When you deploy Exchange 2007 Unified Messaging, users will have access to their e-mail, voice mail, and fax messages from either Microsoft Office Outlook 2007 or the version of Outlook Web Access that is included with Exchange 2007. Additionally, users will be able to use the following features:

• Access to Exchange information   To offer a seamless voice mail experience for the user, UM-enabled users can access a full set of voice mail features from Windows Mobile powered devices, Outlook 2007, and Outlook Web Access. These features include many voice mail configuration options and the ability to play a voice message from either the reading pane by using an integrated Windows Media Player or from the message list by using their computer speakers.
  
• Play on Phone   The Play on Phone feature lets UM-enabled users play voice messages over a telephone. If a UM-enabled user who sits in an office cubicle is using a public computer or a computer that is not enabled for multimedia, or is listening to a voice message that is confidential, the user might not want to or be able to listen to a voice message through their computer speakers. Alternatively, they can play the voice message by using any telephone. This includes home, office, or cellular telephones.
  
• Voice mail form   The Outlook 2007 voice mail form resembles the default e-mail form. It gives users an interface for performing actions such as playing, stopping, or pausing voice messages, playing voice messages on a telephone, and adding and editing notes.
  The voice mail form includes the embedded Windows Media Player and an audio notes field. The embedded Player and notes field are displayed in either the preview pane, when a user previews a voice message, or in a separate window, when a user opens the voice message. If a user is not enabled for Unified Messaging or Outlook 2007 has not been installed on the client computer, the user views voice messages as e-mail attachments. In this case the voice mail form is not available.
  
• Fax receiving   Exchange 2007 Unified Messaging enables voice messages to be delivered to a user's Exchange 2007 mailbox and also lets users receive fax messages in their mailbox. A fax message is sent to the user's mailbox as an e-mail message that has an image file that has a .tif extension attached. When users receive such messages in their mailbox, they can open the attached file by using a software application that can open and view image files that have a .tif extension.
  
• User configuration   A user who is enabled for Unified Messaging can configure several voice mail options for Unified Messaging by using Outlook Web Access. For example, the user can configure telephone access numbers and the voice mail Play on Phone number, and can reset a voice mail access PIN.
  
• Call answering   Call answering includes answering an incoming call on behalf of a user, playing their personal greeting, recording a message, and submitting it for delivery to their Inbox as an e-mail message.
  
• Outlook Voice Access   There are two Unified Messaging user interfaces available to UM-enabled users or subscribers: the Telephone User Interface (TUI) and the Voice User Interface (VUI). In Exchange 2007, these two interfaces together are called Outlook Voice Access. Subscribers can use Outlook Voice Access when they access the Unified Messaging system from an external or internal telephone. They can use Outlook Voice Access to access their Exchange 2007 mailbox. This includes their personal e-mail, voice messages, and calendar information. Users can listen to, reply to, create, and forward unread e-mail messages by using the telephone.
  
• Subscriber access   The subscriber access feature enables dial-in access for your organization's users. UM-enabled users or subscribers who dial in to the Unified Messaging system can access their mailbox by using Outlook Voice Access. By using a telephone, a subscriber or user can do the following:
  
  • Access voice mail.
    
  • Listen, forward, or reply to e-mail messages.
    
  • Listen to calendar information.
    
  • Access or dial contacts who are stored in the global address list or a personal contact list.
    
  • Accept or cancel meeting requests.
    
  • Set a voice mail Out-of-Office message.
    
  • Set user security preferences and personal options.
    
• Auto attendant   An auto attendant is a set of voice prompts that gives external or internal users access to the Exchange 2007 Unified Messaging system. Users can use the telephone keypad or speech inputs to move through the auto attendant menu structure, place a call to a user, or locate a user and then place a call to that user. An auto attendant gives the administrator the ability to do the following:
  
  • Create a customized menu for external users
    
  • Define informational greetings, business hours greetings, and non-business hours greetings
    
  • Define holiday schedules.
    
  • Describe how to search the organization's directory
    
  • Describe how to connect to a user's extension so external callers can call a user by specifying their extension
    
  • Describe how to search the organization's directory so external callers can search the organization's directory and call a specific user
    
  • Enable external users to call the operator
    

For more information about the user benefits of deploying Exchange 2007 Unified Messaging, see the topics listed in the following table.

