Subject: RE: [manet] Re: OPNET 802.11 model ?

From: "Yang, Lily L" <[email-masked]>
Date: Thu, 5 Jun 2003 10:53:08 -0700

Hi, Mihail --

I just started using OpNet for our multi-hop ad hoc network simulation and already had issues with it. For example, static routing doesn't work at all and so it is hard to simulate multi-hop static routes unless using some cumbersome workaround. Since you've had some experience already and would you care to elaborate some of the trouble you've encountered? That might help me make up my mind in picking the right simulation tool. What I heard so far is that the PHY model in OpNet is much better than ns-2 and others. what is your opinion on that?

Thanks,
Lily

-----Original Message-----
From: Mihail L Sichitiu [mailto:[email-masked]]
Sent: Thursday, June 05, 2003 10:06 AM
To: [email-masked]
Subject: [manet] Re: OPNET 802.11 model ?

Sunil,

I have very bad experience with the 802.11 model in Opnet. It seems to
work reasonably well in managed mode (i.e. with access points), but it
breaks badly in ad-hoc mode (which I assume you'd like to use, given the
list orientation).

The 802.11 model keeps changing with every version (every 3-6 months), so
if you fix some of the bugs, you'll have to fix the *same* bug over and
over again in the subsequent versions, on top of finding the new bugs.

Moreover, despite the commercial nature of the product, the support is
very poor: every time you call or email them you talk with a different
person, that understands more or less a part of your problem (from
scratch). The support persons are not the same as the programmers, so they
have no idea how a specific feature is implemented, or whether is
implemented at all.

I am planning to switch to ns-2 this summer, and I suggest you do the
same, and skip the pain we've been going through the last two years. I
also found a small bug in the ns-2 code 1 year ago, I'm not sure if it's
still there.

I didn't see any Opnet 802.11e models, and I expect that it will be a
while until they'll show up.

Best regards,
Mihail Sichitiu

_______________________________________________________
Mihail L. Sichitiu
Assistant Professor,              Phone: (919) 515 7348
Dept. of ECE, Campus Box 7911     Fax:   (919) 515 5523
NC State University
Raleigh, NC 27695-7911   http://www4.ncsu.edu/~mlsichit
_______________________________________________________

> Date: Wed, 4 Jun 2003 18:45:12 -0700 (PDT)
> From: Sunil Sharma <[email-masked]>
> To: [email-masked]
> Subject: [manet] OPNET 802.11 model ?
>
> --0-365983582-1054777512=:67739
> Content-Type: text/plain; charset=us-ascii
>
> Hi,
>
> I am new in modeling. Does anyone know if OPNET has correctly working 802.11 model ? Does anyone even know of 802.11e or 802.16 model in OPNET ?
>
> I am starting with my M.S thesis and I need to decide if I can use OPNET 802.11 model (of which I have already had lot of negative feedback from couple of users). So any feedback and work around would be very useful.
>
> Thanks
>
> Sunil
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---

From: John Stine <[email-masked]>
Date: Thu, 05 Jun 2003 15:00:13 -0400

Lily,

    I did some modeling with the OPNET's 802.11 model in an older version and found that it did not serve my needs so I revised it.  Later I sent my revisions to OPNET and they then added the features I  wanted in the next upgrade.  I believe if you find a deficiency in one of their models they are more than will to correct it.  The key is documenting your changes well and explaining why you are making them.  I used a search string to help the OPNET engineers find my changes.  They want their models to be the best they can be.

    The physical model in opnet is implemented in stages.  You have full control of each stage and can add a number of features unique to your research, for example, a completely different modulation scheme or unique propagation model.  Also, you probably can find some additional models, if not now, later, that users have developed to enhance the physical layer models.  I have not worked with their 802.11 model for a while now but when I last used it, one feature I wished was modeled was the process of selecting the data rate and then the modeling
of interference amongst radios using different data rates.  The model I am familiar with, ( version 7), did not show this interference.

John

---

From: Mihail L Sichitiu <[email-masked]>
Date: Thu, 5 Jun 2003 15:31:50 -0400 (EDT)

I'm very glad you had a good experience with Opnet. Unfortunately it was
not the case for us.

In the end (last 2-3 months) we eventually got shut off the Opnet support
completely: we are at a university (NCSU) with about 100 licenses and the
only persons allowed to talk with the Opnet support are the same persons
that install the software, i.e. the system admins. The students, cannot
access the Opnet support, because the same password used to get on the
Opnet support forum is also used to manage the licenses. Kind of like, I
cannot give the key to my research lab to my students, because the same
key also starts my Porche and opens the front door of my home.

Regarding your observation that they want their models to be the best, I
have no doubt about it; however, I don't see that they are willing to make
the effort to make it so. After six-seven years after the publication of
802.11 standard, they still have bugs in their models. And 802.11 is not
just one of the many wireless standards: for now is "the" standard for
wireless LANs. The hardware you buy from the store works better than their
models (I don't really have the experience, but I would think that the
software would be easier to do than the hardware, as you can gloss over
some details).

For a better 802.11 physical model, look at the model in Opnet 8 (actually
>8.1.C if I remember correctly): it is vastly improved (it drops the
notion of a deterministic transmission radius (with zero probability of
reception after a certain point), and the packets start to be received
with a certain probability depending on the signal to interference + noise
ratio), and yet it's not well tuned (the carrier is sensed with high
probability even at distances many times the transmission radius).

Also, in Opnet you would think that you can replace an Ethernet MAC layer
with an 802.11 MAC and keep the rest of the stack the same, but
unfortunately it's not the case.

On the other hand, it has a great GUI and decent tutorials :-)

Best regards,
Mihail Sichitiu

Thu, 5 Jun 2003, John Stine wrote:

> Lily,
>
>     I did some modeling with the OPNET's 802.11 model in an older
>     version and found that it did not serve my needs so I revised it.
>     Later I sent my revisions to OPNET and they then added the features
>     I wanted in the next upgrade.  I believe if you find a deficiency in
>     one of their models they are more than will to correct it.  The key
>     is documenting your changes well and explaining why you are making
>     them.  I used a search string to help the OPNET engineers find my
>     changes.  They want their models to be the best they can be.
>
>     The physical model in opnet is implemented in stages.  You have full
> control of each stage and can add a number of features unique to your
> research, for example, a completely different modulation scheme or
> unique propagation model.  Also, you probably can find some additional
> models, if not now, later, that users have developed to enhance the
> physical layer models.  I have not worked with their 802.11 model for a
> while now but when I last used it, one feature I wished was modeled was
> the process of selecting the data rate and then the modeling of
> interference amongst radios using different data rates.  The model I am
> familiar with, ( version 7), did not show this interference.
>
> John
>
> "Yang, Lily L" wrote:
>
> > Hi, Mihail --
> >