Interfaces and their protocol stacks

After familiarising with main network elements, time has come to better know interfaces between those elements.
Interfaces are allowing MME, SGW and PGW cooperating with other network elements( e.g. HSS or PCRF).
Each one of them is built in standardised way described by 3GPP.org. Each interface described here is taken from 23.401 3GPP.org documentation.
Please keep in mind, that the documentation is (sometimes) bigger than we need it to be, so not every aspect of interfaces is described here.

Lets start with big picture of situation in which user is not roaming.

Fig.1. Non-roaming architecture by 3GPP