If a 4G subscriber wishes to browse the internet on his mobile phone, he will signal up to the P-GW in the SAE(core network) and connect out to the internet thru the SGi/Gi interface.
If this same subscriber wishes to use an IMS based application, e.g. PoC (Push To Talk), he will also signal up to the P-GW and connect to the P-CSCF node in the IMS core. From diagrams i am looking at, it seems he will connect to the P-CSCF using a different interface, Gx and Rx.
What i'd like to know is are there two seperate interfaces;one to connect to the internet and one to connect to IMS services? It doesnt matter whether sub is using 3G or 4G access network or GPRS core.
Hope you can help me out.