title: What is the difference between Google Service Framework(GSF)&Google Mobile Service(GMS)?
body: <p>I am learning Google Cloud Message recently, it requires both GSF and GMS(which new name is Google Play Service, but not that Google Play app).
  I decompile the code of both, but I don't know the usage of them, and don't know why Google provider these two services, why not one? And what's the difference of them? </p>