For integration with the existing telephone environment, a SIP/CSTA gateway is needed. This gateway is connected to the SIP/CSTA interface provided by the existing PBX. It is possible to have multiple SIP/CSTA gateways connected to Office Communications Server 2007 R2, but a user can be configured to a single SIP/CSTA gateway or PBX. Only one SIP/CSTA gateway per PBX node is recommended to avoid numbering-plan conflicts.

PBX-specific SIP/CSTA gateways and vendor-neutral SIP/CSTA gateways are available on the market. You need to select a SIP/CSTA gateway that supports your existing PBX if the PBX doesn’t offer a SIP/CSTA interface. Refer to your vendor’s SIP/CSTA gateway documentation for configuration.

To configure a user for RCC, you first need to enable the user for RCC in Active Directory by using the Active Directory Users and Computers Management Console. In the Office Communications Server 2007 R2 Active Directory snap-in under Advanced Settings, select the configuration option Enable Remote Call Control, as shown in Figure 9-2.

Figure 9-2. Enabling and configuring a user for RCC

You then configure a Server URI for the user. This Server URI points to the SIP/CSTA gateway. Office Communicator 2007 R2 sends its SIP call control messages to the SIP/CSTA gateway defined in the Server URI field. The syntax of the Server URI entered here must match the requirements of the SIP/CSTA gateway. (Please refer to the documentation provided by your SIP/CSTA gateway vendor.) Here are some examples of Server URIs:

The E.164 number is the phone number of the user in E.164 format (+<Country Access Code><Area Code><local number>, such as +14255550125), and the SIP/CSTA gateway fully qualified domain name (FQDN) is the FQDN of the SIP/CSTA gateway.

Finally, you configure a Line URI for the user. This URI is used to send call control information to and receive it from the SIP/CSTA gateway. The syntax must match the requirements of the SIP/CSTA gateway. (For more information, refer to the SIP/CSTA gateway documentation provided by the SIP/CSTA gateway vendor.) For example, the following syntaxes are common:

All SIP traffic from Office Communicator 2007 R2 goes through Office Communications Server 2007 R2 and is proxied by the server to the SIP/CSTA gateway. Office Communicator 2007 R2 sends its SIP INVITE and SIP INFO call control messages to this SIP/CSTA gateway, which is configured in the Server URI field. This must be the FQDN of the SIP/CSTA gateway. On Office Communications Server 2007 R2, for every Server URI, a route must be configured with the destination address to which Office Communications Server 2007 R2 must proxy SIP call control messages. You can configure this under pool-level settings on the Routing tab, as shown in Figure 9-3.

Figure 9-3. Configuring routes for Server URIs

For each route to a SIP/CSTA gateway, the following settings must be configured:

Phone numbers need to be normalized before they are presented to the client so that they can be used for resolving calling party information to a user name. The process of normalization converts the number into a global E.164 format that can then uniquely map to a single user in the directory. Because normalized numbers are globally unique and routable, they can also be shared with other Communicator users through presence and will work correctly when the Click to Call feature is used in Communicator to call these numbers.

The functionality of matching an incoming E.164 number to an entry in the Global Address List or local Outlook Contacts is called reverse number lookup (RNL). If Office Communicator 2007 R2 successfully applies RNL and finds a name that matches a calling party number, this name is presented to the user in the pop-up window and the Conversation window instead of the calling party number.

For the RCC scenario, Office Communicator 2007 R2 downloads these normalization rules as part of the Address Book Service (ABS) download. These rules are in the form of regular expressions. The normalization rules are applied to phone numbers in Outlook contacts so that these numbers can be dialed, and they are also used for RNL. Office Communicator also applies the normalization rules when a phone number is dialed manually from Office Communicator. The same regular expressions that Office Communicator downloads and applies are also used by Office Communications Server 2007 R2 for normalizing phone numbers that are stored in the ABS.

Some CSTA implementations on PBX provide these RNL functionalities. Thus, instead of or in addition to the calling party number, a display name is transmitted to Office Communicator on an incoming call. Office Communicator 2007 R2 ignores this display name because it is not possible for Office Communicator 2007 R2 to verify the authenticity of the name.

Depending on the implementation in the PBX, the calling party number can have the following formats:

If the calling party number string does not contain a number on an incoming call, Office Communicator 2007 R2 will not apply RNL.