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[manet] Re: mobility physics and mathematics (was: manet] DYMO and other routing protocols)

Krishna Sankar (ksankar) wrote: 
Some adaptability feature in DYMO would be welcome, not necessarily
 proactive, but at least some memory based feature could help.

<KS> Are you talking about spatial interpolation based on history ? Mobility algorithmics based on 1st and 2nd order derivatives of mobility vectors - For example if we know a node is moving, if we can
infer the acceleration and also the spatial topology, we could possibly say where it could be and what the route could be knowing the nodes in that vicinity ... </KS> 

It sounds logic to use the expected future physical position as an
indicator of where the node is.

However, this line of thought is very daring and prone to deep
disappointments when tried in IP practice. Because it misses the
all-important point that 'mobility' as when an object moves, or as when
we draw Brownian dots on paper, is very much different than 'mobility' as implemented in C on some computers. This difference is easily illustrated by the speed paradox of a vehicle moving very fast (130kmph) but whose IP address changes very slow (5 changes per hour).

Thus, if we define 'mobility' as the speed at which a node changes its
address then (1) we're out of MANET scope because in MANET nodes don't
dynamically change their addresses and (2) one realizes physical
location ("space") has no relationship whatsoever with an IP address,
and interpolating a set of physical coordinates can't result into an IP
address whatever trick one applies.

I think in order to be able to use the interpolation mathematical tool
in the MANET context one has to agree on how routes are represented at
intermediary nodes, and how they vary. That agreement is difficult to
obtain, to start with. Then I am almost sure route variation (routing
table changes) can not be expressed mathematically as function of
'space' co-ordinates. Or if it were then it couldn't easily be grasped by a programmer's mind.

That's why I think space can not fit here.  But then people are of
course free to understand whatever they want by 'space' as people
understand whatever they want by 'color'.

Alex


Cheers <k/>
-----Original Message----- From: Philippe Jacquet [mailto:philippe.jacquet at inria.fr] Sent: Friday, June 08, 2007 4:12
AM To: David Murray Cc: manet at ietf.org Subject: Re: [manet] DYMO and other routing protocols

I would say that from a very broad perspective, on-demand protocols
discriminate routes with respect to time and proactive protocols discriminate routes with respect to space. Personnally I have preference to proactive approach because it is richer and gives better internet legacy. Objectively the two approaches have their advantages and drawbacks and the two should be considered.

This said, I don't think that on-demand and proactive approaches are represented at the same level in MANET. OLSRv2 has "space" adaptability: i.e algorithms which automatically adapt to space and
topology variety, including for instance the MPR mechanism. In DYMO I don't see an equivalent "time" adaptibility that goes beyond
the default values in timers. I think this may explain why the protocol performs great in some scenario and very poorly in other.

Some adaptability feature in DYMO would be welcome, not necessarily
 proactive, but at least some memory based feature could help.

Philippe

David Murray a écrit : 
Hi,

I am wondering how DYMO fits in with the other routing protocols.
I have read a number of papers that discuss how on-demand
routing protocols like DSR/AODV work better in highly mobile environments where movement is fast, CPU and memory are low and batteries are limited. Equally, in situations where movement is very low,
and there
are no power limitations, protocols like OLSR/TBRPF/STAR
perform better.
So, I have a mental picture of OLSR/TBRPF being
predominantly used in
stationary 802.11 mesh devices and AODV/DYMO being used to connect users mobile devices ush as phones and PDAs. Is this correct or are things not quite as simple as this? (I know RFC 2501
discusses MANET
applications and characteristics but the discussion is
quite general)
If this is correct, it seems to me that DYMO and AODV are
used in very
similar situations (the ad hoc interconnect between users
devices). I
am aware that DYMO is a simplified version of AODV both in code and network operation. It seems like the major difference is the path accumulation feature in DYMO which allows nodes to append their information to a RREP to give other nodes better knowledge of the topology. It also seems that the hello feature has been removed in DYMO. So, is DYMO likely to be a replacement for AODV or do
they have different uses/applications? 
Thanks for your time

Dave


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