Subject: OPNET & AODV

From: "M. Kamel" <[email-masked]>
Date: Tue, 18 Dec 2001 19:07:19 +0200

Hi,
I'm doing a research on routing protocols for ad hoc networks.. I want to use the OPNET as my developing tool.. I've downloaded the AODV implemenation made by Leonard Miller .. 
BUT, before I begin working, I need to be sure that the results obtained from this implementation match with other results submitted in any AODV research paper such the one attached in this E-Mail..
Did anyone simulate any of the graphs presented in this paper on the downloaded AODV OPNET implemenation ? If so, please send me the graphs so that I can be sure of the similarities between both.. This way, I can begin my research on OPNET..
Please help. I would really appreciate a fast reply..

Regards,
M. Kamel

---

From: Leonard Miller <[email-masked]>
Date: Tue, 18 Dec 2001 15:26:44 -0500

Note:  Mohammed is referring to the NIST model for AODV in OPNET,
developed by guest researcher Lyes Guemari, who is back now in France.

--Len Miller

> "M. Kamel" wrote:
> 
> Hi,
> I'm doing a research on routing protocols for ad hoc networks.. I want
> to use the OPNET as my developing tool.. I've downloaded the AODV
> implemenation made by Leonard Miller ..
> BUT, before I begin working, I need to be sure that the results
> obtained from this implementation match with other results submitted
> in any AODV research paper such the one attached in this E-Mail..
> Did anyone simulate any of the graphs presented in this paper on the
> downloaded AODV OPNET implemenation ? If so, please send me the graphs
> so that I can be sure of the similarities between both.. This way, I
> can begin my research on OPNET..
>                         Name: comparison
>                         Type: unspecified type
>    comparison                 (application/octet-stream)
>                     Encoding: quoted-printable
>              Download Status: Not downloaded with message

-- 

._.. . _.   __ .. ._.. ._.. . ._.   ._ _   _. .. ... _

Leonard E. Miller, Wireless Commun. Technologies Group
    National Institute of Standards & Technology (NIST)
    100 Bureau Drive Stop 8920, Bldg. 820, Room 445
    Gaithersburg, Maryland 20899-8920
Phone: 301-975-8018        Fax: 301-590-0932
email: [email-masked], [email-masked]
http://w3.antd.nist.gov/wctg/
._ _. ._ ._.. _.__ ... .. ...   ._ _. _..  ... .. __ .._
.._. ._ _ .. ___ _. ___...   .__ .. ._. . ._.. . ... ...

---

From: Jason Ballah <[email-masked]>
Date: Tue, 18 Dec 2001 16:46:52 -0500

I have not done any comparisons with the AODV model to other published 
results, but the AODV documentation does point out that they ran into 
problems with OPNET's 802.11 implementation when they enabled the 
RTS/CTS handshake.  This can cause other than desired results under a 
number of scenarios.

Basically the MAC causes segmentation faults in UNIX and NIL pointer 
problems in windows when it tries to send packets of size zero.  I also 
experienced this problem with the DSR model, and have created a fix for 
it using the OPNET 8.0.C 802.11 implementation.  I do not claim that 
this fix is perfect, but it has given me positive results on my 
experimentations and simulations.  If you would like a copy of the 
802.11 module for OPNET 8.0.C please let me know.

Best Wishes
- Jason Ballah  

M. Kamel wrote:

> implemenation made by Leonard Miller <mailto:[email-masked]>  ..
>
> comparison
> Content-Type:
> application/octet-stream
> Content-Encoding:
> quoted-printable

---

From: "M. Kamel" <[email-masked]>
Date: Wed, 19 Dec 2001 00:20:44 +0200

This way, I can't use the AODV on OPNET as a basis of my research..
how can I be sure that it's correct if I can't compare its results with published ones ?! right ?

Thanks for replying..
  ----- Original Message ----- 
  From: Jason Ballah 
  To: M. Kamel 
  Cc: [email-masked] 
  Sent: Tuesday, December 18, 2001 11:46 PM
  Subject: Re: OPNET & AODV

  I have not done any comparisons with the AODV model to other published results, but the AODV documentation does point out that they ran into problems with OPNET's 802.11 implementation when they enabled the RTS/CTS handshake.  This can cause other than desired results under a number of scenarios. 

