Introducing Unified Messaging in Office Communications Server 2007 environment
Published Jul 20 2007 07:29 PM 6,271 Views

The Unified Messaging component of Exchange 2007 SP1 is the designed to be the voice mail solution for Office Communications Server 2007 (OCS). What it means is that anyone can dial an Office Communications Server user and leave a voice mail which will then be delivered to that user's Outlook inbox. The integration of Office Communication Server 2007 and Exchange 2007 Unified Messaging will take users closer to the vision Microsoft has for Unified Communications.

For an enterprise with Office Communications Server 2007, the integration of Unified Messaging (hence Exchange 2007) will give enterprise users the added benefit of having e-mail, voice mail, and fax messages consolidated in their inbox. Moreover, certain voice mail features can now be accessed using Office Communicator clients. The Unified Messaging role must be deployed with Exchange 2007 service pack 1 to support this integration.

In an integrated environment when a call to a person is not answered (busy, ring no answer, or diverted to voice mail) it gets routed to the Unified Messaging server (UM). The front end server role of OCS (or the Director) is responsible for processing and routing the call to the UM server.

Clients for OCS can be one of the following:

  • Office Communicator (OC)
  • OC qualified IP phone device

These clients are also known as Unified Communications Clients or UC Clients. Any user in Active Directory (AD) will have to be enabled and configured for voice capability to talk to the OCS server. The same client will also have to be enabled for Unified Messaging to divert their missed call to the UM server.

Common Scenarios

Following are some of the common scenarios where a call will route through OCS as well as UM. In each of these scenarios the users are enabled for Office Communications as well as Unified Messaging.

Divert to Voice Mail

User A calls User B, who does not answer. The call is then diverted to the UM server by OCS. Exchange UM plays a greeting previously recorded by User B, after which User A records a message. User B receives the voice mail message in their e-mail inbox with contextual information (additional contact information, phone numbers, title) provided in the body of the voice mail message. Callers can are identified through Active Directory or from User B's personal address book in Outlook. Finally, Outlook and Outlook Web Access both display this message along with an embedded player to play the voice message.

Subscriber Access

User A logs on using Office Communicator and selects the option to call voice mail. Since the user is already authenticated through Office Communicator, UM will not require the user to enter their PIN. Exchange UM will play the prompts for voice mail, e-mail, and calendar in Outlook Voice Access, all of which is pulled from User A's mailbox. User A selects to listen to their voice mail.


User A does not know User B's direct line or extension, so User A calls the public access number for User B's organization. User B is connected to the Exchange UM Automated Attendant, which offers various options, including a corporate directory. User A says User B's name verbally, which is recognized by the Automated Attendant and User A's call is transferred to User B's extension in the organization.

Better Together

Integration of OCS and UM gives users a seamless experience to communicate across their entire organization. A UC client has the option to do instant messaging, audio-video conversations, conferencing, and access to all UM functionality from their UC client.

The following are some of the key features of this experience:

  • Provides a single authentication method – A user who has logged into Office Communicator does not need to enter their PIN when they check their voice mail from the Office Communicator interface.
  • Maintain subject name and priority - An OC user can add subject and priority when making a call. If the call gets diverted to UM, the subject is added to the subject line of the message containing the voice mail or the missed call notification. Additionally, the priority of the original call is maintained by UM in the auto-generated notification for missed calls or new voice mails.
  • Integrated missed call notifications - When a call is missed by the receiving party, UM will generate an e-mail notification for the missed call and place it in the inbox for the receiving party.
  • Both missed calls and voice mails show the name and contact information for the calling party user. This information is retrieved through Active Directory or from the called party user's personal contact list.
  • Traversing the firewall - Media streams can be traversed through the corporate firewall securely without complicated configurations.
  • High fidelity voice quality - UM now supports high fidelity codecs for voice mail recording and play back.

E.164 Number Format

The format of the telephone number associated with the UC-enabled user is E.164 (example: +19805551234). Therefore, if a user enters a number that is in different format (example: extension 1234) it has to be manipulated into the E.164 format. OCS will take this number and search the corporate directory to find the user who has a matching number and then voice mail will be routed to the correct user. OCS uses normalization rules to translate these number formats and uses an internal translation service to perform canonicalization transformation. Stay tuned for future blog post on this topic.

A Simple Scenario

In this scenario User A makes a call to user B using Office Communicator. User B does not answer and the call is forwarded to voice mail. User A hears the mailbox greeting and leaves a voice mail for User B.

Call Flow

The following is the call flow for the above scenario:

  1. When User A makes a call to User B, the request is first sent to the OCS front end server as a SIP INVITE. OCS will first try to find the target user (User B) in AD and determine whether User B is OC-enabled. If the user is OC-enabled, the call will be forwarded to the registered SIP endpoint for User B. OCS will send the request as a SIP INVITE.
  2. If User B does not answer the call, a response message will be sent back to OCS server indicating that User B did not answer the call.
  3. OCS will query AD to find out if User B is UM-enabled, and if so, will extract out information such as their proxy address, dial plan name, and the UM server(s) assigned to the dial plan. OCS will use its routing logic to determine the appropriate UM server to route the call to.
  4. A new INVITE request will be sent to the UM server by the OCS server. In this new INVTIE request, User B's SIP address will be added as a diversion header indicating that this is a voice mail call for User B.
  5. A new session will be created between OCS and UM. OCS will exchange media information with UM and indicate that the RTP end point is the IP address of User A. After media negotiation is done, UM will establish a RTP session with User A and play prompts for leaving a voice mail. User A will directly communicate with UM and leave a voice mail for User B.
  6. The remainder of the communication remains the same for any Exchange 2007 environmen t. After the voice mail is received by UM, it will be handed it off to a hub-transport server which will in turn route the voice mail to the user's mailbox on the appropriate mailbox server.


This blog post is a high level introduction to Exchange UM and OCS 2007 integration. It does not cover calls routed to and from the PSTN via OCS, which is also supported in UM-OCS scenarios. Office Communications Server 2007 deployment scenarios can expand cross-forest and resource forest and Exchange 2007 Unified Messaging is supported in complex deployment scenarios as well. For deployment scenarios and more information refer to the Office Communications Server 2007 documentation:

- Seema Rahman

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