Subject: Ad-Hoc Simulation Model Questions

From: "A. Bruce McDonald" <[email-masked]>
Date: Tue, 9 Nov 1999 13:18:10 -0500 (EST)

Hi,

I am in the process of designing a model to simulate moderately large 
(100-1000 nodes) ad-hoc networks with nodes moving at speeds ranging 
from 10 to 50 kph. My research is focused on network-layer issues 
(routing), hence, my post to the MANET group! However, as an inevitable 
consequence of conducting research in wireless networks, it seems that 
some physical and MAC-layer issues arise...

I am seeking opions, advice, and references from others on the following 
modeling issues

(1) What range of radio transmission ranges (distance) would be
    realistic and representative of what is available today or
    might be expected to be available in the near future? Assume
    a free-space propagation model. 

(2) In the simulation of routing protocols one may conclude that 
    it becomes both computationally excessive, as well as requiring 
    assumptions that may not generalize well to simulate the MAC-layer 
    directly. However, MAC-layer contention is an important component 
    that can affect network-layer performance. Hence, it seems that it 
    should be accounted for in some way that is as general and as 
    computationally efficient as possible.

    The question is, does anyone know of any
    analytical, or empirical models that can be used
    to estimate the MAC-layer delay that depend on some reasonable
    set of parameters (eg. node density (mean number of neighbors),
    mean offered load, etc. ) ? For example, Bux derived an
    analytical expression to model the delay on an ethernet (802.3)
    network given a reasonable set of assumptions and parameters.

(3) What sort of workload models can people suggest?
    It seems that CBR sources with uniform traffic distributions
    (random selection of source-destination pairs) is quite
    common in recent ad-hoc simulations. What other models are
    being used? Is something like tcplib outdated because it does
    node reflect current Internet traffic? 

Thanks to anyone for any advice on these matters! Please post answers to 
MANET for everyon's benefit.

Bruce McDonald

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From: Ashish Ahuja <[email-masked]>
Date: Wed, 10 Nov 1999 02:10:40 +0530 (IST)

hi bruce,
>     a free-space propagation model. 

	As a start u can use radio transmission ranges of the order of
200-250 metres. this is the typical transmission range of lucent
wavelan radios. u can lookup the transmission power of ur(or typical) 
wireless cards and estimate a range based on free-space propagation model.
>     node reflect current Internet traffic? 
	I think TCP and CBR sources will suffice for data. We used these
sources to conduct simulations.u can lookup for specific types of sources
if u wish to model multimedia traffic. 
					best wishes,
					Ashish

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From: "Ken Tang" <[email-masked]>
Date: Tue, 9 Nov 1999 14:06:06 -0800

Hi,

----- Original Message -----
From: A. Bruce McDonald <[email-masked]>
To: <[email-masked]>
Cc: A. Bruce McDonald <[email-masked]>
Sent: Tuesday, November 09, 1999 10:18 AM
Subject: Ad-Hoc Simulation Model Questions

>     a free-space propagation model.

For WaveLAN radios, the power range for 2Mbps is 365m for an open
environment and 167m for a semi-open environment.  For 1Mbps, it's 425m
and 198m, respectivley.

>     network given a reasonable set of assumptions and parameters.

Are you writing simulation tools or coming up with analytical models?  If
it's
the former, there are several simulators availabe with detailed MAC and
routing
layers.  One of which is GloMoSim.  You can find more info about it at:

http://pcl.cs.ucla.edu/projects/domains/glomosim.html

>     node reflect current Internet traffic?

Don't know about this one.  I would like to know about this also.

> MANET for everyon's benefit.

Ken

---

From: Miguel Sanchez <[email-masked]>
Date: Wed, 10 Nov 1999 09:59:51 +0100

Hi Bruce,

>     a free-space propagation model.

As other people is posting, a typical value ranges around several hundred
meters outdoor. However, there is a strong relationship between the
transmission range and the MAC layer behavior (i.e., a longer transmission
range means a higher number of neighbors contending for the channel,
therefore, MAC throughput will decrease or at least the available bandwith
for each node will be lower).

So, even if your transceiver is able to reach a long distance, you can
obtain a better MAC-layer throughput by *lowering* the transmission range
adaptively. (Please note too that this not necessary mean higher network
layer throughput!).

Some information about the relationship between mobility models and
transmission range can be found in
http://www.ee.surrey.ac.uk/Personal/G.Aggelou/PAPERS/mmt99.ps.gz

>     computationally efficient as possible.

Even there are several simulators dealing from signal elements to data
packets, it is a common simplicative approach not simulate the whole
system. And this is also related to your question number three: MAC delay
can be very important, but applications are likely the most important
element in simulating a system, and as Prof. Tanenbaum states " .. they are
what the systems are bought for". However you can see that some simulations
use some simplified model for applications too.

>     network given a reasonable set of assumptions and parameters.

A certain MAC layer is only a framework, so in order to obtain the delay
you can expect from MAC layer you should know the coding scheme and the
wireless adapter signal level features and the propagation environment
(i.e., BER, propagation exponent, etc).

>     node reflect current Internet traffic?

Related to my previous comment I see that CBR can be a simple model, but my
question here is: what application service this CBR data is modeling? If
you want a more realistic packet source model, you'll have to fix the
applications that run in the mobiles (which likely is not know in advance,
because it can depend on the network capacity too).

I'm afraid that I'm pointing out more problems that I'm answering you, but
I hope this can be of some help too.

Best regards,

Miguel

--
Miguel Sanchez Lopez                            |       [email-masked]
Universidad Politecnica de Valencia             | voice:+3496 387 9700
Camino de Vera, 14                              | fax:  +3496 387 7579
46071 VALENCIA (Spain)                          |

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From: Rex Buddenberg <[email-masked]>
Date: Wed, 10 Nov 1999 11:38:18 -0700

>environment and 167m for a semi-open environment.  For 1Mbps, it's 425m
We recently had a couple thesis students see just how far they could go
with 802.11 stuff.  The numbers quoted above depend on some assumptions
that one can change.

The colorful version is that the students put AP on the roof of a building,
plugged it into the campus LAN, attached a higher gain antenna, then took
the other end out to a flying club airplane ... they were snapping pictures
of the whales in Monterey Bay and e-mailing them back to the admiral.  The
airborne kit included stock Wavelen cards and a directional yagi antenna
that one of the students hand pointed back in the general direction of the
school.  They were predictably and reliably getting 15-20 miles range.
[!!]  They did not fool with the speeds so all this was running at 2Mbps.
b

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From: Joe Macker <[email-masked]>
Date: Wed, 10 Nov 1999 20:28:59 -0500

There are certainly commercial omnidirectional systems that allow long
ranges (e.g., Metricom, Nova) for sensible reasons (miles,etc often
sacrificing throughput for improved range operation) and those designed
to operate at shorter ranges for sensible reasons (e.g., Bluetooth). 
Wireless LAN technology range designs tend to be in between (when used
without directional antennas). Plenty of good books with propagation
models for link budget analysis but there are several degrees of freedom
and a spectrum of choices..no pun intended.