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

• Microsoft Office Communications Server Standard Edition or Enterprise Edition is installed and operational on your network.
  
  
• All Edge Servers and a reverse proxy are deployed and operational in your perimeter network.
  
  
• Exchange Server 2007 SP1 is installed if you are integrating Exchange Unified Messaging with Office Communications Server.
  
  
• One or more users have been created and enabled for Office Communications Server.
  
  
• 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.
  
  
• Administrators deploying Enterprise Voice should be members of the RTCUniversalServerAdmins group.
  
  
• Office Communicator and Live Meeting are successfully deployed.
  
  
• Public key infrastructure (PKI) is deployed and configured, using either a Microsoft or a third-party certification authority (CA) infrastructure.
  
  
• Each computer on which you install Mediation Server is:
  
  
  • Prepared for Active Directory Domain Services. For details about Active Directory Domain Services 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
      
      
• One or more media gateways are available for deployment. (Media gateways are not required with SIP trunking.)
  
  

Table 1. Enterprise Voice Technical Requirements Table

Implementation method	Technical requirements
PBX coexistence	IP-PBX that natively supports SIP and IP media in a format that is interoperable with Office Communications Server. OR A PBX combined with a media gateway that connects the PBX to the Office Communications Server infrastructure. A/V Edge Server for media relay across network address translations (NATs) and firewalls. Mediation Server configured with the IP address of the PBX and the fully qualified domain name (FQDN) of the A/V Edge Server. Users enabled for Enterprise Voice and PBX integration. Voice mail configured on PBX.
Stand-Alone Options
Departmental	IP-or TDM PBX. Basic, basic hybrid, or advanced media gateway configured to connect departmental deployment with PBX. Additional other gateways as required for PSTN connections. A/V Edge Server for media relay across NATs and firewalls. Mediation server configured with IP address of basic or basic hybrid media gateway (not required for advanced gateway). Users enabled for Enterprise Voice. Call forwarding independently configured separately on Office Communicator and PBX. Exchange Unified Messaging deployed and configured to provide voice mail for Enterprise Voice users (PBX continues to supply voice mail for all other users).
Greenfield	Basic, basic hybrid, or advanced media gateway configured to connect to PSTN. A/V Edge Server for media relay across NATs and firewalls. Mediation server configured with IP address of basic or basic hybrid media gateway (not required for advanced gateway). Users enabled for Enterprise Voice. Call forwarding configured on Office Communicator. Exchange Unified Messaging deployed and configured to provide voice mail. A small PBX for fax and for calling emergency access numbers such as 911 or 999. Additional gateway to connect to small PBX.
PBX integration to stand-alone option Note: This migration path is used only when PBX integration is used as a stepping stone to a stand-alone Office Communications Server deployment.	Basic, basic hybrid, or advanced media gateway configured to connect to PSTN. (If one or more gateways are already deployed, they may have to be repurposed for new role in network.) SIP phones such as the Microsoft Office Communicator 2007 R2 Phone Edition are optional.

To help ensure the physical as well as logical separation of your Enterprise Voice infrastructure from the media gateways, you should install Mediation Server on a computer that is equipped with two network interface cards (NICs). One card faces the gateway; the second card faces the Office Communications Server 2007 server that acts as the Mediation Servers internal next hop.

When you install Mediation Server, the Deployment Wizard detects the presence of the two network cards and writes their IP addresses to the Office Communications Server listening IP address list and the Gateway listening IP address list, both on the Generaltab of the Mediation Server properties dialog box.

The Office Communications Server listening IP address is the address on an advanced media gateway that listens for call traffic from Office Communications Server. Until advanced media gateways are available, this address corresponds to the network card that serves as the internal edge of the Mediation Server.

Important:

The IP address that you select from the Office Communications Server listening IP address must match the address that is returned by a Domain Name System (DNS) query on the Mediation Server’s FQDN. If the two addresses do not match the IP address listed in DNS for your FQDN you will not be able to connect, and call traffic will be directed to an interface that is not listening for Office Communications Server traffic rather than to the one that is listening.

The Gateway listening IP address is the address on the Mediation Server that lists traffic from a basic media gateway or Basic Hybrid Media Gateway. For Office Communications Server 2007, this address corresponds to the network card that serves as the external edge of the Mediation Server.

Note:
It is possible to configure both edges on a single adapter card, but this alternative is not recommended.

