Aug12 sridhar

Kamakshi Sridhar, PhD
Distinguished Member of Technical Staff
Director Wireless CTO organization
August 2012
Introduction to Evolved Packet Core (EPC):
EPC Elements, protocols and procedures

© 2009 Alcatel-Lucent. All rights reserved.
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 (SGW), PDN Gateway (PGW)
 Mobility Management Entity (MME), Policy and Charging Control Function (PCRF)
4. LTE core functions and service procedures
 Core network functions
 Network attachment, service requests, paging, IP addressing, handover

© 2009 Alcatel-Lucent. All rights reserved.3 | Technical Sales Forum | May 2008
1
Introduction to Evolved Packet Core and
Evolved Packet System

LTE: All-IP, simplified network architecture
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
What is EPC ?
LTE+EPC
eNode B
IP channel Evolved Packet Core
(All-IP)
Transport (backhaul and backbone)
 “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

2
LTE and EPC – what is new?

EPC: new all-IP core, new network elements (functions)
EPC elements
LTE/EPC
eNode B
IP channel MME PCRF
PDN GWSGW
GSM
GPRS
EDGE
UMTS
HSPA
Evolved Packet Core
IP channel
Packet Switched
Core
PSTN
Other
mobile
networks
VPN
Internet
Voice
Channels
GGSNSGSN
MGW
MSC
BSC / RNC
Circuit Switched
Core (Voice)
BTS
Node B
Softswitch
GMSC
2G/3G
 Serving Gateway (SGW)
 Packet Data Network (PDN) Gateway (PGW)
 Mobility Management Element (MME)
 Policy and Charging Rules Function (PCRF)

EPC elements
EPC elements
LTE/EPC
eNode B
IP channel MME PCRF
PDN GWSGW
Evolved Packet Core
 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 (MME)
 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)

LTE + EPC elements and interfaces
MME PCRF
SGW
S5/S8
Gx
S11
eNodeB
eNodeB
S1-U
S1-MME
S1-U
X2
HSSS6a
S10
PGW
SGi
Rx
External networks
Operator Services
Applications
IMS
Internet
ACPs
EPC
IP connectivity layer (Evolved Packet System) = E-UTRAN + EPC
UE
Service Connectivity Layer
CONTROL PLANE (CP)
USER PLANE (UP)

“Flat IP” = less hierarchy means lower latency
eNode B
Node B
BTS
data plane
control plane
data plane
control plane
SGSN
PDSN
RNC
BSC
GGSN
HA
SGSN
PDSN
RNC
BSC
GGSN
HA
GSM
UMTS
CDMA
LTE
MME S/P GW
PGWSGW
direct tunnel

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
WCDMA/HSPAGSM/GPRS/EDGE CDMA/EV-DO
PDSNRNCRNCBSC SGSN/GGSN SGSN/GGSN
eNode B
IP channel
LTE
MME PCRF
PDN GWSGW
Evolved Packet Core
Service Delivery
Platforms

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
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
Quick Reference:
Overview of EPC components and functionality
internet
eNB
RB Control
Connection Mobility Cont.
eNB Measurement
Configuration & Provision
Dynamic Resource
Allocation (Scheduler)
PDCP
PHY
MME
S-GW
S1
MAC
Inter Cell RRM
Radio Admission Control
RLC
E-UTRAN EPC
RRC
Mobility
Anchoring
EPS Bearer Control
Idle State Mobility
Handling
NAS Security
P-GW
UE IP address
allocation
Packet Filtering
 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)
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
PDN Gateway
 IP anchor point for bearers
 UE IP address allocation
 Per-user based packet filtering
 Connectivity to packet data network
Policy
PCRF
Decisions

All-IP mobile transformation
RNC
Radio
intelligence
moving to
eNodeB
1 2 4
Node B
BTS
BS SGSN
PDSN
Backhaul (TDM/ATM)
RNC bearer
mobility
evolves to
the SGW
3
Backhaul
transition
to IP/Ethernet
Backhaul (IP/Ethernet)
MSC voice and
packet data
switching
evolve into
the SGW
RNC control
distributed
into
the MME/eNB
Packet data
control
evolves into
the MME
CS Core
5
CS and PS
evolve into a
unified all-IP
domain
Service and mobile aware
all-IP network
Evolved Packet Core
MME
PCRF
PDN GW
SGWeNodeB
PS Core
GGSN
HA
Best effort to
e2e QoS
6 7
Internet
browsing
to
Web 2.0+
2G/3G
LTE

