1. Go do the directory ~ns (this is the ns convention for your source code 
   directory, wherever that might be) and save ncs.tar there. Untar it with

% tar xvf ncs.tar

2. Change the ~ns/Makefile by adding ncs.o to the variable OBJ_CC. 
   Link ncs to the following places in the code. Add:

# Networked Control Systems
Agent/Plant set packetSize_ 64
Agent/Plant set interval_ 0.

to the file ~ns/tcl/lib/ns-default.tcl. Then, go to ~ns/common/packet.h and add

       // NCS packets
       PT_NCS,

as the one element in enum packet_t (it cannot be the last one though), and

name_[PT_NCS] = "ncs";

in the same file in the inline constructor of p_info. 

3. If ns had been previously installed, it could be helpful to 
run make clean and make depend before compiling.