Subject: [manet] Multicast: MAODV and ODMRP

From: Mark Borst <[email-masked]>
Date: Tue, 23 Nov 2004 16:04:02 +0200

Hallo all

We have been doing some research on multicasting in MANETs. Apparently
multicasting is not in the charter of the MANET group, but we could not
find any other group that has information on it, so we ask here anyway. 

The first question is: is there any other place, except the MANET group,
that discusses MANETs and multicasting issues?

It seems that MAODV and ODMRP are the most important multicasting
protocols for MANETs at the moment. However, we cannot find sufficient
information about them.

On ODMRP we found the old draft-ietf-manet-odmrp-04, and the later
draft-yi-manet-odmrp-00, both expired. Furthermore we found some papers
on the protocol, but those didn't contain sufficient information for us,
just as the drafts. They completely skip the matter of mesh creation (it
just creates a lot of trees, that are further independent) and link
failure recovery. Or if they are sufficiently specified, we cannot find
the description of it. We are aware that people have simulated it, which
implies they found sufficient information to solve these questions.
Could you shine some light on this matter?

Another question, of more general nature, is: can you give some comments
on multicasting versus broadcasting/flooding? It seems that flooding is
actually a good alternative to multicasting under certain scenarios, so
is multicasting then still viable?

Thanks,

-- 
Mark Borst
Researcher
Network and Protocols Group
Tampere University of Technology, Finland

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From: Einar Vollset <[email-masked]>
Date: Tue, 23 Nov 2004 15:21:34 +0000

> is multicasting then still viable?

Broadcasting is not the same as flooding. Broadcasting is a 
communication primitive
(1-ALL), where as flooding is a (simple) mechanism (re-transmit 
immediately after
the first time I receive a packet) which attempts to provide the 
broadcast primitive.

In fact, as broadcasting is a special case of multicasting (make the 
group contain ALL
nodes in the system and you've got broadcasting), you could use any 
multicasting
protocol to do broadcast.

I guess the question you're really asking is if it's worth constructing 
routing structures
(such as ODMRP's mesh or MAODV's tree) when a simple flooding approach 
does
quite well?
I think there is much to be said for attempting to lower the 
transmission overhead associated
with simple flooding, though as you observe, there are cases when 
flooding does as
well as a routing structure based approach, both in terms of overhead 
and number of
successful recipients (typically high mobility scenarios)

That being said, flooding is not a panacea when it comes to ensuring a 
broadcast is
_reliable_. A simple example of when flooding fails to achieve this is 
when the network
is transiently partitioned at the time the flooding is initiated  (an 
extreme version of when
such partitioning is considered "normal" is what the guys working on 
delay tolerant
networking (DTNs) are interested in:  http://www.dtnrg.org/ (IRTF DTN 
group))

There is also some work attempting to provide more optimized protocols 
than flooding
(higher reception rate, lower overheads), e.g.
- I. Stojmenovic, M. Seddigh, J. Zunic, "Dominating sets and neighbor 
elimination based broadcasting algorithms in wireless networks"
- J. Lipman, P. Boustead, and J. Chicharo, "Reliable optimized flooding 
in ad hoc networks"
- W. Lou and J. Wu, "Double Covered Broadcast (DCB): A simple reliable 
broadcast algorithm in manets"

or the probabilistic approaches, e.g.:
- J. Luo, P.T. Eugster, and J.-P. Hubaux, "Route Driven Gossip: 
Probabilistic reliable multicast in ad-hoc networks"
- R. Chandra, V. Ramasubramanian, K. P. Birman, "Anonymous Gossip: 
Improving Multicast Reliability in Mobile Ad-Hoc Networks"
- D. Cooper, I. Mitrani and P. Ezhilchelvan, "High Coverage 
Broadcasting for Mobile Ad-hoc Networks"

However, if you want to absolutely, positively 100% ensure that all 
nodes in a group get a given
message, you have to turn to deterministically reliable protocols 
instead. E.g. :

- T. Gopalsamy, M. Singhal, D.Panda, and P. Sadayapan, "A reliable 
multicast algorithm for mobile ad-hoc networks"
- K. Tang, K. Obraczka, S.J. Lee and M. Gerla: " Reliable, congestion 
controlled multicast transport in multimedia multihop networks"
- E. Pagani and G.P. Rossi," Reliable Broadcast in Mobile Multihop 
Packets Networks"

..which is my current research interest.

That was a more general answer to a more general question.. :-)

Cheers,

Einar

----------------------------------------
Einar Vollset
PhD Student
School of Computing Science
University of Newcastle, UK
http://vollset.org
-----------------------------------------

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From: "Pedro M. Ruiz" <[email-masked]>
Date: Tue, 23 Nov 2004 17:28:29 +0100

Definitely a very good general answer... please let me add a very 
concrete appendix ;-)

Regarding the viability of multicasting, you may find interesting the 
following paper which proposes enhancements to the mesh creation 
algorithm in ODMRP to lower the transmission overhead while maintining a 
high packet delivery ratio. You will see how it is possible to have high 
PDRs with high mobility at much lower data-overhead than flooding.

Pedro M. Ruiz, Antonio F. Gomez-Skarmeta, "Mobility-Aware Mesh 
Construction Algorithm for Low Data-Overhead Multicast Ad Hoc Routing", 
to appear in Journal of Communications and Networks, Vol. 6, no. 4, 
December, 2004.

Please, let me know if you need further information. The paper will be 
shortly available in my website: 
http://ants.dif.um.es/staff/pedrom/publications.html

--Pedro

Einar Vollset wrote:

> I guess the question you're really asking is if it's worth 
> constructing routing structures
> - J. Lipman, P. Boustead, and J. Chicharo, "Reliable optimized 
> flooding in ad hoc networks"

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From: Marshall Eubanks <[email-masked]>
Date: Tue, 23 Nov 2004 14:12:45 -0500

Dear Mark;

> that discusses MANETs and multicasting issues?

MANET type networks have not been discussed in any depth in of the
standard multicast WG (such as MBoneD), and as far as I can tell there
is little knowledge of what's going on Ad Hoc networking in that community.

If multicasting is a serious issue in Manet, I would suggest that the
next MBoneD
WG meeting in Minneapolis include some Manet presentations. This was done with
MPLS LSP's with the  idea of informing the community and limiting the amount of
wheel re-creation.

Regards
Marshall Eubanks