System requirements


The RealTime Optimization Pack supports the following Microsoft Skype for Business configurations:

  • Server (back end)
    • Microsoft Skype for Business server 2019
    • Microsoft Skype for Business server 2015
    • Microsoft Skype for Business Online (Microsoft Office 365 hosted Skype for Business Server)
    • Microsoft Lync 2013 server - Updated to at least the February 2015 Cumulative Update. Citrix and Microsoft recommend updating to the most recent Cumulative update.
  • Client (the Skype for Business application installed on the Citrix Virtual Apps and Desktops server). To benefit from the latest fixes and security updates, we recommend that you install the latest version of the Skype for Business client.
    • Microsoft Skype for Business for Office 365
    • Microsoft Skype for Business 2019
    • Microsoft Skype for Business 2016 Click-to-Run minimum version 1611 Build 7571.2072.
    • Microsoft Skype for Business 2016 MSI minimum version 16.0.4483.1000.
    • Microsoft Skype for Business 2015 stand-alone installer (which can be installed on top of Microsoft Office 2016) minimum version 15.0.4875.1001.

    For information about configuring the Skype for Business 2015 client in native UI mode, see

The Optimization Pack is compatible with all currently supported versions of Citrix Virtual Apps and Desktops. For information about the lifecycle of Citrix Virtual Apps and Desktops, see Citrix Product Matrix.

For more information about Citrix Virtual Apps and Desktops editions that include Skype for Business optimization, see Citrix Virtual Apps and Desktops features.

The Optimization Pack is compatible with all currently supported versions of Citrix Workspace app for Windows, Mac, and Linux. For information about the lifecycle of Citrix Workspace app, see Lifecycle Milestones for Citrix Workspace app.


If you are using Workspace app for Windows 2402 or later, you must use the HDX RealTime Optimization Pack 2.9 CU7.

To support FIPS-compliant Skype for Business environments, use the HDX RealTime Optimization Pack 2.9 CU4 or later. However, note that HDX RealTime Optimization Pack isn’t FIPS certified.

RealTime Connector

Install the RealTime Connector on Citrix Virtual Desktops virtual desktops or on servers in your Citrix Virtual Apps site.

  • Supported operating systems:
    • Desktops:
      • Microsoft Windows 11
      • Microsoft Windows 10
    • Servers:
      • Microsoft Windows Server 2019
      • Microsoft Windows Server 2016
      • Microsoft Windows Server 2012
  • Memory: 1 GB RAM (maximum in fallback mode), 120 MB paging file
  • Disk space: minimum 100 MB available
  • Network interface: full-duplex Ethernet TCP/IP local network connection
  • Software:
    • DirectX 9 (minimum)
    • Microsoft .NET 4.0 SP1
    • Microsoft Skype for Business 2015 client - minimum Product Update 15.0.4833.1001 (32-bit or 64-bit)
    • Microsoft Skype for Business 2016 client - minimum Product Update 16.0.7341.2032 (32-bit or 64-bit)

Installation prerequisite

  1. Right-click the Microsoft Skype for Business shortcut on your desktop or in the list of programs in the Start menu and choose Properties.
  2. In the Properties dialog box, select the Compatibility tab.
  3. On the Compatibility tab, ensure the Run this program as an administrator check box is cleared.

RealTime Media Engine

You install the RealTime Media Engine on the client device.

See for HDX Premium client devices verified for Optimization Pack.

Hardware guidelines when the H.264 hardware acceleration is unavailable:


Results vary based on the processor architecture.

  • For CIF (standard) video, 1.4 GHz
  • For VGA, a minimum of 2 GHz.
  • For 720p HD (high definition) video, 2.8 GHz dual core
  • Support for the SSE3 instruction set

Disk space and memory:

  • 50 MB disk space
  • 1 GB total RAM

Supported operating systems:

You can install the RealTime Media Engine on devices running any of the following operating systems:

  • Microsoft Windows Desktop:
    • Microsoft Windows 11
    • Microsoft Windows 10
    • Microsoft Windows 10 IoT Enterprise
    • Microsoft Windows 8.1
  • Linux 32-bit
    • Ubuntu 16.04
    • Red Hat 7
    • CentOS 7
    • HP ThinPro 7.x and later
  • Linux 64-bit
    • Ubuntu 18.04 and 16.04
    • Red Hat 7
    • CentOS 7
    • HP ThinPro 7.x and later
    • IGEL


GNU Binultils must be installed on the Linux endpoint. This can be accomplished by running sudo apt-get install binutils. Please refer to GNU documentation for more details.

  • macOS 13.x, 12.x, 11.x


macOS 11.x (Big Sur) support requires RTOP 2.9 CU3 or later. macOS 12.x (Monterey) support requires RTOP 2.9 CU4 or later. macOS 13.x (Ventura) requires RTOP 2.9 CU5 or later. The Apple Silicon platform is supported on macOS Big Sur, Monterey, and Ventura only by using Rosetta 2.

  • Unicon - Contact Unicon for the version of eLux that they recommend for use by the RealTime Media Engine.


Editing the registry incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of the Registry Editor can be solved. Use the Registry Editor at your own risk. Be sure to back up the registry before you edit it.

The Microsoft Windows 10 Anniversary Update released in August 2016 introduces a new feature called Windows Camera Frame Server. This feature might cause issues including disabling hardware encoding in webcams.

To avoid these issues, install Microsoft updates KB3176938 (Windows 10 CU released on August 31, 2016) and KB3194496 (Windows 10 CU September 29, 2016) for RealTime Media Engine on Windows 10. If you still see performance issues after installing the updates, make these registry changes:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Media Foundation\Platform EnableFrameServerMode=dword:00000000

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows Media Foundation\Platform EnableFrameServerMode=dword:00000000

Requirements for audio and video calling:

  • The RealTime Media Engine can support video calls in high-definition (HD) video. If the camera, host device, bandwidth setting, and remote endpoint support high-definition specifications, the RealTime Media Engine measures the speed of the user device. It then encodes HD video.
  • Camera:
    • Most USB webcams are supported.
    • Minimum resolution: 320 x 240
    • Color space: 1420 or YUY2
    • Frame rate of at least 10 fps, 24 fps for the HD video
    • Windows UVC driver
  • Audio I/O must be DirectSound compatible and capable of 16-bit mono or stereo sound at 16,000, 32,000, or 44,100 samples per second. We recommend a USB headset.

Requirements for Skype for Business compatible audio devices:

The RealTime Connector supports Skype for Business-compatible USB headsets, speaker phones, and phones. For full information about supported devices, see USB audio and video devices.

Third-party video drivers and the Optimization Pack

Windows USB video class (UVC) drivers for web cameras have been included in Microsoft Windows operating systems for many years. Microsoft Windows operating systems on some thin client terminals might not include those drivers. If you install a web camera on a terminal device, the installation program might report that it doesn’t have the required files.

We recommend that you use the standard Windows device drivers for webcams. Vendor-supplied drivers can sometimes cause crashes and Blue Screen events on certain platforms (especially 64-bit Windows).

System requirements