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SAE-EPC Introduction Inam UllahHead of Product Development
ContentsWhat is SAE/EPCSAE AdvantagesSAE ArchitectureDescription of SAE ComponentsServices in EPS Networks
What is SAE/EPCSystem Architecture Evolution (aka SAE) is the core network architectureof 3GPPs LTE wireless communication standardSAE is the evolution of the GPRS Core Network, with some differences:Simplified architectureAll-IP Network (AIPN)Support for higher throughput and lower latency radio accessnetworks (RANs)Support for, and mobility between, multiple heterogeneous accessnetworks, including E-UTRA (LTE and LTE Advanced air interface), 3GPPlegacy systems (for example GERAN or UTRAN, air interfacesof GPRS and UMTS respectively), but also non-3GPP systems (forexample WiMAX or cdma2000)
SAE - AdvantagesImproved data capacity: With 3G LTE offering data download rates of 100 Mbps, and thefocus of the system being on mobile broadband, it will be necessary for the network to beable to handle much greater levels of data. To achieve this it is necessary to adopt asystem 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 switcheddata. 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 fasterresponses, the new SAE concepts have been evolved to ensure that the levels of latencyhave been reduced to around 10 ms. This will ensure that applications using 3G LTE will besufficiently responsive.Reduced OPEX and CAPEX: A key element for any operator is to reduce costs. It istherefore essential that any new design reduces both the capital expenditure (CAPEX)andthe operational expenditure (OPEX). The new flat architecture used for SAE SystemArchitecture Evolution means that only two node types are used. In addition to this a highlevel of automatic configuration is introduced and this reduces the set-up andcommissioning time.
Description of SAE ComponentsLTE SAE Evolved Packet Core, EPC consists of four mainelements as listed below: Mobility Management Entity –MME Serving Gateway –SGW Packet Gateway –PGW Policy Charging and Rule Function -PCRF
Mobility Management Entity, MME 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.
Serving Gateway, SGW: 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 themain border between the Radio Access Network, RAN and the corenetwork.The SGW also maintains the data paths between the eNodeBs and the PDNGateways. In this way the SGW forms a interface for the data packetnetwork at the E-UTRAN.Routing and forwarding user data packetsacts as mobility anchor for the user plane during inter-eNB handovers andfor mobility between LTE and other 3GPPfor idle state UEs, terminates the DL data path and triggers paging when DLdata arrives for the UEperforms replication of the user traffic in case of lawful interception.
PDN Gateway, PGW:Like the SGW, the Packet Data Network Gateway (PDN GW) is the terminationpoint of the packet data interface towards the Packet Data Network(s).As an anchor point for sessions towards the external Packet Data Networks, thePDN 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
Policy and Charging Rules Function, PCRF:the Policy and Charging EnforcementFunction(PCEF) is the generic namefor the functional entity that supportsservice data flow detection , policyenforcement and flow-basedcharging.The Application Function (AF)represents the network element thatsupports applications that requiredynamic policy and/or chargingcontrol.In the IMS model, the AF isimplemented by the Proxy CallSession Control Function (P-CSCF).