3GPP EPC(演进的分组核心网)白皮书.ppt

,System Architecture Evolution:3GPP Releases 8 and 9,June 2010,The 3GPP Evolved Packet Core,White Paper,Authors,Chandramouli,Devaki,Kall,Jan,Liebhart,RainerPasanen,AnttiUngvari,GaborWolfner,Gyorgy,Wong,Curt,Zaus,Robert,(CEF CTO IE 3GPP),EPC,The 3GPP Evolved Packet Core White Paper,2,1233.13.23.33.444.14.24.34.44.54.64.755.15.25.35.3.15.3.1.15.3.25.3.2.15.3.2.25.3.2.35.3.2.45.45.4.15.4.25.4.35.566.16.26.36.46.4.16.4.26.4.36.56.5.16.5.277.17.27.2.17.2.27.2.2.17.2.2.27.2.388.1,ContentsPreface.4SAE Overview.5Brief History.5Drivers for the LTE/SAE Project.5LTE/SAE compared to 2G/3G.6Specifics of Non-3GPP Access Interworking.7SAE Network Architecture.8Introduction.8General(Non-Roaming)Architecture.8Roaming Architecture(home routed).10Roaming Architecture(local breakout).11Home eNodeB Architecture.12Interworking with 2G/3G Networks.14Interworking with Non-3GPP Access Networks.15Session and Bearer Management Procedures.18Overview.18QoS and EPS Bearers.18Establishment of a PDN Connection.193GPP Access.19UE requested PDN Connectivity.20Non-3GPP Access.20Non-3GPP Access Networks with PMIPv6.21Non-3GPP Access Networks with DSMIPv6.22Multiple PDN Connections via Non-3GPP Access Networks.22QoS over Non-3GPP Access Networks.22Allocation of dedicated bearers.23Network initiated Dedicated Bearer Context Activation Procedure.23UE requested Bearer Resource Allocation Procedure.24UE requested Bearer Resource Modification Procedure.24IP Address Allocation.25Mobility Management Procedures.26Overview.26Attach.26Tracking Area Updating.29Intra E-UTRAN Handover.30General.30X2-based Handover.31S1-based Handover.32Inter RAT Handover.342G/3G Handover.34Non-3GPP Handover.36Security Functions.39Confidentiality and Integrity Protection.39Lawful Interception.39Lawful Interception for EPS.40Handover Interface in EPS.42HI2 Interface and IRI Interception.42HI3 Interface and CC Interception.42EPS LawfuI Interception in ETSI.42Features and Functionalities.43Voice and SMS Support.43,EPC,The 3GPP Evolved Packet Core White Paper,3,8.1.18.1.28.1.38.1.48.28.38.3.18.3.28.3.38.3.48.48.59101111.112,Overview.43CS Fallback.43Single Radio Voice Call Continuity.44Short Message Service.45Multimedia Broadcast/Multicast Service.46Emergency Services.48Overview.48Regulations and their Impact on Emergency Services.48Emergency Services in EPS.48Emergency Numbers and Detection of Emergency Calls.49Location Based Services.49Public Warning System(PWS).51Summary and Outlook.52Terminology.53Appendix.56Reference Points.56References.58,EPC,The 3GPP Evolved Packet Core White Paper,4,2,Preface,This white paper is meant as an introduction into the main concepts and design principles of LTE/SAE and especiallythe Evolved Packet Core(EPC),which is a key part of the LTE/SAE system.It provides an overview of the evolutionpath from 2G and 3G networks to LTE/SAE,architecture,most important procedures regarding mobility and sessionmanagement and features to support voice or location based services in the new system.As such it is not an exhaustiveoverview in this topic but can be used as a first introductory course.If the reader is interested in more details,thereferences list at the end of the white paper give some hints for further reading(books are not listed although availableon the market).In parallel to this white paper,corresponding white papers on IP Multimedia Subsystem,PCC/QoS and Charging,andUser Data Convergence were written providing a similar level of detail.These papers together give an overall picture ofseveral important parts of the 3GPP system up to Release 9 and can be found under 10.If time permits the documentswill be updated in the future to cover features of upcoming 3GPP releases.Readers only interested in the basics of LTE/SAE can read sections 3,4 and 8.These chapters are independent of therest of the white paper.Section 9 gives a personal outlook of the authors and provides insights into potential futuredevelopments of the 3GPP core network.June 2010,the Authors,EPC,The 3GPP Evolved Packet Core White Paper,5,3,SAE Overview,3.1 Brief HistoryMain drivers for evolution of mobile networks are still higher bandwidth at the radio interface and better spectralefficiency(the information rate transmitted over a given bandwidth).After improving these key factors for WCDMAover several years by introducing HSPA and HSPA+,the 3rd Generation Partnership Project(3GPP)standardizationforum started end of 2004 evaluating a new radio technology as successor for WCDMA providing even higher peakdata rates(100 Mbit/s Downlink,50 Mbit/s Uplink)and lower latency besides other improvements.This work wascalled Long Term Evolution(LTE)and is nowadays the radio interface name used in most official publications.Inside3GPP the newly developed radio access network is called Evolved UMTS Radio Access Network(E-UTRAN)toindicate the path from GERAN(GSM/GPRS/EDGE)to UTRAN(WCDMA/HSPA)and finally to E-UTRAN(LTE).Inparallel to the work on a new radio interface 3GPP initiated