[Iccrg] draft-irtf-iccrg-welzl-congestion-control-open-research-00.txt

[Bob Briscoe]

Michael, Dimitri,

During the presentation of this at the last ICCRG mtg I identified some 
extra challenges or adjuncts to the existing ones, which I'll record here 
and add a few review comments too (tho I'll do a full review later and at 
the same time I contribute some better thought-thru text if req'd).

Challenge 1 sort of misses the top level question that you (Michael) 
articulated well at the previous ICCRG mtg in LA:
- What's the minimum support in network elements for future-proofed (incl 
hi-speed) congestion control?

Note the term "network elements" not "routers" - as Tim Shepard said, we 
have to work with congestion in lower layers too (and if doing explicit 
congestion notification, we have to propagate congestion info up the layers).

I can probably contribute text to "Challenge 8. Misbehaving S&Rs". For 
instance, I have a fair idea of which aspects of the DoS problem might be 
solved by better congestion control.

I think we need a "Challenge 9: Multicast Congestion Control"
Both streamed-media and messaging types of multicast.

Other more detailed questions:

An additional question in 3.1.4 (which should probably be entitled 
feed-forward notification, not feedback)
- what's the minimum information intensity of congestion notification (More 
than 1-bit per packet? Is sensing congestion delay variation a sufficient 
alternative?)

Also:
- Is a good system & equipment design goal to sacrificially throttle 
bit-rate to avoid CPU overload (so the brain can still work out what to do 
about congestion)?
- distinguishing per-packet congestion from per-byte congestion (similar 
problem to distinguishing congestion from wireless transmission losses)?
- ever-widening range of packet sizes: if design equipment for larger ave 
pkt size, gets overloaded with flurries of small packets.




Bob


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Bob Briscoe, <bob.briscoe at bt.com>      Networks Research Centre, BT Research
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