For basic media gateways, the bandwidth requirement between gateway and Mediation Server is 64 kilobits per second (Kbps) for each concurrent call. Multiplying this number by the number of ports for each gateway is a fair estimate of the required bandwidth on the gateway side of the Mediation Server. On the Office Communications Server side, the bandwidth requirement is considerably lower.

When configuring Mediation Server, you are advised to accept the default media port gateway range of 60,000 to 64,000. Reducing the port range greatly reduces server capacity and should be undertaken only for specific reasons by an administrator who is knowledgeable about media port requirements and scenarios. For this reason, altering the default port range is not recommended.

High-bandwidth traffic such as voice and video tends to stress poorly provisioned networks. Limiting media traffic to a known range of ports makes troubleshooting such problems easier.

The settings that you must configure on your Basic Media Gateway are specified in the following list, but for information about howto configure these settings on a given gateway, refer to the manufacturer’s product documentation. Each gateway must be configured according to the vendor’s documentation. Depending on the vendor, there are potentially many attributes that must be set, but the attributes specific to Enterprise Voice are as follows:

• The FQDN and IP address of the Mediation Server that is associated with the gateway.
  
  
• The listening port (5060) that is used for TCP connections to the Mediation Server.
  
  

Important:
The previous settings must match those of corresponding settings for the Mediation Server. If the settings do not match, the connection between the gateway and Mediation Server will fail.

• SIP Transport – specify either TLS (recommended) or TCP.
  
  

Important:
If you specify TLS as the SIP transport to be used by your basic or basic-hybrid media gateway, you must also configure the corresponding Mediation Server for TLS.

• If the SIP transport for the link between the gateway and the Mediation Server is set to TLS, the gateway must be configured with a certificate for purposes of authentication during the mutual TLS (MTLS) handshake with the Mediation Server. The certificate on the gateway must be configured as follows:
  
  
  • The certificate may be directly signed by the trusted CA configured in the Mediation Server. Alternatively, a certificate chain may have to be traversed to verify the certificate provided by the gateway. The gateway must provide this chain as part of its TLS handshake with the Mediation Server.
    
    
  • The CN part of the subject field should be set to the FQDN of the gateway. If the FQDN in the CN part of the subject field does not match the expected and configured FQDN for the gateway, the certificate must also contain a subject alternate name (SAN) that lists the expected and configured FQDN for the gateway.
    
    The Mediation Server validates the certificate provided by the gateway by checking that the FQDN on the certificate exactly matches the gateway FQDN configured on the Mediation Server. If the FQDNs do not match, the session is terminated. Additional validation includes checking the signature and expiration date, and making sure that the certificate has not been revoked.
    
    
• If the SIP transport for the link between the gateway and the Mediation Server is set to TLS, separate ports must be opened for the TLS connection to the gateway and the TLS connection to the Office Communications Server pool. The port assignments should be configured as follows:
  
  
  • TLS link between media gateway and Mediation Server: 5060.
    
    
  • TLS link between Mediation Server and Office Communications Server pool: 5061.
    
    
• Each gateway must be configured so that the E.164 numbers routed by Enterprise Voice to the gateway are normalized to a locally dialable format.
  
  
• Each gateway must also be configured to pass only E.164 numbers to the Mediation Server. For details about how to normalize source phone numbers to E.164, see each gateway vendor’s documentation.
  
  
• Each gateway should be configured to convert the source number (the number presented as caller ID) to a normalized E.164 number. This ensures the caller ID can be matched to an Office Communicator contact, a Microsoft Office Outlook contact, or a member of the corporate directory, thereby enabling Office Communicator to provide additional information about the caller. This number will also appear in e-mail messages notifying the user of missed calls and voice mail, allowing the user to click the phone number in order to quickly return a call. If the number has been normalized by the gateway, no further processing is required. If for some reason the number cannot be normalized by the gateway, the normalization rules defined by the location profile will be applied when returning a call. It might be necessary to add normalization rules to a location profile to handle numbers that cannot be normalized by the gateway. For details about how to normalize source phone numbers to E.164, see each gateway vendor’s documentation.
  
  
• Each gateway should also be configured to convert numbers in E.164 format into a format that will be accepted on the PSTN network. For example, when +1425xxxxxx is dialed, the gateway should strip the +1425 if the gateway is in Redmond, because these prefixes are not required for a local call.
  
  

For a list of media gateway vendors, see http://go.microsoft.com/fwlink/?LinkId=125757 .