Positions of nodes is define in your TCL code which denotes the X, Y and Z positions of nodes in the topology . and some code generates random position.

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first of all thank you for reply.

but i want to send position in beacon message and receive it by another nodes through wireless commn. how i can do it.  

In this regard, I recommend you to use NSG software. It gives everything with ready made otcl script. It is based on java. Only java should be installed in your pc and you need to run that jar file in terminal. you will get otcl script, copy it and past in .tcl file. That tcl file will execute.