[e2e] link between Kelly's control and TCP's AIMD

[Alex Cannara]

Lordy, Lordy, since when is a threshold or timeout linear?  If I drop 1% of a 
true fluid flow randomly, do I get 30% less out the other end of the pipe? 
One key to TCP's nonlinearity is its naive attempt to protect the network 
layer from congestion.  The folks in the '80s who trembled with anger at 
Metcalfe's prediction of Internet collapse lived through some bad, near-miss 
scares, but instead of fixing IP and the network-layer systems, chose to make 
the transport layer the guardian of the net.  This has always been a band aid, 
or kludge, depending on your upbringing, but it led to complacency and even 
religious fervor about "TCP", with cults even espousing foolery like "TCP 
Friendliness" and forclosing good ideas on doing a real fix for over a decade. 
  Of course the Internet bureaucracy did deal with idiotic IPv4 addressing, 
over as many years, and did so well we have IPv6 (or we hope we never will 
have it)!

{:o]

Alex

Saverio Mascolo wrote:
> well this is not a technical answer!  If you build a system made of linear
> subsystems (i.e. gains, delays and integrators) how can you get a nonlinear
> system?
> 
> Saverio
> 
> 
>>Well, only 15 years of modest network consulting for over 1000 modest
>>companies from GM on down.  :]
>>
>>Have VJ estimate how much delay is incurred by any current TCP under 1%
> 
> random
> 
>>packet loss; then 0.1%.  Or, have him or anyone else, itemize the
> 
> differences
> 
>>among TCPs deployed by, say, the top 10 systems vendors.
>>
>>There've been many archived discussions of how TCP does & doesn't work as
> 
> well
> 
>>as it should, given all the years that have passed, in which continued
>>protocol development could have, but did not, occur.  Thus the Internet --
> 
> a
> 
>>study in insecurity, capacity co-option, performance mediocrity,
> 
> engineering
> 
>>bureaucracy...  But, that's not what folks want to hear.  Which is why the
>>mediocrity continues and those of us in consulting & security have good
> 
> jobs &
> 
>>good profits.  :]
>>
>>Alex
>>
>>Saverio Mascolo wrote:
>>
>>>why do you think TCP congestion control is  not linear? I tend to agree
> 
> with
> 
>>>Van Jacobson when syas that a network is to a large extend  a linear
> 
> system
> 
>>>made of integrators, delays and gains.
>>>
>>>Saverio
>>>
>>>----- Original Message -----
>>>From: "Cannara" <cannara at attglobal.net>
>>>To: <end2end-interest at postel.org>
>>>Sent: Friday, February 18, 2005 6:12 AM
>>>Subject: Re: [e2e] link between Kelly's control and TCP's AIMD
>>>
>>>
>>>>And, without understanding/modelling TCP's nonlinear behaviors, it
> 
> will
> 
>>>only
>>>
>>>>serve for gross predictions.
>>>>
>>>>Alex
>>>>
>>>>Ted Faber wrote:
>>>>
>>>>>On Thu, Feb 17, 2005 at 01:31:08AM +0000, Damon Wischik wrote:
>>>>>
>>>>>>Roy Xu wrote:
>>>>>>
>>>>>>>I'm looking for a pointer to literatures that link the
>>>>>>>TCP's (discrete) AIMD to Kelly's (continuous) control
> 
> formulation.
> 
>>>>>>Kelly's continuous-time formulation uses a differential equation
> 
> model
> 
>>>>>>(also called a fluid model) for TCP. You should look at the
> 
> literature
> 
>>>>>>which describes this fluid model, starting with
>>>>>>
>>>>>>"A Fluid-based Analysis of a Network of AQM Routers Supporting TCP
>>>
>>>Flows
>>>
>>>>>>with an Application to RED", V. Misra, W. Gong, D. Towsley,
> 
> SIGCOMM
> 
>>>2000.
>>>
>>>>>Fluid flow congestion control analysis goes beck to these guys at
> 
> least:
> 
>>>>>%A D. Mitra
>>>>>%A T. Seery
>>>>>%T Dynamic Adaptive Windows for High Speed Data Networks: Theory and
>>>>>%Simulation
>>>>>%J Proc. SIGCOMM Symposium on Communications Architectures and
> 
> Protocols
> 
>>>>>%P 30-29
>>>>>%I ACM SIGCOMM
>>>>>%C Philadelphia, PA
>>>>>%D Sept 24-27, 1990
>>>>>