Introduction to Evolved Packet Core: Protocols and

Transcription

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


4.
Serving Gateway (SGW), PDN Gateway (PGW)
Mobility Management Entity (MME), Policy and Charging Control Function (PCRF)
LTE core functions and service procedures


Core network functions
Network attachment, service requests, paging, IP addressing, handover
© 2009 Alcatel-Lucent. All rights reserved.
1
Introduction to Evolved Packet Core and
Evolved Packet System
3 | Technical Sales Forum | May 2008
LTE: All-IP, simplified network architecture
LTE+EPC
Evolved Packet Core
IP channel
(All-IP)
eNode B
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
4 | Introduction to EPC | July 2010 | v6
REF: http://www.comsoc.org/livepubs//ci1/public/2009/feb/pdf/ciguest_bogineni.pdf
Mobile core in 2G/3G
2
LTE and EPC – what is new?
EPC: new all-IP core, new network elements (functions)
2G/3G
GSM
GMSC
Voice
Channels
UMTS
Other
mobile
networks
MSC
IP channel
BTS
PSTN
MGW
Circuit Switched
Core (Voice)
GPRS
EDGE
Softswitch
BSC / RNC
Node B
HSPA
SGSN




EPC elements
Internet
Packet Switched
Core
GGSN
VPN
Serving Gateway (SGW)
Packet Data Network (PDN) Gateway (PGW)
Mobility Management Element (MME)
Policy and Charging Rules Function (PCRF)
LTE/EPC
MME
IP channel
SGW
eNode B
PCRF
Evolved Packet Core
PDN GW
EPC elements
LTE/EPC
MME
IP channel
SGW
eNode B
PCRF
Evolved Packet Core
PDN GW
 Serving Gateway
 Serving a large number of eNodeBs, focus on scalability

EPC elements


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)
USER PLANE (UP)
LTE + EPC elements and interfaces
CONTROL PLANE (CP)
S6a
HSS
Rx
S10
External networks
Operator Services
MME
S1-MME
PCRF
Applications
S11
Gx
eNodeB
Internet
S1-U
SGi
S5/S8
X2
S1-U
SGW
UE
IMS
eNodeB
PGW
EPC
IP connectivity layer (Evolved Packet System) = E-UTRAN + EPC
Service Connectivity Layer
ACPs
“Flat IP” = less hierarchy means lower latency
GSM
UMTS
CDMA
control plane
RNC
BSC
Node B
BTS
GGSN
HA
direct tunnel
data plane
RNC
BSC
LTE
SGSN
PDSN
SGSN
PDSN
GGSN
HA
control plane
MME
eNode B
data plane
SGW
S/P GW
PGW
Key implications on user plane (UP) and control plane (CP)
Control plane gets new mobile-specific attributes
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
BSC
SGSN/GGSN
GSM/GPRS/EDGE
RNC
 Mobility across networks (and operator domains)
 Distributed mobility management
 Massive increase in scalability
 Dynamic policy management
SGSN/GGSN
RNC
WCDMA/HSPA
PDSN
CDMA/EV-DO
Service Delivery
Platforms
LTE
IP channel
MME
SGW
eNode B
PCRF
Evolved Packet Core
PDN GW
Quick Reference:
Overview of EPC components and functionality
eNB
 eNodeB:
 all radio access functions
Policy, Charging & Rules Function
Inter Cell RRM
 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
RB Control
 Radio admission control
 Scheduling of UL and DL data
Connection Mobility Cont.
 Scheduling and transmission of
paging and system broadcast
Radio Admission Control
 IP header compression (PDCP)
 Outer-ARQ (RLC)
MME
NAS Security
eNB Measurement
Configuration & Provision
PCRF
Idle State Mobility
Handling
Dynamic Resource
Allocation (Scheduler)
Policy
EPS Bearer Control
Decisions
RRC
PDCP
S-GW
P-GW
RLC
Mobility
Anchoring
MAC
UE IP address
allocation
PDN Gateway




