Subject: [manet] Technical issue #6 - Non-optimal routes (warning - long post)

From: "Susan Hares" <[email-masked]>
Date: Mon, 14 Jan 2013 01:01:00 -0500

(Warning this is a longer post) 

Non-optimal routes comes from the post by : Marius (Rice), Rob van Glabbeek,
Peter Höfner,  Marius Portmann, Wee Lum Tan.  W

In order to bring us to my questions, I’m going to provide a synopsis of
what I understand: 

Their Comments:   On-demand/reactive routing protocols (such as AODV, DYMO
and LOADng) often fail to discover the best (shortest) routes [1,2].

 The problem is that during route discovery the destination (target) node
does not forward route requests; so, nodes that lie downstream of the
destination node frequently create non-optimal routes to the source.
Knightly and Miskovic [1] have shown that "poorly selected paths can have
significantly higher routing-metric costs, and their duration can extend to
minute time scales". 

Glabbeek et al. (2013)  have verified that this problem exists in DYMO and
LOADng.

 As a possible solution, Glabbeek  et al. (2013) propose that route requests
are always forwarded, even by nodes generating a route reply [2,3]. The
forwarded request should include a flag stating that a reply has already
been initiated. In [3] it is shown that this increases the quality of
routes. Of course this could increase the overhead of control messages, but
in most of the cases the additional overhead is minimal, since a request
floods the entire network anyway.

Charlie’s comments:  This is certainly true.  There have been measurements
about how far from optimal the routes can be, and if I remember correctly
it's typically somewhere in the neighborhood of 10%, depending on congestion
and node mobility.

Charlie:  [Always forwarded route requests] can be made into an optional
behavior, controllable either by a system-wide configuration parameter, or a
new RREQ option.  I would not expect that it should be the default behavior

Sue’s Comments: 

1.  Distance Vector (DV)  vector by distribution may fail to create optimal
routes if multicast distribution is not complete.  BGP has this problem as
well. It is a tradeoff of message flood and optimal routes.

2.  Best optimal routes are from Link-state OLSRv2, ISIS, or others with
tuning to reduce the flood

Questions: 

1.  Where are the use cases for the MANET protocols that provide these
tradeoffs for congestion, node mobility, link loss and flooding?  

2.  How is MANET judging the tradeoffs? 

3.  Stretch is a description of non-optimality. For example the stretch
value of 120 means the path is 20% longer. What is the normal stretch in
MANET? How does this compare with BGP’s stretch? 

4.  Is the MANET WG looking for stretch range for their reactive protocol?  

Thank you for any comments. Again, if I have missed papers or a discussion –
just let me know and I will find and read. 

Sue Hares

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From: Abdussalam Baryun <[email-masked]>
Date: Wed, 16 Jan 2013 00:30:21 +0100

Hi Sue,

answers/comments in line,

> tradeoffs for congestion, node mobility, link loss and flooding?

I asked that before, but the group don't like to put that in each
document, it is done in MANET WG that we refer to RFC2501 which has
all the use cases,

> 2.  How is MANET judging the tradeoffs?

I think by testing or simulating codes, this is what I do,

> MANET? How does this compare with BGP’s stretch?

I never measured that or seen work done for that. Could you please
give me a best reference so I get beter understanding,
>
> Thank you for any comments. Again, if I have missed papers or a discussion

I try to do my best,

> –

Me too I would like similar intentions. Regarding engineering
referencing papers or discussions referencing is not done much in the
IETF, which I hope to fix,

All the best,

AB