Eng Rony hi all, I'm having some problems while I'm=A0trying to run the example4(about xgrap= h) in section VIII from Marc Greis' tutorial. when I was trying to=A0run the example by g= iving the command "ns=A0example4.tcl" it's saying that: xgraph: cannot open display i use cygwin,ns2.29. how can i solve this problem? thanks