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Cisco Public 1 2010 Cisco and/or its affiliates. All rights reserved.
4G Mobile NetworksLong Term Evolution (LTE)
Vladimir Settey
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The revolution is here (smartphones / tablets / netbooks) Broadband, anytime, anywhere Flat-rate data ? Data growth exponential; revenue growth linear. Scaling the network for data
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Evolution of Mobile Networks
LTE Architecture Overview
EPC Mobility
Services in LTE
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Voice oriented architecture Re-define fixed wireline services (e.g. SS and IN) SMS is a signalling transport rather than a data service Network transport based on TDM
There was wireless ISDN (aka GSM)
Base Station
Controller
(BSC)
Mobile Switching Center +
Visitor Locatio(MSC/VLR)
n Register
Base Transceiver
System (BTS)Mobile
Station
GSM
Radio
GSM
Radio16/64
kbps
16/64
kbps
64/2048
kbps
64/2048
kbps
LAP-Dm LAP-Dm LAP-D LAP-D
RadioResource
Mgmt RR BTSM BTSM
RR
BSSAP
MobilityMgmt
ConnectionMgmt
BSSAP
DTAP
MobilityMgt
ConnectionMgmt
64 kbps
MTP
TUP
SCCP
TCAP
ISUP
INAP
MAP
BSSMAP
MTP/MTPb
SCCP
MTP/b
SCCP
Home Location
Register (HLR)Service Control
Point (SCP)
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One burst every TDMA frame was sufficient to transport a speechframe with source rate of 13 kbit/s
GSM Phase 2 (circa 1996) added Circuit Switched Data supportoffering 9.6 kbit/s service
High Speed CSD consisted in aggregating multiple timeslot for asingle user but resource intensive
BSC MSC
Modem Interworking Function (IWF)
Modified V.110
3.1 kHz audio
or
V110 64k UDI
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BSCMSC/VLR Gateway MSC
BTS
GSM
Radio
GSM
Radio64 kbps 64 kbps L1bis
MAC
IP
RLC
LLC
SNDCP
Relay MAC
RLC
Nw Services
BSSGP
Relay
L1bis
Nw Services
BSSGP
LLC
SNDCP
L1
L2
IP
UDP
GTP
Relay
L1
L2
IP
UDP
GTP
IP
Packet Control
Unit (PCU)Serving GPRS
Support Node
(SGSN)
Gateway GPRS
Support Node
(GGSN)
IP
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First step towards an all IP network Designed to accommodate greater packet throughput (up to
2Mbits/s announced In reality, can support up to 384 kbit/s)
Core network remains largely unchanged from 2.5G Migration to ATM for Radio Access Transport More control into the RNC
3G RNC
3G MSC
3G SGSN GGSN
IP
ATM/AAL2
ATM/AAL5
Node B
PSTN
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So hopefully WCDMA got it right on packet services
Radio NetworkController (RNC)
3G SGSN GGSN
Iu-ps Gn/Gp
WCDMA
Radio
WCDMA
RadioATM
MAC
IP
RLC
PDCP
Frame
Protocol
AAL2
ATM
AAL2
MAC
RLC
PDCP
ATM
AAL5
IP
UDP
GTP-U
IP
UDP
GTP-U
IP
UDP
GTP-U
ATM
AAL5
L1
L2
IP
UDP
GTP-U
L1
L2
IP
NodeB
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Still Voice over CS bearer on the radio access, data bearer notsuitable (latency, overhead)
Option to transport Voice over IP in the Core (see TS 23.205) Introduction of SS7oIP transport
Iu-cs
IP
MGW MGW
MSC-s MSC-s
HLR
ATM
Iu-UP
L1/2IPAAL2
UDP
RTP
L1/2
IP
M3UA
TCAP
INAP
MAP
SCTP
SCCPBICC
orSIP-T
H.248
Nb-UP
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L1
RLC
PDCP
MAC
UDP
GTP-U
IP
Serving RNC 3G SGSN GGSN
GnIu-ps
IP
UDP
GTP-U
L1
L2
IP
IP
UDP
GTP-U
L1
L2
IP
UDP
GTP-U
L1
AAL5/ATMAAL5/ATM
L1
FrameProtocol
AAL2/ATM
RLC
PDCP
WCDMA
IP
