The basic building block of Office Communications Server 2007 R2 is the Standard Edition Server role. A Standard Edition Server includes all of the server roles that are required to provide presence, instant messaging (IM), and conferencing. The Standard Edition Server is both a Session Initiation Protocol (SIP) registrar and a SIP proxy, as defined in Request for Comment (RFC) 3261, in a single physical server. When installing a Standard Edition role, the Microsoft SQL Server Express database is automatically installed. This database stores data for all users who are enabled for SIP Communications. These users are "homed" on the Standard Edition Server.

The data that is stored for each user includes the following:

Contact information refers to the list of contacts and groups created by the user.

Permissions refer to whether contacts are allowed or blocked from viewing the presence state of users. Office Communications Server 2007 R2 uses an extensible permission model referred to as enhanced presence, which is described in Chapter 1.

Endpoints refer to each of the clients from which the same user is signed in to Office Communications Server. It is not uncommon for users to be signed in from multiple devices at the same time. Users might be simultaneously signed in to Office Communications Server from Microsoft Office Communicator on their desktop computers, from their laptops, from their smart phones running Microsoft Office Communicator Mobile, or from Microsoft Office Communicator Web Access running on Web browsers. The server tracks each of these endpoints to determine the most accurate presence state of the user. When an incoming invitation is sent to the user, Office Communications Server forks the invitation by sending the invitation to all of the user’s endpoints. When the user responds from one of her devices, the server stops forking incoming messages from that contact, and it routes all subsequent messages for this session to the device from which the user accepted the original invite. After the session is terminated, any new messages from the same contact or any other contact are again forked to all endpoints to which the user is signed in.

Subscription information tracks all of the contacts for which the user wants to get presence updates. Presence updates occur when one of the user’s contacts changes state, such as signing in to Office Communications Server, joining a phone call, and so on.

Figure 3-1 and Figure 3-2 show the Office Communications Server user settings stored in Active Directory. User information and global Office Communications Server settings stored in Active Directory are synchronized to the database by a component of the Office Communications Server service called the user replicator (UR). The UR reads information from the closest Active Directory global catalog (GC). If a GC is unavailable, the Standard Edition Server cannot start; or if it is already running, it will fail to synchronize any updates.

Figure 3-1. User settings

Figure 3-2. Advanced user settings

Because a Standard Edition Server maintains user information, it is important to periodically back up the database so that, in the event of a server failure, this data can be restored. Because of its scale, characteristics, and ease of deployment as a standalone server, the Standard Edition Server targets small- to medium-sized businesses or branch offices within large organizations. This topology is appropriate for organizations with fewer than 5,000 users or for pilot deployments where the main goals are simplicity and ease of management and where high availability is not a requirement.

Table 3-1 lists the system requirements for Office Communications Server 2007 R2, Standard Edition.