[Olsr-dev] Little change to olsr core

[Henning Rogge]

On 07/27/2012 01:01 PM, Teco Boot wrote:
> Op 27 jul. 2012, om 11:28 heeft Henning Rogge het volgende geschreven:
>> The current core doesn't support asymmetric links.
> Could be.
> When all nodes send out their own TC (no topology reduction), all
> with outbound costs, what is the problem?

At the moment there is no such thing as "outbound/inbound" cost in our 
TCs. LQ/NLQ are always combined into a symmetric value.

>> I am not even sure
>> the Dijkstra implementation can handle it.
> Should be fixed.
Yes, maybe.

But we have to keep track of the case that we did not got a TC from 
another node. There is a reason why you can send out- and inbound cost 
in OLSRv2 TCs.

>> Setting your local ETX to "a" but having your neighbor announcing an
>> ETX of "b" sounds like a lot of trouble.
> But this is normal during convergence. Local ETX is changing more
> rapidly than arrived messages, send out with fixed intervals.
> (yes, there could be loops)

Might be interesting to only use the LQs from the sent TCs instead of 
the local measurements to decrease the chance of loops.

>> We should not implement
>> something like this before checking the Dijkstra very carefully.
> OK, this has to be checked.
>
>> Whats about this, instead of implementing a static LQ/ETX, we could
>> allow a user to define a maximum LQ for a link (between 0 and 1).
>> Calculation will be running as normal, just that it doesn't go higher
>> than a certain value.
> We can make a new lq_plugin, for experimentation. Based on
> lq_plugin_default_ffeth. All enhancements are configured, so default
> is 100% compatible. Messages should be compatible too, for mixed mode
> operation. Candidate enhancements:
>   - hysteresis (suppress frequent small changes), with config option
>     (LQHYST 0.00 - 0.99)

The hysteresis is already there, just not with tuning parameters.

>   - factor for LQ-WEIGHT and NLQ-WEIGHT, so we have asymmetric costs.
>     NLQ is (far) more important than LQ. Sensible value: 0.80 for NLQ-WEIGHT,
>     0.20 for LQ-WEIGHT.

Yes.

I hope I will be able to put this kind of "metric post processing" 
outside the raw-metric calculation in OLSRv2.

>   - LQ window size
>   - max costs and max LQ thresholds
>   - mixing available L2 feedback with LQ, such as RSSI / DLEP info.

I think we should push this to a different experiment.

>   - a more exponential increase of costs, so links with higher losses
>     have much higher costs could be something like
>     ( 255 * 255 * 255 ) / ( LQ * NLQ * NLQ)

Not easy because of the small range of possible values for LQ/NLQ.

Henning

>> Henning
>>
>> On Fri, Jul 27, 2012 at 10:17 AM, ZioPRoTo (Saverio Proto)
>> <(spam-protected)> wrote:
>>>> @Saverio: why is the LQ multiplier not enough?
>>>
>>> 1) First problem is that I cannot configure asymetric cost:
>>> in the current implementation the ETX of the link is the same in both
>>> directions (you can have a little shift because cost from A to B is
>>> computed on A and cost from B to A is computed on B, but results
>>> should be the same).
> What happens when unequal LQ multipliers are configured, on A and B?
>
>>>
>>> 2) Second problem is granular costs
>>> the ETX using multipliers will be
>>>
>>> ETX = 1 / ( LQa  * multA * LQb * multB)
> I guess it is ETX =  ( 255 * 255 ) / ( LQa  * multA * LQb * multB)
>
> Yes, this may improve optimal route calculation.
>
>>>
>>> when the link is perfect I can simplify in
>>>
>>> ETX = 1 / (multA * multB)
> ?
> This will follow automatically.
>
>>>
>>> But the is very tricky to configure ETX of 18,19,20,21,22,23 adjusting
>>> these two multipliers values on the two routers.
> I don't follow.
>
>>>
>>> Moreover a packet loss on the link will add a multiplicating factor to
>>> my link, that most of the time will go quickly above LINK_COST_BROKEN
> Max_costs needs a parameter.
>
> Teco
>
>
>>>
>>> I would like to set ETX = 18, and then just delete the link if the
>>> normal computation of ETX without multiplier goes above
>>> LINK_COST_BROKEN
>>>
>>> Saverio
>>
>>
>>
>> --
>> Steven Hawkings about cosmic inflation: "An increase of billions of
>> billions of percent in a tiny fraction of a second. Of course, that
>> was before the present government."
>
>


-- 
Diplom-Informatiker Henning Rogge , Fraunhofer-Institut für
Kommunikation, Informationsverarbeitung und Ergonomie FKIE
Kommunikationssysteme (KOM)
Neuenahrer Straße 20, 53343 Wachtberg, Germany
Telefon +49 228 9435-961,   Fax +49 228 9435 685
mailto:(spam-protected) http://www.fkie.fraunhofer.de
GPG: E1C6 0914 490B 3909 D944 F80D 4487 C67C 55EC CFE0

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 6169 bytes
Desc: S/MIME Cryptographic Signature
URL: <http://lists.olsr.org/pipermail/olsr-dev/attachments/20120727/141b3bf6/attachment.bin>