IP anchor point for bearers
UE IP address allocation
Per-user based packet filtering
Connectivity to packet data network
S1
PHY
Packet Filtering
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
All-IP mobile transformation
2G/3G
CS Core
Backhaul (TDM/ATM)
PS Core
Node B
BTS
BS
SGSN
PDSN
RNC
GGSN
HA
1
2
3
4
5
6
7
Radio
intelligence
moving to
eNodeB
Backhaul
transition
to IP/Ethernet
RNC bearer
mobility
evolves to
the SGW
MSC voice and
packet data
switching
evolve into
the SGW
CS and PS
evolve into a
unified all-IP
domain
Best effort to
e2e QoS
Internet
browsing
to
Web 2.0+
RNC control
distributed
into
the MME/eNB
Packet data
control
evolves into
the MME
LTE
Backhaul (IP/Ethernet)
PCRF
MME
Service and mobile aware
all-IP network
eNodeB
SGW
Evolved Packet Core
PDN GW
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)
Mapping UMTS traffic types to IP QoS (DiffServ Code Points)
Conversational
Streaming
Interactive
Background
End-to-end QoS in UMTS
“Flat-IP” also implies need for a sound QoS mechanism
Shared radio resource allocation for all users
Dedicated radio resource allocation per user
TDM
TDM
IP
IP
IMS
CS
PS
EPC
2G/R99 3G Access
Shared
resources
PS resources
CS resources
LTE (and HSPA)
 By nature, 2G and Rel99 3G legacy network
architecture provides dedicated CS resources
ensuring:
 Without QoS control in flat-IP mobile networks,
the end-user would experience (e.g. for
voice/video service):
 Low latency (optimized for voice service)
 High latency when cell/network is congested
 A guaranteed bit rate for the whole duration of the CS
call (even in case of congestion)
 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
From: 4 classes in UMTS and CDMA to: 9 classes in LTE
One of LTE standards goals:
backward compatibility with UMTS QoS
Priority
Packet Delay
Budget
Packet Error
Loss
Rate
2
4
3
100 ms
150 ms
50 ms
10
-3
10
-3
10
5
300 ms
5
1
6
7
QCI
1
2
3
4
Resource Type
Guaranteed
Bit Rate
(GBR)
-2
Conversational voice
Conversational video (live streaming)
Real-time gaming
10
-6
Non-conversational video (buffered streaming)
100 ms
10
-6
IMS signalling
Video (buffered streaming)
6
300 ms
10
-6
TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing,
progressive video, etc.)
7
100 ms
10
-3
8
300 ms
10-6
Voice, video (live streaming), interactive
gaming
“Premium bearer” for video (buffered
streaming),
9
300 ms
10-6
Non-GBR
8
9
Example Services
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
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
UE
EPC
eNodeB
SGW
Internet
PGW
peer
End-to-end service
External
bearer
EPS bearer
Radio
bearer
S1
bearer
S5/S8
bearer
LTE-Uu
S1
S5/S8
SGi
3
EPC elements
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 MMEs
• Mobility Management
• Bearer handling
• Security settings
Pool of SGWs
MME
SGW
MME
SGW
• User plane tunnels for
UL and DL data delivery
eNode B
• 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
eNode B
UE
User Equipment
eNode B
Other eNodeBs
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
IP channel
MME
SGW
eNode B
PCRF
Evolved Packet Core
PDN GW
MME is control plane element that manages network access and mobility
MME:
Other MMEs
HSS
USER PLANE (UP)
CONTROL PLANE (CP)
