Connecting Users with Office Communications Server 2007

Alan Maddison


At a Glance:

  • Office Communications Server architecture
  • Conferencing features
  • Enterprise Voice
  • Enhanced Presence

Unified communication is here. The impending launch of Office Communications Server 2007 will provide a complete overhaul of the experience available though Live Communications Server 2005. In addition to architectural and administration improvements, Office

Communications Server 2007 includes a new client, Office Communicator. It also features new and enhanced capabilities such as Enterprise Voice, on-premise Web conferencing, enhanced presence and instant messaging, and federation. Combined, these features provide the platform for the Microsoft® Unified Communication strategy, and promise to improve productivity and enhance long-distance collaboration.

This update also includes a streamlined Microsoft Management Console (MMC) snap-in interface. Figure 1 shows one of the new administrative enhancements for performance counters.

Figure 1 The new MMC snap-in includes performance counters

Figure 1** The new MMC snap-in includes performance counters **(Click the image for a larger view)

The new Office Communications Server 2007 comes in two editions: Standard and Enterprise. Office Communications Server 2007 Standard is ideal for deployments involving fewer than 10,000 users. In a Standard edition deployment, a single front-end server would host all of the services.

For larger deployments, the Enterprise edition is available and can be deployed in either a consolidated or expanded configuration. In a consolidated topology all of the hardware is arranged in a single pool of front-end servers. For maximum scalability, you can use the expanded configuration, which allows you to use dedicated Web servers running Internet Information Services (IIS), Web conferencing, and audio/visual (A/V) conferencing servers outside of the enterprise pool of front-end servers. Figure 2 shows an expanded configuration topology.

Figure 2 Expanded configuration topology

Figure 2** Expanded configuration topology **(Click the image for a larger view)


The Office Communications Server 2007 architecture is built upon a foundation of core servers: front-end servers, edge servers, and application servers. Front-end servers provide user authentication, address book maintenance, presence management, conference management, and application hosting, as well as signal handling among servers and clients, media management (including file sharing), and routing of instant messaging (IM) and conferencing traffic.

The core conferencing functionality of Office Communications Server 2007 is provided through a series of integrated servers also known as multipoint control units (MCUs). Figure 3 provides a summary of these servers and their roles.

Figure 3 Conferencing servers and their functions

Conferencing Server (MCU) Supported Functionality
Instant Messaging Enables group IM by routing IM traffic among participants. Integrated into the front-end server and cannot be installed on a separate server.
Telephony Enables support for inbound and outbound dial tone. Integrated into the front-end server and cannot be installed on a separate server.
Web Responsible for collaboration functionality such as white­boarding, application sharing, and Q & A. This server also provides support for Office document sharing and PowerPoint presentations. Can be installed on the front-end server or in the expanded pool configuration on a separate server.
A/V Used for multiparty IP audio/video mixing and relaying. Can be installed on the front-end server or in the expanded pool configuration on a separate server.

Another important function of the front-end server is as host to the address book server. Those of you familiar with Live Communications Server 2005 SP1 will recognize this service. In Office Communications Server 2007, it plays a central role and is now no longer an optional component. The address book server consists of two components: the address book service and the address book file store. This server is responsible for providing contact information from both internal and external sources. The Global Address List and distribution lists from Active Directory® and Exchange Server are typical examples of internal sources. External sources include users from federated partners or public IM contacts.

Office Communications Server 2007 enhances the external user connectivity introduced in Live Communications Server 2005 and allows external users to participate in on-premise conferences. This additional functionality requires two new edge servers: Web conferencing edge server and A/V edge server. In another change, what was formerly the access proxy server is now known as the access edge server. The Office Communications Server edge servers are designed to be placed in your network perimeter (screened subnet) and provide critical external user connectivity. Figure 4 provides a summary of the edge server roles and what they are used for.

Figure 4 Edge server roles

Server Supported Functionality
Access edge server Federation; remote user connectivity; Public IM Connectivity (PIC).
Web conferencing edge server External Web conferencing.
A/V edge server A/V conferences and point-to-point A/V calls with external users.
Reverse proxy server Group expansion, address book file download, Web conferencing access to meeting content. Not strictly an Office Communications Server role, but provides critical functionality. ISA Server 2006 can also provide reverse-proxy functionality.

In addition to the integrated servers described previously Office Communications Server takes advantage of various application servers to perform essential functions such as authentication, storing conference metadata, and providing distribution list functionality. The application servers commonly used with Office Communications Server include IIS, certificate servers, global catalog servers from your Active Directory environment, SQL Server® 2005, Exchange Server 2007, and file servers.

IIS is used to provide access to meeting content, address book updates, expansion of Active Directory distribution groups for IM, expansion of Outlook® distribution lists for external users, and to facilitate the underlying communication between Office Communications Server components.

Certificate servers play a crucial role within Office Communications Server in terms of securing both client/server communication and server/server communication. If you use an internal enterprise certificate server, all internal clients and servers must trust the issuing certificate authority (CA). As such, each CA certificate chain must be installed in the Trusted Root store on each computer. If you use Office Communications Server federation services, then your partner organization must do the same.

