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Overview of Pool Components

Microsoft Office Communications Server 2007 and Microsoft Office Communications Server 2007 R2 will reach end of support on January 9, 2018. To stay supported, you will need to upgrade. For more information, see Resources to help you upgrade your Office 2007 servers and clients.

Office Communications Server supports the following three scenarios or workloads: instant messaging (IM) and presence, conferencing (including Web conferencing, desktop sharing, audio/video conferencing), and Enterprise Voice, which encompasses telephony. This section describes all of the architectural components of an Office Communications Server 2007 R2 Standard Edition server or Enterprise pool. Collectively, these components support all three workloads.

This section focuses on the services that run on the core Office Communications Server roles, the components within those services, and relationships between them. This section does not cover network architecture or deployment architecture, which complement component architecture. For details about those aspects of architecture, see the Office Communications Server 2007 R2 Planning Guide documentation.

While this section describes components in the context of an Enterprise pool, it also applies to most aspects of a Standard Edition server. All server components (that is, services, database, and so on) described in this section run together on a single instance of a Standard Edition server. This is a typical configuration for simple or relatively small deployments (that is, up to a few thousand users) where high availability is not a requirement.

Conceptually, a pool consists of one or more Front End Servers and one or more databases on the Back-End Database Server with a single SQL Server. In a pool, all persistent states are stored in the database on the Back-End Database Server, so that when a Front End Server component fails, failover can be quick. Figure 1 shows a sample Enterprise pool.

Figure 1. Sample Enterprise pool

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Figure 1 illustrates the components of Front End Servers and the Back-End Database Server. There is a hardware load balancer for the Front End Servers, which are required for an Enterprise pool that has more than one Enterprise Edition server. (If your pool consists of only one Front End Server, which is connected to a separate Back-End Database Server running SQL Server, a load balancer is not required.) All Front End Servers in a consolidated configuration pool are homogeneous and identical to each other. Therefore, all relevant Office Communications Server services and applications are installed on all Front End Servers in this type of a pool.

On each Office Communications Server 2007 R2 Front End Server, the main components can be classified as follows:

  • Common infrastructure components. These components are required for the operation of any Office Communications Server workload, and provide a foundation for conferencing and voice components. The common infrastructure components include:

    • RTCSrv. This is the main Office Communications Server service that runs the Office Communications Server Session Initiation Protocol (SIP) stack, performs presence functions, performs directory replication functions and interfaces with the database, hosts application interfaces, and has modules to capture archiving and call detail recording (CDR) data.

    • Back-end database. This is a SQL persistent store with information on user identities and capabilities that are replicated from Active Directory, user contact lists, and dynamic presence and conferencing data.

    • RTCHost. This process hosts several Office Communications Server applications for presence, conferencing, and Enterprise Voice that are required for core functioning of these scenarios.

    • OCS Application interfaces. These interfaces enable the applications on RTCHost (as well as third-party applications built on the same API) to interface with the main server process RTCSrv (for example, to inspect the SIP stream).

    • Web Components infrastructure. This infrastructure, which is built on Microsoft Internet Information Server (IIS), hosts various HTTP components required for presence, conferencing, and Enterprise Voice functions.

    • UCAS infrastructure. The Unified Communications Application Services (UCAS) infrastructure enables Office Communications Server to host robust, scalable, middle-tier server endpoint applications. Several UCAS applications for Enterprise Voice are hosted by this infrastructure.

  • Conferencing components. These components include various conferencing-specific components hosted by the common infrastructure discussed previously (for example, an RTCHost application, several web components), as well as a set of conferencing servers which perform mixing functions for IM conferencing, Web conferencing, desktop sharing conferencing, and audio/video conferencing.

  • Voice components. These are the additional Office Communications Server components required for enterprise telephony functions. These components include RTCHost applications for inbound telephony routing, outbound telephony routing, and phone number normalization, as well as UCAS applications for dial-in conferencing, response groups (that is, similar to Automatic Call Distribution for Voice), and Outside Voice Control (which extends enterprise telephony functionality to cellular phones).

Each of these classes of components is described in the topics that follow.