Subject: RE: [Ospf-manet] Initial Scenario Description

From: "Henderson, Thomas R" <[email-masked]>
Date: Thu, 12 Jan 2006 23:12:19 -0800

> 
> Tom: Can you elaborate on why you think that a sparse network may be
> uninteresting ?. A dense network may not be always the worst case
> scenario for sparse network. 

I am not questioning the applicability of sparse networks, but was
mainly reacting to the range of numbers that you proposed.  For
instance, if the range is 500/50 = 10 m, and you have ~100 nodes
uniformly on the 500m^2 grid, no nodes can communicate.

I think that what we want to do is to adjust the parameters so that the
average physical degree of the nodes is reduced, to obtain sparser
networks, but if the connectivity gets too poor, it gets uninteresting,
IMO.

> 
> It is true that not all networks are 802.11 radios. I will take a look
> at the directory cited by Tom to see whether different channel model
> characteristics is an easy parametric exercise. Changing the channel
> model, if/when deemed necessary can be a second step, taken up only if
> we all feel its burning need. 

We are not using the most accurate (validated?) 802.11 model, but it
does have the property that the loss probability gradually drops off
with range, which is in line with experiments such as the Rooftop
(Aguayo, Sigcomm 04) study.  This is one of the main properties that I
wanted to make sure was in the model, and the slope of the dropoff is
configurable.  Regarding the MAC, in some earlier work we used a simple
TDMA model to replace 802.11 MAC (with same physical layer) and the
results on how OSPF performed didn't change signficantly.

> 
> Some more thoughts on pause time increasing range.... This parameter
> could be a second level factor which makes the range ratio a dynamic
> variable creating an effect of the network switching between sparse
> connectivity to dense connectivity and vice-versa during the network's
> life. I remember a 802.15 like fixed wireless network which 
> would behave
> like this on clear mornings and later change when a lot of delivery
> trucks parked around the network in the afternoon. Don't we need to
> consider the effect of such changes on algorithm behavior....

It seems feasible to be able to model this, but it would be nice to have
some data about how the range changes rather than picking magic numbers.

Tom

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From: Alvaro Retana <[email-masked]>
Date: Fri, 13 Jan 2006 11:26:25 -0500

On 1/13/2006 2:12 AM, Henderson, Thomas R wrote:

> uniformly on the 500m^2 grid, no nodes can communicate.

Yes...but by the nature of the model, each node should chose it's next 
position in the grid randomly -- the situation in which all the nodes 
"randomly" chose a uniform distribution shouldn't happen.  In fact, I 
remember reading somewhere that random waypoint tends to concentrate the 
  nodes towards the center of the grid (??)...increasing the probability 
of connectivity.

Even if the radio range is small and the probability of complete 
connectivity is low, the model serves to look at the behavior of 
(potentially) small groups as they come in touch with others and their 
members move from one group to another...

Is there any prior agreement that keeps us from testing scenarios with 
noncontiguous networks??  [Just asking...]

> networks, but if the connectivity gets too poor, it gets uninteresting,

Is there a variable in the model that can control the physical degree?? 
  Or are you suggesting that it be controlled by changing the radio 
range, the size of the grid and the number of nodes in the network to 
guarantee a certain meshiness??

Regards,

Alvaro.