• Authentication and Security
•Location management
• User profiles
SGWs
MME
MME
SGW
• Handovers between MMEs
• Idle state mobility between MMEs
SGW
• Control of user plane tunnels
MME
•
•
•
•
User Equipment
eNode B
UE
eNode B
Inter eNodeB handovers
State transitions
Bearer management
Paging
Other eNodeBs
Serving Gateway and Packet Data Network (PDN) Gateway
SGW is local mobility anchor
PGW is IP anchor for bearers
 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
 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
MME
SGW
eNode B
eNode B
PCRF
Evolved Packet Core
PDN GW
SGW:
PCRF
MMEs
PCRF
USER PLANE (UP)
CONTROL PLANE (CP)
PMIP S5/S8
• IP service flow <-> GTP tunnel
mapping information
PGWs
MME
MME
PGW
• Control of GTP tunnels and IP service flows
• SGW Mobility control
PGW
GTP S5/S8
• Control of GTP tunnels
• GTP tunnels for UL and DL
data delivery
PMIP
• IP service flows
SGW
• 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
eNode B
eNode B
Other SGWs
SGW
SGW
PGW:
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
Offline Charging
Systems
SGWs
SGW
SGW
End-to-end protocol stack (User Plane)
MME
IP channel
PCRF
SGW
eNode B
PDN GW
Evolved Packet Core
applications
services
user traffic = end-to-end IP
IP
IP
RELAY
RELAY
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
L1
L1
L1
L1
L1
S1-U
LTE-Uu
UE
eNodeB
S5/S8
SGW
SGi
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)
PCRF:
USER PLANE (UP)
CONTROL PLANE (CP)
AF
External networks
PCRF
• PCC rules
• QoS rules when S5/S8 is PMIP
SGWs
SGW
SGW
• QoS rules when S5/S8 is PMIP
• QoS rules for mapping IP service flows
and GTP tunnel in S1 when S5/S8 is
PMIP
PGWs
PGW
PGW
Policy Charging and Control (PCC) Architecture
SPR
AF
Rx
Sp
PCRF
Gxx
Gx
OCS
Gy
BBERF
PCEF
Gz
SGW
PGW
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
SDF-based credit control
OFCS
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
PDN-GW
UE
SDF-1
Default bearer
SDF-2
Dedicated bearer (GBR)
UE-IP1@
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
4
Core procedures
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!)
Interworking with 3GPP ANs
Interworking with non 3GPP ANs
(EVDO/EHRPD treated as a special case)
Interconnection
Roaming – breakout through home PDN
Gx
HSS
PDN
Gateway
SGi
HPLMN
S6a
VPLMN
UTRAN
SGSN
GERAN
S3
S8a
MME
S1-MME
X2
S11
S4
S12
eNode B
E-UTRAN
eNode B
S1-U
H-PCRF
Serving
Gateway
Rx
Home Operator’s IP
Services
Roaming – local breakout (through visiting PDN)
Rx
HSS
H-PCRF
Home Operator’s IP
Services
HPLMN
S6a
VPLMN
S9
UTRAN
SGSN
GERAN
S3
V-PCRF
MME
Gx
S1-MME
X2
S11
S4
S12
eNode B
eUTRAN
E-UTRAN
S1-U
Serving
Gateway
S5
PDN
Gateway
eNode B
SGi
IP Network
Network attachment and IP address assignment
PCRF
S7c
Always-on IP connection is
established and anchored at
PDN-GW
S7
MME
S1-MME
X2
S11
SGi
eNode B
E-UTRAN
S1-U
Serving
Gateway
S5
IP Network
PDN
Gateway
IPv4
direct
eNode B
IP
IPv6
shorter
IP address assignment
IPv6
IPv4 via
DHCP
(after)
IPv6 /64
stateless
UE and service requests
PCRF
S7c
1. UE sends NAS
Service Request
message towards MME
S7
2. Update Bearer Request
is sent to the S-GW
to establish/modify
S1-bearer
MME
S1-MME
X2
3. Dedicated bearer
established after
interaction with PCRF
S11
eNode B
