Secure messaging app Signal has increased its video group call limit to 40 members. The app released its end-to-end encrypted group call feature a year ago, supporting only 5 participants.
In a blog post, Signal detailed that the feature required some new engineering. “There is no off the shelf software that would allow us to support calls of that size while ensuring that all communication is end-to-end encrypted, so we built our own open-source Signal Calling Service to do the job,” it reads.
Signal now supports 40 person group calls. Building large end-to-end encrypted group calls required some new engineering. Learn how we did it here: https://t.co/i27rRqkI4l
— Signal (@signalapp) December 15, 2021
Generally, there are 3 architectures that allow for video and audio transfer – Full Mesh, Server Mixing, and Selective Forwarding. Full mesh only works with small calls, while server mixing, despite supporting large participants, is not end-to-end encrypted.
So, using their own open-source SFU (Selective Forwarding Unit), the company was able to ensure media flow securely. Each participant sends their media to a server. Then, the server “forwards” the media to recipients without viewing or altering it. “This works with many participants, and is compatible with end-to-end encryption,” the post reads.
The newly developed SFU has been in action for the past 9 months and has now been scaled up to support 40 participants.
Its competitor, WhatsApp, on the other hand, has offered end-to-end encrypted group video calls since 2018. However, it can only handle eight participants at a time. With Signal’s new SFU architecture in place, it is possible that WhatsApp could soon be scaling up its call limit as well, in time.