[ns] how to change MAC_MIB, PHY_MIB default values?

["Susan Tsao" <SusanTsao@WoodsideNet.Com>]

Hello,

I like to vary some of the MAC_MIB parameters (ex. RTSThreshold,
ShortRetryLimit) , 
PHY_MIB parameters (ex. CWMin, CWMax), and Phy/WirelessPhy parameters
in my simulation scripts. I was able to change Phy/WirelessPhy values by
inserting following lines in my script:

	Phy/WirelessPhy set bandwidth_ 4e6
	Phy/WirelessPhy set CPThresh_   2000

However, when I try 
	MAC_MIB set RTSThreshold_       4000
	PHY_MIB set CWMin_0               15 

I get errors:
	invalid command name "PHY_MIB"
  	  while executing
	"PHY_MIB set CWMin_0             15            "
  
Is there a command for which I can set PHY_MIB or MAC_MIB values?
I know I can go into mac-802_11.cc and change these  values, recompile
ns, 
and then run my script.  But I like to find out how I can modify it
directly from 
my simulation script.  Any suggestion/advice/hints will be greatly
appreciated.

Thanks in advance!!

Susan