2.1 Overview


Communications Server is used to provide unified communications for real-time multimedia communications and collaboration. Communications Server is an enterprise software server solution that provides four different workloads in an integrated and unified user experience: instant messaging (IM) and presence, applications sharing, audio/video and Web conferencing, and enterprise voice. Voice over IP (VoIP) is part of enterprise voice, but enterprise voice also includes voice-specific server applications. Each workload uses different protocols and performs different functions.

Communications Server operates under the common client-server architecture, where a protocol client connects to Communications Server using the Session Initiation Protocol (SIP) . The protocol client initiates communications with other protocol clients that Communications Server establishes by using signaling and control channel protocols. Once the communication channel is established between two or more parties, the communication workload is transferred by using the media protocols.

Behind the simplicity of the client-server architecture lies a vast set of functionality that spans from basic storage to accessing, updating, and synchronizing user information configured in Active Directory (SIP URI, phone number, home server, and so on), presence information, in-band provisioning settings, and address book data.

The protocol clients that interoperate with the protocol server perform tasks such as subscribing to presence information of remote users (contact), updating the local user’s presence, initiating and accepting communication workloads (instant messaging, Web conferencing, application-sharing, audio/video, and voice calls) with other protocol clients, and requesting ancillary supporting services (such as address book downloads and distribution list expansion).

Systems that interface with Communications Server include both internal and external protocol clients, Communications Server servers from other organizations connected over a federated link, public Instant Messaging (IM) providers using Public IM Connectivity (PIC), SIP/public switched telephone network (PSTN) as well as Remote Call Control gateways, Exchange Unified Messaging servers, and server applications built using Communications Server’s Unified Communications Managed API (UCMA 2.0). Dependencies on these systems are listed in more detail in section 2.3.1.

Below are a high level architectural reference diagram(s) for the communications server and the component and protocol interactions for various workloads.

Communications server architectural reference

Figure 1: Communications server architectural reference


IM and presence workload

Figure 2: IM and presence workload

Application sharing workload

Figure 3: Application sharing workload

Enterprise voice workload

Figure 4: Enterprise voice workload

A/V and Web Conferencing Workload

Figure 5: A/V and Web Conferencing Workload