For an optimum experience when deploying Enterprise Voice, make sure that your IT infrastructure, network, and systems meet the following prerequisites.

Prerequisites

Microsoft Office Communications Server 2007 R2 Standard Edition or Enterprise Edition is installed and operational on your network.
All edge servers are deployed and operational in your perimeter network, including Access Edge Server, Audio/Video Conferencing Edge Server, Web Conferencing Edge Server, and a reverse proxy.
Exchange Server 2007 SP1 is required for integrating Exchange Unified Messaging with Office Communications Server and to provide rich notifications and call log information to the client endpoints.
One or more users have been created and enabled for Office Communications Server 2007.

A primary phone number has been designated, normalized, and copied to the msRTCSIP-lineattribute for each user who is to be enabled for Enterprise Voice. The administrator is responsible for ensuring that this number is unique.

Note:
Office Communications Server 2007 R2 supports E.164 numbers as well as non-Direct Inward Dialing (DID) numbers. Non-DID numbers can be represented in the format <E.164>;ext=<extension>or as a string of digits, with the requirement that the private extension is unique across the enterprise. For example, a private number of 1001 can be represented as +1425550100;ext=1001, or as 1001. When represented as 1001, the expectation is that this private number is unique across the enterprise.

Note:

Office Communications Server 2007 R2 supports E.164 numbers as well as non-Direct Inward Dialing (DID) numbers. Non-DID numbers can be represented in the format <E.164>;ext=<extension>or as a string of digits, with the requirement that the private extension is unique across the enterprise. For example, a private number of 1001 can be represented as +1425550100;ext=1001, or as 1001. When represented as 1001, the expectation is that this private number is unique across the enterprise.

Administrators deploying Enterprise Voice should be members of the RTCUniversalServerAdmins group.
Office Communicator 2007 is successfully deployed.
MKI (Managed Key Infrastructure) is deployed and configured, using either a Microsoft or a third-party certification authority (CA) infrastructure.
Each computer on which you install Mediation Server must be:
- A member server of a domain, and prepared for Active Directory. For Active Directory preparation procedures, see Preparing Active Directory Domain Services for Office Communications Server 2007 R2in the Deployment documentation.
- Running one of the following operating systems:
  - The 64-bit edition of the Windows Server 2008 Standard operating system or the 64-bit edition of the Windows Server 2008 Enterprise operating system
  - The Windows Server 2003 R2 Standard x64 Edition operating system with Service Pack 2 (SP2) or the Windows Server 2003 R2 Enterprise x64 Edition operating system with SP2
  - The Windows Server 2003 Standard x64 Edition operating system with SP2 or the Windows Server 2003 Enterprise x64 Edition operating system with SP2
If the connection to the public switched telephone network (PSTN) or Private Branch Exchange (PBX) is by means of a Time Division Multiplexing (TDM) connection, one or more media gateways are available for deployment. (If the connection is by means of a Session Initiation Protocol (SIP) trunk, a media gateway is not required.)