Frequently Asked Question

Broadcast Desktop issues (versions 22.5 and higher)

Last Updated about a month ago

Issues described in this article:

  • No image on student computers
  • Poor performance (even when a small number of computers are selected)
  • Poor performance when a large number of computers are selected (but good performance when a small number of computers are selected)
  • White screen with a moving cursor, no image
  • A limited rectangular portion of the screen is displayed only


1. No image on student computers: the Net Control 2 logo on a gray background appears on student computers, no change within one minute or more.

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In the teacher module settings (N – Options – Options), on the Control/Broadcast page, please enable the DirectBroadcast mode, click OK and restart the session:

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2. Poor performance, even when a few only computers are selected: image is garbled, incomplete, long delays in screen updates.

Please try to adjust the performance settings on the sender side (on the teacher computer when a teacher is broadcasting his/her screen to students, or on the corresponding student computers).

In the teacher module settings, N – Options – Options; Control/Broadcast page:

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Please set up the settings as follows:

Broadcast compression: 30 – 50;

Scale: AUTO; or 75% for screen resolutions above 1920x1080; or 50% for screen resolutions above 3840 x 2160 .

Latency: 10 and higher.

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Broadcast protocol: DirectBroadcast


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To modify the respective settings on student computers, please select them in the teacher console, use the main menu command N – Options – Client Options; modify the settings on the Control/Broadcast tab:

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3. Good performance when a small number of random student computers are selected but poor performance when a large number of computers are selected.

The issue may be connected with a low bandwidth of the network, high latency or poor overall performance of the network.

3.1. Use multicast/UDP broadcast protocols, when are supported by the network.

In the teacher module settings (N – Options – Options), on the Control/Broadcast page, please enable the Multicast protocol, click OK and restart the session:

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If a gray logo appears on student computers instead of the teacher’s screen, please try to change the protocol to Broadcast:

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If the screen is gray in this mode as well, and the computer has multiple network adapters, please try to select a network adapter that is actually used by Net Control 2 software: on the Advanced Options page of the teacher module settings, or the student module settings, please select the network adapter and restart the Broadcast Desktop session:

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Multicast and UDP Broadcast protocols are often limited by the bounds of the current subnetwork, router or access point where the students are connected. Please refer to the documentation on the network hardware for possible adjustments in settings for the Multicast/Broadcast protocols support.

If a network consists of several VLANs or subnetworks, and the Multicast protocol is not supported across the VLANs/subnetworks, you may need to use the Broadcast protocol instead and to specify a list of Broadcast addresses of the VLANs on the Advanced Options page:

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Enable the Custom UDP Broadcast subnetworks option and specify a comma-separated list of broadcast addresses. The broadcast address may be calculated using a network address and network mask with any online broadcast address calculator.

If computers are connected over a wired (Ethernet) connection, please also try to use the PGM/Multicast protocol:

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This protocol is not adapted for wireless connections.




4. White screen with a moving cursor, no image.

If the version used on student or teacher computers is 22.1 - 22.5, please try to update the software with a version above 22.5.

In the teacher module settings (N – Options – Options), on the Control/Broadcast page, please disable the VHD driver acceleration, by enabling the Do not use option and click OK:

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5. A limited rectangular part of the screen is displayed only.

In the Broadcast toolbar, please click the Select the capture area button, and click then the Reset button:

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