[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[ih] Detlef's TCP questions

Am 19.05.2014 21:36, schrieb Bob Braden:
> Detlef,
> As Craig and Vint has pointed out, TCP never was GBN.

Interestingly, even some lectures take a different position.
It would be interesting to have an overview, how TCP is typically presented.
> Yes, any network researcher who wants to call him/herself a computer
> scientist should take seriously the experimentalist's task of fully
> understanding the assumptions and implementations of their test
> environment. That includes NS-2 simulations of TCP.

Myself, I have to admit that I trusted too much in the NS-2. And quite
some papers I've read rely heavily on the NS-2.
> Yes, in broad generality, the level of network science taught in many
> graduate schools is abysmal.  How can those with clue resist the
> temptation of real mony in industry or getting rich from a startup? So
> the next generation of largely clueless PhDs learn from clueless
> predecessors.

When I refer to the aforementioned slides, even the typical "model" of
TCP delay (serialization latency, MAC latency, propagation latency,
queueing latency) is taken as "word of god".

That doesn't mean, simulations were worthless. But I think, we should
treat them with a certain professional distance.

In my own simulator, I used GBN for TCP. After some discussions, I
decided to re-write my TCP code completely and eventually read RFC 793 a
bit more thoroughly than before, and eventually detected that RFC 793
explicitely requests an individual timeout for each packt.

I'm afraid, I'm not the only one who detects this discrepancy between
RFC 793 and many implementations quite late...

The reason for doing this work is, once again, TCP flow control - which
I think is not completely understood.

Admittedly, I did not always make friends with my colleagues. But this
is not my primary goal. My goal is to understand TCP and TCP flow
control and resource allocation.

And as for the first time, I did a TCP implementation for a simulator, I
thought, I understood TCP. And learned, I only understand a little part.

> During the period of Van Jacobson's development of the algorithms that
> bear his
> name, he wrote many lengthy, pithy, and informative messages to
> various public
> mailing lists about the hazards of the Internet and how his algorithms
> cope.

Some of these are (so my impression ;-)) im Craigs memory :-) And
perhaps, we can even ask Van himself :-)

What I want to do is to understand the questions and challenges during
the development, the alternatives - and the choices made.
And the reason for the decisions.


Detlef Bosau
Galileistra?e 30   
70565 Stuttgart                            Tel.:   +49 711 5208031
                                           mobile: +49 172 6819937
                                           skype:     detlef.bosau
                                           ICQ:          566129673
detlef.bosau at web.de                     http://www.detlef-bosau.de