Simple Gnuplot script for PNG:

set terminal png size 500,350 large

set output "file.png"

set xlabel "Link Bandwidth (Mbps)"
set ylabel "Migration Time (sec)"

set xtics 250
set mxtics 2
set ytics 10
set mytics 2

plot "input.txt" using 1:($2+$3) with lp title "Default Xen" lw 2, \
     "" using 1:4 with lp title "Optimized Xen" lw 2