SAE-EPCIntroduction

Inam UllahHead of Product Development

What is SAE/EPC SAE Advantages SAE Architecture Description of SAE Components Services in EPS Networks

Contents

System Architecture Evolution (aka SAE) is the core network architecture of 3GPP's LTE wireless communication standard

SAE is the evolution of the GPRS Core Network, with some differences: Simplified architecture All-IP Network (AIPN) Support for higher throughput and lower latency radio access

networks (RANs) Support for, and mobility between, multiple heterogeneous access

networks, including E-UTRA (LTE and LTE Advanced air interface), 3GPP legacy systems (for example GERAN or UTRAN, air interfaces of GPRS and UMTS respectively), but also non-3GPP systems (for example WiMAX or cdma2000)

What is SAE/EPC

Improved data capacity: With 3G LTE offering data download rates of 100 Mbps, and the focus of the system being on mobile broadband, it will be necessary for the network to be able to handle much greater levels of data. To achieve this it is necessary to adopt a system architecture that lends itself to much grater levels of data transfer.

All IP architecture: When 3G was first developed, voice was still carried as circuit switched data. Since then there has been a relentless move to IP data. Accordingly the new SAE, System Architecture Evolution schemes have adopted an all IP network configuration.

Reduced latency: With increased levels of interaction being required and much faster responses, the new SAE concepts have been evolved to ensure that the levels of latency have been reduced to around 10 ms. This will ensure that applications using 3G LTE will be sufficiently responsive.

Reduced OPEX and CAPEX: A key element for any operator is to reduce costs. It is therefore essential that any new design reduces both the capital expenditure (CAPEX)and the operational expenditure (OPEX). The new flat architecture used for SAE System Architecture Evolution means that only two node types are used. In addition to this a high level of automatic configuration is introduced and this reduces the set-up and commissioning time.

SAE - Advantages

LTE SAE Evolved Packet Core, EPC consists of four main elements as listed below: Mobility Management Entity –MME Serving Gateway –SGW Packet Gateway –PGW Policy Charging and Rule Function -PCRF

Description of SAE Components

The MME is the main control node for the LTE SAE access network, handling a number of features: Idle mode UE tracking Bearer activation / de-activation Choice of SGW for a UE Intra-LTE handover involving core network node location Interacting with HSS to authenticate user on attachment and implements roaming restrictions It acts as a termination for the Non-Access Stratum (NAS) Provides temporary identities for UEs The SAE MME acts the termination point for ciphering protection for NAS signaling. As part of

this it also handles the security key management. Accordingly the MME is the point at which lawful interception of signaling may be made.

Paging procedure The S3 interface terminates in the MME thereby providing the control plane function for

mobility between LTE and 2G/3G access networks. The SAE MME also terminates the S6a interface for the home HSS for roaming UEs.

It can therefore be seen that the SAE MME provides a considerable level of overall control functionality.

Mobility Management Entity, MME

 The Serving Gateway, SGW, is a data plane element within the LTE SAE.

Its main purpose is to manage the user plane mobility and it also acts as the main border between the Radio Access Network, RAN and the core network.

The SGW also maintains the data paths between the eNodeBs and the PDN Gateways. In this way the SGW forms a interface for the data packet network at the E-UTRAN.

Routing and forwarding user data packets acts as mobility anchor for the user plane during inter-eNB handovers

and for mobility between LTE and other 3GPP for idle state UEs, terminates the DL data path and triggers paging

when DL data arrives for the UE performs replication of the user traffic in case of lawful interception.

Serving Gateway, SGW:

Like the SGW, the Packet Data Network Gateway (PDN GW) is the termination point of the packet data interface towards the Packet Data Network(s).

As an anchor point for sessions towards the external Packet Data Networks, the PDN GW supports: Policy enforcement features (applies operator-defined rules for resource

allocation and usage) Packet filtering (for example, deep packet inspection for application type

detection) Charging support (for example, per-URL charging)

One bearer, a datapath between a UE and a PDN, has three segments: Radio bearer between UE and eNodeB Data bearer between eNodeB and SGW Data bearer between SGW and PGW

PDN Gateway, PGW:

the Policy and Charging Enforcement Function(PCEF) is the generic name for the functional entity that supports

service data flow detection , policy enforcement and flow-based charging.

The Application Function (AF) represents the network element that supports applications that require dynamic policy and/or charging control.

In the IMS model, the AF is implemented by the Proxy Call Session Control Function (P-CSCF).

Policy and Charging Rules Function, PCRF:

Services in IMS Network

End