Serious question: why does an SFU need TURN? Is it just because you already had centralized stream broadcasting and making it TURN compliant was low-hanging fruit?
Technically an SFU doesn't need it. But clients connecting to the SFU will probably need it.
Also having a TURN server allows for very restricted corporate scenarios, such as everybody connecting through a single, well known port (as Sean's S.O. reply mentions in the sibling comment).
For example in OpenVidu (not trying to plug it here so won't put a link) a Coturn server is deployed, and TURN credentials are automatically shared with all clients (web browsers, mobile phones) so they can access the SFU through the Coturn instance, if needed. People are using this on very restricted networking setups for allowing connections between differently segmented networks, some of them not even connected to the internet.
I see, so the TURN server negotiates the access authorization (and provides a single connection point), but then the SFU handles the routing between peers.
Is there a way to get a standard TURN server to reuse outbound streams for 3+ user chat? E.g. I have a CoTURN install that is strictly used for audio and while I'm not too concerned about bandwidth at my server, I'm very concerned about uplink bandwidth for users with asymmetric connections (which is practically all of them).
I'm sorry to bug you here, but it's so hard to find anyone who actually knows much of anything about WebRTC who isn't just parroting stuff they read on Stack Overflow. Half the time I get the same, subtly-wrong answers about basic signaling, even when my question isn't even about signaling.
