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Comparing VoIP PBX solutions for Unified Messaging

Before a Unified Messaging server can be configured to receive calls, you'll need a VoIP solution. Exchange 2007 Unified Messaging does not support many IP PBXs, but their number is expected to multiply as this server role increases in popularity. In this excerpt from "Microsoft Exchange Server 2007: The Complete Reference," find out which VoIP solution works best for your Exchange Server configuration: a legacy PBX connected to an IP gateway or a supported IP PBX.

PBX and IP gateways vs. IP PBXs

Unified Messaging server roles are deployed as part of the Exchange 2007 Server deployment. The Unified Messaging role need only be added with the default configurations during the server installation.

This is part #5 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.
However, before the UM server can be configured to receive calls, a VoIP solution must be in place. Two VoIP solutions are supported by the Unified Messaging role with the RTM version of Exchange 2007. You can have a legacy PBX connected to an IP gateway or you can use a supported IP PBX.

In short, a three-step process is used to integrate UM with a VoIP solution: Install the UM Server role, install and configure the IP gateway with the legacy PBX or install an IP PBX, and then configure the UM Server role to use the IP gateway or IP PBX.

Legacy PBX and IP gateways

Legacy PBXs vary greatly. Your choice of an IP gateway should be based on its support for the legacy PBX. The critical features that need to be supported by the IP gateway are:

  • Line provisioning type - T1 PRI CAS trunk, T1 PRI, ISDN BRI, individual voice lines.
  • Signaling integration - SMDI, Q.SIG, or digital set emulation (DSE). Q.SIG and DSE have built-in signaling integration. T1 CAS requires SMDI for signaling.
  • Line call plan - Settings on the PBX that define the supported call scope. This can be as broad as worldwide and as limited as internal calls only.
  • Hunt group/pilot number - If existing hunt groups and pilot numbers are in place from an existing solution, consider whether you want to reuse voicemail numbers or create new ones.

It is important to review the, "PBX Configuration Notes – Tested by Microsoft or Gateway Vendor Partners," at to locate the configuration notes document for the PBX and IP gateway that you will be using.

These documents are created by the vendor specifically to show how to configure their devices to work with your PBX. Reviewing the capabilities of these documents prior to purchasing an IP gateway is recommended so you can make an informed decision. The supported IP gateways are listed in Table 3.

Vendor IP Gateway Supported Protocols
AudioCodes MediaPack 114/8 FXO Analog with In-Band DTMF
Analog with SMDI
AudioCodes Mediant 1000 T1/E1 Q.SIG
AudioCodes Mediant 2000 T1/E1 CAS
Dialogic PIMG80PBXDNI Digital Set Emulation
Dialogic PIMG80LS Analog with In-Band DTMF
Analog with SMDI
Dialogic TIMG300DTI, TIMG600DTI T1 CAS
Table 3 Supported IP Gateways


The IP PBXs that are supported by Exchange 2007 Unified Messaging Server are few and far between. However, the list is expected to grow as adoption of Unified Messaging increases. The key to their integration is support for SIP over TCP. Table 4 lists the currently supported IP PBXs.

PBX Manufacturer PBX Model/Type Minimum Software Version
Avaya Avaya Communication Manager V2.0
Cisco CallManager 5.0, 5.1
Interactive Intelligence Customer Interaction Center 2.4
Mitel 3300 CXi, CX/MXe 7.1 UR2
Nortel Networks CS 1000 (a.k.a. CS1K) 5.0
Table 4 Supported IP PBXs

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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