LTE: more than an evolution for the packet core
Existing paradigm (3G) LTE
Voice Circuit switched (CS)
No (CS) core in LTE
- e2e IP: VoIP (IMS), OneVoice
- Through EPC: OTT, SR-VCC
-Alternatives: CS fallback, VOLGA
Broadband
services
Best effort,
Limited expensive “broadband”
Real-time, interactive,
low latency, true broadband QoS
Multisession
data
- Rudimentary in 3G (none in 2G/2.5G)
- On request
Based on service data flows (IP flows)
- user-initiated sessions
- network-initiated sessions
QoS
- Driven by UE
-Control-plane intensive setup
- theory: up to 8 CoS, practice: 2 – 4
(voice/control, best effort data)
-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

Example of UMTS QoS mapping to IP (transport perspective)
Conversational
Streaming
Background
Interactive
Mapping UMTS traffic types to IP QoS (DiffServ Code Points)
End-to-end QoS in UMTS

“Flat-IP” also implies need for a sound QoS mechanism
2G/R99 3G Access
CS PS
IPTDM
LTE (and HSPA)
EPC
IPTDM
IMS
Dedicated radio resource allocation per user Shared radio resource allocation for all users
PSresources
CSresources
Shared
resources
 By nature, 2G and Rel99 3G legacy network
architecture provides dedicated CS resources
ensuring:
 Low latency (optimized for voice service)
 A guaranteed bit rate for the whole duration of the CS
call (even in case of congestion)
 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

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

LTE QCI (QoS Class Identifier), as defined by 3GPP TS23.203
QCI Resource Type Priority
Packet Delay
Budget
Packet Error
Loss
Rate
Example Services
1
Guaranteed
Bit Rate
(GBR)
2 100 ms 10
-2
Conversational voice
2 4 150 ms 10
-3
Conversational video (live streaming)
3 3 50 ms 10
-3
Real-time gaming
4 5 300 ms 10
-6
Non-conversational video (buffered streaming)
5
Non-GBR
1 100 ms 10
-6
IMS signalling
6 6 300 ms 10
-6
Video (buffered streaming)
TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing,
progressive video, etc.)
7 7 100 ms 10
-3 Voice, video (live streaming), interactive
gaming
8
8 300 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
9 9 300 ms 10-6
“Default bearer” for video,
TCP-based services, etc. for non-privileged subscribers
From: 4 classes in UMTS and CDMA to: 9 classes in LTE
One of LTE standards goals:
backward compatibility with UMTS QoS

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)
eNodeB SGW PGW peerUE
LTE-Uu S1 S5/S8 SGi
End-to-end service
EPS bearer
External
bearer
Radio
bearer
S1
bearer
S5/S8
bearer
E-UTRAN EPC Internet

3
EPC elements

eNode B
MME
SGW
eNodeB (E-UTRAN) (not a part of the EPC), but let’s look at…
Interactions with other functional elements
eNode B
MME SGW
UE
eNode B
Pool of SGWsPool of MMEs
Other eNodeBs
• Mobility Management
• Bearer handling
• Security settings
• Radio Resource
Management
• Mobility management
• Bearer handling
• User plane data delivery
• Securing and optimizing
radio interface delivery
• User plane tunnels for
UL and DL data delivery
• Inter eNodeB handovers
• Forwarding of DL data
during handovers
User Equipment
CONTROL PLANE (CP)
USER PLANE (UP)

Mobility Management Entity
MME 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
eNode B
IP channel
MME is control plane element that manages network access and mobility
MME PCRF
PDN GWSGW
Evolved Packet Core

MME SGW
MME:
MME SGW
UE
eNode B
SGWsOther MMEs
Other eNodeBs
• Handovers between MMEs
• Idle state mobility between MMEs
• Authentication and Security
•Location management
• User profiles
• Control of user plane tunnels
• Inter eNodeB handovers
• State transitions
• Bearer management
• Paging
User Equipment
MME
HSS
eNode B
CONTROL PLANE (CP)
USER PLANE (UP)

Serving Gateway and Packet Data Network (PDN) Gateway
SGW 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
eNode B
IP channel
eNode B
MME PCRF
PDN GWSGW
Evolved Packet Core

