Conferencing Components on the Front End Server

Focus

The Focus is the conference state server. It is implemented as a SIP user agent that is addressable by using a conference URI. The Focus runs in the User Services module of all Front End Servers. All group IM, multiparty A/V, and data collaboration sessions are managed on the server by the Focus.

The Focus is responsible for the following tasks:

• Initiating conferences

• Enlisting required conferencing servers

• Authenticating participants before allowing them to enter a conference

• Enforcing the policy that specifies whether the meeting organizer is authorized to invite external users

• Maintaining SIP signaling relationships between conference participants and conferencing servers

• Managing conference state

• Accepting subscription to conferences and notifying users of changes in conference state, such as the arrival and departure of participants and the addition or removal of media

• Maintaining and enforcing conference policies and rosters

The Focus also enables the organizer to lock a meeting so that no more participants can enter after a certain time. For more information about how the Focus manages the lifetime of the meeting, see Meeting Deactivation and Meeting Expiration (both sections are in On-Premise Web Conferencing).

Focus Factory

The Focus Factory is responsible solely for scheduling meetings. When a user creates a new meeting, the meeting client sends a SIP SERVICE message to the Focus Factory, which creates a new instance of the meeting in the conference database and returns information about the newly created meeting to the client. A separate instance of the Focus exists for each active conference.

Conferencing Servers (MCUs)

Supporting multiparty conferences requires a new server role known as a conferencing server (also known as an MCU or multipoint control unit). A conferencing server is a pluggable component that is responsible for managing one or more media types. Office Communications Server 2007 includes four conferencing servers and the extensible architecture for adding more:

• IM Conferencing Server. Enables group IM by relaying IM traffic among all participants. When a third participant is added to a peer-to-peer IM conversation, the initiating client invites the IM Conferencing Server to the conversation. From that point, all messages among the participants are routed through the IM Conferencing Server. The IM Conferencing Server is an integral part of the Front End Server and cannot be installed on a separate computer.

• Telephony Conferencing Server. Responsible for ACP (audio conferencing provider) integration. Supports both dial-out and dial-in, as well as standard third-party call control features such as mute and eject. The Telephony Conferencing Server does not support mixing VoIP and PSTN in the same call. To connect dial-out to PSTN endpoints, a Mediation Server is required, as described later in this overview. The Telephony Conferencing Server is an integral part of the Front End Server and cannot be installed on a separate computer.

• Web Conferencing Server. Manages conference data collaboration, including native support for Microsoft Office PowerPoint presentations, Microsoft Office document sharing, white boarding, application sharing, polling, Q&A, compliance logging, annotations, meeting summaries, handouts, and various multimedia formats. The Web Conferencing Server uses PSOM (Persistent Shared Object Model), a Live Meeting protocol, for uploading slides to a meeting. The Web Conferencing Server can reside either on the Front End Server (Standard Edition and Enterprise Edition Consolidated Pool) or on a separate physical computer (Enterprise Edition Expanded Pool).

• A/V Conferencing Server. Provides multiparty IP audio and video mixing and relaying, including Microsoft RoundTable, by using industry standard RTP (Real-time Transport Protocol) and RTCP (Real-time Transport Control Protocol). The A/V Conferencing Server can reside either on the Front End Server (Standard Edition and Enterprise Edition Consolidated Pool) or on a separate physical computer (Enterprise Edition Expanded Pool).

Conferencing Server Factory

When the Focus requests a particular conferencing server for a meeting, the Focus sends the request to Conferencing Service Factory, which determines which conferencing server is available to service the request and returns its URL to the Focus. The Conferencing Server factory is responsible for provisioning a meeting for a particular media type on a Conferencing Server by using the local policies for creating meetings. A Conferencing Server factory provisions meetings according to local policies and takes into account the current load on the Conferencing Servers before assigning one to a meeting.

Other Server Components Required for Conferencing

Other important Front End Server components include the following:

• SIP Proxy. The SIP Proxy (also known as the protocol stack or SIP stack) is the core protocol platform on which all other services are built. It provides the basic structure for networking and security and performs connection management, message header parsing, routing, authentication, and state management.

• HTTP.SYS. The IIS (Internet Information Services) kernel-mode HTTP protocol stack. HTTP.SYS queues and parses incoming HTTP requests and caches and returns application and site content. IIS can reside either on the Front End Server (Standard Edition and Enterprise Edition Consolidated Pool) or on a separate physical computer (Enterprise Edition Expanded Pool).

• User Services. Provides closely integrated IM, presence, and conferencing features built on top of the SIP Proxy. It also includes the Focus and Focus Factory.

• User Replicator. Updates the user database to be synchronized with Active Directory. The Address Book Server uses information provided by User Replicator to update information from the global address list.

• Server API. Provides basic scripting capability for creating custom message filters and routing applications. The scripts can either run in process or, where required, can be dispatched to a managed code application that is running in a separate process.

• RTC Aggregate Application. Handles the aggregation of presence information across multiple endpoints.

• Address Book Server. Provides global address list information from Active Directory to the Office Communicator client. Address Book Server was introduced with Live Communication Server 2005 SP1 as an optional separate application to be installed and managed separately. With Office Communications Server 2007, Address Book Server is mandatory and installed at the same time as other Front End Server components.

• Outbound Routing Application. Manages all SIP message routing for Office Communications Server 2007.

• Intelligent IM Filter. Filters incoming IM traffic by using administrator-specified criteria. It is used to block unsolicited or potentially harmful IM items from unknown endpoints outside the corporate firewall.

Internet Information Services (IIS)

Office Communications Server 2007 requires IIS either on every Front End Server (Consolidated Configuration) or on separate dedicated computers (Expanded Configuration). Office Communications Server 2007 relies on IIS for the following functions:

• The Live Meeting 2007 client uses IIS to download meeting content (such as PowerPoint presentations).

• Office Communicator uses IIS to download Address Book Server files when the client is outside the corporate firewall.

• An ASP.NET application running on top of IIS is used for the Group Expansion Web Service, which enables Office Communicator to expand distribution groups for purposes of group IM.

In Enterprise Edition: Expanded Configuration, IIS can be installed on computers that are separate from the Front End Servers. Multiple IIS servers must be fronted by a hardware load balancer.