Is Microsoft Office Communications Server your next IP PBX?

OCS shines with Office Communicator 2007 front end and Exchange 2007

Microsoft is getting ready to make a big splash into the VoIP pool with its OCS 2007, expected to ship this summer.

When OCS's software-based VoIP engine is coupled with Microsoft Office Communicator 2007 client software, users have access to IP telephony, instant messaging and presence awareness. Furthermore, when Microsoft Exchange 2007's unified messaging services (see story detailing these capabilities) are added to the mix, voice mail and autoattendant features also are on the table.

The pieces add up to a solid foundation for presenting voice at the desktop. Microsoft is quick to point out that it is not proposing to replace the traditional IP PBX with this combination; rather, it touts its standards-based Session Initiation Protocol (SIP) ties for trunking and communications with traditional PBX systems. To that end, we note that some core IP PBX features, such as call park and whisper page, are not available in this version of OCS, nor are many of the call-routing and -handling features of traditional IP PBX back-end systems.

How does OCS stand up as an IP PBXWhen run in combination with the Office Communicator 2007 client and Exchange 2007 at the back end, Microsoft's new Office Communication Server (OCS) 2007, aims to deliver a formidable voice communications platform. This chart shows which of the 15 IP PBX features we'd consider necessary for a basic IP PBX platform to succeed in an enterprise deployment.
Basic call conferenceYes
Call dropYes
Call forward allYes
Call holdYes
Call park/retrieveNo
Group pickupNo
Call transferYes
Multiple line appearanceYes1.
Caller IDYes
Last number redialYes2.
Message waiting light/indicatorYes
Missed call indicatorYes
Music on holdNo
One-button speed dialYes3.

1. User can be logged into OCS from multiple computers, each running Office Communicator at the same time. A call that comes in for that user will ring at all computers.

2. The last numbered called is added to the recent contacts within Office Communicator.

3. There are no "Speed Dial" buttons. Users can add individuals to their "Contacts" list in Office Communicator and with a single click call that contact.

That said, taking into account the IP-telephony focus the combination -- OCS 2007, Office Communicator 2007 and Exchange 2007 -- offers Microsoft shops, our testing of the public beta code evaluates how far Microsoft does go in terms of providing enterprise-ready IP PBX capabilities.

All testing was conducted by Miercom engineers in our central New Jersey lab. We looked at the general setup and administration of OCS along with its back-end features and endpoint offerings. We also took into account the voice quality and user experience for calls placed with Office Communicator 2007 in conjunction with OCS.

Overall, this combination lets users choose the best means of communication required at any given moment from within a single application. The overall desktop experience was intuitive and simple, as facilitated by Office Communicator 2007. While lacking the advanced features noted earlier, OCS 2007 did provide the core fundamental telephony features the majority of users need. The voice quality was suitable for business communications. On the administrative side, the integration of OCS 2007 with Active Directory and Exchange 2007 kept daily tasks centralized, such as account creation and enablement for OCS services.

We downloaded a copy of the OCS 2007 beta and installed it in a test environment consisting of a Windows 2003 Domain Controller running on a server with a Pentium 4 2.6GHz processor with 2GB of RAM, an 18GB hard drive and Microsoft Windows 2003 R2 Enterprise Edition running on it; the required instance of Exchange 2007 running on a second server with the same specs and Microsoft Windows 2003 R2 Enterprise x64 Edition; and several Windows XP clients running Office Communicator 2007 beta code.

There were no other IP hard- or soft phones that supported Microsoft's Real-Time codec when we conducted our testing. However, Microsoft since has announced partnerships with several vendors to develop additional endpoints. To have used any other SIP phone would have required a mediation server, SIP proxy and a more-extensive test-bed setup than we used for this preliminary testing.

OCS 2007 also requires Active Directory running in Native Mode, Domain Name Services, Microsoft's Certificate Authority, and Internet Information Server with Active Server Pages components.

We installed the enterprise edition, but OCS is available also in a standard edition for smaller installations that has all components loaded onto a single server. The enterprise edition is designed for higher capacities, letting companies spread components across a pool of servers. Functionally speaking, both editions are the same.