MME PGW
SGW:
MME PGW
eNode B
PGWsMMEs
Other SGWs
• Control of GTP tunnels and IP service flows
• SGW Mobility control
PMIP S5/S8
• IP service flow <-> GTP tunnel
mapping information
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
SGW
eNode B
SGW SGW
•Indirect forwarding of DL data
during handovers (in S1-U)
when direct (X2) inter-eNodeB
connection is not available
PCRF
eNodeBs
PCRF
CONTROL PLANE (CP)
USER PLANE (UP)

PGW:
SGWs
• Policy and Charging Control requests
• PCC rules
• IP flows of user data
PGW
SGW SGW
• Control of User Plane tunnels
• UP tunnels for UL and DL data
delivery
PCRF
External networks
PCRFs
Online Charging
Systems
Offline Charging
Systems
CONTROL PLANE (CP)
USER PLANE (UP)

End-to-end protocol stack (User Plane)
MAC
RLC
PDCP
L1
S1-ULTE-Uu
eNodeBUE
L2
UDP/IP
GTP-U
L1
S5/S8
L2
UDP/IP
L1
L2
UDP/IP
L1
L2
UDP/IP
L1
MAC
RLC
L1
PDCP
SGW PGW
SGi
IP
applications
services
* 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)
user traffic = end-to-end IP
eNode B
IP channel
MME
PCRF
PDN GW
SGW
Evolved Packet Core
GTP-U
RELAY
IP
GTP-U GTP-U
RELAY

PCRF:
SGWs
PCRF
SGW SGW
PGW
External networks
PGWs
AF
PGW
• PCC rules
• QoS rules when S5/S8 is PMIP
• QoS rules when S5/S8 is PMIP
• QoS rules for mapping IP service flows
and GTP tunnel in S1 when S5/S8 is
PMIP
CONTROL PLANE (CP)
USER PLANE (UP)

Policy Charging and Control (PCC) Architecture
BBERF
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
OCS
SDF-based credit control
OFCS
AF
PCEF
Gy
Gz
PCRF
Rx
GxGxx
SGW PGW
SPR
Sp

Service level policy control
 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
PDN-GW
IP-Connectivity Access Network Session  UE-IP1@
Dedicated bearer (GBR) UE-IP1@
UE
Default bearer
SDF-1
SDF-3
SDF-2
UE-IP1@
Service Data Flow (SDF)
• Packet filters
• QoS parameter: QCI, Guaranteed bit rate (UL/DL),
Maximum bit rate (UL/DL), Aggregate maximum bit rate

4
Core procedures

EPC: Core functions and service procedures
Core Functions
Charging
Subscriber management
Mobility management (new!)
Bearer management
Policy management (new!)
Interconnection
Core Procedures
Network attachment
Service requests (paging, buffering)
Handovers and (X2 routing)
Roaming (home/visiting PDN breakout)
Interworking with 3GPP ANs
Interworking with non 3GPP ANs
(EVDO/EHRPD treated as a special case)

Roaming – breakout through home PDN
SGi
GERAN
UTRAN
S11
S3
S8a
HSS
S4
S1-U
S1-MME
MME
S6a
SGSN
S12
HPLMN
VPLMN
X2
Gx Rx
H-PCRF
eNode B
PDN
Gateway
Serving
GatewayE-UTRAN
Home Operator’s IP
Services
eNode B

Roaming – local breakout (through visiting PDN)
GERAN
UTRAN
S11
S3
HSS
S4
S1-U
S1-MME
MME
S6a
SGSN
S12
HPLMN
VPLMN
X2
Rx
H-PCRF
eNode B
Home Operator’s IP
Services
SGiS5
PDN
Gateway
Serving
Gateway
IP Network
eUTRAN
eNode B
V-PCRF
Gx
S9
E-UTRAN

IP address assignment
Network attachment and IP address assignment
S7c
SGi
S11
S5
E-UTRAN
S1-U
S1-MME
MME
Serving
Gateway
PDN
Gateway
IP Network
S7
X2
PCRF
Always-on IP connection is
established and anchored at
PDN-GW
eNode B
eNode B
IP
IPv4
direct
IPv4 via
DHCP
(after)
IPv6 /64
stateless
IPv6
IPv6
shorter

