Instructions

• Install Ubuntu
• Download NS-2.35 (http://sourceforge.net/projects/nsnam/files/allinone/ns-allinone-2.35/ns-allinone-2.35.tar.gz/download)
• Unzip or untar it to any folder (recommended is /home/loginname) using the following commands one by one

sudo apt-get update

sudo apt-get build-essential autoconf automake libxmu-dev

tar zxvf ns-allinone-2.35.tar.gz

cd ns-allinone-2.35

./install

• Once installed the PATH information will be provided to you.
• Copy the PATH and LD_LIBRARY_PATH Variable to .bashrc (see a dot in the beginning)

Input the path information in .bashrc file like this  

export PATH=$PATH:<Place your paths here>

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH: <place the LD_LIBRARY_PATHS> here.

Once done, save the file and close

execute the command

source .bashrc

try ns or nam to see whether your installation succeeded.