Introduction to Evolved Packet Core (EPC): EPC Elements, protocols and procedures Kamakshi Sridhar, PhD Distinguished Member of Technical Staff Director Wireless CTO organization August 2012
Agenda 1. Introduction to Evolved Packet Core (EPC) and Evolved Packet System (EPS) 2. LTE and all-ip: What is new? 3. EPC components Serving Gateway (), PDN Gateway (PGW) Mobility Management Entity (), Policy and Charging Control Function (PCRF) 4. LTE core functions and service procedures Core network functions Network attachment, service requests, paging, IP addressing, handover
1 Introduction to Evolved Packet Core and Evolved Packet System 3 Technical Sales Forum May 2008
LTE: All-IP, simplified network architecture LTE+EPC IP channel Evolved Packet Core (All-IP) Transport (backhaul and backbone) What is EPC? New, all-ip mobile core network introduced with LTE End-to-end IP (All-IP) Clear delineation of control plane and data plane Simplified architecture: flat-ip architecture with a single core EPC was previously called SAE (System Architecture Evolution) enodeb is also called E-UTRAN Evolved Packet System = EPC + E-UTRAN The EPC is a multi-access core network based on the Internet Protocol (IP) that enables operators to deploy and operate one common packet core network for 3GPP radio access (LTE, 3G, and 2G), non-3gpp radio access (HRPD, WLAN, and WiMAX), and fixed access (Ethernet, DSL, cable, and fiber). The EPC is defined around the three important paradigms of mobility, policy management, and security. Source: IEEE Communications Magazine V47 N2 February 2009 REF: http://www.comsoc.org/livepubs//ci1/public/2009/feb/pdf/ciguest_bogineni.pdf 4 Introduction to EPC July 2010 v6
Mobile core in 2G/3G 5 Introduction to EPC July 2010 v6
2 LTE and EPC what is new? 7 Technical Sales Forum May 2008
EPC: new all-ip core, new network elements (functions) 2G/3G GSM GPRS EDGE UMTS HSPA Voice Channels IP channel BTS Node B BSC / RNC MSC SGSN Softswitch GMSC Circuit Switched Core (Voice) Packet Switched Core MGW GGSN PSTN Other mobile networks Internet VPN EPC elements Serving Gateway () Packet Data Network (PDN) Gateway (PGW) Mobility Management Element () Policy and Charging Rules Function (PCRF) LTE/EPC IP channel PCRF Evolved Packet Core PDN GW 8 Introduction to EPC July 2010 v6
EPC elements LTE/EPC IP channel PCRF Evolved Packet Core PDN GW EPC elements Serving Gateway Serving a large number of enodebs, focus on scalability and security Packet Data Network (PDN) Gateway IP management ( IP anchor ), connection to external data networks; focus on highly scalable data connectivity and QoS enforcement Mobility Management Element () Control-plane element, responsible for high volume mobility management and connection management (thousands of enodebs) Policy and Charging Rules Function (PCRF) Network-wide control of flows: detection, gating, QoS and flow-based charging, authorizes network-wide use of QoS resources (manages millions on service data flows) 9 Introduction to EPC July 2010 v6
USER PLANE (UP) LTE + EPC elements and interfaces CONTROL PLANE (CP) S6a HSS S1- S11 S10 PCRF Gx Rx External networks Operator Services Applications IMS X2 enodeb S1-U S1-U S5/S8 PGW SGi Internet ACPs UE enodeb EPC IP connectivity layer (Evolved Packet System) = E-UTRAN + EPC Service Connectivity Layer 10 Introduction to EPC July 2010 v6
Flat IP = less hierarchy means lower latency GSM UMTS CDMA control plane RNC BSC SGSN PDSN GGSN HA Node B BTS data plane direct tunnel RNC BSC SGSN PDSN GGSN HA LTE control plane S/P GW data plane PGW 11 Introduction to EPC July 2010 v6
Key implications on user plane (UP) and control plane (CP) User plane has many common attributes with fixed broadband Broadband capacity QoS for multi-service delivery Per-user and per-application policies Highly available network elements Control plane gets new mobile-specific attributes Mobility across networks (and operator domains) Distributed mobility management Massive increase in scalability Dynamic policy management BSC SGSN/GGSN RNC SGSN/GGSN GSM/GPRS/EDGE WCDMA/HSPA RNC PDSN CDMA/EV-DO Service Delivery Platforms LTE IP channel PCRF Evolved Packet Core PDN GW 12 Introduction to EPC July 2010 v6
