[tmrg] Fwd: An aggression metric?
Michael Welzl <michawe@ifi.uio.no> Thu, 14 July 2011 09:17 UTC
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From: Michael Welzl <michawe@ifi.uio.no>
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Date: Thu, 14 Jul 2011 11:17:16 +0200
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Subject: [tmrg] Fwd: An aggression metric?
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Hi TMRGers, I sent this message to ICCRG, but I think it should be of interest to TMRG'ers too, so here I'm forwarding it. Please carry out discussion on the ICCRG list, though. Cheers, Michael Begin forwarded message: > From: Michael Welzl <michawe@ifi.uio.no> > Date: July 14, 2011 11:15:19 AM GMT+02:00 > To: "iccrg@cs.ucl.ac.uk list" <iccrg@cs.ucl.ac.uk> > Subject: An aggression metric? > > Hi! > > Here's an idea. Our group's charter says: "The key goal of the > Internet Congestion Control Research Group (ICCRG) therefore is to > move towards consensus on which technologies are viable long-term > solutions for the Internet congestion control architecture, and what > an appropriate cost/benefit tradeoff is." > > For a "viable long-term solution", I think that the "aggression" of > a congestion control mechanism is important, but most evaluations > focus on its efficiency in terms of bandwidth utilization, fairness > among flows of their own kind, etc. By aggression, I mean: > - what happens when it fights against a standard TCP? > - what happens when it fights against its competitors, e.g. (insert > your favorite mechanism here)? > It's not uncommon to have a diagram that shows one of these things > in papers too, but what would really be good, I think, would be to > have a unified way of looking at it - an aggression metric. > Something that lets me conclude that, e.g., CUBIC is 7-aggressive, > HTCP is also 7-aggressive (of course these two are surely equal! he > he :) ), FAST is 3-aggressive, Westwood is 12-aggressive, whatever! > Something like that. > > Standard TCP could be the base unit (the number 1) here. We recently > finished a paper in which we present an extension of the TCP steady- > state throughput equation for multiple flows - i.e. from the packet > size, loss event rate, RTT, and now also the number of flows (N) and > the actual packet loss ratio, one can calculate the rate at which N > flows would send. This is the paper: > > Dragana Damjanovic, Michael Welzl: "An Extension of the TCP Steady- > State Throughput Equation for Parallel Flows and its Application in > MulTFRC", accepted for publication in IEEE/ACM Transactions on > Networking, 2011. > http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5756471&tag=1 > > The equation is also included in our MulTFRC draft: > http://tools.ietf.org/html/draft-irtf-iccrg-multfrc-01 > (btw, we're just about to finish an update of this document, stay > tuned) > > It wouldn't be hard to turn this equation around such that, from the > packet size, loss event rate, RTT, packet loss ratio and sending > rate, one could calculate how many standard TCP's (N) must have > produced (or would be represented by) this rate. This would also > work with floats, e.g. a calculation could yield N=3.52 or something > like that. Thus, one could carry out a "benchmark test" simulation > of a high-speed mechanism where it's confronted with different loss > and RTT conditions, and from its resulting rate, one could then say > that it's between X and Y-aggressive, i.e. representing between X > and Y TCPs. > > Would that be a useful "aggression" metric? > > e.g. an alternative could be to produce a simpler equation which is > not so much based on all the specifics of TCP (slow start etc), > maybe just use N * MSS/RTT * (1/sqrt(p)), see where a modern TCP > with slow start stands in relation to that, and where high-speed > mechanisms stand in relation to that. Or should use an even simpler > equation? > > Do we even need or want such a metric? > > Cheers, > Michael >
- [tmrg] Fwd: An aggression metric? Michael Welzl