[Tinyos-help] Regarding 4 bit link estimation

[Omprakash Gnawali]

On Thu, Jun 4, 2009 at 2:03 AM, Rémi Villé<ville.remi at gmail.com> wrote:
>>>> 2 What is the inage field in each entry of neighbor table? Why is it
>>>> initialized to MAX_AGE, rather than 0?
>>>
>>> I didn't  look closely to  this parameter but it allow to estimate the
>>> number of round (a round correspond to have received BLQ_PKT_WINDOW beacon
>>> packets) we haven't be able to update the in-bound quality link of a
>>> neighbor (we haven't received beacon from this neighbor).
>>> It's initialized to MAX_AGE and decremented to 0 every BLQ_PKT_WINDOW
>>> beacon packets received.
>>> When you look in the updateNeighborTableEst(...) function we can see that
>>> if ((ne->inage == 0) && (ne->outage == 0)) then ne is set to be a invalid
>>> entry (like if the neihbor was evicted).
>>
>> I'm still not quite sure why we need this inage field. It is set to
>> MAX_AGE every time a beacon is received (in function
>> updateNeighborEntryIdx()) and decreased by 1 every round.
>
> The calculation of a bidirectional quality link is like 1/Qi * 1/Qo, where
> Qi is the ratio msg_received/total_msg_send from a neighbor to the current
> mote and Qo this ratio from the current mote to the neighbor.
> I think inage and outage are used to know when the connection whith a
> neighbor is lost, i.e. when we have received BLQ_PKT_WINDOW * MAX_AGE beacon
> packets without having any information about in-bound quality and out-bound
> quality from a neighbor.
> In-bound quality is compute with the sequence number in the LEEP frame sent
> by a neighbor (when there's a gap between two seq number we can deduce how
> many packets have been lost). Out-bound quality is compute thanks to the
> in-bound quality from the current mote to a neighbor, this information is
> sent in the LEEP footer frame from this neighbor to the mote, if the
> neighbor have keep the mote in its neighbor table.
> So we can have in-bound quality information from a neighbour without having
> out-bound one (if the neighbor haven't keep the mote in its neighbor table),
> but I do not think we can have out-bound quality information from a
> neighbour without having in-bound (because we must receive a packet to have
> the out-bound quality, and this packet allows to compute in-bound quality
> thanks to the seq number), so maybe inage is useless.

inage is used to keep track of freshness of the link entry. If it gets
too stale, we invalidate the entry.

- om_p