MAC
L1
FrameProtocol
AAL2/ATM
WCDMA
Drift RNC
L1
FP
L1
FP
AAL2 AAL2
Node B
HSDPA Removes Drift RNC and
adds intelligence to the Node B
Direct Tunnel allows
SGSN to remove itselffrom data plane
HSPA+: Distribute RNC
Data plane to Node B
MAC-HS MAC-HSL2
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DL: 384 kps
UL: 384 kbps
DL: Up to
14.4 MbpsUL: 384 kbps
2007 2008 2009 2010+
DL:Up to
14.4 MbpsUL: 5.7 Mbps
DL: 28 MbpsUL: 11 Mpbs
DL: 42 MbpsUL: 11 Mpbs
Rel-99
WCDMA
Rel-5
HSDPA
Rel-6
HSUPA
Rel-7
MIMO 2x2
Rel-8
64 QAM
HSDPA:16 QAM DL
14.4 Mbps
HSDPA: Alwayson scaling
HSUPA:
5.7 Mbps
HSDPA:64 QAM, MIMO
HSUPA: 16QAM
Always on
scaling
HSDPA:64 QAM
and MIMO
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Highlighting the growing importance of IP transport
3G MSC-S
3G SGSN GGSN
Core IP
IP RAN
w/ ATM PW
or Native IP
Node B
PSTN
3G RNC
3G MGW
HLR/HSS
SGW
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Evolved Packet System (EPS) is the technology direction for 3GPPbased networks
Long Term Evolution (LTE) is the next generation 3GPP radio accessnetwork
Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)
System Architecture Evolution (SAE) is the 3GPP next generationstandard for mobile networks providing:Increased Bandwidth
End-to-End IP
Simplified Architecture
Support for multiple radio access technologies
Evolved Packet Core (EPC) is the next generation 3GPP packet coreConsists of (3) main components (MME, SGW, and PGW)
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Radio Side (Evolved UTRAN - EUTRAN)Improvements in spectral efficiency, user throughput, latency
Simplification of the radio network
Efficient support of packet based services: Multicast, VoIP, etc.
Network Side (Evolved Packet Core - EPC)Improvement in latency, capacity, throughput, idle to active transitions
Simplification of the core network
Optimization for IP traffic and services
Simplified support and handover to non-3GPP access technologies
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Higher Bandwidth (>100 kbps per user on average) and improvedlatency
Transmission and transition delays
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Duplex FDD and TDD
Channel Bandwidth 1.25 20 MHz
Modulation Type QPSK, 16-QAM, 64-QAM
Multiple Access Technique DL: OFDMA, UL: SCFDMA
TDMA Frame Duration 10ms with 1ms subframe
Number of symbols per frame 140
Sub-carrier Spacing 15 kHz
Symbol Duration 66.7 us
Cyclic Prefix 4.69 us, 16.67 us
Multipath Mitigation OFDM / Cyclic Prefix
eNB Synchronization Frequency (FDD, TDD)
Time (TDD, MBSFN)
Forward Error Correction 1/3 Convolutional and Turbo
Advanced Antenna Techniques MIMO 2x2, 4x4
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Frequency
Time"CDMA"(3G)"
OFDM"
TDMA"(2G)"
OFDMA"(LTE & WiMAX)"
Sub-Cha
nnel
(Group
of
Frequencies)
S
ub-Channel
(Groupof
Frequencies)
user A
user B
user C
Frequency
FDMA"
Freque
ncy
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Frequency One Resource Element
Sub-carrier Spacing
15 kHz
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5 MHz 10 MHz
20 MHz
3 MHz
1.4 MHz
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QPSK ( 55% of cell area)
16QAM (18% of cell area)
64QAM (13% of cell area)
256QAM (14% of cell area)
Maximising the bandwidth made available to the users by selecting theoptimum modulation scheme (QPSK, 16QAM, 64QAM, etc.)
