[Tinyos-devel] retransmissions in networking protocols

[Matt Welsh]

Actually these protocols perform retransmissions at the *link* layer,
not the network layer (the latter would imply end-to-end).

I'm firmly in the camp that link-layer ARQ is a necessity with these
kinds of radios, due to interference and collisions (the MAC could
perhaps be tuned to help avoid the latter).  Better route selection -
choosing only 'symmetric' links - can cut down on duplicate packets. One
could imagine a node detecting many duplicates from its children telling
those children to reduce their ARQ threshold. Even so I think filtering
out duplicates hop-by-hop or at the base station is perfectly
acceptable.

On Thu, 2007-10-04 at 14:02 +0200, Andreas Koepke wrote:
> Hi guys in the net group,
> 
> looks like MultihopLqi and Ctp all do retransmissions on the network
> level if the MAC reports a transmission failure. So whenever the MAC did
> not receive an ACK the packet is duplicated. This happens quite often in
> our testbed, because the TX power of the nodes seems to have a
> siginficant variance.
> 
> What is your experience, should we do something about it?
> 
> Best, Andreas
> 
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