E.6 Usage of NAT in GPRS/EPS

23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS

There should be no NAT (or its existence should be kept transparent towards the UE) located between the GGSN/P‑GW and the P‑CSCF, which is possible as they are either located within the same private network and share same address space, or both the UE and the P‑CSCF are assigned globally unique IP addresses (see Annex M).

NOTE: If the UE discover a NAT between the UE and the P‑CSCF, the UE might send frequent keep-alive messages and that may drain the UE battery.