[e2e] First rule of networking: don't make end-to-end promises you

[David P. Reed]

At 07:29 PM 4/23/2004, Cannara wrote:
>Dropping packets is
>always how router programmers must manage queues under excessive load, so
>those packets should fairly come from all flows.

And they do.   But that's not managing congestion.   Managing congestion is 
done by the high level protocols.

You seem to think that UDP-based protocols are open loop.   UDP is not a 
complete protocol - it is a means to allow other (closed loop) transport 
protocols to be developed (such as RTP or Gnutella) in the Internet 
architecture, the job of congestion control is pushed to the edges, as it 
should be, since there is no way that a router can understand how to manage 
congestion in a way that takes into account the application semantics (for 
protocols like "digital fountains" or like variable quality speech, or 
overlay networks that select routes based on measured quality, the response 
to congestion may be to change coding, take alternate actions that shift 
load, etc. - all of them servo off of congestion indication, which is 
pretty robustly detected by Little's Theorem/lemma, which is that queue 
length rises non-linearly with load/capacity).