[Olsr-users] getting second best route from dikjstra's algorithm

[Henning Rogge]

On 06/14/2013 06:36 AM, Vigneswaran R wrote:
>> b) the "x'nd best" routing table is monotonous throughout the
>>     network. For Dijkstra and the best route, this is the case
>>     (if there are no zero or negative costs involved). For a definition
>>     of "second best" I wouldn't be so sure.
>
> We are just thinking of a mesh where we may have 2 or 3 different paths
> between one end to the other. Second best or third best is actually
> alternate routes (could be of same cost or higher cost than the best path).
>
>> If nodes have different views on the network, or your routing table is
>> not monotonous, routing loops are likely to occur.
>
> Ok.
>
>> How about not using the "second best route", but calculating a second
>> routing graph based on a different metric?
>
> Ok. Though I am not sure how this can be done, we can do some thought
> process on these lines. Thanks.

There is another problem you have to take care of.

Imagine a node A, which thinks that B,C,D,E,F is the "second best" path 
through the network. Is there any guarantee that B will think that 
C,D,E,F is the "second best" path? In fact I don't think so.

If not, you would have to use source routing, because your decision to 
use "the second best" path will not be stable as a hop-by-hop decision.

Henning Rogge

-- 
Diplom-Informatiker Henning Rogge , Fraunhofer-Institut für
Kommunikation, Informationsverarbeitung und Ergonomie FKIE
Kommunikationssysteme (KOM)
Fraunhofer Straße 20, 53343 Wachtberg, Germany
Telefon +49 228 9435-961,   Fax +49 228 9435 685
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