Unified Messaging topics about user benefits

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Deploying Exchange 2007 Unified Messaging offers the following benefits to administrators:

• A complete unified messaging system   Exchange 2007 Unified Messaging offers a true unified messaging solution by using a single store, transport, and directory infrastructure. The store is provided by the Exchange 2007 Mailbox server role. The transport is provided by the Exchange 2007 Hub Transport server role. When you locate all e-mail and voice mail messages in a single store, you can manage this information from a single management point. For example, you can back up all e-mail, voice mail, and fax messages by using a single administration interface and toolset. This greatly reduces the overall cost of administration by combining infrastructure and training.
  
• An Exchange 2007 deployment and administration model   By using the Exchange 2007 Unified Messaging solution, you take advantage of the Exchange 2007 server design. You don't have to purchase a new server to run the Unified Messaging server role. More important, you can reuse your Exchange knowledge, including training and troubleshooting methodology, and apply it to managing your voice mail and fax messaging infrastructure.
  
• An Exchange 2007 security model   The Microsoft Exchange Unified Messaging service runs as an Exchange server account. This means that you do not have to create or manage a super user account for Exchange 2007 Unified Messaging.
  
• Consolidation of voice mail systems   Currently, most voice messaging systems require that all the voice messaging system components be installed in every physical office location in an organization. In this kind of arrangement, the voice messaging systems in those branch offices are located outside the central office and must be administered onsite. This distributed management scenario can frequently result in increased administration costs and complexity. Exchange 2007 Unified Messaging lets you manage your voice mail system from a central location. To create a centralized management system for Unified Messaging, you can put all Unified Messaging servers in a datacenter or location, and then deploy IP/VoIP gateways in each of your branch offices that replace the voice messaging system for each branch office. If you deploy a centralized voice messaging system in this manner, you can make significant savings in hardware and administrative costs.
  
• Speech enabled auto attendants   When internal or external callers call in to the Exchange 2007 Unified Messaging system, a series of voice prompts assists them in moving through the menu system called an auto attendant. The auto attendant enables the caller to connect to a person in an organization or locate a person in the organization so that they can place a call without assistance from a human operator. With an auto attendant, callers hear voice prompts instead of a human operator or receptionist.
  You can create multiple auto attendants in Exchange 2007 Unified Messaging. Within the Active Directory directory service, each auto attendant is represented as an object. Configuration settings for an auto attendant are made on the Active Directory object and can include language settings, customized menus, and other menu navigation settings. You can also configure each UM auto attendant so that when a user calls in to an auto attendant, the caller can use either dual tone multi-frequency (DTMF) inputs (also known as touchtone inputs) or voice inputs (available in English) to move through the Unified Messaging auto attendant menu system.
  

For more information about the administrator benefits of deploying Exchange 2007 Unified Messaging, see the topics in the following table.

Unified Messaging topics about administrator benefits

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Exchange 2007 Unified Messaging features and services rely on static and dynamic TCP and UDP ports to ensure correct operation of the computer that is running the Unified Messaging server role. The following protocols are required for Unified Messaging:

Session Initiation Protocol   Session Initiation Protocol (SIP) is a protocol that is used for initiating, modifying, and ending an interactive user session that involves multimedia elements such as video, voice, instant messaging, online games, and virtual reality.

Realtime Transport Protocol   Realtime Transport Protocol (RTP) defines a standard packet format for delivering audio and video over a given network, such as the Internet. RTP carries only voice or video data over the network. Call setup and tear-down are generally performed by SIP.

T.38   T.38 is a faxing standard and protocol that enables faxing over an IP-based network. The IP-based network then uses SMTP and MIME to send the message to a recipient's mailbox. T.38 allows for IP fax transmissions for IP-enabled fax devices and fax gateways.

UM Web Services   The Unified Messaging Web Services that are installed on an Exchange 2007 Client Access server use IP for network communication between a client, the Unified Messaging server, the Client Access server, and computers that are running other Exchange 2007 server roles. There are several Exchange 2007 Outlook Web Access and Microsoft Office Outlook 2007 client features that rely on the UM Web Service to operate correctly. Unified Messaging client features such as Play on Phone rely on Unified Messaging Web Services.

