Product Documentation

Technical overview

Jul 07, 2016

Citrix HDX RealTime Optimization Pack offers clear, crisp high-definition audio/video calls with Microsoft Skype for Business in an optimized architecture. Users can seamlessly participate in audio-video or audio-only calls to and from other Skype for Business 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.

Key features

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

  • Optimizes Skype for Business audio and video calling on Windows, Mac, and Linux devices.
  • Compatible with Skype for Business Server 2015, Lync Server 2013, Skype for Business Online, and Lync Online (Office 365).
  • Enables call initiation from the Skype for Business dialpad, dial-in bar, contacts list, Conversation window, and Outlook or other Office application.
  • 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) and SILK, which delivers higher audio quality across a wide range of network environments, including the public Internet and mobile networks.
  • Supports RT-Video, H.264 Scalable Video Coding (SVC) and H.264 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:
    • 4CIF resolution (704 X 576 pixels)
    • VGA resolution (640 X 480 pixels)
    • CIF resolution (352 X 288 pixels)
    • SIF (352 X 240)
    • 360p (640x360)
    • QCIF resolution (176 X 144 pixels) or QSIF (176 X 120)
  • Supports Quality of Service (QoS) by observing the audio and video port ranges configured on the Skype for Business server (see and 
  • Supports Differentiated Services Code Point (DSCP) marking for media packets. For Windows push out QoS policies to the endpoints. For Linux and Mac OS X, there are RealTime Optimization Pack registry settings that must be applied in the user's profile on the server. 
  • 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.
  • Improves audio and video quality over lossy connections by enabling forward error correction (FEC).


Citrix recommends that you deliver the Skype for Business 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. 


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.

  • Lync basic is not supported by the RealTime Connector. Workaround: Use the full version of Skype for Business.
  • The Media Bypass mode of the Skype for Business Mediation Server ( is not supported. Workaround: Disable media bypass to enable public switched telephone network (PSTN) calls through Mediation Server. 
  • When the Skype for Business client is delivered as a published application, desktop sharing is not supported and should not be used as the server desktop will be shared rather that the local desktop. Application sharing can be used to share other hosted applications during a Skype for Business call. 
  • 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 Skype for Business multiparty calls using Optimization Pack.
  • Panoramic webcams that deliver a 360-degree view of the meeting room are not supported.
  • Optimized delivery (redirection of media processing to the user device) in a double-hop XenApp/XenDesktop-Receiver scenario is not supported.
  • Web proxy limitations:
    • HTTP proxy authentication is not supported. Configure proxies with white lists to allow unauthenticated access to target Skype For Business servers (for example, Office 365 servers for cloud-based deployments).
    • Web Proxy Auto-Discovery Protocol (WPAD) and dynamic proxy detection are supported with Windows endpoints only. Configure Linux and Mac endpoints with a static HTTP proxy address.
  • 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 Plantronics Clarity P340 audio device is not supported. 
  • 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)

Considerations and recommendations

  • In Fallback mode (when RealtTime Media Engine is not available on the endpoint and audio/video processing occurs on the server), video quality might degrade to the point of failure on virtual desktops with a single virtual CPU.

    We recommend you change the VDA configuration to have a minimum of two CPUs for users who may encounter Fallback mode. For more information, see and
  • Users might hear an echo or other artifacts when using any built-in microphone and speakers on endpoints.

    We recommend you use a headset on an endpoint or a speakerphone with hardware-based echo cancellation. 
  • When attempting to make high-definition video calls from a home office, take into account your users' network bandwidth and ISP routing policies. If you observe pixilation of the video or problems with lip sync, adjust the Maximum Packet Size (MTU) on the network interface card properties to a lower value such as 900 to avoid situations where ISPs perform traffic shaping based on packet size.
  • Various scenarios (for example, combining content sharing and audio/video conferencing) might not work properly when some conversation participants run previous versions of the RealTime Optimization Pack.

    We recommend participants using older versions of HDX RealTime Optimization Pack upgrade to this version of HDX RealTime Optimization Pack.