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DownlinkPhysical Broadcast Channel (PBCH)
Physical Downlink Shared Channel (PDSCH)
Physical Downlink Control Channel (PDCCH)
Physical Control Format Indicator Channel (PCFICH)
Physical Hybrid ARQ Indicator Channel (PHICH)
UplinkPhysical Random Access Channel (PRACH)
Physical Uplink Shared Channel (PUSCH)
Physical Uplink Control Channel (PUCCH)
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3GPP Access
E-UTRANPGWSGWeNodeB
PCRF
OperatorsIP Services
(e.g. video, IMS)
HSS
S11
(GTP-C)
S1-U
(GTP-U)
S2b
(PMIPv6,
GRE)
MME
S5/8 (PMIPv6, GRE)
S6a
(DIAMETER)
S1-MME
(S1-AP)
GERAN
S4 (GTP-C, GTP-U)
UTRAN
SGSN
Trusted
Non-3GPPIP Access
Untrusted
Non-3GPPIP Access
S3
(GTP-C)
S12 (GTP-U)
S10
(GTP-C)
S5/8 (GTP-C, GTP-U)
Gx (DIAMETER) Gxb
SWx (DIAMETER)
STa (RADIUS,
DIAMETER)
ePDG
AAA
SWn
S6b
(DIAMETER)
SWm
(DIAMETER)
SGi
SWa
Gxa
Rx+ (DIAMETER)
S2c
UE
S2a
(PMIPv6, GRE
MIPv4 FACoA)
Gxc
UEUE
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3GPP Access
E-UTRAN PGWSGWeNodeB
PCRF
OperatorsIP Services
(e.g. video, IMS)
HSS
S11
(GTP-C)
S1-U(GTP-U)
S2b
(PMIPv6,
GRE)
MME
S5/8 (PMIPv6, GRE)
S6a
(DIAMETER)
S1-MME
(S1-AP)
GERAN
S4 (GTP-C, GTP-U)
UTRAN
SGSN
Trusted
Non-3GPPIP Access
Untrusted
Non-3GPPIP Access
S3
(GTP-C)
S12 (GTP-U)
S10
(GTP-C)
S5/8 (GTP-C, GTP-U)
Gx (DIAMETER) Gxb
SWx (DIAMETER)
STa (RADIUS,
DIAMETER)
ePDG
AAA
SWn
S6b
(DIAMETER)
SWm
(DIAMETER)
SGi
SWa
Gxa
Rx+ (DIAMETER)
S2c
UE
S2a
(PMIPv6, GRE
MIPv4 FACoA)
Gxc
UEUE
Mobility Management Entity
E-UTRAN Control Plane with 2G/3G interworking
(no user plane handling) Interacts with HSS for user
authentication, profile download, etc. Interacts with eNodeB and SGW for
SGW selection, tunnel control, paging,
handovers, etc. Interacts with SGSN for 2G/3G
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3GPP Access
E-UTRAN PGWSGWeNodeB
PCRF
Operators
IP Services(e.g. video, IMS)
HSS
S11
(GTP-C)
S1-U
(GTP-U)
S2b
(PMIPv6,
GRE)
MME
S5/8 (PMIPv6, GRE)
S6a
(DIAMETER)
S1-MME
(S1-AP)
GERAN
S4 (GTP-C, GTP-U)
UTRAN
SGSN
Trusted
Non-3GPPIP Access
Untrusted
Non-3GPPIP Access
S3
(GTP-C)
S12 (GTP-U)
S10
(GTP-C)
S5/8 (GTP-C, GTP-U)
Gx (DIAMETER) Gxb
SWx (DIAMETER)
STa (RADIUS,
DIAMETER)
ePDG
AAA
SWn
S6b
(DIAMETER)
SWm
(DIAMETER)
SGi
SWa
Gxa
Rx+ (DIAMETER)
S2c
UE
S2a
(PMIPv6, GRE
MIPv4 FACoA)
Gxc
UEUE
Home Subscriber Services (HSS)
Centralised database holding user profile:
Interacts with MME for userauthentication and profile download
Stores current location information (e.g.assigned MME, Serving SGW)
One or more subscription profilescontaining IMSI, QoS, Services, etc.