The following table shows the IP ports that are used for Unified Messaging for each protocol and whether the IP ports can be changed.

IP Ports that are used for Unified Messaging protocols

For more information, see Understanding Protocols, Ports, and Services in Unified Messaging.

A Unified Messaging server will not process incoming calls unless the operational state is set to Enabled. By default, the operational status of the Unified Messaging server is set to Enabled after installation. This enables the Unified Messaging server to process incoming and outgoing voice calls and incoming fax calls and to route the messages to the intended recipients in your Exchange organization.

Although the operational status of the Unified Messaging server is set to Enabled after installation, the Unified Messaging server also maintains a logical status parameter that is used to control the operational status of the Unified Messaging server. The intention of the logical status variable is to let you stop call processing so that the Unified Messaging server can be taken offline in a controlled way.

The operational status of the Unified Messaging server can be controlled by the Enable and Disable commands in the Exchange Management Console and the Exchange Management Shell. There are three status modes for Unified Messaging servers:

• Enabled   Process all incoming calls.
  
• Disable immediately   Do not accept any new calls and drop all existing calls.
  
• Disable after completing calls   Do not accept any new calls but process all existing calls.
  

When the Unified Messaging server starts, it locates all IP/VoIP gateways that are associated with the UM dial plans and are associated with the Unified Messaging server. To detect and identify any configuration changes on either UM dial plans or UM IP gateways, the Unified Messaging server will either register a change notification or re-check the configuration every 10 minutes.

If the UM IP gateway list changes, the Unified Messaging server will react accordingly and either start to use or stop using the appropriate IP/VoIP gateways. After a Unified Messaging server is working as an associated member of a UM dial plan and is communicating with an IP/VoIP gateway or a PBX, you can run a set of diagnostic operations to verify the correct operation and connectivity.

For more information about Unified Messaging servers, see the topics listed in the following table.

Unified Messaging topics about Unified Messaging servers

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By default, a user who has an Exchange 2007 mailbox is not enabled for UM. You must create a mailbox for the user before the user can be enabled for UM. After the user is enabled for UM, you can manage, modify, and configure the UM properties for the user.

Note:
To enable multiple UM users, use the Enable-UMMailbox cmdlet in the Exchange Management Shell.

There are two locations in which UM properties are stored for a user: the Mailbox object and the user's Active Directory object. When you enable a user for Unified Messaging, you set the UM property on the user's Mailbox object. After the Mailbox property is set to Enabled for Unified Messaging, the user can use the Unified Messaging features that are found in Exchange 2007.

After a user is enabled for UM, the user's Unified Messaging properties are stored in the user properties and the user's mailbox. The user's Unified Messaging properties, such as the user's extension number, spoken name, and other properties for the user, are stored in the user's properties in Active Directory.

You can manage Unified Messaging properties for an Active Directory user on the mailbox of the Exchange 2007 Unified Messaging user by using the Exchange Management Shell or the Exchange Management Console.

When you enable a user for Unified Messaging, the user must be associated with or linked to an existing UM mailbox policy and you must provide the extension number for the user. You can associate a user with a UM mailbox policy by using the Enable-UMMailbox cmdlet or by selecting the UM mailbox policy when you create the user's Exchange mailbox.

A UM mailbox policy contains settings such as the dialing restrictions and PIN policies for a user. When a UM mailbox policy is created, the UM mailbox policy must be associated with only one UM dial plan. The UM dial plan is then associated with at least one Unified Messaging server. Any Unified Messaging server that is associated with the UM dial plan can provide Unified Messaging services for a UM-enabled user who uses the UM dial plan. Associating these Active Directory objects in this manner delivers the Unified Messaging services by using Active Directory. After the user is enabled for UM, the settings from a UM mailbox policy object are applied to the UM-enabled user.

Note:
In a circuit-switched telephony environment, the user's telephone must be programmed in the PBX to forward busy or unanswered calls to a UM IP/VoIP gateway that is associated with the user's dial plan.

For more information about Unified Messaging users, see the topics listed in the following table.