Conference participant authentication is supported by the global catalog servers in your Active Directory environment. For internal and federated users your global catalog servers will use Kerberos for authentication. Remote users employed by your company will use their Active Directory credentials over NTLM and anonymous users will be authenticated using Digest Authentication.

SQL Server 2005 is used to maintain state data about conferences, user registration and presence information. In the event of a failure, you can quickly restore a meeting by using the data stored in SQL Server, thus providing a quick and reliable method of recovery without loss of content.

Exchange Server 2007 and its unified messaging features provide an important adjunct to Office Communication Server 2007 via the inclusion of voice messaging and auto attendant capabilities.

File servers are used for storing data that needs to be accessed by clients. For example, the physical files required by clients when downloading the address book are stored on a file server. Likewise, additional meeting content is also stored on a file server.

The underlying protocol architecture of Office Communications Server 2007 is based on a mix of standard Internet protocols and Microsoft protocols. For instance, Session Initiation Protocol (SIP) is used extensively for functionality such as IM, conferencing, and presence subscriptions. The protocols used by the various components of Office Communications Server provide the maximum amount of power and flexibility. Figure 5 provides a summary of the core protocols and their use.

Figure 5 Protocols and their usage

Protocol Supported Functionality
Hypertext Transfer Protocol (HTTP) Client access, downloading meeting content, and address book data. Also used for communication between the conferencing servers and Focus, a component of Office Communications Server.
Session Initiation Protocol (SIP) Session creation and management by the various components of Office Communications Server, including Enterprise Voice, IM, conferencing servers, and enhanced presence.
Centralize Conference Control Protocol (CCCP) A custom protocol used for establishing and controlling of conferences and conference clients.
Persistent Shared Object Model (PSOM) A custom protocol used in the transport of Web conferencing content, including security keys and user roles and rights.
Real-Time Transport Protocol (RTP) Delivery of real-time data. Within Office Communications Server 2007, it provides the transport mechanism for Enterprise Voice and A/V conferencing.
Secure Real-Time Transport Protocol (SRTP) Security services such as encryption, message authentication, and integrity for RTP data. Within Office Communications Server 2007 it is used for the secure transport of audio and video content to media devices such as microphones and speakers.
Real-Time Transport Control Protocol (RTCP) Used together with SRTP to convey information about the signal quality of A/V conferencing sessions among media devices.

Enterprise Voice

Enterprise Voice is the Microsoft implementation of Voice over Internet Protocol (VoIP) telephony and is the single most significant addition to the product. Based on an implementation that uses Session Initiation Protocol (SIP) for signaling and Real Time Protocol (RTP) for voice traffic, Enterprise Voice allows you to make and receive calls from PC to PC as well to any other phone. In addition, Enterprise Voice provides functionality such as call control and routing and number normalization. There is support for the Public Switched Telephone Network (PSTN) and interoperability with Private Branch Exchanges (PBXs) that support either SIP, Computer-Supported Telecommunications Applications (CSTA) or that interface directly with the Office Communications Server 2007 API.

Office Communications Server 2007 can be deployed without significant alterations to your existing voice infrastructure while still allowing you to achieve significant benefits. As such, Enterprise Voice supports three deployment configurations: SIP–PBX, SIP–IP–PBX, and IP-PSTN.

In the SIP–PBX setup, all remote calls are controlled by the PBX and you maintain your existing telephones. This integration is made possible by the Remote Call Control (RCC) gateway and CSTA.

The SIP–IP–PBX configuration takes advantage of the IP-PSTN gateway, which eliminates the need for CSTA and allows the Office Communicator client to dial numbers and control the IP-PBX phone. If you do not have existing handsets you can configure Office Communicator as a "softphone."

Deploying Office Communications Server 2007 with the IP-PSTN component allows you to route call controls to the front-end servers. Office Communicator can interface with VoIP or Microsoft-certified third-party SIP endpoints (in many organizations this endpoint is typically a handset) to make and receive calls over the Internet.

Media gateways are third-party gateways that provide signaling and media conversion between VoIP and the PSTN. Office Communications Server 2007 supports three types of media gateways, which can be categorized as basic, advanced and basic hybrid. In order to support gateways other than advanced, Office Communications Server 2007 offers the Mediation Server role, providing critical protocol and media translation functionality. Remote office integration is also possible using the components available with Office Communications Server.

As with other components of Office Communications Server 2007, Enterprise Voice relies on edge servers to provide external user connectivity. Specifically, the access edge server is required (for its role in SIP signaling) for users outside the corporate perimeter, while the A/V edge server allows external users accessing voice or video services to connect through perimeter network services such as your firewall and Network Address Translation (NAT) implementation.

Although Enterprise Voice will ultimately support a large number of clients, the currently recommended client for Enterprise Voice is the latest version of Office Communicator. In addition, Microsoft and its partners have announced plans for new VoIP phone hardware that will integrate with Office Communications Server.

Enterprise Voice also integrates with the Unified Messaging role of Exchange Server 2007, offering a single interface for voice mail, e-mail, calendars, contacts, and receipt of faxes that is accessible from either a telephone using Outlook Voice Access or from a computer. In addition, Unified Messaging provides auto-attendant services, which gives you the means to implement an automated phone menu system.

