IMS and VoLTE Overview

This is an attempt to make 3GPP TS 23.228 more approachable, starting with the basic requirements of IMS for VoLTE and deconstructing it into base parts. Minor technical corrections: PCRF's C is "Charging" (I will always screw that up). In IMS roaming it's a pull procedure between the visited network's PCRF, not a push (I drew the line in the wrong direction). I meant to say PCRF was defined within the 29 series, not 32 series. Somehow charging and policy always blur together in my mind.