Unified Messaging topics about UM users

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When you integrate a telephony network together with Unified Messaging, there must be an IP/VoIP gateway that connects your telephony network together with your IP-based network. Each IP/VoIP gateway in your organization is represented by a UM IP gateway object in Active Directory. Exchange 2007 Unified Messaging requires that you create at least one UM dial plan and that the UM dial plan has a Unified Messaging server and a UM IP gateway associated with it. After you install the Unified Messaging server role on a computer that is running Exchange 2007, you must associate the Unified Messaging server with at least one UM dial plan before it will answer calls. You can also associate a single Unified Messaging server with multiple UM dial plans. After the Unified Messaging server is associated with a UM dial plan, you must create a UM IP gateway and associate it with the UM dial plan that was created.

Important:
Each time that you create a UM dial plan by using the Exchange Management Console, a UM mailbox policy will also be created. The UM mailbox policy will be named <DialPlanName> Default Policy.

If you create the first UM IP gateway and do not specify a UM dial plan at the time that you create it, a default UM hunt group is also created. Creating and associating these objects in Active Directory enables the Unified Messaging server to receive calls from the IP/VoIP gateway and then process incoming calls for users who are associated with the UM dial plan. When a call comes in to the IP/VoIP gateway, the IP/VoIP gateway forwards the call to a Unified Messaging server and the Unified Messaging server tries to match the extension number of the user to the associated UM dial plan. The dial plan is identified from the pilot numbers to which the gateway presents the call.

For more information about Unified Messaging dial plans, see the topics listed in the following table.

Unified Messaging topics about UM dial plans

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The UM IP Gateway object is an Active Directory container object that contains one or more Active Directory UM hunt groups and other UM IP gateway configuration settings. UM IP Gateway objects are created in Active Directory to logically represent a physical hardware device called an IP gateway or IP/VoIP gateway. The UM IP gateway can represent either an IP/VoIP gateway or an IP/PBX. The combination of the IP Gateway object and a UM Hunt Group object establishes a logical link between an IP/VoIP gateway hardware device and a UM dial plan.

After the UM IP Gateway object is created, the IP gateway can be linked to or associated with a single or multiple UM hunt groups and UM dial plans. The UM hunt group provides a link between the UM IP gateway and a UM dial plan. By creating multiple UM hunt groups, you can associate a single UM IP gateway with multiple UM dial plans.

Note:
Before an IP/VoIP gateway can be used to process calls, a UM IP gateway must be associated with at least one UM dial plan. Also, at least one Unified Messaging server must be associated with at least one UM dial plan.

By default, UM IP gateways are left in an enabled state after they are created. However, the UM IP gateway can be enabled or disabled. If you disable a UM IP gateway, it can be in one of two disabled modes. The first disabled mode forces all associated Unified Messaging servers to drop existing calls. The second disabled mode forces the Unified Messaging server that is associated with the UM IP gateway to stop handling any new calls presented by the IP/VoIP gateway.

Note:
If a UM IP Gateway object is deleted, the Unified Messaging servers associated with the UM IP gateway will no longer be able accept or process new call requests from the IP/VoIP gateway.

For more information about Unified Messaging IP gateways, see the topics listed in the following table.

Unified Messaging topics about UM IP gateways

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Unified Messaging hunt groups are very important to the operation of the Unified Messaging system. The UM hunt group is a logical representation of an existing PBX or IP/PBX hunt group. UM hunt groups act as a connection or link between the UM IP gateway and the UM dial plan. A single UM hunt group is associated with at least one UM IP gateway and one UM dial plan.

Unified Messaging hunt groups are used to define the PBX or IP/PBX hunt group from which incoming calls will be received. A pilot number that is defined for a hunt group in the PBX or IP/PBX must also be defined within the UM hunt group. The pilot number is used to match the information presented for incoming calls through the Session Initiation Protocol (SIP) header on the message. The pilot number enables the Unified Messaging server to interpret the call together with the correct dial plan so that the voice or fax message can be routed correctly. It is very important to configure Unified Messaging hunt groups correctly, because incoming calls that do not correctly match the pilot number defined on the UM hunt group will not be answered and incoming call routing will fail.

When you create a Unified Messaging hunt group, you are enabling all Unified Messaging servers that are specified within the UM dial plan to communicate with an IP/VoIP gateway. If you delete the Unified Messaging hunt group, the associated IP/VoIP gateway will no longer service calls by using the specified pilot number. If the IP/VoIP gateway is left without remaining UM hunt groups, the IP/VoIP gateway will be unable to handle incoming calls.