Quick Reference: Overview of EPC components and functionality enodeb: all radio access functions Radio admission control Scheduling of UL and DL data Scheduling and transmission of paging and system broadcast IP header compression (PDCP) Outer-ARQ (RLC) enb Inter Cell RRM RB Control Connection Mobility Cont. Radio Admission Control enb Measurement Configuration & Provision Dynamic Resource Allocation (Scheduler) RRC PDCP RLC MAC PHY S1 S-GW NAS Security Idle State Mobility Handling EPS Bearer Control Mobility Anchoring P-GW PCRF Policy Decisions UE IP address allocation Packet Filtering Policy, Charging & Rules Function Network control of Service Data Flow (SDF) detection, gating, QoS & flow based charging Dynamic policy decision on service data flow treatment in the PCEF (xgw) Authorizes QoS resources PDN Gateway IP anchor point for bearers UE IP address allocation Per-user based packet filtering Connectivity to packet data network internet E-UTRAN EPC Mobility Management Entity Authentication Tracking area list management Idle mode UE reachability S-GW/PDN-GW selection Inter core network node signaling for mobility between 2G/3G and LTE Bearer management functions Serving Gateway Local mobility anchor for inter-enb handovers Mobility anchoring for inter-3gpp handovers Idle mode DL packet buffering Lawful interception Packet routing and forwarding 13 Introduction to EPC July 2010 v6
All-IP mobile transformation 2G/3G Backhaul (TDM/ATM) CS Core PS Core Node B BTS BS RNC SGSN PDSN GGSN HA 1 2 3 4 5 6 7 LTE Radio intelligence moving to enodeb Backhaul transition to IP/Ethernet RNC bearer mobility evolves to the RNC control distributed into the /enb MSC voice and packet data switching evolve into the Packet data control evolves into the CS and PS evolve into a unified all-ip domain Best effort to e2e QoS Internet browsing to Web 2.0+ enodeb Backhaul (IP/Ethernet) Service and mobile aware all-ip network Evolved Packet Core PCRF PDN GW 14 Introduction to EPC July 2010 v6
LTE: more than an evolution for the packet core Voice Broadband services Multisession data QoS Existing paradigm (3G) Circuit switched (CS) Best effort, Limited expensive broadband - Rudimentary in 3G (none in 2G/2.5G) - On request - Driven by UE -Control-plane intensive setup - theory: up to 8 CoS, practice: 2 4 (voice/control, best effort data) LTE No (CS) core in LTE - e2e IP: VoIP (IMS), OneVoice - Through EPC: OTT, SR-VCC -Alternatives: CS fallback, VOLGA Real-time, interactive, low latency, true broadband QoS Based on service data flows (IP flows) - user-initiated sessions - network-initiated sessions -Driven by policy management, not UE -Faster setup through EPC --9 QoS classes - End-to-end, associated with bearers Policy Management - PCRF introduced in 3GPP R7 - Not widely adopted (static policy mgt used) Network-wide, dynamic policy charging and control (PCC) Mobility Management - Historically very much aligned (part of) with RAN - no RNCs - radio mgt. by enodeb - Mobility and session management important functions of the core 15 Introduction to EPC July 2010 v6
Example of UMTS QoS mapping to IP (transport perspective) Mapping UMTS traffic types to IP QoS (DiffServ Code Points) Conversational Streaming Interactive Background End-to-end QoS in UMTS 16 Introduction to EPC July 2010 v6
Flat-IP also implies need for a sound QoS mechanism Dedicated radio resource allocation per user TDM CS IP PS 2G/R99 3G Access CS resources By nature, 2G and Rel99 3G legacy network architecture provides dedicated CS resources ensuring: PS resources Low latency (optimized for voice service) A guaranteed bit rate for the whole duration of the CS call (even in case of congestion) Shared radio resource allocation for all users TDM IMS EPC IP LTE (and HSPA) Shared resources Without QoS control in flat-ip mobile networks, the end-user would experience (e.g. for voice/video service): High latency when cell/network is congested High voice packet loss when cell/network is congested Degraded perception for the end-user QoS control becomes mandatory to offer real-time services (Voice, Video or Gaming) over flat-ip mobile networks 17 Introduction to EPC July 2010 v6
