stp: help please! Thanks a lot

I hold H1-B and now teaching in a university for two years. Someone told me that my income is exempt from federal tax under the tax treaty between US and China since I am teaching here.
Is it true? I only know the J-1 holders don't need to pay tax for a couple of years, but didn't know if it is applicable to my case. Can you please give me some answers if you happened to know this?
Thanks a million!!!!!