For more information about Unified Messaging hunt groups, see the topics listed in the following table.

Unified Messaging topics about UM hunt groups

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There are situations in which you may have to provide callers with auto attendants that have different languages. The language setting that is available on a UM auto attendant enables you to configure the default prompt language on the auto attendant. When you are using the default system prompts for the auto attendant, the default prompt language is the language that the caller will hear when the auto attendant answers the incoming call. This language setting will affect only the default system prompts that are provided when the Unified Messaging server role is installed. This setting will not affect custom prompts that have been configured on an auto attendant. The language that is selected as the default for the auto attendant is based on the version of Exchange 2007 that is installed.

When you install the U.S.-English version of Exchange 2007, there will be only one language available to configure on UM auto attendants: U.S. English. However, if you install a localized version of Exchange 2007, for example, Japanese, you will be able to configure the auto attendant that you create to use Japanese or U.S. English as the default language. Additional UM language packs can be installed on a Unified Messaging server to enable you to use other default language options on an auto attendant.

Caution:
You cannot install UM language packs by using the .msi file for the language.

For example, if you have a business that is based in the United States but requires a menu system that gives callers the options of moving through the system in U.S. English, Spanish, and French, you must first install the UM language packs that you need. In this case, if you have installed the U.S.-English version of Exchange 2007, you would install the UM language packs for Spanish and French. However, because a Unified Messaging auto attendant can have only one language configured at a time, you would create four auto attendants: a main auto attendant that is configured to use U.S. English and then one auto attendant for each language: U.S. English, Spanish, and French. You would then configure the main auto attendant to have the appropriate key mappings to access the other auto attendants that you have created for each language. In this example, the main auto attendant would answer the incoming call and the caller would hear, "Welcome to Contoso, Ltd. For English, press or say 1. For Spanish, press or say 2. For French, press or say 3".

The following examples demonstrate how you can use UM auto attendants together with Exchange 2007 Unified Messaging:

• Example 1   At a company called Contoso, Ltd., external customers can use three external telephone numbers: 425-555-1111 (Corporate Offices), 425-555-2222 (Customer Support), and 425-555-3333 (Sales). The Human Resources, Administration, and Accounting departments have internal telephone extensions and must be accessed from the Corporate Offices UM auto attendant.
  To create a UM auto attendant structure that supports this scenario, create and configure three UM auto attendants that have the appropriate external telephone numbers. Create three other UM auto attendants for each department in the Corporate Offices. Then you configure each UM auto attendant based on your requirements, such as the greeting type or other navigational information.
  The following figure is a graphical representation of how UM auto attendants can be used in Example 1.
  
  How to configure multiple UM auto attendants with multiple outside business telephone lines
  
• Example 2   At a company called Contoso, Ltd., external customers call one main number for the business, 425-555-1000. When an external caller calls the main number, the UM auto attendant answers and prompts the caller by saying, "Welcome to Contoso, Ltd. Please press or say 'One' to be transferred to corporate administration. Please press or say 'Two' to be transferred to product support. Please press or say 'Three' to be transferred to corporate information. Please press or say 'Zero' to be transferred to the operator". To create a UM auto attendant structure that supports this scenario, you create a UM auto attendant that has customized extensions that route the call to the appropriate extension number.
  The following figure is a graphical representation of how UM auto attendants can be used in Example 2.
  
  How to configure multiple UM auto attendants with a single outside business telephone line
  

For more information about UM auto attendants, see the topics listed in the following table.

Unified Messaging topics about UM auto attendants

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Voice and fax calls that come in to an Exchange 2007 organization can be placed by callers who are inside or outside the organization. When a caller places a call to a UM-enabled user's telephone extension and the user is unavailable to answer the call, the PBX forwards or routes the incoming call to an IP/VoIP gateway and then to the Unified Messaging server. In a Unified Messaging system that uses an IP/PBX, the IP/PBX forwards the incoming message to the Unified Messaging server. The IP/VoIP gateway or the IP/PBX translates or converts the incoming audio stream into RTP for incoming voice messages or the T.38 protocol for incoming fax messages. The stream of IP data is then passed to the Unified Messaging server. After the Unified Messaging server receives the call, the Unified Messaging server processes the message and determines how to route the message.

