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To: cs551@merlot.usc.edu
Subject: Re: lecture 16 slide 21 
Date: Tue, 01 May 2007 21:57:22 -0700
From: william@bourbon.usc.edu

Someone wrote:

  > Its kind of confusing for me  what u replied back in the last
  > mail. Actually its clearly indicated in the research paper by
  > Ramakrishnan page no 159 paragraph 2
  > 
  > "We call the point at which throughput falls
  > off rapidly before the network reaches congestion collapse as the
  > cliff. This is
  > also the point at which the response time approaches infinity.
  > The purpose of a
  > congestion control scheme [2, 14] is to detect the fact that the
  > network has
  > reached the cliff, resulting in packet losses, and to reduce the
  > load so that the
  > network can recover to an uncongested state. "

So far so good...  Like you said, this is about the "cliff".

  > this clearly means that they also mean the cliff and knee as the
  > same thing as in congestion control mechanism

I don't know why you said that!  If you read the next two
sentenses, it defines the "knee" to be at a different point
(same as what we showed in our slides).

  > So i guess there should be no reason for multiple understanding
  > of knee and cliff

I would disagree.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>




  ----- Original Message -----
  From: william@bourbon.usc.edu
  Date: Tuesday, May 1, 2007 1:44 pm
  Subject: Re: lecture 16 slide 21
  To: cs551@merlot.usc.edu
  
  > Hi,
  > 
  > Just want to mention that not all people agree on the
  > terminology used in [Ramakrishnan90a].  In [Ramakrishnan90a],
  > the authors used the term, "knee of the delay curve" to mean
  > what others would call the "knee of the throughput curve".
  > 
  > Others would argue that the "knee of a curve" is the part
  > that "bend the most" (i.e., smallest radius of curvature).
  > If you look at the delay curve, it bends the most at the
  > point that corresponds to the "cliff of the throughput curve".
  > --
  > Bill Cheng // bill.cheng@usc.edu 
  > <URL:http://merlot.usc.edu/william/usc/>
  > 
  > 
  >  -----Original Message-----
  >  Date: Mon, 30 Apr 2007 22:00:12 -0700
  >  From: william@bourbon.usc.edu
  >  To: cs551@merlot.usc.edu
  >  Subject: Re: lecture 16 slide 21 
  > 
  >  Someone wrote:
  >  
  >    > In lecture 16 slide no 21(power and load) I guess in the graph
  >    > the Knee line is shown wrong and it should be the first line..
  >  
  >  You are correct.  There are other slides that show the knee
  >  at the right place:
  >  
  >      slide 50 of lecture 12
  >      slide  4 of lecture 13
  >  
  >  Thanks for catching this one.
  >  --
  >  Bill Cheng // bill.cheng@usc.edu 
  > <URL:http://merlot.usc.edu/william/usc/>