Office Communications Server 2007 & Office Communicator 2007 Interoperability Specifications

Today, Jeff Raikes, the president of Microsoft’s Business Division, (my boss’s boss) did a keynote at VoiceCon and announced that we’re making the interoperability specifications for Office Communicator 2007 and Office Communications Server 2007 (OCS) available to our partners.  I’ve been writing that specification over the last few months, so I wanted to blog about what it really means.


I have been talking to a lot of customers about the upcoming Office Communications Server 2007 and Office Communicator 2007. A lot of the features, such as integration with Office applications, rich presence, anywhere access for VoIP and other media, etc. resonate with the customer very well. However, they also told us that they want their existing PBX to interop with OCS and Office Communicator, so they can enjoy the new OCS features without having to rip and replace the existing PBX, network or desk phones.   


OCS is actually designed to co-exist with PBX’s well.


First, OCS and Office Communicator continue to support the CSTA-based PBX interop model that we introduced with Live Communications Server 2005 and Office Communicator 2005. With this support, users can control the PBX phone inside Communicator to click to call, answer calls, set forwarding rules, etc. With the help from partner solutions, we cover a lot of PBXes on the market. Some of the PBX vendors also started to build native support of this feature into their PBXes.


Second, OCS extends interop story to include the new VoIP capabilities that are being introduced for the first time. With an off-the-shelf IP/PSTN gateway from one of our partners, customers can easily connect OCS with the PBX for PC-to-phone and phone-to-PC calls. The interface between OCS and the partner IP/PSTN gateway is just standard SIP and RTP/RTCP. In the case of IP/PBX or IP-enabled PBX, the PBX can talk to OCS directly with SIP and RTP/RTCP without requiring an IP/PSTN gateway. With the basic connectivity established, the admin can move extensions on the PBX to OCS depending on the business needs. For example, IT can move the working-from-home users to OCS while keeping the other users on the PBX. This way, IT can solve the business needs for the home users while getting the most out of the existing PBX. The admin can use the same approach to move groups of internal users to OCS for pilots and departmental deployments. After the move, OCS will take care of all the voice features for the user, including basic calls, advanced call controls, anywhere access, and voice mail. The desk phone won’t ring any more.


Third, we are releasing the details of one more interop model for VoIP with this specification. Customers asked us to enable people to use the PBX phone in the office and use Office Communicator when they are on the road. We thought hard about this requirement and finally came up with a dual-forking model that would work. The gist of the solution is that both the PBX phone and Office Communicator will ring at the same time for any call to the user, no matter where the call is from. The design uses the same standard SIP and RTP/RTCP interface between the PBX and OCS and adds a couple of optional headers to optimize a few things between the two systems. Certain advanced features will have to be disabled on the OCS side, but the user will get most of the capabilities of OCS. One added benefit of this design is the added backup. As long as one system is working, these dual-homed users can always make calls to each other. We are releasing the details of this design to our partners so that they know how best to interop with OCS to provide this feature to our common customers.


Fundamentally, the specification is all about letting customers keep their existing systems as they migrate to a fully-software based communications platform over the long term.


Check out the public beta and/or request the specification at


Click here to go directly to the Public Beta pre-registration site.


-  Mu Han

   Director, Unified Communications Group

Comments (9)

  1. Anonymous says:

    Jeff Raikes Pre-Announces OCS 2007 Public Beta at VoiceCon (March 7, 2007) In the keynote address at

  2. Anonymous says:

    I suppose you’re wondering about the title of this post? Of course Office Communicator will integrate

  3. Anonymous says:

    For information on how OCS will interop with your existing PBX and systems check out the Unified Communications

  4. Anonymous says:

    We’ve released some really good information on how OCS 2007 interoperates with traditional PBXes and

  5. Anonymous says:


    We are aware of this feature request and it is being investigated. No further information is available at this time.

    Tom Laciano

    Program Manager- Customer Experience

  6. Antoine Plantier says:

    So why does the current Beta don’t support SIP trunking with IP PBX such as CCM ?

  7. David Peet says:

    Will Office Communicator 2007 still require an OCS server to be available to place VoIP calls, even if OC 2007 can talk SIP directly with the IP/PBX? My main concern is maintaing 99.99% availability if there are WinTel servers involved in call placement.

  8. Michael Kerle says:

    The simple answer is YES. Office Communicator 2007 always registers against Office Communications Server 2007. There is no way to register against a third party IP-PBX. The SIP interface mentioned is between the IP-PBX and OCS 2007. To place or to receive a call the  inbound and outbound routing functionality of OCS 2007 is required but once a call has been established, the actual media (voice) flow is point to point. There is usually no server (neither IP-PBX nor OCS 2007) involved anymore.

    High availability is not exclusively reserved for PBX network, there are plenty of standard mechanisms (redundancy, etc.) in place to achieve the same availability in data networks.

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