[e2e] Congestion control as a hot topic in IETF

Ted Faber faber at isi.edu
Tue Mar 19 12:31:33 PDT 2013

On Tue, Mar 19, 2013 at 02:21:45PM +0100, Detlef Bosau wrote:
> Looks like quite some moving target to me.
> I only repeat my three goals - because these are not invented by me but 
> (nearly word by word) from the papers by Van Jacobson and Raj Jain.

Let's be precise.

Your sources are impeccable, but you're picking out the mechanisms and
not the problem.  Jain's A Timeout-Based Congestion Control Scheme for
Window Flow-Controlled Networks in JSAC 1986 is beautifully clear on the
spirit of the issue:

	A strategy to reduce the impact of overload in a network is
	called congestion control. 

He goes on to clarify:
	We distinguish between the terms flow control and congestion
	control as follows. Flow control is an agreement between a
	source and a destination to limit the flow of packets without
	taking into account the load on the network. The purpose of flow
	control is to ensure that a packet arriving at a destination
	will find a buffer there. Congestion control is primarily
	concerned with controlling the traffic to reduce overload on the
	network. Flow control limits traffic based on buffer
	availability at the destination, whereas, congestion control
	limits traffic based on buffer availability at intermediate
	nodes. Flow control is a bipartisan agreement Congestion control
	is a social (network-wide) law.  Different connections on a
	network can choose different flow control strategies but nodes
	on the network should follow the same congestion control
	strategy, if it is to be useful.

Keshav's thesis (http://dl.acm.org/citation.cfm?id=115995 ) takes this
further, recognizing that each user perceives congestion - Jain's
network overload - differently. He posits a utility/load tradeoff which
nicely frames the problem.  Congestion is perceived by a user when
asking the network for more service results in less utility. I
try to download another movie and all the things I'm doing suffer

Congestion control is about trying to keep the network providing more
utility for increasing load for the most users.

That's a lot of jibbering to say that we need congestion control so that the
#%$%^ network is worth using.

> Hence, the famous quote by Mark Twain comes to my mind: "//Having lost 
> sight of our goals, we redouble our efforts"

I believe you've saddled Mr. Clemens with another statement he never
made. Citation?

Ted Faber
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