[ns] error when installing ns-2.1b9a (when configure otcl)

[tdinhtoan]

hi,

I install ns-2.1b9a, and it asks to install otcl-1.0a8. However I could  
install otcl-1.0a8 because of the following error:
        checking for X11 header files
        can't find X includes
when I configure the otcl-1.0a8.

I do not how to fix the error.

Could anyone help me.

Looking forward to hearing the solutions.

thanks very much.

-toan.