Subject: Re: When the AODV Hello Packet is exchanged withunidirectionallinks?

From: [email-masked]
Date: Fri, 27 Oct 2000 11:20:59 +0200

Hello Ravi,

A 13:06 25/10/00 -0500, vous avez écrit :
>If I understand your suggestion correctly, you are suggesting that the
>routing protocol should ignore all unidirectional links and restrict
>itself to bidirectional links only. 

I don't have the pretention to make such statement! I just noticed that
some (most) protocols needs bidirectional routes (because of the underlying
data link layer) but certain can deadlock in presence of unidirectional
links even if the appropriate bidirectional routes exist. The "black list"
is an attempt to solve this particular case.

Regarding the general concept of routing over unidirectional links, I
understood this is a very difficult issue. There would be the need of
deeply dedicated MAC layers as you mention in your long mail. 

Regards,
Philippe

---

From: Ravi Prakash <[email-masked]>
Date: Fri, 27 Oct 2000 10:58:19 -0500 (CDT)

HI Philippe,

I agree with you that several MANET routing protocols implicitly or
explicitly restrict themselves to bidirectional links only, and that they
will not work correctly in the presence of unidirectional links. 

I can think of situations of wrong routes being detected. This will either
result in unnecessary transmissions or incessant route discovery attempts
on the receipt of routing errors. 

However, I could not come across a situation in which where nodes would
deadlock. The situations that I have come across would appear more
like livelock. Here, I am interpreting "deadlock" in the operating
system/distributed computing context. So, could you please describe a
situation where a deadlock might occur? I am really interested.

With best regards,

----Ravi.
========================================================================
Ravi Prakash ([email-masked])		www.utdallas.edu/~ravip
Department of Computer Science
The University of Texas at Dallas
Richardson, TX 75083-0688.  Phone: (972) 883-2289,   Fax: (972) 883-2349

---

From: [email-masked]
Date: Fri, 27 Oct 2000 19:31:24 +0200

Dear Ravi,

Deadlock or livelock, sorry, I am a little confused. I just meant that the
route discovery permanently fails for some pairs source-destination, not
that the whole network crashes. 

Network crashes might occur if the protocol has no way to get rid of wrong
information. But if the protocol has an efficient information refresh
process (timeout, sequence numbers), then it should be OK. 

Best regards,
Philippe

---

From: "wooighee" <[email-masked]>
Date: Mon, 30 Oct 2000 13:35:40 +0900

Hello All
    
     I wonder why DSR is not selected as one of the on-demand
protocol in MANET ? Any significant shortcame of the protocol
that make it not robust enough to be considered as a standardized 
protocol ?

thank you

ghee

---

From: Dave Johnson <[email-masked]>
Date: Sun, 29 Oct 2000 23:53:19 -0600

ghee,

There has been no selection yet of *any* standards in the MANET
Working Group of the IETF.  DSR is still very much under consideration
in the IETF, and we are still very actively working on DSR.  As shown
through many detailed simulations such as those in our paper "A
Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing
Protocols" in MobiCom'98, DSR has excellent performance.  We have also
implemented the protocol and demonstrated the protocol in real
operation with substantial mobility and substantial load from real
application and transport protocols, showing that the protocol really
works as designed and is indeed quite robust.  For more information on
our implementation results, see the paper "Quantitative Lessons From a
Full-Scale Multi-Hop Wireless Ad Hoc Network Testbed" in WCNC 2000, or
the longer technical report "Experiences Designing and Building a
Multi-Hop Wireless Ad Hoc Network Testbed", both of which are
available from our web pages at http://www.monarch.cs.cmu.edu/.

The current Internet-Draft for DSR has expired, but it is still
available also from our web pages above.  All Internet-Drafts expire
and are automatically deleted if not revised within 6 months.  We have
been busy over this time completing the initial version of QoS support
in DSR and demonstrasting it in a real implementation for DARPA
running Microsoft NetMeeting over a moving DSR network.  Also over
this time, by the way, I have moved from Carnegie Mellon University
(where I had been on the faculty for 8 years) to Rice University.  We
are currently working on DSR at both CMU and at Rice, since I am still
working with the same graduate students, although they are still at
CMU temporarily.  We are currently revising the DSR Internet-Draft
and will be resubmitting it soon.

If I can answer any other questions about DSR, please let me know.

					Dave

--
David B. Johnson, Associate Professor
of Computer Science and Electrical and Computer Engineering

Department of Computer Science - MS 132    [email-masked]
Rice University                            http://www.cs.rice.edu/~dbj/
6100 Main Street                           Phone: (713) 348-3063
Houston, Texas 77005-1892 USA              Fax:   (713) 348-5930