Media Recorder sizing for voice, video, screen - application share recording

Voice recording CPU sizing

The table below shows the supported number of simultaneous voice calls per CPU core: 

• The system was tested up to 16 core servers, where 2 cores must be reserved for the OS, leaving up to 14 CPU cores for the application.
• When certain features are enabled on the Recording Servers, the capacity numbers change:
  • Encryption: when storage file encryption is enabled, capacity numbers must be decreased by 10%
  • Voice quality check: when voice quality check is enabled, capacity numbers must be decreased by 15%
• Numbers in red denotes default values, should be used for server sizing
• Numbers only applicable when Receive-side scaling (RSS) is enabled in the OS

¹ Simplex stream recording, e.g recording channel mixing on turrets

² BT ITS supports PCM streams only

Sample calculations

Voice recording on co-located Proxy and Media Recorder server CPU sizing

A standalone proxy server can handle 200 concurrent sessions per CPU core in the case of Skype for Business, and 150 in the case of Cisco. The following table shows the sizing in the case of co-located proxy and recording services.

Video and Screen Share recording sizing

CPU sizing

When recording video, besides the number of recorded endpoints, the video bandwidth also has to be taken into account.

With a single CPU core, 125 Mbps total video or screen share stream can be recorded. So with the minimum server requirements (4 cores, 2 cores considered as reserved for the OS), the system can record up to 250 Mbps video or screen share streams total.

Video recording 

The bandwidth usage of the video endpoints can vary based on the device types, their configuration, and the available network bandwidth. The following table shows the bandwidths with different video resolutions when using fullscreen video call:

However, when using a smaller client window size, or the default, the video resolution changes, therefore the bandwidth as well. The following table shows the bandwidths with different client window sizes in the case of 1080p video call:

For more information, refer to the following articles:

https://docs.microsoft.com/en-us/skypeforbusiness/plan-your-deployment/network-requirements/network-requirements
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab12/collab12/cac.html

It is important to note, that the numbers above have to be multiplied by two because there is always an incoming and an outgoing stream.

Calculating with 2*2 Mbps video streams per endpoint, with a single CPU core, 31 concurrent video sessions can be recorded. Therefore, a 4-core Recording Server (2 cores considered as reserved for OS) can record 62 concurrent video sessions.

Numbers only applicable when Receive-side scaling (RSS) is enabled in the OS

Screen Sharing recording

While in the case of the Video calls the bandwidth depends on the resolution and the client window size, in the case of Screen Sharing, the bandwidth depends only on the resolution.

The following table shows the bandwidths with different resolutions, depending on the available network bandwidth:

Acceptable bandwidth provides a decent user experience. When the optimal bandwidth is available, the screen-sharing experience will be much smoother.

Calculating with 2 Mbps screen share streams per endpoint, with a single CPU core, 62 concurrent video sessions can be recorded. Therefore, a 4-core Recording Server (2 cores considered as reserved for OS) can record 124 concurrent video sessions.

Video recording and storage devices

In the case of a high number of recorded video endpoints, the type of the storage device also has to be considered. An HDD usually has a write speed of 50-120 MB/s, while an average SSD has 200-520 MB/s, or even more in the case of high-end devices. The disk utilization for the recording shouldn't be more than 60% and the disk must provide sustained I/O performance at this rate. Numbers only applicable when Receive-side scaling (RSS) is enabled in the OS.

The following table shows some examples for maximum total video bandwidth per Recording Server: