Office Communications Server 2007 R2 Video Interoperability: What Works? What Doesn’t?

Video interoperability was introduced in Microsoft Office Communications Server 2007 R2 in 2008 with both Polycom and TANDBERG video conferencing to enable specific interoperability scenarios. Our ongoing work in this space continues to evolve in Office Communications Server 2007 R2. This article describes these interoperability scenarios and their respective usage cases: which ones work and which ones don’t.

Author: Rui Maximo and Andrew Sniderman

Publication date: June 7, 2010

Product version: Microsoft Office Communications Server 2007 R2

Microsoft Office Communications Server 2007 R2 has a rich partner ecosystem that enables compelling Unified Communications scenarios. This ecosystem includes client or endpoint devices. They include phones, USB handsets and headsets, webcams-and even personal computers and Macintosh computers. You can find a complete list of all optimized devices in Phones and Devices Optimized for Microsoft Office Communicator at Office Communications Server 2007 R2 also has a certification program for server-side integration that includes public switched telephone network (PSTN) gateways, IP-PBXs, and Session Initiation Protocol (SIP) trunk services in the Microsoft Unified Communications Open Interoperability Program at

Third-party video interoperability guidance and certification isn’t currently available on the previously mentioned sites. There is, however, guidance from Microsoft as well as Polycom and TANDBERG about how to enable these Unified Communications scenarios. This article goes through some of the technical details about how these scenarios work. You can then determine which configurations are appropriate for your needs as well as understand which configurations work and which ones don’t.

Office Communications Server 2007 R2 provides video interoperability at the protocol level. You can find most of these protocols documented in Microsoft Office Protocol Documentation at

Note: References to documented protocols are shown in brackets where appropriate; for example, [MS-SIPREGE].

Video Scenarios

The scenarios we’ll walk through are client registration, peer-to-peer video for two internal users as well as with an external user, and finally multiparty or video conferencing. Let’s step through each of these scenarios from a protocol view as follows to determine what’s required to enable each scenario:

1. RegistrationClients authenticate and register to Office Communications Server 2007 R2 as shown in Figure 1. The following protocols are used in this scenario:

  • SIP-specifically [MS-SIPREGE]
  • Transport Layer Security encryption (TLS) for encrypted signaling
  • Kerberos or Windows NT LAN Manager (NTLM) for authentication

Note: Although internal clients can use Kerberos, external clients must use NTLM version 2 for authentication because they are outside the Active Directory directory service forest. As a result, they cannot access the Kerberos Key Distribution Center (KDC). For video interoperability, both Polycom and TANDBERG support NTLM version 2-be sure NTLM authentication is enabled on the server that runs Office Communications Server 2007 R2.

Figure 1. Registration

2. Peer-to-Peer Video internalTwo internal clients negotiate a peer-to-peer video session as shown in Figure 2. In Office Communications Server 2007 R2, the RTVideo codec supports the following three resolutions in this scenario:

  •  Common Intermediate Format (CIF) is the lowest resolution that is supported. It corresponds to the small video window in Microsoft Office Communicator 2007 R2 or Microsoft Office Live Meeting 2007 and is 352×288 pixels.
  • Video Graphics Array (VGA) is standard definition video that corresponds to the large video window in Office Communicator 2007 R2 and is 640×480 pixels.
  • High Definition (HD) is the highest resolution that is supported. It corresponds to full-screen video and is 1280×720.
  •  In addition to SIP, TLS and NTLM version 2, the following additional protocols and codecs are used in this scenario:
  • Secure RTPSpecifically [MS-RTP] and [MS-SRTP]
  • RTVideo codec (for the video payload)Specifically [MS-RTVPF]

Note: Although signaling will always go through Office Communications Server 2007 R2, media will flow directly between the two internal clients in this scenario.

Figure 2. Peer-to-peer video internal

3. Peer-to-peer video externalTwo external clients (or an external client with an internal client) negotiate a peer-to-peer video session as shown in Figure 3. The same RTVideo resolutions are supported as shown in the previous scenario. If one party is internal and the other party is external, media flows through the A/V Edge service. Firewall traversal and media path optimization is accomplished by the A/V Edge service. If both parties are external, media flows peer-to-peer when possible.

  • In addition to SIP, TLS, NTLM version 2, SRTP and RTVideo, another protocol is used in this scenario: ICE v19-specifically [MS-ICE2].

Figure 3. Peer-to-peer video external

4. Multi-party video conferencingThree or more clients join a video conference hosted on an Office Communications Server A/V Conferencing service multipoint control unit (MCU) as shown in Figure 4. The A/V Conferencing service supports the RTVideo codec at CIF resolution. There is another protocol in this scenario: Centralized Conferencing Control Protocol (C3P). It manages provisioning the conference and maintaining it: validating security and policy, adding and removing participants, and so on.

