TODO

+ Make speed measurement inexpensive by using an iptables rule counter
+ Filter the result of the sessions command and return at most 50 entries
  ordered by some criteria (like most recent first). Also add a new command
  in the relay to report back all active sessions (only their call_id) to
  allow the dispatcher to purge obsolete sessions when a relay reconnects
  with it, as the sessions command will no longer return all sessions and
  is also very expensive as it returns a lot more information than
  necessary, including stream counters which are very expensive to gather.
  Define some ordering rules for the selection here and also define what
  fields to search with the filter that is provided (from/to/callid...)
+ Add a new command to the dispatcher to terminate a session. This should
  be available for any session that has a dialog_id and should allow the
  media sessions web interface to terminate a dialog by clicking a button
  In result the dispatcher should trigger dialog termination.

- Lawful intercept for RTP media
- Selection of mediaproxy based on proximity
- Add ability to relay to restart on the fly without losing the sessions
- Minimize interruption caused by a dispatcher restart
- Make traffic calculation more efficient
- Only log connection state transitions to avoid too much logging in case
  the dispatcher is down and the relay can't reconnect.
- Allow the NAT address to change during a call to accomodate ISPs that
  dynamically allocate IP addresses and change them at regular intervals.
  This has to work even without any signaling support, based on the SSRC
  field in the RTP media stream. For protection, switching the NAT address
  should only happen if the old NAT address didn't send anything for a while,
  while the new NAT has sent a stream with the same SSRC field.