The following figure illustrates how incoming voice and fax messages flow in an Exchange 2007 organization.

The flow of incoming voice and fax messages in an Exchange 2007 organization

In the previous example, a call arrives at the PBX and is then forwarded to the Unified Messaging pilot number. The pilot number is mapped to the hunt group that goes to the IP/VoIP gateway. The IP/VoIP gateway presents the call to the Unified Messaging server. The Unified Messaging server then receives SIP invitation header information such as who the call is for, who the caller is, and why the call was redirected. The Unified Messaging server then looks up the number that was called and identifies which user was called and which dial plan the user belongs to. From there, the Unified Messaging server looks in Active Directory to see whether the user is enabled for UM. If the user is enabled for UM, the caller receives a greeting for the user. Users' greetings are securely stored in their mailbox. This lets them manage their greetings. After the caller reaches the user's voice mail greeting, they can leave a voice message that will be sent to the user's mailbox. The Unified Messaging server then records the message, locates a Hub Transport server, and submits the voice message to the Mailbox server that contains the UM-enabled user's mailbox.

For more information, see Unified Messaging Voice and Fax Call Processing.

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When external or anonymous callers place a call by using an external business telephone number, or an internal anonymous caller places a call to an internal extension number, they are presented with voice prompts to help them move through the Unified Messaging menu system. The UM auto attendant is a set of voice prompts or .wav files that are played to callers instead of a human operator or receptionist when they call in to an organization that has Exchange 2007 Unified Messaging. Exchange 2007 Unified Messaging enables you to create one or more auto attendants, depending on the needs of your organization.

Auto Attendant Message Flow

When a call is received by a Unified Messaging server, the Unified Messaging server performs a Lightweight Directory Access Protocol (LDAP) query to an Active Directory domain controller to determine how to handle the incoming call.

The following figure illustrates the message flow when UM auto attendants are used in an Exchange 2007 organization.

UM auto attendant message flow

After you have created and enabled the auto attendant for your organization and associated it with a UM dial plan, the auto attendant can start to process calls. When a call for an auto attendant is received, it is first processed by the IP/VoIP gateway and mapped to the appropriate hunt group. The call is then sent to the Unified Messaging server. The Unified Messaging server looks up the auto attendant object in Active Directory and then provides the correct auto attendant to handle the call.

For more information, see Unified Messaging Auto Attendant Call Processing.

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With Exchange 2007 Unified Messaging, UM-enabled users or subscribers can access their e-mail, contacts, and calendaring information by using a standard analog, digital, or cellular telephone. When a UM-enabled user uses Outlook Voice Access, they can perform the following tasks:

• Listen to new and saved e-mail and voice mail messages
  
• Forward, reply to, save, and delete e-mail and voice mail messages
  
• Interact with their calendar
  
• Locate a person in the global address list (GAL) or their personal contacts
  
• Send a voice message to a person
  
• Change their PIN, spoken name, or greetings
  

Outlook Voice Access Message Flow

Incoming calls that are received by a Unified Messaging server from an Outlook Voice Access user are only routed to a Mailbox server to enable the user to access their mailbox. However, if a message is submitted by using Outlook Voice Access, for example, a change in the schedule of a meeting, the message is first submitted to a Hub Transport server within the same Active Directory site as the Unified Messaging server before it is routed to the recipient's mailbox.

The following figure illustrates how incoming calls and messages placed by subscribers or UM-enabled users flow in an Exchange 2007 organization.

Outlook Voice Access message flow in an Exchange 2007 organization

When a user calls in to Outlook Voice Access, the PBX receives the call for the Unified Messaging number and the IP/VoIP gateway presents the call to the Unified Messaging server. The Unified Messaging server then looks up the user account information in Active Directory and gathers information about the user. This information includes dial plan information. If the user places the call from their own extension, they are prompted for their PIN. The Unified Messaging server contacts the Mailbox server and authenticates the user. From there, the Unified Messaging server and the Mailbox server communicate information back to the user, as requested.

For more information, see Unified Messaging Outlook Voice Access Call Processing.