5. In addition to SIP, TLS, NTLM version 2, SRTP, RTVideo, and ICEv19, another protocol is used in this scenario: C3P-specifically [MS-CONFBAS] and [MS-CONFAV].

Note: Video streams to and from the A/V Conferencing service are asymmetrical. The A/V Conferencing service sends the video of the dominant speaker to all participants and video of the prior speaker to the dominant speaker. When there is an outbound video stream from the A/V Conferencing service to all participants, there can be only two inbound video streams from clients to the A/V Conferencing service at any time.

Figure 4. Multiparty video conferencing

Interoperability Scenarios

Now that you have a better understanding of the video scenarios that are supported by Office Communications Server 2007 R2, let’s determine how third-party video devices can be incorporated into these scenarios. Third-party videoconferencing devices can classified into the following two categories:

  • H.323Legacy endpoints that support only the H.323 signaling protocol. Office Communications Server 2007 R2 doesn’t support H.323, so these endpoints must either join through a bridge or go through a gateway such as the TANDBERG Video Communication Server (VCS).
  • SIPEndpoints that can be either desktop or conference room video systems that support SIP. Some examples are the Polycom HDX and the TANDBERG MXP.

Within the SIP category, there is special-purpose equipment that is used to either connect multiple endpoints to a conference or provide protocol translation services. This equipment is described as follows:

  • MCUsHardware devices used to host multiparty video conferences. Typically sized and priced by port, they can fill an entire rack and are packed with Digital Signal Processors (DSPs) to optimize media mixing and transcoding. Some examples here are the Polycom RMX and the TANDBERG Codian. In addition to mixing and distributing video streams, the Polycom bridge can manage both SIP and H.323 devices in the same conference.
  • GatewaysIntermediary protocol translation devices. They can either be signaling (H.323 <-> SIP) or media (RTVideo <-> H.264). The TANDBERG VCS is a common signaling gateway that can be used to register H.323 devices to Office Communications Server 2007 R2.

Now let’s go back to the protocols that we went through in the previous scenarios. I’ll summarize them (as shown in Table 1) in the following three phases:

  • Protocols that are currently supported by our video partners.
  • Protocols that will be coming soon and can be added to existing equipment by using firmware upgrades.
  • Protocols that are planned but are not yet available in products. Polycom and TANDBERG are our two primary partners in this space today. Check with them directly to validate available capabilities as well as their product roadmap for future capabilities.

Table 1. Third-party video protocol support



Coming Soon

Future Capabilities


SIP, TLS, NTLM v2, RTP and H.263

SRTP and ICEv19

C3P and RTVideo

Note: Although the RTVideo codec is not supported by third-party video conferencing products today, the video codec, H.263, is supported by Office Communicator 2007 R2 and video vendors. This video codec is used in interoperability scenarios to support CIF-resolution video.

 Let’s look at Table 2 to overlay this mapping with the scenarios that we went through before to see what works and what doesn’t.

Table 2. Third-party video scenarios






Note the requirement for NTLM. You also need to provision the root certification on devices for TLS/secure signaling. Presence publication varies among units. Most just show basic states: offline (light pink); available (green); or in a call (red). The TANDBERG VCS can proxy presence for H.323 endpoints. You can publish bridge ports as virtual conference rooms but don’t typically publish presence.

Peer-to-Peer Internal-Works


+ (S)RTP and H.263 Codec

Note that H.263 is a common codec. It supports CIF video for these calling scenarios. SRTP support is not yet broadly available, so this may require enabling unencrypted media in Office Communications Server 2007 R2.

Peer-to-Peer External-Works

SIP, TLS, NTLM, (S)RTP, H.263 Codec

+ ICEv19

ICE support is not yet broadly available; however, it is required for this scenario.

Conferencing-Doesn’t Work

SIP, TLS, NTLM, (S)RTP, H.263 Codec, ICEv19

+ C3P and RTVideo

Currently, C3P and the RTVideo codec are not supported. All calls are peer-to-peer from an Office Communications Server 2007 R2 perspective. This means, for example, that you cannot move a third-party endpoint into a video call to escalate it to a conference. What does work today is multiple communicator and third-party endpoints, all dialing in to the same bridge port or virtual conference room. In this scenario, Office Communicator 2007 R2 will display whatever video stream is sent by the MCU (could be a mixed stream with multiple participants). It will, however, appear to be a peer-to-peer call in the Office Communicator 2007 R2 roster.


I hope this helps to demystify what is going on under the hood in video interoperability and gives you an understanding of the interoperability with third-party video products and why. Keep an eye on this fast-evolving space, and look for new announcements as the video interoperability story for Office Communications Server 2007 R2 continues to evolve.

Additional Information

To learn more, check out the following:

Communications Server Resources

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