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3GPP Access
E-UTRAN PGWSGWeNodeB
PCRF
Operators
IP Services(e.g. video, IMS)
HSS
S11
(GTP-C)
S1-U
(GTP-U)
S2b
(PMIPv6,
GRE)
MME
S5/8 (PMIPv6, GRE)
S6a
(DIAMETER)
S1-MME
(S1-AP)
GERAN
S4 (GTP-C, GTP-U)
UTRAN
SGSN
Trusted
Non-3GPPIP Access
Untrusted
Non-3GPPIP Access
S3
(GTP-C)
S12 (GTP-U)
S10
(GTP-C)
S5/8 (GTP-C, GTP-U)
Gx (DIAMETER) Gxb
SWx (DIAMETER)
STa (RADIUS,
DIAMETER)
ePDG
AAA
SWn
S6b
(DIAMETER)
SWm
(DIAMETER)
SGi
SWa
Gxa
Rx+ (DIAMETER)
S2c
UE
S2a
(PMIPv6, GRE
MIPv4 FACoA)
Gxc
UEUE
Serving Gateway
Data plane anchoring for 3GPP access and 2G/
3G bearer plane interworking Anchor point in visited network for
3GPP Access (2G/3G/LTE) Processes all IP packets to/from UE
(QoS control, LI)
Uses network-based mobility towardsPDNGW (GTP or PMIPv6)
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3GPP Access
E-UTRAN PGWSGWeNodeB
PCRF
Operators
IP Services(e.g. video, IMS)
HSS
S11
(GTP-C)
S1-U
(GTP-U)
S2b
(PMIPv6,
GRE)
MME
S5/8 (PMIPv6, GRE)
S6a
(DIAMETER)
S1-MME
(S1-AP)
GERAN
S4 (GTP-C, GTP-U)
UTRAN
SGSN
Trusted
Non-3GPPIP Access
Untrusted
Non-3GPPIP Access
S3
(GTP-C)
S12 (GTP-U)
S10
(GTP-C)
S5/8 (GTP-C, GTP-U)
Gx (DIAMETER)Gxb
SWx (DIAMETER)
STa (RADIUS,
DIAMETER)
ePDG
AAA
SWn
S6b
(DIAMETER)
SWm
(DIAMETER)
SGi
SWa
Gxa
Rx+ (DIAMETER)
S2c
UE
S2a
(PMIPv6, GRE
MIPv4 FACoA)
Gxc
UEUE
Packet Data Network Gateway (PGW)
Subscriber-aware data plane anchoring for all
access networks Anchor point in home or visited network
for all IP-based access (3GPP or not) Session-based user authentication and
IP address allocation (IPv4/v6)
Processes all IP packets to/from UE(QoS control, PCEF, LI)
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3GPP Access
E-UTRAN PGWSGWeNodeB
PCRF
Operators
IP Services(e.g. video, IMS)
HSS
S11
(GTP-C)
S1-U
(GTP-U)
S2b
(PMIPv6,
GRE)
MME
S5/8 (PMIPv6, GRE)
S6a
(DIAMETER)
S1-MME
(S1-AP)
GERAN
S4 (GTP-C, GTP-U)
UTRAN
SGSN
Trusted
Non-3GPPIP Access
Untrusted
Non-3GPPIP Access
S3
(GTP-C)
S12 (GTP-U)
S10
(GTP-C)
S5/8 (GTP-C, GTP-U)
Gx (DIAMETER) Gxb
SWx (DIAMETER)
STa (RADIUS,
DIAMETER)
ePDG
AAA
SWn
S6b
(DIAMETER)
SWm
(DIAMETER)
SGi
SWa
Gxa
Rx+ (DIAMETER)
S2c
UE
S2a
(PMIPv6, GRE
MIPv4 FACoA)
Gxc
UEUE
Policy&Charging Rule Function (PCRF)
User and application-aware policy decision point:
Interacts with PGW to enforce persession or per flow policies
Gets event notification from PGW(mobilty and/or traffic related)
Interacts with application for admissioncontrol and policy definitiion
Supports roaming capabilities
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3GPP Access
E-UTRAN PGWSGWeNodeB
PCRF
Operators
IP Services(e.g. video, IMS)
HSS
S11
(GTP-C)
S1-U
(GTP-U)
S2b
(PMIPv6,
GRE)
MME
S5/8 (PMIPv6, GRE)
S6a
(DIAMETER)
S1-MME
(S1-AP)
GERAN
S4 (GTP-C, GTP-U)
UTRAN
SGSN
Trusted
Non-3GPPIP Access
Untrusted
Non-3GPPIP Access
S3
(GTP-C)
S12 (GTP-U)
S10
(GTP-C)
S5/8 (GTP-C, GTP-U)
Gx (DIAMETER) Gxb
SWx (DIAMETER)
STa (RADIUS,
DIAMETER)
ePDG
AAA
SWn
S6b
(DIAMETER)
SWm
(DIAMETER)
SGi
SWa
Gxa