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Incoming calls that are placed by users who are using the Play on Phone feature are received and routed by a computer that is running Exchange 2007 that has the Unified Messaging server role installed. This section discusses the message flow for calls that are made by a UM-enabled user who uses the Play on Phone feature in Exchange 2007 Unified Messaging.

Understanding the Unified Messaging Play on Phone Feature

The Exchange 2007 Unified Messaging Play on Phone feature enables a UM-enabled user to access a voice mail message. However, instead of playing the media file over their computer speakers, they can listen to the message on a telephone.

When users sit in office cubicles, use a public computer, have a computer that is not enabled for multimedia, or have a voice message that is confidential, a UM-enabled user may not want to or may be unable to play a voice message over their computer speakers. The Play on Phone feature lets the UM-enabled user play the voice message over a telephone. The Play on Phone feature is available in Exchange 2007 Outlook Web Access and in Office Outlook 2007.

The following figure illustrates how Exchange 2007 Unified Messaging routes the incoming calls for UM-enabled users who use the Play on Phone feature.

Message flow for incoming calls when the Play on Phone feature is used

For more information, see Unified Messaging Play on Phone Call Processing.

Every incoming call that is received from an IP gateway will generate IP-based network traffic and will consume some amount of your available network bandwidth. Prior to deploying Unified Messaging, you should perform an analysis of the network traffic to determine current usage patterns and identify any potential issues. On most networks, bandwidth demand is not evenly distributed throughout business hours. Because all the IP-based calls are routed directly to your Unified Messaging servers from the IP gateways on your network and this IP-based network traffic consumes some available bandwidth, we recommend that you follow the following recommendations and guidelines:

• Place your PBXs physically close to your IP gateways.
  
• Place your IP gateways and your Unified Messaging servers on the same well connected network or within the same physical site.
  
• Place your Unified Messaging servers on the same well connected network or within the same physical site as other computers that have Exchange 2007 server roles installed, including Mailbox, Hub Transport, and Client Access servers.
  
• Terminate the Wide Area Network (WAN) connections that are close to where your telephony equipment is located.
  
• In branch office scenarios or over WAN connections, use the G.723.1 codec instead of the G.711u or G.711A codec to minimize the network traffic that is passed between your IP gateways and your Unified Messaging servers.
  

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Generally, Unified Messaging scalability is determined by the number of concurrent calls. By default, a single Unified Messaging server can accept a maximum of 100 concurrent voice calls and 100 concurrent incoming fax calls. These calls can be either incoming or outgoing and can be generated when a user leaves a voice mail message, when an Outlook Voice Access user accesses their Exchange 2007 mailbox, or by a user who uses the Play on Phone feature to listen to their voice messages. Although the number of concurrent calls is an important factor to consider when you build a scalable Unified Messaging infrastructure, you must also determine the best codec to use to encode the voice messages and the types and number of users who you have to support.

• Number of concurrent calls   By default, although a Unified Messaging server can accept 100 concurrent voice messages and 100 concurrent fax messages, a single Unified Messaging server can be configured to accept a maximum of 200 concurrent voice messages and 200 concurrent incoming fax messages. When you increase the number of concurrent connections on a single Unified Messaging server, more system resources are required than if you decrease the number of concurrent connections. It is especially important to decrease this setting on low-end, slower computers on which the Unified Messaging server is installed. Performance counters are available and the Get-UMActiveCalls cmdlet can also be used to monitor the current number of concurrent calls that are connected to a Unified Messaging server.
  If the number of concurrent calls required by your organization is larger than the number that is supported by a single Unified Messaging server, you can scale horizontally and increase the capacity of concurrent calls by installing the Unified Messaging server role and then adding the Unified Messaging server to a dial plan.
  
