[e2e] How can we "model" mobile networks? was:Re: TCP Loss Differentiation

Detlef Bosau detlef.bosau at web.de
Tue Feb 10 02:46:48 PST 2009

David P. Reed wrote:
> My main point was that these loss processes are not characterizable by 
> a "link loss rate".  They are not like Poisson losses at all, which 
> are statistically a single parameter (called "rate"), memoryless 
> distribution.  They are causal, correlated, memory-full processes.  
> And more  importantly, one end or the other of the relevant link 
> experiences a directly sensed "loss of connectivity" event.
> Thus my point: one SHOULD NOT model practical TCP/IP congestion/flow 
> control based on an assumption of "links" with "loss rates" as if they 
> were Poisson loss processes.  One should instead focus on modeling 
> loss processes that come from congestion and from loss of link 
> connectivity or route changes arising from responses to connectivity 
> loss in the appropriate ways that reflect practical reality.
Your statement is somewhat discouraging in the sense that we know, how 
we SHOULD NOT model a mobile network.
And you put in question the _practical_ relevance of  quite a lot of 
work which models mobile networks using gilbert markov models and the 
like: The results may well hold in theory, however they might not hold 
in practical applications.

This leads to the question: How can we build some kind of a "model"?

Perhaps, these are actually two questions:

1.: What do we want to achieve?
2.: How can we assess a given approach, e.g. in a paper?

My question well points into the direction whether we deal with a 
"scientific" question - or a "technological" one. And of course it could 
be the simple question whether mobile networks are suitable for TCP at all.

One could well take the position:

TCP is sufficiently generic to run about any packet switching network, 
including IPoAC (RFC 1149), which has actually seen practical 
implementations. (Please note the particular meaning of "loss" and 
"conservation principle" in that context ;-))

Whether or not the system's behaviour is satisfactory to the user, 
depends on the technology in use and is not subject of a scientific 

Detlef Bosau                          Mail:  detlef.bosau at web.de
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