[e2e] Agility of RTO Estimates, stability, vulneratibilites

[Detlef Bosau]

"David P. Reed" wrote:
> 
> Sireen Habib Malik wrote:
> 
> >
> > What "network" should one consider when estimating RTO's (as given in
> > the topic)?
> >
> >
> A discursive answer - from the abstract to the concrete - follows:
> 
> That depends on why you are doing the measurement - in particular, what
> you intend to use the measurement for...   a corollary of my rant is
> that measurements acquire their meaning partly from their context of use.


O.k. Perhaps it is helpful for me to return to the starting point of
this discussion.

Basically, I want to understand the system model of TCP. Thus, I want to
talk about the RTO measurement used in TCP and its inherent limitations.
I don´t want to fix them. I only want to understand them.

Lucky me, I found Raj Jains Paper on Divergence of Timeout Algorithms...
online. And now I´m trying to obtain the paper by Lixia Zhang, Why TCP
Timers don´t work well. And primarily of course I want to get and to
read the paper on Edge´s algorithm. I think, that´s what I want and what
is my next step. Understanding the rationale behind Edge´s algorithm,
which is used until today AFAIK.

The discussion whether to use Edge´s algorithm or not has surely been
conducted quite thoroughly during the past twenty years, so I simply
assume that Edge´s algorithm is a good choice.

And once again: When I startet this discussion, my interest was not
primarily to build the one, perfect, phantastic universal network model.
There are numbers of them around, they may be right or wrong, I don´t
know. And I don´t have the possibility to check that.

The rationale behind this is my Path Tail Emulation algorithm, it may be
convincing or not at the moment.

The simple question is: When I hide a network´s last mile, e.g. a mobile
wireless network, behind some kind of PEP and thus provide the sender
with a "changed RTT behaviour", which any spoofing or splitting PEP
does, what is the ideal RTT behaviour? I.e. an RTT behaviour which makes
Edge´s algorithm work perfect?

And I don´t even care for any kind of network in between. Neither do I
for the often so beloved cross traffics. Whenever I get a paper
rejected,
at least one reviewer misses cross traffics. Perhaps the most stupid
comment on this one was: "You simply must simulate all possible
scenarios,
Mr. Bosau, it´s a matter of industry!" Wow. Perhaps I´m stupid, but to
the best of my knowledge, the number of network scenarios is infinite.

Now, 1 as an approximation for infinity is not better and not worse then
2 or 10 or 100. So, perhaps this standard excuse for paper rejection
should undergo some careful rethinking in that way, that of course a
reasonable choice of scenarios should be provided - but that´s enough.

In addition, I know that cross traffic does not improve network
performance. This is similar to bad plugs, a sudden system crash at a
computer
or a failure of the public utilities. (N.B. From my experience, this is
one of the worsest reason for system failure ever. Thus it should
be part of any simulatin *SCNR*)

However, this does not matter for my little playground. I want to make a
PEP behave as good as possible. And when there are bad guys who flood a
network with crosstraffics, or Al Quaida bombs the utilities - sorry, I
can´t help it. This is far beyond my sphere of influence. And it´s far
beyound a PEP´s sphere of influence. My only intention is to have
splitting and spoofing PEP´s not worsen the situation. 


Therefore my only simulation scenario is:

Sender----------------PTE/PEP-----Receiver

"------------" are some networks in betwwen.

For a TCP Sender this appears as 

Sender---------------"Receiver".

And now, it´s my intention to have the "Receiver" as well behaved as
possible.

Whatever will be placed in between could be designed best, that´s my
firm conviction, if existing systems are well behaved and compliant 
to _explicit_ requirements. It´s some sort of induction argument: Any
system/node/structure/.... placed into a network must not worsen
it´s performance, at least not more then inevitably necessary.

So, first of all it´s my interest: What are the vulnerabilities of
Edge´s algorithm? (This is more concrete as the original question. But I
have learned, that Edge´s algorithm is the matter of interest here.) 

When I _know_ them, I (hopefully) can _avoid_ an inappropriate
behaviour.

That´s all I want to do.

As I said: This is my little playground.

Detlef

-- 
Detlef Bosau
Galileistrasse 30
70565 Stuttgart
Mail: detlef.bosau at web.de
Web: http://www.detlef-bosau.de
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