Four-Bit Wireless Link Estimation Rodrigo Fonseca (UCB), Omprakash
Gnawali (USC), Kyle Jamieson (MIT), and Philip Levis (Stanford)

Summary: Rodrigo highlighted the importance of estimating wireless link quality.
The estimators use information from various layers, and are many a times coupled
with platforms or radios.  

The talk attempts to highligh what information is available at different layers,
define an interface, and implementation.

Physical layer exposes bit decoding errors, link layer exposes the unicast
packet delivery rate, and on the network layer can provide information about
which links are useful in terms of "utitlity" from say routing perspective.  

Rodrigo also described the interface and implementation.  He described
how ACK is used to fine-tune the estimates.   

Q: On slide 8, Why are you using just one bit from phy, when it
provides much richer information.

Ans: We were looking for simplest useful interface.

Q:  I am not convinced why phy layer information is not sufficient.  

A: There could be intelligence in higher layers that can help us.

Q:  In an ideal world, should not the higher layer information
be sufficient.

A: That is a good question; it might be redundant on links where you
already have sent the traffic and learned what the behavior is. But for newer
links it is useful.  

Q: If you are not memory constrained, would you mind keeping
information about all the links?

A: That is true, however our focus is sensor applications where memory is a
constraint.

Q: What is the take away;

A: The interface has to be narrow to be portable.