LTE QoS terms Service Data Flow = IP flow SDFs are mapped to bearers by IP routing elements (gateways) QoS Class Identifier (QCI) A scalar that is used as a reference to node specific parameters that control packet forwarding treatment (e.g., scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.), and that have been pre-configured by the operator owning the access node Allocation and Retention Priority (ARP) The primary purpose or ARP is to decide if a bearer establishment/modification request can be accepted or rejected in case or resource limitation Guaranteed Bit Rate (GBR) Maximum Bit Rate (MBR) Aggregate Maximum Bit Rate (AMBR) (for non-gbr bearers) QCI + ARP + GBR + MBR + AMBR bearers 18 Introduction to EPC July 2010 v6
LTE QCI (QoS Class Identifier), as defined by 3GPP TS23.203 From: 4 classes in UMTS and CDMA to: 9 classes in LTE One of LTE standards goals: backward compatibility with UMTS QoS QCI Resource Type Priority Packet Delay Budget Packet Error Loss Rate Example Services 1 2 100 ms 10-2 Conversational voice 2 Guaranteed 4 150 ms 10-3 Conversational video (live streaming) 3 Bit Rate 3 50 ms 10-3 Real-time gaming (GBR) 4 5 300 ms 10-6 Non-conversational video (buffered streaming) 5 1 100 ms 10-6 IMS signalling 6 6 300 ms 10-6 TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc.) Video (buffered streaming) 7 7 100 ms 10-3 Voice, video (live streaming), interactive Non-GBR gaming 8 8 300 ms 10-6 9 9 300 ms 10-6 Premium bearer for video (buffered streaming), TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc) for premium subscribers Default bearer for video, TCP-based services, etc. for non-privileged subscribers 19 Introduction to EPC July 2010 v6
EPC bearer management Data plane needs to support fine-granularity of QoS and charging enforcement functions beyond transport / bearer level Uplink (UL) and Downlink (DL) packet filters are defined for each bearer and QoS enforcements (policing, shaping, scheduling, etc.) are applied PGW acts as the Policy and Charging Enforcement Function (PCEF) point to maintain QoS / SLA for each of the bearers (and SDFs) E-UTRAN EPC Internet UE enodeb PGW peer End-to-end service EPS bearer External bearer Radio bearer S1 bearer S5/S8 bearer LTE-Uu S1 S5/S8 SGi 20 Introduction to EPC July 2010 v6
3 EPC elements 21 Technical Sales Forum May 2008
enodeb (E-UTRAN) (not a part of the EPC), but let s look at Interactions with other functional elements USER PLANE (UP) CONTROL PLANE (CP) Pool of s Pool of s Mobility Management Bearer handling Security settings User plane tunnels for UL and DL data delivery Radio Resource Management Mobility management Bearer handling User plane data delivery Securing and optimizing radio interface delivery Inter enodeb handovers Forwarding of DL data during handovers User Equipment UE Other enodebs 22 Introduction to EPC July 2010 v6
Mobility Management Entity controls how UE interacts with the network via non-access stratum (NAS) signalling Authenticates UEs and controls access to network connections Controls attributes of established access (e.g., assignment of network resources) Maintains EPS Mobility Management (EMM) states for all UE s to support paging, roaming and handover Manages ECM (EPS Connection Management) states IP channel PCRF Evolved Packet Core PDN GW is control plane element that manages network access and mobility 23 Introduction to EPC July 2010 v6
: Interactions with other functional elements USER PLANE (UP) CONTROL PLANE (CP) Other s Handovers between s Idle state mobility between s HSS Authentication and Security Location management User profiles s Control of user plane tunnels Inter enodeb handovers State transitions Bearer management Paging User Equipment UE Other enodebs 24 Introduction to EPC July 2010 v6
Serving Gateway and Packet Data Network (PDN) Gateway is local mobility anchor Terminates (S1-U) interface towards E-UTRAN Local anchor point for inter-enb handover and inter-3gpp mobility Support ECM-idle mode DL packet buffering and network-initiated service request IP routing and forwarding functions PGW is IP anchor for bearers Terminates (SGi) interface towards the PDN Provides UE IP address management (allocation) Provide Policy and Charging Enforcement Function (PCEF) Per-SDF based packet filtering Interface to Online and Offline Charging Systems IP channel PCRF Evolved Packet Core PDN GW 25 Introduction to EPC July 2010 v6