a study to evolve the 2G/3G packet core network(known asGPRS core)in order to cope with the new demands of LTE.This core network study was called System ArchitectureEvolution(SAE)and it was documented in the Technical Report 23.882 6.The final outcome of this work was a newpacket core design in Release 8 documented in Technical Specifications 23.401 3 and 23.402 4,called the EvolvedPacket Core(EPC).3GPP Release 8 was officially completed in March 2009.EPC allows connecting LTE,GERAN/UTRAN,non-3GPP access systems like WLAN,WiMAX and CDMA and also 3GPP compliant small FemtoAccess Points installed at home or in companies.Special emphasis was put on optimized handover procedures betweenLTE and CDMA2000 eHRPD(Evolved High Rate Packet Data)access due to requirements from some CDMA networkoperators in the US and Japan,who plan to introduce LTE very rapidly(starting already in 2010).The EPC togetherwith these access systems is called Evolved Packet System(EPS).In contrast to the 2G and 3G systems EPS does nolonger contain a circuit switched part.For that reason supporting voice in EPS and providing a migration story from2G/3G voice and SMS to voice and SMS in EPS is extremely important for the acceptance of the new system.A lot ofeffort was put in specifying solutions for the above mentioned issues during Release 8 and 9.An overview of voice andSMS support can be found in section 8.1,while migration of CS voice in 2G/3G to IMS voice in LTE has differentflavours(IMS Centralized Services,Session Continuity and Single Radio Voice Call Continuity amongst others).Formore details on voice migration aspects see the IMS related white paper 10.As already mentioned EPC is an evolution of the 3GPP system architecture with the finally realized vision of an all-IPnetwork.EPC in conjunction with the IP Multimedia Subsystem(IMS)delivers various services such as VoIP,SMS,Video call,Picture share,Instant Messaging and Presence.EPC and IMS support mobility with the existing 2G/3Gwireless networks as well as fixed networks to facilitate smooth migration,interworking,and service continuity acrossall these networks.Nevertheless,as a pure IP based network the main application for LTE/SAE(a term used in parallelto EPS)will be the”Internet”with its rapidly increasing demands for more bandwidth and lower latency coming fromP2P services or applications like online gaming,Mobile TV and possibly Machine-to-Machine network deploymentssuch as smart traffic control or smart grid.We have seen that LTE/SAE was designed to cope with the challenges of the growing broadband mobile market:moredata per user,always-on with high expectation on quality and reliability,connected everywhere,network efficiency,more users who are not humans and connecting with an all-IP world.How this was finally realized will be shown in thefollowing chapters.3.2 Drivers for the LTE/SAE ProjectAs mentioned in the previous chapter the main drivers to start work on LTE/SAE were the need for higher data rates(which can be at least partly achieved by HSPA as well)and a significant reduction of control plane latency and roundtrip delay to support future high quality services.Higher data rates are a must when recognizing the tremendousincrease of mobile broadband data traffic:forecasts indicate that over 90%of the traffic will be data traffic in 2012 withmobile data traffic four to five times more in 2012 compared to 2010.The increasing number of mobile subscribersusing Internet services like email,browsing,chatting,data transfer or community applications much more frequentlythan pure voice and SMS showed the limitations of 2G/3G radio and packet core networks very clearly.Reducedcontrol plane latency is a need to provide a high-quality always-on experience to the end user.Latency of control planemessages and rather big round trip delays were seen as drawbacks of existing 2G/3G systems by many operators.Another driver for a flat,pure IP based and simplified architecture with less radio and core network nodes was certainlythe pressure to decrease overall costs(OPEX and CAPEX).Finally,a purely IP based architecture provides the,EPC,6,The 3GPP Evolved Packet Core White Paperpossibility for introducing a PS optimised system while e.g.the 3G system had to make some compromises in thesupport of packet based services as it contains a CS and PS part.An important design principle of EPC was backward compatibility.As such EPC and more general EPS are providinginherent mechanisms to support mobility for devices when changing between 2G,3G and LTE,either based on GTP orPMIP mobility protocols.With EPC a new GTP version was introduced,GTPv2(see TS 29.274 8),but only forcontrol plane signalling.For transport of user plane packets still GTPv1-U is used.Regarding non-3GPP access systemslike WLAN or WiMAX,LTE/SAE is supporting mobility by re-use of generic mobility protocols defined in IETF,namely PMIPv6 and DSMIPv6.For CDMA2000 eHRPD handover to LTE was improved by introducing specialcontrol plane and