[Tinyos-help] packet acknowledgement

[João Paulo Amaro da Costa Luz Carneiro]

Hi all,

Low Power Listening TEP recommends sending duplicate packets and  
enabling acknowledgements while this http://www.etantdonnes.com/Motes/report_mica2/ 
  concludes PRR is higher when acknowledgments are disabled. Can  
someone explain?
About the acknowledgement mechanismand how do ACKs work in tinyos2/WSNs:
Does the system automatically retransmits when the ACKs aren't received?
How does a node knows how many ACKs it should receive?
Is it enabled or disabled by default, and how to change configurations?
Thanks, regards.

Joao