In this tutorial, we will discuss on the LTE EPC Overview.
| CS – Circuit Switch PS — Packet Switch PSTN — Public Switched Telephone Network IMS – IP Multimedia Subsystem |
- LTE Consists of the evolution of the radio access through the E-UTRAN Technology (Evolved-UMTS Terrestrial Radio Access Network). So it is accompanied by an evolution of the non-radio aspects under the term ‘System Architecture Evolution’ (SAE).
- EPS (Evolved Packet System) = Core Network (EPC) + Evolved UTRAN (E-UTRAN)
EPS Interfaces:
Uu: This is an Air interface between UE and eNB.
S1-U: This is User plane interface between eNB and SGW. GTP-U v1 is the application protocol that encapsulates payload of the UE.
S1-MME: This is control plane interface between EnB and MME. S1-AP is application layer interface. The transport protocols used here is SCTP which is known as Stream control transmission protocol.
S5: Provides user plane tunnel management between S-GW and P-GW.
S6a: This enables the transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between MME and HSS.
S10: This is the interface between two MMEs. It also used for MME relocation and MME to MME information transfer.
S11: Interconnection between MME and Serving GW.
S4: Supports user plane data transfer for inter-system mobility
S3: Interconnect between MME and SGSN. Also it uses for bearer information exchange to inter 3GPP access network in idle and/or active state.
S7: Interface between PDN GW and PCRF.
SGi: It is the connection between the PDN GW and the packet data network. PDN GW may be an operator external public or private packet data network or an intra operator packet data network. For instance, provision of IMS services. It corresponds to Gi for 3GPP accesses.
EPC Identities:
<GUTI> = <PLMN_ID><MMEGI><MMEC><M_TMSI> <GUMMEI> = <MCC><MNC><MME Identifier> <MME Identifier> = <MMEGI><MMEC> <S-TMSI> = <MMEC><M-TMSI> UE ID: International Mobile Subscriber Identity (IMSI) International Mobile Equipment Identity (IMEI) NW ID: GUTI: Globally Unique Temporary Identifier GUMMEI: Globally Unique MME Identifier MMEGI: MME Group Identifier MMEC: MME Code M-TMSI: MME-Temporary Mobile Subscriber Identity S-TMSI: SAE-Temporary Mobile Subscriber Identity
Now we have understood the LTE EPC Overview. Let’s discuss LTE Network Interface in next tutorial.