Page 318 - ITU-T Focus Group IMT-2020 Deliverables

5 ITU-T Focus Group IMT-2020 Deliverables

A.4 4G

UTRAN

SGSN
GERAN HSS
S3
S1-MME S6a
MME
PCRF
S12
S11 S4 Gx Rx
LTE-Uu S10
Serving PDN SGi Operator's IP
UE E-UTRAN Gateway Gateway Services
S1-U (e.g. IMS, PSS etc.)

Figure A-4 – Non-roaming EPS architecture for 3GPP accesses
The EPS (Evolved Packet System) provides IP connectivity using the E-UTRAN (Evolved Universal Terrestrial
Radio Access Network).
The EPC(Evolved Packet Core) network is the core network of EPS, and only Packet Switched services no
Circuit Switched service could be accessed by EPC network, and Mobility Management Entity (MME), S-GW
(Serving GW), P-GW (PDN GW), HSS (Home Subscriber Server) are the main network elements, and the non-
roaming EPS architecture for 3GPP accesses is shown as Figure A-4. The multi-mode LTE-capable terminals
could support interworking and service continuity between 2G/3G and LTE networks by S3/S4/S12 interfaces.
According to 3GPP TS 23.401, MME is the pure control plane element in charge of mobility management,
NAS signalling, P-GW & S-GW selection, Authentication, Idle mode UE Tracking and Reachability. Two logical
Gateways, S-GW and P-GW exist in EPC network. The PDN GW and the Serving GW may be implemented in
one physical node or separated physical nodes. S-GW is responsible for the Local Mobility Anchor point for
inter-eNB handover, Mobility anchoring for inter-3GPP mobility and Packet routing & forwarding, and the P-
GW is the logical element for Policy Enforcement, Per-user based packet filtering, Charging, UE IP address
allocation and so on.

In some operators’ commercial networks, S-GW and P-GW may be combined with GGSN, and MME may be
combined with SGSN, so the 2G/3G and LTE packet switched networks are converged for supporting multiple
accesses, such as GERAN, URTAN, E-UTRAN, even non-3GPP access like WLAN. The converged 2G/3G/LTE
network supports interworking and service continuity between 2G/3G and LTE, multi-mode LTE-capable
terminals may connect over 2G/3G when no LTE present.

A.5 5G
NOTE – To be filled in after IMT-2020 architecture is elaborated.

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