[Tinyos-help] lost messages in TOSSIM (T2.0.2)

[Philipp Engel]

Hello.

Philip Levis wrote:
>>> Now the problem is that there is packet loss: not all messages that 
>>> should be (and are) generated are received by the nodes in range.

ok, thank you for the information. But I am currently not creating a 
braodcast storm: I work with sequence numbers and each node forwards 
each message just once.

I do a broadcast into the network, that means that the transmitting node 
does not know it's receivers. So CSMA worked correctly without changing 
the exponent before, but I oversaw the point that CSMA is not enough, as 
there is the hidden terminal problem, and CSMA can't avoid that. Also, 
using packet acknowledgements is not an option for broadcasts, so I had 
two choices:

- Find a node's neighbours using another approach (e.g. using a beacon 
system) and make unicasts, which will not make the hidden terminal go 
away, but I could check for lost messages with package acknowledgements.
- Try avoiding the concurrent transfer of messages by delaying the 
transfer by a random time period.

I went for the second option, as that is easier and faster to implement. 
I played around with the delay intervall, and it works quite well for me 
now. The packet loss is now down from 30% to around 3-5%, which is ok 
for me.
I think the beacon-based approach for connection discovery could produce 
even better results.

Philipp
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