Here are some links in support of this figure:
This TS defines the Stage 2 service description for the Evolved Packet System (EPS).
The specification covers both roaming and non-roaming scenarios and covers all aspects, including mobility between E‑UTRAN and pre‑E‑UTRAN 3GPP radio access technologies, policy control and charging, and authentication.
short Table of Contents for TS 23.401 Word version: 16.5.0
each title links to the equivalent title in the full ToC