[ns] Why the change on RXThresh etc. doesn't work?

[Z Sun <esrub@eng.warwick.ac.uk>]

Hello,

I download the example simple-wireless.tcl from Marc Greis's tutorial
site. Then I added the following in the tcl file:

Phy/WirelessPhy set CPThresh_ 10.0
Phy/WirelessPhy set CSThresh_ 1.559e-11
Phy/WirelessPhy set RXThresh_ 3.652e-10
Phy/WirelessPhy set Rb_ 2*1e8
Phy/WirelessPhy set Pt_ 0.02818
Phy/WirelessPhy set freq_ 914e+6 
Phy/WirelessPhy set L_ 1.0

To check how is the change of these parameters will affect the simulation
result, I change RXThresh_  to 3.652e-9, -8. But the trace file doesn't
change any (even for 3.652e-0). 

Anybody can tell me what's going on? Many thanks.

Ziran