapter 9 of the book Microsoft Exchange Server 2007: The Complete Reference, published by McGraw-Hill Osborne Media.
Dedicating hardware to the Unified Messaging server will make it easier to properly size the hardware required for your environment. Microsoft's deployment of Unified Messaging servers in North America supports 30,000 users on only five dedicated Unified Messaging servers.

To deploy Unified Messaging in your Exchange 2007 environment, you need to carefully consider a number of factors from the number of Unified Messaging users, and the type of features you will provide them to the voice codec you select.


Consider the hardware requirements for the UM server role. Table 1 shows the recommended processor and memory configurations from Microsoft.

Resource Minimum Recommended Maximum
Processor One core Four cores Four cores
Memory 2GB 1GB per core 4GB
Table 1 Unified Messaging Serve Role Processor and Memory Requirements

As a general rule of thumb and a default limit, a single Unified Messaging server can support up to 100 simultaneous connections for phone calls and 100 for inbound fax connections. The server can be configured to support twice that number of connections for phone calls and faxes, respectively, but the hardware would need to be scaled up to support that load.

It is suggested that if you need to scale a Unified Messaging server for more than 100 connections that you add more Unified Messaging server roles to your organization. If you need to adjust the number, you can change it to a value between 0 and 200. You will need to use cmdlets like these:

[PS]C:>Set-UmServer -Identity OCS-EX1 -MaxCallsAllowed 70
[PS]C:>Set-UmServer -Identity OCS-EX1 -MaxFaxCallsAllowed 60

Microsoft recommends that you configure a Unified Messaging server role with four processor cores to support the processor intensive conversion of voice messages to digital files. Disk requirements are nominal because there is no critical data stored on the Unified Messaging server, except during the processing of voice and fax messages.

The factor that impacts scalability the most is the size of the voicemail messages. Voice messages can vary in size depending on the codec used by the IP gateway and Exchange 2007. The Exchange Unified Messaging server role supports WMA, GSM 0.610, and PCM G.711. Each codec has different storage formats. WMA generates .wma files whereas the others generate .wav files. The longer the voice message, the larger the file attachment will be when it is delivered to the recipient's mailbox. Choosing a codec that keeps the size of long messages down, while keeping the integrity of the voice message, is essential to UM's performance.

Next to WMA, GSM 06.10 has the best compression, but GSM uses an 8-bit sampling rate whereas WMA and G.711 use a 16-bit rate. The bit rate directly impacts the quality of the voice message (16-bit is better than 8-bit). WMA is a Microsoft proprietary codec and is the recommended codec as long as the IP gateway UM connection supports it as well.

If you use WMA, you can anticipate supporting up to 60 concurrent calls on each of your Unified Messaging servers and 75 concurrent calls if you use GSM. With that in mind, Microsoft estimates that it is possible to support a minimum of 2000 users and a maximum of 10,000 users per server, depending on the volume of messages and the length of the messages. It is important to note that a user who is making an inbound call to leave a voicemail (unauthenticated user) that actually uses fewer resources on a Unified Messaging server than a user who calls in to check their voicemails (authenticated user) via OVA.

Deployment process

The size of an organization and the complexity of the existing phone system will affect the amount of time the deployment of Unified Messaging will take. The process of deploying Unified Messaging in an organization is custom built by administrators to meet the organization's needs. However, there are some lessons you can learn from what others have already deployed for Unified Messaging.

For example, Microsoft documented their deployment of Unified Messaging in a showcase article titled, "Using Exchange Server 2007 for Unified Messaging." They devised a deployment process that allowed them to not only implement Unified Messaging, but also to integrate with a variety of PBXs and migrate off of the third-party Unified Messaging solutions that they have been using for many years. Here are the high-level phases to the process they utilized:

  • Preparation phase Install the Exchange UM server, configure the PBX, and gather all the required data for installation: IP addresses, hunt group, and operator numbers. Identify test users group.
  • Procurement phase Procure the gateway, cables, patch panels, interface cards, and other hardware.
  • Gateway installation and configuration phase Install IP gateways. Configure, test, and validate the installation.
  • UM server integration phase Configure the IP gateway with the UM partner servers with which the IP gateway can communicate.
  • Testing phase Use a test account and detailed checklists to test and verify that all UM components are operational.
  • Pilot number and production rollout phase Create a pilot number to use with the PBX and IP gateway. Verify that when the pilot number is dialed that the PBX forwards it to the IP gateway with call details. After successful testing, roll out UM services to users.
  • User support and education phase Live testing with test user group. Document any issues that arise during live testing. Make changes to configurations as necessary. Communicate changes to the users along with timeframes and options. Provide documentation with step-by-step procedures for user self-service, such as PIN resets.

Unified Messaging coexistence and Migrations

When you have an established voicemail system or Unified Messaging system, you will have to determine how and when the transition to Exchange 2007 Unified Messaging will occur. Among the factors to weigh are the connectivity, signaling integration, and PBX requirements for each site as well as the IP gateway options.

Because existing solutions may have more or fewer features than Exchange 2007 Unified Messaging, it may be necessary to keep some of the legacy components around to support your current service levels. Some of the additional considerations are:

  • PBX integration
  • IP gateway selection
  • Consolidation
  • Fax integration
  • System monitoring
  • Security

Table 2 can be used to help you evaluate how you should transition. The options are to stage your migration or to perform an overnight migration.

Migration Considerations Overnight Staged
All hardware must be implemented at once. X
Hardware can be deployed over time. X
User migration can occur in phases. X
Requires configuration and testing. X X
User education required prior to migration. X
User support and education occurs in line with migration. X
Can monitor system capacity and performance for design miscalculations before they reach critical mass. X
Allows periodic issue resolution. X
Can pilot with smaller set of users. X
Table 2 Overnight Migration vs. Staged Migration

Microsoft Exchange Server 2007 Unified Messaging for administrators

 Home: Introduction to Unified Messaging on Exchange 2007
 Part 1: An intro to voice systems for Exchange administrators
 Part 2: Unified Messaging features in Exchange Server 2007
 Part 3: Defining Exchange Unified Messaging architecture
 Part 4: Deploying Unified Messaging servers on Exchange Server 2007
 Part 5: Comparing VoIP PBX solutions for Unified Messaging
 Part 6: Integrating Unified Messaging servers with a VoIP solution
 Part 7: Creating a Unified Messaging Dial Plan
 Part 8: Configuring a Unified Messaging IP gateway
 Part 9: Mailbox policy configuration for Unified Messaging
 Part 10: Creating and assigning a Unified Messaging hunt group
 Part 11: Dialing rules and restrictions for Unified Messaging users
 Part 12: Assigning Unified Messaging dialing rules to a mailbox policy
 Part 13: Executing Unified Messaging grammar generation
 Part 14: Enabling Unified Messaging mailboxes and users

Microsoft Exchange Server 2007: The Complete Reference This chapter excerpt from Microsoft Exchange Server 2007: The Complete Reference, by Richard Luckett, William Lefkovics and Bharat Suneja, is printed with permission from McGraw-Hill Osborne Media, Copyright 2008.

Click here for the chapter download or purchase the book here.

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