: Interactions with other functional elements USER PLANE (UP) CONTROL PLANE (CP) s PCRF Control of GTP tunnels and IP service flows Mobility control PCRF PMIP S5/S8 IP service flow <-> GTP tunnel mapping information PGW PGW PGWs GTP S5/S8 Control of GTP tunnels GTP tunnels for UL and DL data delivery PMIP IP service flows User Plane tunnels for DL and UL data delivery Indirect forwarding of DL data during handovers (in S1-U) when direct (X2) inter-enodeb connection is not available enodebs Other s 26 Introduction to EPC July 2010 v6
PGW: Interactions with other functional elements USER PLANE (UP) CONTROL PLANE (CP) PCRFs PCRF Policy and Charging Control requests PCC rules External networks IP flows of user data PGW Control of User Plane tunnels UP tunnels for UL and DL data delivery Online Charging Systems s Offline Charging Systems 27 Introduction to EPC July 2010 v6
End-to-end protocol stack (User Plane) IP channel PCRF PDN GW applications Evolved Packet Core services user traffic = end-to-end IP IP RELAY RELAY IP PDCP PDCP GTP-U GTP-U GTP-U GTP-U RLC RLC UDP/IP UDP/IP UDP/IP UDP/IP MAC MAC L2 L2 L2 L2 L1 LTE-Uu L1 L1 S1-U L1 L1 S5/S8 L1 SGi UE enodeb PGW * S5/S8 reference point between S-GW and PDN-GW can also be GTP based Key role of S-GWs and PDN-GWs = to manage the user plane (bearer traffic) 28 Introduction to EPC July 2010 v6
PCRF: Interactions with other functional elements USER PLANE (UP) CONTROL PLANE (CP) AF External networks Policy and Charging Control requests PCRF Policy and Charging Control requests PCC rules QoS rules when S5/S8 is PMIP s QoS rules when S5/S8 is PMIP QoS rules for mapping IP service flows and GTP tunnel in S1 when S5/S8 is PMIP PGW PGW PGWs 29 Introduction to EPC July 2010 v6
Policy Charging and Control (PCC) Architecture SPR Sp PCRF Rx AF Gxx Gx Gy OCS SDF-based credit control BBERF PCEF PGW Gz OFCS BBERF = Bearer Binding and Event Reporting Function OCS = Online Charging System OFCS = Offline Charging System PCEF = Policy and Charging Enforcement Function SPR = Subscription Profile repository 30 Introduction to EPC July 2010 v6
Service level policy control Service Data Flow (SDF) Packet filters QoS parameter: QCI, Guaranteed bit rate (UL/DL), Maximum bit rate (UL/DL), Aggregate maximum bit rate UE PDN-GW SDF-1 Default bearer SDF-2 UE-IP1@ Dedicated bearer (GBR) SDF-3 UE-IP1@ IP-Connectivity Access Network Session UE-IP1@ The PGW needs to support fine-granularity of QoS and charging enforcement functions beyond transport / bearer level Multiple Service Data Flow (SDF) can be aggregated onto a single EPS bearer Uplink and downlink packet filters are defined for each bearer, and QoS enforcements are applied 31 Introduction to EPC July 2010 v6
4 Core procedures 32 Technical Sales Forum May 2008
EPC: Core functions and service procedures Core Functions Core Procedures Charging Network attachment Subscriber management Service requests (paging, buffering) Mobility management (new!) Handovers and (X2 routing) Bearer management Roaming (home/visiting PDN breakout) Policy management (new!) Interconnection Interworking with 3GPP ANs Interworking with non 3GPP ANs (EVDO/EHRPD treated as a special case) 33 Introduction to EPC July 2010 v6
Roaming breakout through home PDN HPLMN VPLMN HSS S6a PDN Gateway Gx H-PCRF SGi Rx Home Operator s IP Services UTRAN SGSN GERAN S3 S8a X2 S1- S11 S4 S12 E-UTRAN S1-U Serving Gateway 35 Introduction to EPC July 2010 v6
Roaming local breakout (through visiting PDN) HSS H-PCRF Rx Home Operator s IP Services HPLMN VPLMN S6a UTRAN S9 SGSN GERAN S3 V-PCRF Gx X2 S1- S11 S4 S12 eutran E-UTRAN S1-U Serving Gateway S5 PDN Gateway SGi IP Network 36 Introduction to EPC July 2010 v6
Network attachment and IP address assignment PCRF S7c S7 Always-on IP connection is established and anchored at PDN-GW X2 S1- S11 SGi IP Network E-UTRAN S1-U Serving Gateway S5 PDN Gateway IPv4 direct IP address assignment IPv6 shorter IP IPv4 via DHCP (after) IPv6 IPv6 /64 stateless 37 Introduction to EPC July 2010 v6
UE and service requests PCRF 1. UE sends NAS Service Request message towards S7c S7 2. Update Bearer Request is sent to the S-GW to establish/modify S1-bearer 3. Dedicated bearer established after interaction with PCRF X2 S1- S11 E-UTRAN S1-U Serving Gateway S5 PDN Gateway SGi IP Network 38 Introduction to EPC July 2010 v6
