Product Documentation

Technical overview

Aug 04, 2016

Citrix HDX RealTime Optimization Pack offers clear, crisp high-definition audio/video calls with Microsoft Skype for Business  and Lync in an optimized architecture. Users can seamlessly participate in audio-video or audio-only calls to and from other Skype for Business  and Lync users and other standards-based video desktop and conference room multipoint control unit (MCU) systems. All audio/video processing is offloaded from the Server to the end-user device or terminal, optimizing the quality of the call with minimal impact on server scalability.

The Citrix HDX RealTime Optimization Pack provides XenApp and XenDesktop customers the following key features:

  • Optimizes Lync audio and video calling on Windows, Mac, and Linux devices.
  • Compatible with Skype for Business Server 2015, Lync Server 2013, Lync Server 2010, and Lync Online (Office 365).
  • Enables call initiation from the Lync dialpad, Lync dial-in bar, Lync contacts list, Lync Conversation window, and Outlook or other Office application.
  • Provides separate call window that displays optimized video and provides call controls (hold, transfer, hang-up, and so forth).
  • Supports both point-to-point and multi-party calling.
  • Supports Microsoft’s proprietary RT-Audio codec. Also supports industry standards G.771, G.722, G.722.1, and G722.1c for audio calls from 3 kHz to 14 kHz (ultra wideband).
  • Supports RT-Video, H.264, H.263, H.263+, and H.263++ video codecs. Video call rates range from 128kb/s to 2048kb/s. All video is encoded at up to 30fps (depending on the webcam used) and transmitted over RTP or TCP.
  • Includes HD support and the following video resolutions on Windows and Linux client devices:
    • 720P30 (1280 X 720 pixels)
    • 4CIF resolution (704 X 576 pixels)
    • VGA resolution (640 X 480 pixels)
    • CIF resolution (352 X 288 pixels)
    • SIF (352 X 240)
    • QCIF resolution (176 X 144 pixels) or QSIF (176 X 120)
  • Optimizes Quality-of-Experience (QoE) through adaptive jitter buffer, packet loss concealment, call rate adaptation, and other techniques.
  • Provides fallback to server-side media processing (Generic HDX RealTime) if there is no HDX RealTime Media Engine present on the user device.
  • Supports most webcams including built-in webcams on Windows devices.
  • Supports built-in webcams (Facetime cameras) on Mac devices.

Limitations in version 1.8

Citrix recommends that you deliver the Lync client using generic HDX RealTime technologies, Local App Access, or Microsoft Lync 2013 VDI Plug-in if your users need the following features that are not supported by HDX RealTime Optimization Pack for Lync. For more information, see Delivering Microsoft Lync to XenApp and XenDesktop Users.

For a feature matrix of alternative methods of delivering the Lync client from XenApp and XenDesktop, see

Caution: Editing the registry incorrectly can cause serious problems that may require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.
  • The dialpad is not supported with the Lync 2010 client.
  • The HDX RealTime Connector for Lync 2013 installer does not support Lync when installed using the Office 365 Click-to-Run. 
  • Lync basic is not supported by the RealTime Connector. Workaround: Use the full version of Lync.
  • Response groups is not supported.
  • Delegation is not supported.
  • Voicemail access and playback is not supported. Use Microsoft Outlook to view, access, and playback voicemail messages.
  • Recording is not supported. Citrix recommends evaluating third-party server-based recording solutions.
  • Gallery view is not supported in multiparty calls. Active speaker view is used in Lync multiparty calls using Optimization Pack.
  • There are no Call and Video Call buttons in the Lync Contact Card.
  • On Linux terminals, the RealTime Media Engine installer disables multimedia redirection in Linux Receiver. This avoids Optimization Pack and Linux/Unix Receiver getting into a conflict when accessing video devices. However, this means that other Unified Communications applications cannot work with Generic USB redirection when accessed on a Linux terminal that has RealTime Media Engine installed.
  • The date and time strings on USB telephone devices with display capabilities are not properly localized.
  • The Lync dial pad and Lync dial-in bar do not support mnemonic dialing (for example, 1800CALLATT).
  • The Optimization Pack disables the use of hardware accelerated H.264 video using the Logitech C920 camera to prevent an issue with bad video. To use hardware acceleration with the Logitech C920 create or modify the following registry key:

    On 32-bit Windows:


    Name: DisableHardwareAcceleratedH264

    Type: REG_DWORD

    Data: 0 (enables the hardware acceleration);

    On 64-bit Windows:


    Name: DisableHardwareAcceleratedH264

    Type: REG_DWORD

    Data: 0 (enables the hardware acceleration)

Special considerations

  • Skype for Business client must be in Lync UI mode. For information about putting Skype for Business client into Lync UI mode, see
  • If you are using older versions of Lync 2013, menu items inserted by RealTime Connector will not display when you right click on a Lync contact. This is due to a bug in Lync. Update your Lync to the SP1 update (15.0.4569.1503) or later. RealTime Connector checks for Lync SP1 as a minimum requirement for installation.
  • Lync automatically disables the set location functionality when running in a virtual desktop. This is expected behavior. For more information, see
  • To distinguish the keys between RealTime Connector for Lync 2010 and 2013, registry keys for RealTime Connector for Lync 2013  and Lync 2010 are in the registry at:

    On 32-bit Windows:



    On 64-bit Windows:



  • Version 1.0.1l of OpenSSL is used in this version of the Optimization Pack. Please review all security bulletins pertaining to this version of OpenSSL.
  • Applies to Windows terminals only. Plantronics provides additional software/SDK for their devices, which interferes with RealTime Media Engine. RealTime Media Engine works only with native Windows device drivers for USB headsets and handsets. Uninstall any such vendor-provided software. For example,