Signal, a secure messaging service, has doubled the number of people who may participate in video group calls to 40. The app’s end-to-end encrypted group call capability was first published a year ago, with only 5 participants.
Signal explained in a blog post that the feature necessitated some new engineering. “We designed our own open-source Signal Calling Service to accomplish the job because there is no off-the-shelf software that would allow us to support calls of that scale while ensuring that all communication is end-to-end encrypted,” it continues.
Full Mesh, Server Mixing, and Selective Forwarding are the three designs that allow for video and audio transport. Full mesh only works with tiny calls, and server mixing, despite its support for huge groups, is not encrypted end-to-end.
As a result, the organization was able to safeguard media flow using their own open-source SFU (Selective Forwarding Unit). The media is sent to a server by each participant. The media is then “forwarded” to receivers without being viewed or altered by the server. The post says, “This works with numerous participants and is compatible with end-to-end encryption.”
The newly created SFU has now been scaled up to support 40 participants after being in use for 9 months.
WhatsApp, on the other hand, has been offering end-to-end encrypted group video calls since last year. However, it can only accommodate eight people at a time. With Signal’s new SFU architecture in place, it’s probable that WhatsApp’s call limit may soon be increased as well.