Device Clients

All data and examples are based from Windows device clients with a single 1920 x 1080 (1080p) display.  For other operating systems the numbers are expected to vary.  The biggest variables being the number of screens and their resolution and also the operating system used.

Idle

While there are no users in Backdrop the device clients will idle at 0kbps. Only using network activity when sending a capture that is triggered by the in-built Wellbeing module. Telemetry data, (open applications and chrome tabs) will be sent to Backdrop around once every 15 seconds, though only text is sent.  Making the packages sent to Backdrop extremely small.

Thumbnail

While there are staff members viewing a student in Classroom on the thumbnail page. The device client will send an image to classroom once every 3 seconds at around 1-3Kbps. If they are not being viewed either on the thumbnail page or the Single Device View page they will return to idle. Thumbnails are compressed to be a maximum of 10Kb in size.  For thumbnails, the number of screens and their resolutions should not impact the bandwidth requirement.

Single Device

While a staff member is looking at a single student on the Single Device View page the device client will use WebRTC. This requires more bandwidth from the device client.  Testing on a single 1080p display the device client was sending video data around 4-8Mbps. This will increase/decrease depending on the number of display and their resolutions.

Broadcast Screen

A student can receive a broadcasted screen from either another student’s device or from the teacher. A student can also broadcast their screens to other students. In both cases WebRTC is used, testing on a single 1080p display the device client was sending video data around 1.5Mbps.

Capture Upload (Wellbeing)

When a capture is triggered a device client will send a screenshot(s) to Backdrop.  During our testing, this peaked at 10Mbps for around 1 second. This operation only happens when the device client is reporting captures.

Mobile device clients (Android & iOS)

The mobile clients are built as web browsers, therefore in addition to the above requirements please take into account the requirements for normal Internet use including video playback.

Classroom

Idle

Idle means the teacher is not viewing the thumbnails or on the single device view page, (they are using another part of Backdrop).  Activity with the devices can only occur within the Classroom section of Backdrop. Therefore, please take into account the requirements for normal Internet use including video playback.

Thumbnail View

Thumbnails have a maximum size of 10KB and are requested at a rate of 1 every 3 seconds.  Here are a few scenarios, all assuming the maximum of 10KB is sustained:

1. 8 students are visible on the teacher’s screen.  10KB * 8 = 80KB downloaded per second.
2. 30 students are visible on the screen.  10KB * 30 = 300KB downloaded per second.
3. 10 teachers in a school are all using Classroom at the same time for different classes. 5 of them have a class size of 25 and are viewing the entire class. The other 5 are only viewing the top 8. ((10KB * 25) * 5) + ((8KB * 5) * 5) = 1450KB downloaded per second.

Images downloaded are not stored on the teacher’s device, they are rendered in the browser. During our testing, a single thumbnail for a device client using a 1080p screen required less than 10Kbps on the network. Thumbnail sizes also ranged between 5KB and 10KB depending on what was on the screen.

Single Device View

While a staff member is looking at a single student on the Single Device View page the device client will use WebRTC. This requires more bandwidth from the teacher’s machine to download the video being sent.  In testing, on a single 1080p display for the device client, the teacher’s machine was sending video data around 4-8Mbps. This will increase/decrease depending on the number of display and their resolutions.

Broadcast Screen

The teacher has the ability to broadcast their screen to the students. WebRTC is used to accomplish this. In testing, on a single 1080p display for the device client, the teacher’s machine was sending video data around 1.5Mbps. This will increase/decrease depending on the number of display and their resolutions.

Controlling Devices

Classroom has the ability to send commands to students’ devices. All commands are text-based payloads and are fulfilled via HTTPS requests. During our testing we did not observe any significant load on the network, however, the more devices selected for the same command the larger the payload. Locking the screens of an entire class for example.

Memory requirements

Device Clients

All data and examples are based from Windows device clients with a single 1920 x 1080 (1080p) display.  For other operating systems, the numbers are expected to vary.  The biggest variables are the number of screens and their resolution and also the operating system used.