using a trace file as input of a traffic generator in ns2

[mahesh]

Hi
I'm trying to use a trace file in a traffic generator, here is what i put so far in my input trace file:

0.000000 50
0.000404 50
0.020404 50
0.040404 50
0.060404 50
0.080404 50
0.100404 50
0.120404 50
0.140404 50

but i'm getting an error saying: bad file size in /home/sami/Desktop/ns2/input.tr

probably, this is due to the fact that fields in the trace format file are not appropriate, so what is the appropriate format ?
any help will be very appreciated