UE and service requests
S7c
SGi
S11
S5
E-UTRAN
S1-U
S1-MME
MME
Serving
Gateway
PDN
Gateway
IP Network
S7
X2
PCRF
1. UE sends NAS
Service Request
message towards MME
2. Update Bearer Request
is sent to the S-GW
to establish/modify
S1-bearer
3. Dedicated bearer
established after
interaction with PCRF
eNode B
eNode B

eNode B
Handover and X2 routing
SGi
S11
S5
E-UTRAN
S1-U
S1-MME
MME
Serving
Gateway
PDN
Gateway
IP Network
X2
S7c S7
PCRF
eNode B
eNode B
X2 = active mode mobility
- User Plane (UP) ensures lossless mobility
- Control Plane (CP) provides eNB relocation capability
UDP
IP
L2
L1
GTP-U
UDP
IP
L2
L1
GTP-U
eNB eNB
X2-U
SCTP
IP
L2
L1
X2-AP
SCTP
IP
L2
L1
X2-AP
eNB eNB
X2-C
X2 protocol stacks

4a
SMS and legacy voice

SMS service for initial “data-only” devices
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
GERAN
UTRAN
SGSN
MSC
CS Network
PDN
E-UTRAN
eNode B
PGWSGW
MME
Data
Paging/SMS
New interface
“SGs” from MSC to
MME
SMS-C

GERAN
UTRAN
SGSN
MSC
CS Network
PDN
E-UTRAN
eNode B
PGWSGW
MME
GERAN
UTRAN
SGSN
MSC
CS Network
PDN
E-UTRAN
eNode B
PGWSGW
MME
Voice support using “CS Fallback” (CSFB)
Simultaneous Voice + Data
 Handset falls back to legacy circuit coverage for voice
 Incoming calls to MSC trigger paging over SGs and delivered via MME
 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
Data
Data
Circuit Voice
Paging/SMS
New interface
“SGs” from MSC to
MME

GERAN
UTRAN
SGSN
MSC
CS Network
PDN
E-UTRAN
eNode B
PGWSGW
MME IMS
TAS
SCC AS
GERAN
UTRAN
SGSN
MSC
CS Network
PDN
E-UTRAN
eNode B
PGWSGW
MME IMS
TAS
SCC AS
Voice via IMS
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)
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
1
2
3
1
2
3
Circuit Voice Packet Voice IMS Signaling Packet DataCircuit signaling

Alcatel-Lucent EPC Solution
Gxc
SGi
GERAN
UTRAN
S11
S3
S5/S8
8650 SDM
HSS
S4
S1-U
S1-MME
S6a
7500
SGSN
IP Network
Gx
X2
AFs
5780 DSC
(PCRF)
7750 SR
Serving
Gateway
S101
S12
7750 SR
PDN
Gateway
CDMA/EVDO9271
eRNC
HSGW
S2a
9471
MME
9326
eNB
Data Plane
Control Plane
Rf Ro
8615
IeCCF
OFCS 8610
ICC
OCS
Gn
Gp
UE
eUTRAN
9326
eNB
5620 SAM
End-to-end IP management (incl. services)

Alcatel-Lucent
Ultimate Wireless Packet Core
7750 Service Router
Mobile Gateway
9471 Wireless
Mobility Manager
5780 Dynamic
Services Controller
5620 SAM
Service Aware Manager
User Plane Scalability
First mobile gateway
to deliver over 100 Gbps
Deployment Flexibility
As SGW, PGW/GGSN
or combo
Performance/QoS
Per-UE, per-app, per-flow
hierarchical QoS
Reliability
99.999+ % field proven
48,000+ units shipped
7750 Service Router-based
Architecture
Optimized split of
router and gateway functions
Control Plane Scalability
Millions of subscribers
Thousands of eNodeBs
Deployment Flexibility
As SGSN, MME
or SGSN/MME combo
Performance
Superior paging capabilities
High-signallng loads
Reliability
Geo-redundancy, pooling
No single point of failure
Platform/Architecture
ATCAv2 platform
for all CP functions
Full UP and CP Management
Full GUI management
of bearers (UP and CP)
Deployment Universality
e2e wireless IP management:
RAN, core and backhaul
Integration in OSS/BSS
Part of full NM portfolio
Full OSS/BSS integration
Reliability
Geo-redundancy
Scalability/Architecture
Suited for Tier X to Tier1
operator environments
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
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

www.alcatel-lucent.com

Aug12 sridhar

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Aug12 sridhar