  Basically the MAC causes segmentation faults in UNIX and NIL pointer problems in windows when it tries to send packets of size zero.  I also experienced this problem with the DSR model, and have created a fix for it using the OPNET 8.0.C 802.11 implementation.  I do not claim that this fix is perfect, but it has given me positive results on my experimentations and simulations.  If you would like a copy of the 802.11 module for OPNET 8.0.C please let me know.

  Best Wishes
  - Jason Ballah  

  M. Kamel wrote:

    Hi,

    Regards,
    M. Kamel
          comparison Content-Type: application/octet-stream 
                Content-Encoding: quoted-printable

---

From: Leonard Miller <[email-masked]>
Date: Wed, 19 Dec 2001 10:17:00 -0500

Jason,

I hope you will report the bugs to OPNET and your fixes for them.  At
NIST, we have been paying close attention to the OPNET 802.11 MAC layer
model and found some small bugs in the operation of the backoff
algorithm.  Fixes have been found by the very responsive OPNET folks and
will be incorporated in the next patch for OPNET.  None of these bugs
seem to have a great impact on the overall performance of the network as
modeled, but did affect the detailed statistics of the backoff algorithm
slightly.  It only mattered to us because we are doing a comparison of
backoff algorithms.

Speaking to Mohammed Kamel's concern about choosing an AODV model for
study, I can sympathize with his wanting to have a validated model in
hand before investing his time and effort.  The NIST AODV model was
subjected to independent review for correctness and was found to be
faithful to the IETF draft that was used in its development.  Although
many people use OPNET for MANET simulation (not as many as use ns-2,
apparently), there are few published results using OPNET.  The
documentation for the NIST AODV model does include some graphical
results that indicate the operation of the model for a particular
scenario, but none that are direct comparisons with published results. 
At the moment, we don't have the personnel needed to do such a
comparison.

Mohammed and others faced with choosing a simulation model should
consider that, even if a simulation model has been proven, when you
actually use it you have to be extremely alert all the time in order to
ensure reasonable results!  In other words, the model could be a decent
and reasonable abstraction of the protocol or algorithm, but it is
always possible to set up a scenario and set of parameters for it that
are invalid or unreasonable.  It's comforting to get the same results as
another researcher for the same assumptions, but that doesn't guarantee
that you won't make a mistake in applying the model in the next case you
study.

People using simulations must be aware of the limitations and not take
the results too literally.  A good example is the paper in the June 2001
issue of IEEE Communications Magazine entitled, "Does the IEEE 802.11
MAC Protocol Work Well in Multihop Wireless Ad Hoc Networks?"  The
authors used an ns-2 simulation, which (unlike OPNET) models the
different sensitivities of an 802.11 receiver for carrier sense and for
correct packet demodulation.  Setting aside the issues of realistic
propagation models, possible capture effects, etc. that separate real
world physical layer performance from most simulations, the authors of
the paper effectively demonstrated by their choice of a linear
configuration of wireless nodes that the IEEE 802.11 MAC layer can
behave unfairly because the carrier-sense distance is greater than the
communications range.  It was valid for the authors to set up such a
scenario to prove this point.  But everyone should realize that the
scenario is an abstraction and results for other scenarios will
certainly differ (not to mention results in practice), so perhaps the
authors went too far in saying "this wireless LAN protocol does not
function well in multihop ad hoc networks."  They may be right, but the
fact that the scenario studied will almost never be encountered in
practice does weaken the argument, in my opinion.

I hope these comments don't discourage Mohammed or others who are
beginning to work with network simulations, just open their eyes a bit.

Jason Ballah wrote:
> problems in windows when it tries to send packets of size zero.  I
> also experienced this problem with the DSR model, and have created a
> fix for it using the OPNET 8.0.C 802.11 implementation.  I do not
> claim that this fix is perfect, but it has given me positive results
> on my experimentations and simulations.  If you would like a copy of
> the 802.11 module for OPNET 8.0.C please let me know.
> 
> Best Wishes
> - Jason Ballah
> 
> M. Kamel wrote:
> 
> > Hi,
> > I'm doing a research on routing protocols for ad hoc networks.. I
> > want to use the OPNET as my developing tool.. I've downloaded the
> > AODV implemenation made by Leonard Miller  ..
> > downloaded AODV OPNET implemenation ? If so, please send me the
> > graphs so that I can be sure of the similarities between both.. This
> > way, I can begin my research on OPNET..
>                         Content-Type: application/octet-stream
>          comparison

--