[ih] Global congestion collapse

Joe Touch touch at ISI.EDU
Wed Dec 15 07:09:03 PST 2004



David L. Mills wrote:
> Perry,
> 
> Not so fast. Steve Wolff of NSF and I had a nasty little secret we did 
> not tell the NSFnet maintenance crew who could never keep a secret. I 
> built in priority queueing and preemption in the fuzzball routers. The 
> former wiretapped the telnet port and made it just below NTP on the 
> priority scale. We put mail on the bottom just below ftp. A lot of 
> telnet users stopped complaining because they thought we "fixed" the 
> network.
> 
> The other thing was to shoot the elephants. When a new packet arrived 
> and no buffer space was available, the output queues were scanned 
> looking for the biggest elephant (total byte count on all queues from 
> the same IP address) and killed its biggest  packet. Gunshots continued 
> until either the arriving packet got shot or there was enough room to 
> save it. It all worked gangbusters and the poor ftpers never found out.

RED would benefit from two variants - per packet (when per-packet ops 
are the bottleneck) and per-byte weighting, though it doesn't seem to be 
described that way much. This sounds a lot like per-byte (the more 
common case now anyway), except that RED is statistical (everyone gets 
slammed, proportional to their load) and this hits each in series 
(largest user first, then next-largest when largest backs off, etc.). 
Was there ever any backlash (software oscillation or people complaining) 
from that?

Joe
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