Re: Delivery times in mobile networs? Re: Are there any persons interested in TCP over mobile wireless networks in Germany?

Am 13.12.2012 15:57, schrieb Jim Gettys:
>
>
>
> On Thu, Dec 13, 2012 at 6:15 AM, Eggert, Lars <[email protected] 
> <mailto:[email protected]>> wrote:
>
>     On Dec 12, 2012, at 16:38, Detlef Bosau <[email protected]
>     <mailto:[email protected]>> wrote:
>     > My central question at the moment is: Do we have stationary
>     packet delivery times on mobile wireless links?
>
> Not sure what you mean by "stationary".
>
> This crossed my radar screen:
>
> http://conferences.sigcomm.org/sigcomm/2012/paper/cellnet/p1.pdf
>

And there you find

> Simply speaking, the static value could be too
> small in large BDP (Bandwidth-Delay Product) links but too large
> in small BDP links.

And if you compare this to the "BDP Definition" as used e.g. in

> @article{ meyer,
>     author ="Michael Meyer and Joachim Sachs and Markus Holzke",
>     title  ="{Performance Evaluation of A TCP Proxy in WCSMA Networks}",
>     journal ="IEEE Wireless Communications",
>     year = "2003",
>     month = "October"
> }

you see, what I'm talking about.

Particularly, as the quoted paper uses the GPRS link's gross data rate 
for the calculation of the "Bandwidth-Delay Product", a term which is, 
decently spoken, complete nonsense in the context of mobile wireless 
networks.

I have to apologize for being upset, if you knew me a bit closer, you 
would surely understand my attitude.

If you have a look hat Little's paper (I think it's commonly known that 
the "Bandwidth-Delay Product" is the CS "conception" of Little's 
Theorem, of course used with the "CS conception" of the term 
"bandwidth", which was a subject of discussion in this list some weeks 
ago, you'll find that this is an equation between several expectations.

The average (i.e. expected) number of jobs in a queueing system equals 
the product of the average (i.e. expected) arrival rate times the 
avarage (i.e. expected) sojourn time.

As TCP employs a self clocking mechanism for clocking out sent packets 
and the delivery times in mobile links are non stationary (I did not ask 
for papers, because this were an open question, that mobile link's 
delivery times are not stationary is obvious, however the people I talk 
to don't believe me, this is a cause for my anger) neither the arrival 
rate nor the sojourn time have an expectation, hence Little's theorem 
simply does not apply here.

More simply: When you offer lots of load to a wireless interface (be it 
window- or rate-controlled, this doesn't make a difference) and the 
delivery time suffers from a sudden increase (I well know the lots of 
paper with Gilbert-Markov-Models and "link outages" - what is a "link 
outage" in mobile wireless networks? We work with mobile wireless 
networks for 20 years now and many guys still think in the black and 
white manner of a link being up or down! Although a simple look into the 
standards will tell you that e.g. for a GPRS link the .95 quantile for 
the delivery of 1024 byte packet varies (depending on the chosen QoS 
class and the link's properties) from 7 seconds to 375 seconds.

And please note the meaning of 0.95 quantile. When the mentioned 6 
minutes are over, it may well be that your packet is lost and no one 
told you about that.

So, when the delivery time suffers from a sudden increase - why do we 
wonder about buffer bloats then?

And when delivery times of, say, a HSDPA interfaces vary on a time range 
from some few milliseconds, why do we wonder, that TCP sending sockets 
seeing a RTT of, say, 50 ms, do not timely adapt?

  I first discussed this issue with academics in Germany 6 years ago, 
they did not believe me. I noted that the term BDP is completely 
inappropriate for mobile networks, no one believed me. For some reasons 
which don't belong here, I cannot afford papers at visible conferences 
and when I submit papers on that issue to conferences or papers, no one 
believes me.

I'm frequently taken for an idiot and rejected and offended - and when I 
claim, rain would consist of water, no one believes me.

On the one hand, I'm glad to see this paper.

On the other hand, I'm extremely upset and I hardly can describe my 
anger and bitterness here, although this must not be part of this list. 
But I'm only a human being, so I cannot ignore my emotions.

Detlef

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