[Galene] Re: Logging

[Juliusz Chroboczek <jch@irif.fr>]

> So in this case, how is using a TURN server different than just having
> Galene itself listen on a bunch of UDP ports and offer each of those?

Short answer: Galène needs hundreds or even thousands of ports.  TURN can
use a single port, which you can pick such that it's accessible from your
clients.

Long answer.  Galène uses WebRTC.  WebRTC uses RTP.  RTP transmits
a collection of tracks.  RTP can work in two modes:

  - port multiplexing: use the UDP port to associate packets with tracks;
  - SSID multiplexing: multiplex over a single UDP 5-uple, and use data in
    the RTP header to associate packets with tracks (this is called
   "bundling" in WebRTC).

Now, there are two limitations:

  1. Pion is unable to use a single local UDP port for multiple RTP
     sessions: it uses a distinct UDP port for every RTP session, even if
     sessions have dinstinct remote addresses;

  2. Galène uses a distinct RTP session for every stream (pair of audio
     and video tracks); in other words, Galène ony bundles at most one
     video and one audio track.

Fixing (2) is not a high priority, since it would make the code way more
complex (bundling is fragile, there are some limitations to what you can
do when bundling streams with different configurations and some limitations
to how you can mutate a bundle without tearing it down).  It might
cause issues with AQMs (is it a good idea to use the same 5-uple for
different videos?), but you're the specialist here.

-- Juliusz