Enhanced Presence

The concept of presence that you may be familiar with from Live Communications Server 2005 has been extended and enhanced in Office Communications Server 2007. In general, presence is associated with the status and availability of users. In Office Communications Server, the supporting infrastructure has created a richer experience with improved granularity for configuring presence-related information.

Users now have the option of selecting from six different status modes: status can be set to Online, Busy, Do Not Disturb, Be Right Back, Away, or Appear Offline. Users also have the ability to customize this status with additional information. For example, if a user's status is set to Do Not Disturb, the user can provide additional information as to why they should not be disturbed.

Enhanced presence also permits users to filter the information that is displayed to other users through the use of five optional presence levels: these presence levels are Personal, Team Members, Workplace, Public, and Block. These levels provide a hierarchical approach to presence management. For example, the Personal presence level allows contacts the greatest amount of flexibility by permitting such actions as contact through IM even when the user's status is set to Busy. Presence levels also control the amount of information that is displayed to contacts.

Furthermore, when using the Office Communicator, a user is able to set their location status, which can be a custom location or one of the default choices of home or office. Location information is available to contacts classified as Personal or Team.

While the enhancements to presence are welcome and will prove themselves in terms of streamlining communications, it is the underlying infrastructure of Office Communications Server and the presence engine that will have the biggest impact on organizations. For example, Office Communications Server 2007 comes with the Member Web Part, an Office SharePoint Server 2007 Web Part, that allows users to view the presence of other users associated with a SharePoint Web site or portal. This Web Part can be easily added to your SharePoint sites to facilitate presence information across your critical collaboration infrastructure.

Presence information is integrated into the entire Microsoft® Office 2007 application suite through the use of document workspaces and smart tag action buttons. For example, smart tag action buttons can display the status, contact, and calendar information of users. Users can employ the smart tag actions to share work, schedule meetings or start an IM conversation.

On-Premise Conferencing

Another significant improvement in Office Communications Server 2007 is the on-premise conferencing capability. The ability to host real-time conferences with internal or external users (anonymous or federated) should be a valuable tool for many organizations. These conferences can be scheduled or ad hoc and can include IM conferences, A/V conferences, and Web conferences as well as other collaborative tools such as file sharing, whiteboarding, slide annotation, participant polling, and participant Q&A sessions. Office Communications Server also supports transitioning from one type of conference to another. For example, a user can choose to add collaboration to an existing IM session and create an ad hoc conference.

While Office Communicator is the recommended client for conferencing, Office Communications Server 2007 also supports Office Live Meeting 2007 and Office Live Meeting Add-In for Outlook 2007. Office Communicator 2007 supports IM, A/V session participation, application sharing, whiteboarding, and file transfer. Office Live Meeting 2007 includes support for conference participation as well as schedule sessions, record sessions, participant polling, and Q&A.

Office Live Meeting 2007 Add-In for Outlook 2007 includes support for conferencing tasks using Outlook 2007 as well as the ability to designate individual participants as attendees or presenters and to send separate invitations to the different roles. In addition to users holding the role of Organizer, Presenter or Attendee, they are also categorized as belonging to an internal or external user groups based on their location and credentials. Internal users have an Active Directory logon and are on the corporate LAN. External users are subdivided into three categories: Remote, Federated, and Anonymous.

Remote users denote anyone with an Active Directory account within an organization. This could include remote workers or contractors. All remote users can host, join, and present conferences.

Federated users have credentials defined by the establishment of a federation within Office Communications Server. Federated users can attend meetings and act as presenters, but they cannot organize a meeting.

Anonymous users are the most restricted group; they can only attend meetings to which they have been invited.

To provide an additional layer of security for any given meeting, it is possible to specify different types of entry control settings. Office Communications Server 2007 provides the following: open authenticated, closed authenticated, and anonymous.

An open authenticated meeting allows any remote or internal user with an Active Directory login to join. Any federated user can also join. A closed authenticated meeting restricts the meeting to those users invited by the meeting organizer. Federated users cannot participate in the meeting.

An anonymous meeting is open to anyone who receives an invitation. To join, a user must present a conference key and pass Digest authentication in order to have his credentials verified. Unless promoted to presenter after joining, an anonymous user can only be an attendee. Some of the available settings are shown in Figure 6.

Figure 6 Meeting settings

Figure 6** Meeting settings **(Click the image for a larger view)

Dialing In

By streamlining communications, integrating different communication mediums, and putting control in the hands of the user, Office Communications Server 2007 has the potential to revolutionize the way your company works. The concept of contextual communications, where both presence information and a means to communicate are embedded within the application, will be the basis for this revolution. If Office Communications Server 2007 is not in your lab, it should be.

For more information about Office Communications Server 2007 and to try the beta, take a look at the TechNet Office System TechCenter at Also, be sure to check out the Unified Communications Group Team Blog at

Alan Maddison is a Senior Consultant at MTI Technology Corporation. His primary focus is on Active Directory, Exchange Server, and virtualization.

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