• Voice mail storage codec   The term "codec" is a combination of the words "coding" and "decoding" and relates to digital data. A codec is a computer program or software that transforms digital data into an audio file format or streaming audio format.
  In Exchange Unified Messaging, there are two general types of codecs: the codec that is used between IP/VoIP gateways and the codec that is used to encode voice messages. The Windows Media Audio (WMA), Group System Mobile (GSM) 06.10, and G.711 Pulse Code Modulation (PCM) Linear audio codecs are used to create .wma and .wav audio files for voice messages. However, the file type that is used depends on the audio codec that is used to create the voice message audio file. In Exchange Unified Messaging, the .wma audio codec creates .wma audio files and the GSM 06.10 and G.711 PCM Linear audio codecs produce .wav audio files. However, depending on the codec that is used, an audio file in .wma or .wav format is sent together with the e-mail message to the intended voice mail recipient. The size of Unified Messaging voice messages depends on the size of the attachment that holds the voice data. Additionally, the size of the attachment depends on the following factors:
  
  • The duration of the voice mail recording
    
  • The audio codec that is used
    
  • The audio file storage format
    
  The following figure illustrates how the size of the audio file depends on the duration of the voice mail recording for the three audio codecs that you can use in Unified Messaging.
  

  Note:
  In this figure, the average length of a call-answered voice message is approximately 30 seconds.

  Audio file size
  
  The sample bit rate (bit/sec) and compression properties for each audio codec that is used in Unified Messaging are as follows:
  
  • WMA – 16-bit – compressed file
    
  • G.711 – 16-bit – uncompressed file
    
  • GSM 06.10 – 8-bit – compressed file
    
  Using the WMA codec, we estimate that each Unified Messaging server can handle 60 to 75 concurrent IP-based calls. This estimate is also based on the assumption that 14 percent of all the IP-based calls arrive during the single busiest hour of a day. Based on these two assumptions, and assuming that users access their voice messages frequently by using Outlook Voice Access, we estimate that each Unified Messaging server can support between 2,000 and 10,000 users.
  Generally, you should allow for the following number of concurrent calls per Unified Messaging server:
  
  • 60 if the default dial plan codec is WMA
    
  • 75 if the default dial plan codec is GSM
    
• Types of users   There are two types of users who access the Unified Messaging system: authenticated users and unauthenticated users. These two types of users consume Unified Messaging resources. When you build a scalable Unified Messaging environment, you must consider the effect that these users will have and the resources that each of these users will consume.
  
  • Authenticated   Authenticated users are UM-enabled and can access their mailbox by using Outlook Voice Access. Authenticated users consume Unified Messaging server resources in several ways. This includes by directly calling in to a subscriber access number, logging on to their mailboxes, accessing their messages, calendar, contacts or the directory, and by using a Unified Messaging server to play voice messages over a telephone using the Play on Phone feature. They can also indirectly consume resources by transferring a call, sending a voice message, or calling a user's extension number and leaving a voice message or sending a fax.
    
  • Unauthenticated   Users who call in to a Unified Messaging auto attendant or call in to a subscriber access number but do not log on to their mailbox are unauthenticated callers. However, Unified Messaging resources are used to service their requests. Every time that a caller calls in to a UM auto attendant or uses a subscriber access number but does not log on to their mailbox, they still consume resources by transferring a call, sending a voice message, transferring to another auto attendant, transferring to another telephone number, or listening to recorded audio prompts.
    

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Unified Messaging relies on the ability of the IP/VoIP gateway to translate TDM or telephony circuit-switched based protocols, such as Integrated Services Digital Network (ISDN) or QSIG, from a PBX to protocols based on VoIP or IP, such as SIP, RTP, or T.38 for real-time facsimile transport.

IP/VoIP gateways are available from multiple manufacturers in sizes and models that range from 4 ports to 32 ports. You can deploy as many IP/VoIP gateways as necessary to provide for capacity and fault tolerance. If the number of calls or ports that are required is larger than the number of calls or ports that are supported by a single IP/VoIP gateway, you can scale horizontally and increase the number of calls that can be accepted or the number of ports by installing and configuring additional IP/VoIP gateways, creating the UM IP gateway object, and configuring the appropriate hunt groups to support your environment.

It is equally important to match the number of IP/VoIP gateways that you have in your environment to the number of Unified Messaging servers that are available. For example, you should not configure 10 IP/VoIP gateways that are each connected by using a T-1 line to a single Unified Messaging server. This would mean that the Unified Messaging server would have to support 240 concurrent incoming calls. You should consider this and scale your IP/VoIP gateways to Unified Messaging servers appropriately.

For more information, see Planning for Unified Messaging Availability and Scalability.

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