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Defining Exchange Unified Messaging architecture

Exchange Unified Messaging architecture

The Exchange Unified Messaging architecture is quite different from the legacy voicemail systems. There are three major components in the architecture: Microsoft Exchange Unified Messaging Service, Unified Messaging Worker Process, and the Speech Engine Services. Figure 3 details the architecture.

Figure 3 Exchange 2007 Unified Messaging architecture

In terms of running processes on the UM server, the architecture is based on two executables: UMservice.exe and SpeechService.exe. The executable UMService.exe spawns UMWorkerProcess.exe and is responsible for voice and fax message access and storage in the Exchange 2007 mailbox store.

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This is part #3 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.
The executable SpeechService.exe spawns the SESWorker.exe worker process and is responsible for DTMF, ASR, and TTS. The UM Worker Process Manager starts each of the UM worker processes defined for the UM server and monitors their activity. The UM Worker Process Manager is responsible for directing inbound calls to the correct UM worker process. Each UM worker process works with the speech worker process to process all requests made to the UM server. Communications to and from the UM server are established using SIP over TCP. This is different from many other VoIP solutions from other vendors. Most other vendors use SIP over UDP. The UM server listens for communications on port 5060 (unsecured) and port 5061(MTLS). Service Pack 1 allows the UM server to listen to both ports simultaneously. The worker processes listen for communications on TCP port 5056 and 5066 (unsecured). Service Pack 1 allows the worker processes to listen on 5057 and 5058 for secure connections. The RTP traffic that carries voice input from an IP gateway will use UDP ports 1024–65535. The UM worker process also contains a fax service provider that uses UDTL and the T.38 protocol to receive inbound faxes.

SP1: Service Pack 1 improves the security of the UM architecture by extending support for secure connections.

Microsoft Unified Messaging cannot communicate directly with a legacy PBX. It is necessary to use an IP gateway device between the Unified Messaging server and the legacy PBX. However, if an organization has deployed an IP PBX, there is a chance an IP gateway is unnecessary if the IP PBX is compatible with the Exchange 2007 Unified Messaging server. Figure 4 shows how the Exchange Unified Messaging server integrates with both types of PBXs. Note that the connection from the IP PBX to an IP gateway device is necessary if Exchange 2007 does not support the IP PBX.

Figure 4 Exchange 2007 Unified Messaging PBX integration

The "Inbound call handling" and "Retrieving messages with OVA" sections illustrate how the IP PBX and the legacy PBX integrate with the Exchange 2007 Unified Messaging server.

Inbound call handling

The inbound call handling steps performed by the UM server role are as follows:

  1. An external caller dials a UM user's phone number on the PSTN.
  2. The UM user's office phone rings for a preset number of times.
  3. The legacy PBX routes the call to the IP gateway or the IP PBX establishes a direct VoIP connection to UM server.
  4. The IP gateway identifies an available UM server. Once the UM server is determined, the voice input is converted to VoIP: SIP and RTP.
  5. The UM server queries AD to determine the mailbox server of the recipient by filtering for a user with the extension specified by the caller.
  6. The UM server plays the user's greeting, encodes the voice message, and attaches it to an email.
  7. The UM server sends the message to a Hub Transport server.
  8. The Hub Transport server in the same Active Directory site as the user's mailbox server submits the voicemail/email to the database where the user's mailbox data is stored.

Retrieving messages with OVA

The process to retrieve a voice mail from the UM server role is as follows:

  1. The UM user dials a preconfigured OVA call-in number from the PSTN.
  2. The legacy PBX routes the call to the IP gateway or the IP PBX establishes a direct VoIP connection to UM server.
  3. OVA requests the user's extension number and PIN.
  4. OVA queries AD to determine which mailbox database belongs to the UM user and to validate the PIN.
  5. The UM server waits for input from the user. When a request for a message is made, the appropriate menu of options is presented.
  6. If the user requests that the message is read, the Text-To-Speech engine will read the mail header and content (it cannot read the attachments to the email).
  7. The UM server retrieves the message from the Mailbox server role and plays the voice message.

For more details on PBXs, see "PBX and IP Gateways vs. IP PBXs" later in this excerpt.

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

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.

This was first published in January 2009

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