[ns] issue in understanding coding simulation of tcl file..

dear all,

when i run my simulation then i got on terminal window these lines

num_nodes is set 10
INITIALIZE THE LIST xListHead
Starting Simulation...
channel.cc:sendUp - Calc highestAntennaZ_ and distCST_
highestAntennaZ_ = 1.5, distCST_ = 550.0
SORTING LISTS ...DONE!

what does "distCST_ = 550.0" mean??

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thanks..