Handover and X2 routing PCRF enb X2-AP enb X2-AP enb GTP-U enb GTP-U SCTP SCTP UDP UDP S7c S7 IP L2 IP L2 IP L2 IP L2 L1 X2-C L1 L1 L1 X2-U X2 S1- S11 X2 protocol stacks E-UTRAN S1-U Serving Gateway S5 PDN Gateway SGi IP Network X2 = active mode mobility - User Plane (UP) ensures lossless mobility - Control Plane (CP) provides enb relocation capability 39 Introduction to EPC July 2010 v6
4a SMS and legacy voice 40 Technical Sales Forum May 2008
SMS service for initial data-only devices GERAN UTRAN MSC CS Network SMS-C SGSN New interface SGs from MSC to E-UTRAN PDN PGW Data Paging/SMS Data and SMS only Handset uses LTE network where possible to achieve highest throughput Handset served by an MSC in legacy network for voice and SMS SMS delivered over SGs without requiring inter-rat handover 41 Introduction to EPC July 2010 v6
Voice support using CS Fallback (CSFB) GERAN UTRAN MSC New interface SGs from MSC to CS Network GERAN UTRAN MSC CS Network SGSN SGSN E-UTRAN E-UTRAN PDN PDN PGW Data Paging/SMS PGW Circuit Voice Data Simultaneous Voice + Data Handset falls back to legacy circuit coverage for voice Incoming calls to MSC trigger paging over SGs and delivered via Data sessions handover to SGSN if possible Tradeoff: Re-uses legacy circuit infrastructure But at the cost of Inter-RAT handover per voice call, and reduced capacity (3G) or suspended (2G) data sessions 42 Introduction to EPC July 2010 v6
Voice via IMS GERAN UTRAN E-UTRAN MSC SGSN PGW CS Network 2 3 IMS TAS PDN SCC AS 1 Simultaneous Voice and Data on LTE Handset has concurrent access to: 1. Data services including internet access 2. IMS Services including VoIP end-end calling 3. IMS interworking towards legacy PSTN/PLMN networks Uses IMS nodes Telephony Application Server (TAS) and Service Centralization and Continuity Application Server (SCC AS) GERAN UTRAN E-UTRAN MSC SGSN PGW 2 CS Network IMS TAS PDN 3 1 SCC AS IMS Services outside of LTE coverage For service transparency, IMS Centralized Services (ICS) provides IMS services even when the handset is out of LTE coverage Handset has concurrent access to: 1. Data Services including internet access 2. IMS Services including circuit-mode transport of voice path 3. Calls to-from the PSTN/PLMN legacy network as well as calls to VoIP end users in IMS Circuit Voice Circuit signaling Packet Voice IMS Signaling Packet Data 43 Introduction to EPC July 2010 v6
Alcatel-Lucent EPC Solution 8650 SDM HSS X2 UTRAN GERAN 9326 enb 7500 SGSN S3 9471 S1- S6a S11 S4 S101 5780 DSC (PCRF) S12 Gxc 9271 ernc Gn Gp Gx CDMA/EVDO H 8615 IeCCF OFCS 8610 Rf Ro ICC OCS S2a Data Plane Control Plane AFs UE 9326 enb eutran S1-U 7750 SR Serving Gateway S5/S8 7750 SR PDN Gateway SGi IP Network End-to-end IP management (incl. services) 5620 SAM 44 Introduction to EPC July 2010 v6
User Plane Scalability First mobile gateway to deliver over 100 Gbps Full UP and CP Management Full GUI management of bearers (UP and CP) Deployment Flexibility As, PGW/GGSN or combo Deployment Universality e2e wireless IP management: RAN, core and backhaul Performance/QoS Per-UE, per-app, per-flow hierarchical QoS Integration in OSS/BSS Part of full NM portfolio Full OSS/BSS integration Reliability 99.999+ % field proven 48,000+ units shipped 7750 Service Router-based Architecture Optimized split of router and gateway functions 7750 Service Router Mobile Gateway 5620 SAM Service Aware Manager Alcatel-Lucent Ultimate Wireless Packet Core Reliability Geo-redundancy Scalability/Architecture Suited for Tier X to Tier1 operator environments Control Plane Scalability Millions of subscribers Thousands of enodebs Deployment Flexibility As SGSN, or SGSN/ combo Mobile Core Business Engine Policy Convergence Monetization and Personalization Deployment Agility Flexi rules engine with wizards Up and running in minutes Add new rules easily Performance Superior paging capabilities High-signallng loads Reliability Geo-redundancy, pooling No single point of failure 9471 Wireless Mobility Manager 5780 Dynamic Services Controller Integration with NM Part of full NM portfolio Same NM/GUI paradigm Reliability Geo-redundancy No single point of failure Platform/Architecture ATCAv2 platform for all CP functions Platform/Architecture ATCAv2 platform for all CP functions
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