Reply to Straight Serial Cable vs. Not Null Modem

I just bought a cable from Amazon.com
http://www.amazon.com/gp/product/B00066HPU6

It says it is a modem cable.
So is this a null modem cable ???

And when I briefly went through this site
http://digital.ni.com/public.nsf/all...256F720071DECF

I'm still not sure what is the difference between two.
Do I need to purchase a new cable ???
Or
Can I still use the cable I have bought before???