user plane interfaces to the EPC in order to deliver information from one access system to the otherbefore the actual handover takes place to speed up the handover process.This harmonized core network architecturesupporting 2G/3G,LTE and non-3GPP access systems was another important objective when designing EPC.While cost reduction is the main driver for network operators to introduce LTE/SAE,delay optimizations(minimizedlatency and round-trip-delay leads to high TCP traffic throughput,low UDP/RTP traffic jitter to high quality real timeservices)and fast service availability caused by low bearer set-up times are the benefits for the end user.These benefitsincrease the acceptance of the new technology and will pay back the investments of operators,terminal andinfrastructure vendors.3.3 LTE/SAE compared to 2G/3GWhen comparing E-UTRAN with UTRAN or GERAN the obvious change(besides use of the radio technology OFDMinstead of WCDMA or EDGE)is that E-UTRAN knows only one network element,the so-called Evolved NodeB(eNodeB or eNB)while in UTRAN NodeB and RNC and in GERAN BTS and BSC exist.Main reasons for thissimplified E-UTRAN architecture were reducing complexity,latency and costs while increasing data throughput.On the core network side the obvious difference between the GPRS core and EPC is the strict and in-build separation ofcontrol and user plane in EPC.While this is possible in GPRS as well by using the Direct Tunnel feature,i.e.user planetraffic is directly tunnelled from RNC to GGSN bypassing the SGSN,EPC was from the very beginning designed inthis way.There are two functional elements in the user plane,the Serving Gateway(S-GW)and Packet Data NetworkGateway(P-GW or PDN-GW),and one element in the control plane,the Mobility Management Entity(MME).As aconsequence in minimum two(eNodeB and combined S-GW/P-GW)and in maximum three nodes(eNodeb,S-GW andP-GW)are in the EPS user plane path when LTE/SAE is deployed(1-2 less then in 2G/3G).This means a higher degreeof simplicity,higher throughput and less latency.Besides support of legacy 2G/3G access systems and LTE,the EPCsupports also non-3GPP access systems that are trusted or non-trusted from the EPC point of view.This means thatEPC provides means to authenticate,authorize and charge subscribers who are using these non-3GPP access systems,the user plane is securely routed to and through the EPC core elements towards a Packet Data Network(PDN)like theInternet and last but not the least seamless mobility(i.e.the IP mobility anchor is in the EPC and not changed duringhandover)between 3GPP and non-3GPP access systems is enabled.This kind of enhanced support of non-3GPP accesssystems is not supported by the 2G/3G core network,also called GPRS core.One technical detail that is not obvious is the concept of network initiated bearer establishment.This was introduced to2G/3G rather late and is more an exception than the usual procedure to establish bearers.In LTE/SAE it is now themain mechanism to setup dedicated bearers once the mobile device is connected with a PDN and the network hasallocated an IP address,Ipv4 address or Ipv6 prefix,or a pair of both Ip4 address and Ipv6 prefix.Nevertheless,adevice initiated bearer establishment procedure still exists in LTE/SAE.To reduce the number of signalling messages between device and core network for the purpose of mobility managementand based on the lessons learned from 2G/3G deployments two new concepts resp.features were introduced withLTE/SAE.The first one is the concept of a Tracking Area(TA)list that is allocated to a User Equipment(UE),which isa mobile device including an USIM,instead of single Routing Areas in 3G and Location Areas in 2G.Different TA listsallocated to different UEs in one area reduce the probability of simultaneous Tracking Area updates when a hugenumber of UEs is moving from one TA to another at the same time(e.g.when the users are sitting in the same train).On the other hand a whole TA list allocated to one UE naturally decreases the need of the UE to perform TA updates.The TA list concept however comes with the drawback of bigger paging areas.Besides the TA list concept Idle ModeSignalling Reduction(ISR)was introduced to reduce the number of TA and RA updates when a UE is moving betweendifferent Radio Access Types(RAT).If ISR is activated by the network,the UE in idle-mode is registered with bothLTE/SAE and 2G/3G.The UE can reselect between E-UTRAN and GERAN/UTRAN(within the already registeredRAs and TAs)without a need to perform TA update or RA update procedures with the network.This is similar to theoption in 2G/3G networks to include GERAN and UTRAN cells in one RA so that the UE can reselect between these,EPC,7,The 3GPP Evolved Packet Core White PaperGERAN and UTRAN cells without performing a RA update procedure.However,whereas in 2G/3G this requires acombined 2G/3G SGSN that is supporting interfaces for both RATs,in EPS the core network entities supporting ISRand serving the E-UTRAN and the GERAN/UTRAN,r