[ns]: What is gnuplot? Where can I find it

[ongun@ee.bilkent.edu.tr]

Dear all

I am trying to simulate the files of Sally floyd for Dyamics of Slowly Responsive Congestion Control Algorithms. I ran the run-RED.tcl and it calls plot-RED.tcl but there is an error 

couldnt find gnuplot: there is no such file or folder
while executing 

gnuplot plot-RED

Now Where can i find that gnuplot.

PS: I couldnt copy paste the error but it is something like this. I use suse 6.4 on amd processor

Thank You for Help 
Ongun Yucesan