E-UTRAN
S1-U
Serving
Gateway
S5
PDN
Gateway
eNode B
SGi
IP Network
Handover and X2 routing
PCRF
S7c
S7
eNB
eNB
eNB
eNB
X2-AP
X2-AP
GTP-U
GTP-U
SCTP
SCTP
UDP
UDP
IP
IP
IP
IP
L2
L2
L2
L2
L1
L1
L1
L1
MME
S1-MME
X2
X2-C
X2-U
X2 protocol stacks
S11
eNode B
E-UTRAN
S1-U
Serving
Gateway
S5
PDN
Gateway
SGi
IP Network
eNode B
X2 = active mode mobility
- User Plane (UP) ensures lossless mobility
eNode B
- Control Plane (CP) provides eNB relocation capability
4a
SMS and legacy voice
SMS service for initial “data-only” devices
MSC
GERAN
UTRAN
SMS-C
CS Network
New interface
“SGs” from MSC to
MME
SGSN
MME
E-UTRAN
PDN
SGW
PGW
Data
eNode B
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
Voice support using “CS Fallback” (CSFB)
New interface
“SGs” from MSC to
MME
MSC
GERAN
UTRAN
MSC
GERAN
UTRAN
CS Network
SGSN
SGSN
MME
E-UTRAN
CS Network
MME
E-UTRAN
PDN
eNode B
SGW
PGW
PDN
Data
eNode B
SGW
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 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
Voice via IMS
MSC
GERAN
UTRAN
CS Network
3
SGSN
2
MME
E-UTRAN
TAS
IMS
SCC AS
PDN
eNode B
GERAN
UTRAN
PGW
SGW
MSC
CS Network
SGSN
3
2
MME
E-UTRAN
TAS
IMS
PDN
eNode B
1
SGW
Circuit Voice
PGW
Circuit signaling
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)
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
Packet Voice
IMS Signaling
Packet Data
Alcatel-Lucent EPC Solution
8650 SDM
HSS
S6a
9271
eRNC
UTRAN
S101
7500
SGSN
5780 DSC
(PCRF)
S3
Gxc
AFs
8615
IeCCF
OFCS
Gx
9471
MME
X2
S1-MME
eUTRAN
UE
9326
eNB
S1-U
Control Plane
HSGW
GERAN
9326
eNB
Data Plane
CDMA/EVDO
Ro
Rf
S11
S4
7750 SR
Serving
Gateway
S12
Gn
Gp
S5/S8
8610
ICC
OCS
S2a
7750 SR
PDN
Gateway
IP Network
SGi
End-to-end IP management (incl. services)
5620 SAM
User Plane Scalability
Full UP and CP Management
First mobile gateway
to deliver over 100 Gbps
Full GUI management
of bearers (UP and CP)
Deployment Universality
Deployment Flexibility
As SGW, PGW/GGSN
or combo
e2e wireless IP management:
RAN, core and backhaul
Performance/QoS
Integration in OSS/BSS
Per-UE, per-app, per-flow
hierarchical QoS
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
Reliability
7750 Service Router
Mobile Gateway
5620 SAM
Service Aware Manager
Geo-redundancy
Scalability/Architecture
Alcatel-Lucent
Ultimate Wireless Packet Core
Suited for Tier X to Tier1
operator environments
Control Plane Scalability
Mobile Core Business Engine
Millions of subscribers
Thousands of eNodeBs
Policy Convergence
Monetization and Personalization
Deployment Agility
Deployment Flexibility
Flexi rules engine with wizards
Up and running in minutes
Add new rules easily
As SGSN, MME
or SGSN/MME combo
Integration with NM
Performance
Superior paging capabilities
High-signallng loads
Reliability
9471 Wireless
Mobility Manager
5780 Dynamic
Services Controller
Part of full NM portfolio
Same NM/GUI paradigm
Reliability
Geo-redundancy, pooling
No single point of failure
Geo-redundancy
No single point of failure
Platform/Architecture
Platform/Architecture
ATCAv2 platform
for all CP functions
ATCAv2 platform
for all CP functions
www.alcatel-lucent.com

Introduction to Evolved Packet Core: Protocols and

Transcription

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