Kahevo's own call engine, written in Rust, is now in production: it sets calls up and carries their audio.
The engine we started on in September is now in production.
What it does now
When we last wrote about it, the engine converted voice between codecs and carried audio. It now does the rest of a phone call as well:
- registers with providers and keeps those registrations alive,
- signs desk phones in,
- sets calls up, rings, answers, holds and transfers them,
- carries the audio, plain or encrypted,
- and converts between codecs when the two sides differ.
Over UDP, TCP and TLS, on the same ports as before.
The numbers, again
Nothing about these changed, and they are why we did it.
- Before
- With the engine
- Before
- With the engine
Encryption, without writing any
Signaling is encrypted with TLS and audio with SRTP, both inside the engine. We kept one rule from the first day: no home-made cryptography. Both come from a widely used, audited library, and the engine only passes bytes to it and says who is to be trusted.
A provider's certificate is checked against the server's own list of trusted authorities, so it stays current as the server is updated.
Finding a provider
A provider is given by name, and the engine works out where that name leads, including providers that publish several servers. If one stops answering, a registration moves to the next.
Built to be shouted at
Software that listens on the internet hears from everyone. The engine refuses any message that is too large before reading it, and checks a message's claims about itself against what actually arrived. One of our tests damages a real call request three hundred thousand different ways and feeds it every one. Nothing breaks.
How it went in
| Piece | What it replaced |
|---|---|
| Codecs | Voice conversion |
| Audio | Carrying each call's packets |
| Signaling | Registering, and setting calls up |
| Encryption | TLS for signaling, SRTP for audio |
Each piece went in behind its own switch and was run against the full test suite with the switch on and off. Those switches are still there. Turn a piece off and Kahevo carries on the way it did before.
What is not on it yet
Calls from the browser phone and the iPhone app use a different kind of encryption, and those still run on the older path. So does the last step of joining the two sides of a call. Both are next.
Why it matters to you
A server that carries the same calls on less than half the processor is a smaller server, or the same one with more room. And the core of Kahevo now answers to nobody's license terms but our own.
Mahalo to everyone who put up with us talking about packet timings for a month.