[Galene] About UDP multiplexing

[Juliusz Chroboczek <jch@irif.fr>]

Hi,

By default, Galene will use random UDP ports for media traffic.  If the
high ports are inaccessible for some reason (say, because there is
a firewall in the way), it will fall back to routing through the built-in
TURN server.  While this is the right approach, it makes Galene
challenging to install for people who wish to put it behind a firewall.

There is another approach, which is to put all the UDP traffic on a single
port; this is called UDP multiplexing.  I tried it a couple of years ago,
and it did not work well, apparently Pion (our WebRTC library) had some
issues with double-stack hosts when multiplexing.  It appears to work now,
and I've implemented it in the branch "udpmux".

UDP muxing is very simple to use: just add the option "-udp 10000", where
10000 is the port that you wish to use for UDP traffic.  There are some
caveats:

  - there is a slight performance penalty, but it should be negligible;

  - if the server is renumbered (its IP address changes), you will need
    to restart Galene.

The code is live on galene.org, and it seems to work fine.  I've
reimplemented it just today, so if you did test before, please test again.

Note that UDP muxing, in its current state, does not solve the NAT
problem: if your server is behind NAT, Galene will still fallback to TURN,
even if the mux port is forwarded on the NAT.  I'll see if I can implement
something, but please don't hold your breath, I'm not really interested in
working around NAT issues.

-- Juliusz