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LTE EPC Network Interfaces-S1 MME,S1-U,S3,S4,S5,S6a,Gx,S11,SGi

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Network elements viz. EPC(Evolved Packet Core), MME(Mobility Management Entity), Serving Gateway & PDN gateway construct the LTE network. Figure depicts interfaces between these network elements.This page of LTE tutorial covers LTE EPC network interfaces viz. S1 MME, S1-U, S3, S4, S5, S6a, Gx, S11, SGi etc.

LTE system network interfaces

MME is the control plane entity which implements procedure used for EPS mobility management and EPS session management in the EPS.

Serving gateway terminates interface towards the radio network. It takes care of user plane trafficrouting and also forwarding of uplink and downlink packets between PDN gateway and radio network.

PDN gateway provides PDN connectivity to the UE for different IP services provided by the operators. Following network interfaces have been defined for the EPC (Evolved Packet Core).

LTE EPC interface Description
S1 MME Interface for control application protocol between E-UTRAN and MME
S1 U Interface for S1 user plane data for each bearer between the E-UTRAN and serving gateway. It enables serving gateway to anchor inter-eNB handover.
S3 Connection between SGSN and MME is provided by S3 interface. It enables information exchange for mobility between inter-3GPP access networks.
S4 Interface between SGSN and serving gateway is referred as S4 interface. It provides user plane support for mobility support between GPRS core and the serving gateway. It also enables serving gateway to anchor the inter-3GPP handover.
S5 S5 interface provides user plane tunneling and tunnel management function between the serving gateway and PDN gateway. It enables serving gateway to connect to multiple PDN gateways for providing different IP services to the LTE UE. Also used for serving gateway relocation associated with the UE mobility.
S6a Interface between MME and HSS is S6a. It is used for transfer of subscription, authentication and authorization of users.
Gx This Gx interface provides transfer of QoS policy and charging rules from PCRF to the Policy and Charging Enforcement Function in the PDN gateway.
S11 This control plane interface S11 is used between MME and serving gateway for EPS management.
SGi This SGi interface is used between PDN gateway and intranet or internet. This interface is equivalent to Gi interface of GPRS


Other System Network Interfaces

GSM Network Interfaces
GPRS Network Interfaces

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