[e2e] Is a control theoretic approach sound?
ygu1 at cs.uic.edu
Wed Jul 30 09:31:43 PDT 2003
On Wed, 30 Jul 2003, Panos Gevros wrote:
> my assumption is that for any adaptive transport protocol the issue is to
> discover the (subjective) "target" operating point (as quickly as possible)
> and stay there (as close as possible) - tracking possible changes over time,
> so one optimisation plane is
> (smoothness, responsiveness)
> another optimisation plane is
> (capacity, traffic conditions)
> and I think it is a fair assumption that there is no single scheme that
> operates better than the rest over the entire spaces. (if there are claims to
> the contrary any pointers would be greatly appreciated).
> the question is at the boundaries of the ( Capacity, Traffic) space
> particularly at the (hi, low) end of this space
> *simple* (and appropriate) modifications to the existing TCP control mechanisms
> (i.e no rtt measurements and retransmission schemes more aggresive slow start
> and/or more aggresive AI in congestion avoidance)
> could have the same effect in link utilisation and connection throughput.
> I believe that this is possible but the problem with this approach is that it
> is "TCP hostile".
Well, I think to decide how "aggressive" the AI will be is not that
*simple* a problem :) It is not the more aggressive the better (even if
the per flow throughput is the only objective), right?
> Also my guess is that most of the complexity in "new" TCPs is because
> implementors attempt to be "better" (by some measure) while remaining
> "friendly" to the standard.
Yes, I agree, this is a headache problem.
> I have seen TCP implementation which in the case of the remote endpoint being
> on the same network it allows a very high initial cwnd value at slowstart -
> solving all performance problems (in the absence of "social" considerations..
> of course)
> Wouldnt this be a much simpler answer to the problems of the "demanding
> scientists who want to transfer huge data files across the world" (citing form
> the article in the economist magazine)
> ..in their case they know pretty much that the links they are using are in the
> gigabit range and there are not many others using these links at the same time.
But what if there are loss, especially continuous loss during the bulk
data transfer? No matter how large the cwnd is initially, it can decrease
to 1 during the transfer, then the problem arise again.
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