Although Exchange 2007 Unified Messaging has many Active Directory objects that must be created and configured during deployment, UM dial plan objects are the central component of the Unified Messaging system. A UM dial plan object is an Exchange 2007 organization-wide object that is created in Active Directory.

The Unified Messaging dial plan is an Active Directory container object that logically represents sets or groupings of Private Branch eXchanges (PBXs) that share common user extension numbers. In practical terms, users' extensions that are hosted on PBXs share a common extension number. Users can dial one another’s telephone extensions without appending a special number to the extension or dialing a full telephone number. A UM dial plan is a logical representation of a telephony dial plan.

For more information about telephony components, see Overview of Telephony Concepts and Components.

In Exchange 2007 Unified Messaging, the following UM dial plan topologies can exist:

• A single dial plan that represents a subset of extensions or all extensions for an organization that has one PBX.
  
• A single dial plan that represents a subset of extensions or all extensions for an organization that has multiple networked PBXs.
  
• Multiple dial plans that represent a subset of extensions or all extensions for an organization that has one PBX.
  
• Multiple dial plans that represent a subset of extensions or all extensions for an organization that has multiple PBXs.
  

Users who belong to the same dial plan have the following characteristics:

• An extension number that uniquely identifies the user mailbox in the dial plan.
  
• The ability to call or send voice messages to other members in the dial plan by using only the extension number.
  

For more information about how to enable a user for Unified Messaging, see How to Enable a User for Unified Messaging.

UM dial plans are implemented in Exchange 2007 Unified Messaging to make sure that user telephone extensions are unique. In some telephony networks, multiple PBXs can exist. In these telephony networks, there could be two users in Active Directory who have identical telephone extensions. UM dial plans resolve this situation. You can put the two users into two separate UM dial plans. This makes their extensions unique.

The following figure illustrates how Unified Messaging dial plans can be used in an organization that has a single forest and multiple physical sites.

When you integrate a telephony network together with Exchange 2007 Unified Messaging, there must be a hardware device called an IP gateway that connects your telephony network together with your IP-based network. IP gateways convert circuit-switched protocols that are found in a telephony network to a data-switched protocol such as IP. Each IP gateway in your organization is represented by a Unified Messaging IP gateway in Active Directory. For more information about UM IP gateways, see Understanding Unified Messaging IP Gateways.

Exchange 2007 Unified Messaging requires that you create at least one UM dial plan and that the UM dial plan has a UM 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 UM server together with at least one UM dial plan. You can also associate a single UM server with multiple UM dial plans. After the UM server is associated with a UM dial plan, you must create a UM IP gateway and associate it to the UM dial plan that was created.

When you create the first UM IP gateway and 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 gateway and then process incoming calls for users who are associated with the UM dial plan. When a call comes in to the IP gateway, it forwards the call to a UM server and the Unified Messaging server tries to match the extension number of the user to the associated UM dial plan.

For more information about how to add a Unified Messaging server to a UM dial plan, see How to Add a Unified Messaging Server to a Dial Plan.

A Uniform Resource Identifier (URI) is a string of characters that is used to identify or name a resource. In Unified Messaging, the main purpose of a URI is to enable Voice over IP (VoIP) devices to communicate with other devices by using specific protocols. A URI defines the naming and numbering format or scheme that is used for the calling and called party information that is contained within a Session Initiation Protocol (SIP) header for an incoming or outgoing call.

The types of UM dial plans that you create in Exchange 2007 Unified Messaging will depend on the URI types that are supported by the IP gateways, PBXs or IP PBXs in your organization. When you create a dial plan, you should know the specific URI types that are supported by your PBXs or IP PBXs. There are three formats or URI types that can be configured on Unified Messaging dial plans:

• Telephone Extension
  
• Session Initiation Protocol (SIP) URI
  
• E.164
  

In Unified Messaging, each time that you create a dial plan, the dial plan will, by default, be created to use the telephone extension URI format type. However, you can configure the URI type when you create a dial plan by using the New Dial Plan wizard or the New-UMDialPlan cmdlet. After you create a dial plan, you will be unable to change the URI type.

Telephone Extension

SIP URI

E.164

There are several security methods that can help you protect your Unified Messaging servers and the network traffic that is sent between your IP gateways and Unified Messaging servers and between your Unified Messaging servers and other Exchange 2007 servers in your organization. You can use Mutual Transport Layer Security (MTLS) to encrypt VoIP traffic that is passed between IP gateways, IP PBXs, and other Exchange 2007 servers and the Unified Messaging servers on your network. Using MTLS to encrypt the VoIP data is the best choice for protecting this data.

Unified Messaging can communicate with IP gateways, IP PBXs, and other Exchange 2007 computers in either a secured or an unsecured mode depending on how the UM dial plan has been configured. By default, UM dial plans communicate in an unsecured mode. You can use the Get-UMDialPlan cmdlet in the Exchange Management Shell to determine the security setting for a given UM dial plan.

Unified Messaging uses the VoIP protocols Realtime Transport Protocol (RTP) and SIP to communicate with other devices and servers. When you configure the UM dial plan to use VoIP security or secured mode, the SIP signaling channel will be encrypted. The SIP signaling channel can use SIP that is encrypted by using MTLS. However, the media channels that use RTP will still use Transmission Control Protocol (TCP), which is unsecured.

New in Service Pack 1 (SP1)

There are two types of callers who will access the Unified Messaging system by using the subscriber access number that is configured on a UM dial plan: unauthenticated callers and authenticated callers. When a caller dials the subscriber access number that is configured on a dial plan, the caller is considered anonymous or unauthenticated until they input information including their voice mail extension and a PIN. However, the only option that is available to anonymous or unauthenticated callers is the directory search feature. After the caller inputs their voice mail extension and their PIN, they will be authenticated and given access to their mailbox. After they gain access to the system, they are using Outlook Voice Access. Outlook Voice Access is a series of voice prompts that give the caller access to e-mail, voice mail, calendar, and other information. Subscriber access lets authenticated callers navigate their personal information in their mailbox, place calls, or locate users by using dual tone multi-frequency (DTMF) or voice inputs.

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