A conferencing server is responsible for mixing and managing one or more media types. The following types of conferencing servers are included in Office Communications Server 2007 R2:
- Web Conferencing Server for data collaboration.
- A/V Conferencing Server for audio and video.
- Instant messaging (IM) Conferencing Server for multiparty IM.
- Telephony Conferencing Server for interfacing with audio
- Application Sharing Server for multiparty or Communicator Web
Access-based application sharing.
The architecture allows the addition of other conferencing servers as needed in the future. The IM Conferencing Server, Application Sharing Server, and Telephony Conferencing Server can only be installed as part of a Front End Server, but you can install A/V Conferencing Servers and Web Conferencing Servers independently of other components.
Web Conferencing Servers, A/V Conferencing Servers, and IM Conferencing Servers each have two logical components: a media controller and a media processor.
MC (Media Controller)
The media controller on a conferencing server is responsible for managing the control commands between a Focus and a conferencing server.
MP (Media Processor)
The media processor is responsible for media management (for example, mixing, relaying, and transcoding). In a Web Conferencing Server, the media processor is a software component that is responsible for managing data collaboration for Office Communications Server. In an A/V Conferencing Server, the media processor mixes audio streams, switches video streams, and converts the media for clients who are on slow links. Of all the conferencing components, the media processor can be the most CPU and network intensive component. In our architecture, a media controller and media processor are collocated on the same computer to simplify deployment.
A/V Conferencing Server
The A/V Conferencing Server enables multiparty audio and video mixing and relaying capabilities. It is built on industry standard real-time transport protocol (RTP) and real-time transport control protocol (RTCP).
The A/V Conferencing Server also incorporates elements of the Internet Engineering Task Force (IETF) drafts for Interactive Connectivity Establishment (ICE) as a means to enable the exchange of media between two or more clients that are using Network Address Translators (NATs). ICE is an extension to Session Description Protocol (SDP) that enables media streams to traverse NATs by including in the SDP multiple IP address and port combinations for a particular transport protocol, known as candidate transport addresses, that the client can use to communicate with other clients. In an Office Communications Server environment, a client uses Session Traversal Utilities for NAT (STUN) and Traversal Using Relay NAT (TURN) protocols to obtain its candidate transport addresses from the Office Communications Server A/V Conferencing Edge Server. During negotiation, clients on either end exchange SDPs and then test candidate addresses for peer-to-peer connectivity. After the connectivity checks, clients renegotiate by including only the candidate transport address that succeeded in the SDP for a SIP re-INVITE request and response.
For details about IETF drafts for ICE, see “Interactive
Connectivity Establishment (ICE): A Protocol for Network Address
Translator (NAT) Traversal for Offer/Answer Protocols” at
Web Conferencing Server
The Web Conferencing Server adds data collaboration functionality to Office Communications Server. The Web Conferencing Server is built on the same Persistent Shared Object Model (PSOM) technology that is used by the Live Meeting service. Both signaling and media are sent to and from a Web Conferencing Server using the PSOM protocol. The Web Conferencing Server supports Live Meeting features, such as Microsoft Office PowerPoint presentations, document presentations, chat, voting, white boarding, and application sharing.
The Web Conferencing Server uses shared folders on a file system to store conference state and conference contents. Universal Naming Convention (UNC) paths are configured on the Web Conferencing Server to refer to the shared folders, which are created by an administrator during Office Communications Server deployment. These folders for conference metadata and conference content can be located on the same computer as the Web Conferencing Server or, preferably, on a dedicated computer.
For information about the way that a Web Conferencing Server works, see Web Conferencing Server for Office Communications Server 2007 R2.
IM Conferencing Server
The IM Conferencing Server is installed automatically on the Front End Server. The IM Conferencing Server enables multiparty instant messaging (IM). The IM Conferencing Server uses SIP for signaling and media.
Telephony Conferencing Server
The Telephony Conferencing Server is installed automatically on the Front End Server. The Telephony Conferencing Server enables Office Communications Server to communicate with audio conferencing providers.
Application Sharing Server
The Application Sharing Server is a new conferencing server role introduced in Office Communications Server 2007 R2, and is used specifically for multiparty desktop sharing from the Office Communicator client and desktop sharing from the Communicator Web Access client. The Application Sharing Server uses the Remote Desktop Protocol (RDP), with RTP as the transport for remote access scenarios.
Although the Web Conferencing Server also supports Application Sharing (that is, by using the PSOM protocol and the Live Meeting client), the Application Sharing Server provides desktop sharing functionality that users can access directly in Office Communicator and Communicator Web Access, instead of requiring users to start the Live Meeting client separately.