On Jul 5, 2007, at 11:35 AM, Pedro Almeida wrote:
Hello, all!
I have some doubts:
Let's suppose i have a CTP network made out of 2 nodes only (this
is a test I ran), the sink and a "standard". Now let's assume that
I step apart these two nodes for as far as they're barely "visible"
to each other (I found this to be around 60 meters).
Faced whith this situation, I observed several packages being re-
sent by the "standard" node into the sink, never failing the order
(i analysed the sequence number), and i presume this to be caused
by the ACKs that never got back, thus causing the re-sending.
Stepping them a little bit farther apart, i started noticing some
gaps in the sequence number, as if some packets were totally lost.
I also noticed that if I stay at 60 meters and have relatively fair
transmission, going to 80 and getting back to 60 doesnt always
provide same delivery rates (sometimes i didnt get anything when
going back to 60, even though i received something before).
So my questions are:
- How many attempts does it take for a packet to be discarded from
retransmission, after many attempts without getting ACKs back? TEP
123 says they're placed in a queue for future retransmission, but I
presume they don't stay there forever? Or else I wouldnt notice
sequence number gaps in the received packages...? Does the CTP tree
breaks here and starts looking for a new path?
- If the link gets weak enough, does the "standard" node re-attempt
to recreate a CTP tree and discards all queued messages? How weak
(or strong) needs a link to be for the nodes to establish a route?
I ask this because the apart/together thing, where it seems the
tree wasnt being "rebuilt" when it was perfectly healthy minutes
before in the same position (with the several retransmission to
assure packet delivery).
Thank you for your help!
Reception isn't always constant over time; so it might be that you
put the node back at 60 feet, but the orientation was slightly
different, or the environment had changed, such that there was a 1dB
difference in signal strength, which could have a big effect on
delivery rates.
What I would recommend doing is either hook your transmitter up to a
serial port and see what debug messages it is sending (if you have
debugging enabled) or set up a BaseStation to see if it's sending
routing beacons, data packets, or both.
One possibility is that at 60ft, the node can't discover a route due
to broadcast packet losses, but it can maintain a route through data
traffic.
Phil
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