VoIP communication between the Office Communicator and the OCS occur via SIP. As with most IP PBX systems, the RTP streams travel directly between the endpoints, with call-control signaling going through the OCS. We loaded Office Communicator 2007 on two client machines and specified the user credentials and the OCS name. Once logged on, we were immediately able to place calls and send instant messages between clients. The voice quality was very clean and responsive.

To optimize voice quality over the internal network and the public Internet with minimal user and administrator intervention, Microsoft has developed a new codec called Real-Time. This adaptive codec automatically adjusts the sampling rate depending on the bandwidth available. Microsoft says it is certifying gateway partners that will support the Real-Time codec directly. For noncertified gateways, an instance of Microsoft's Mediation Server, a component of OCS 2007, provides transcoding services (converting Real-Time packets to G.711 or another codec supported by the gateway).

Among the enhancements to Office Communicator 2007 over its predecessor, Communicator 2005, are richer presence awareness and soft-phonelike VoIP features. Some of these enhanced VoIP features are call-control functions -- including call deflect, call forwarding, call hold, call transfer and call waiting -- which are supported by OCS 2007 at the back end.

Users can set call forwarding to a specific number or to ring an additional number simultaneously. Alternatively, unanswered calls can be directed to voice mail or a secondary phone number. A call log of incoming, outgoing and recent calls is stored in a conversation-history folder in Outlook for the clients and as call-detail records on the OCS. These represent the basic features every user would expect.

All the features were straightforward and easy to implement. With Office Communicator 2007, they were presented logically and intuitively. New calls are shown as a pop-up at the bottom of the screen. We could accept the call or immediately deflect it. Office Communicator 2007 indicates when call forwarding is activated, and we could quickly change what number it went to. During a call the call-hold and call-transfer options were self-evident.

An administrator can restrict a user centrally to making or receiving only certain types of calls (for example, only U.S. calls). Calls also can be encrypted via Secure Real-time Transport Protocol. For interaction with an interactive voice-response system -- the menu tree (press 1 for sales, press 2 for marketing) you get when you call into companies -- dual-tone multifrequency digits can be generated. Again, these are fairly standard features for a PBX.

Office Communicator 2007 has some unique features compared with other soft-phone and unified-messaging clients we have tested. The call-context feature lets users add an importance ranking or subject to a call. This information is displayed to a call recipient using Office Communicator 2007. We could change this information any time during the call.

Call-sensitivity control lets users prevent other parties being added to the call. Because the VoIP features are part of Office Communicator 2007, users can add IM and video with a click of an icon once a call is established. We initiated conversations via IM and added voice and then video with the click of two icons. During a multiparty call we opened an IM session to specific users effective for offline conversation.

While this ability to pull in multiple modes of communication is not entirely unique to Microsoft, its implementation is certainly on the leading edge of unified communication options.

What further distinguishes the OCS-Office Communicator 2007 combination is desktop application integration. Anywhere presence information is displayed in Office applications, right-clicking the presences icon will reveal the call options, so the the user won't have to launch the call from a separate phone application.

Also common in PBX systems and available in OCS are voice mail and conferencing. We established a call and added users by dialing their extensions or selecting their names from the contacts-available menu. We also launched a predefined conference group and a conference call from a distribution list within Microsoft Outlook. A conference can include any mix of internal and external participants.

Voice mail is accomplished with Microsoft Exchange 2007 with the unified messaging feature. The OCS handles call processing, but messages are stored in users' mailboxes on the Exchange server and presented within their e-mail client. OCS handles voice mail completely within a unified messaging environment instead of a stand-alone or separate voice mail system, which eliminates the management of a separate voice=mail system.

Hommer is engineering manager and Smithers is CEO of Miercom. They can be reached at and, respectively.

NW Lab Alliance

Hommer and Smithers are also members of the Network World Lab Alliance, a cooperative of the premier reviewers in the network industry, each bringing to bear years of practical experience on every review. For more Lab Alliance information, including what it takes to become a member, go to

Learn more about this topic

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Copyright © 2007 IDG Communications, Inc.

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