Rx+ (DIAMETER)
S2c
UE
S2a
(PMIPv6, GRE
MIPv4 FACoA)
Gxc
UEUE
Enhanced Packet Data Gateway (ePDG)
Support for untrusted non-3GPP access
EPC point of attachment for useraccessing over other non-owned access
Terminates IPSec tunnel from UEestablished with IKEv2 & EAP-AKA
Supports network-based IP mobilitytowards the selected PGW (PMIPv6)
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E- UTRAN
MME
eNB
UE
HSS
S6a
(Auth Vectors)
EPS AKA via S6a
Challenge and keysexchange
Mutual Authentication
NAS Integrity/CipheringRRC Integrity and ciphering
U-Plane Ciphering
USIM required for LTE Different set of keys used for ciphering, derived from the same
original K stored in the USIM/HSS
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UE
MME
S-GW
Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)
HSS
PCRF
PDN-GW
MAC
RLC
PDCP
OFDMA
NAS
MAC
RLC
PDCP
OFDMA
L2
IP
L1
SCTP
S1-APRRC RRC
L2
IP
L1
SCTP
S1-AP
NAS
S1-MME
36.413
S1-MME
eNodeB
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UE
MME
S-GW
Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)
HSS
PCRF
PDN-GW
IP
L1
L2
IP (user)
IPUDP
GTP-U
L1
L2MAC
RLC
PDCP
OFDMA
IP (user)
MAC
RLC
PDCP
OFDMA
IPUDP
GTP-U
L1
L2
IPUDP
GTP-U
L1
L2
PMIP
S1-U S5/S8
S1-U
36.414
GRE GREUDP
PMIP GTP-US5/S8
29.274
(GTP)-
29.275
(PMIPv6)
eNodeB
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UE
MME
S-GW
Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)
HSS PCRF
PDN-GW
X2
L2
IP
L1
SCTP
X2-AP
L2
IP
L1
SCTP
X2-AP
X2-C
L2
IP
L1
UDP
GTP-U
L2
IP
L1
UDP
GTP-U
X2-U
36.423 36.424
eNodeB
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UE
eNodeB
MME
S-GW
Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)
HSSPCRF
PDN-GW
Gx
L2
IP
L1
SCTP
DIAMETER
Gx
L2
IP
L1
SCTP
DIAMETER
L2
IP
L1
SCTP
DIAMETER
S6a
L2
IP
L1
SCTP
DIAMETER
29.272 29.212
S6a
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Extract from 3GPP TS 23.401 V8.3.0 (2008-09)
A UE shall perform the address allocation procedures for at least one IPaddress (either IPv4 or IPv6)
PDN types IPv4, IPv6 and IPv4v6 are supported
/64 IPv6 prefix allocation via IPv6 Stateless Address autoconfigurationaccording to RFC 4862, if IPv6 is supported (Mandatory)
IPv6 parameter configuration via Stateless DHCPv6 according toRFC 3736 (Optional)
During default bearer establishment, the PDN GW sends the IPv6 prefix
and Interface Identifier to the SGW, and then the S-GW forwards theIPv6 prefix and Interface Identifier to the MME or to the SGSN. The MMEor the SGSN forwards the IPv6 Interface Identifier to the UE.
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Idle Mode Mobility proceduresUE Initial Attach
Periodic Location Update / Inter- and intra-RAT reselection
UE Detach
Active Mode MobilityIntra-RAT Intra- and inter-area handover
Inter-RAT handover
RRC StatesRRC-IDLERRC-CONNECTED
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3G UE 3G RNC 3G SGSN 3G GGSN HLR
1. Attach Request
2. Identity Request/Response
3. UE Authentication (EAP-AKA) and Ciphering Start
4. User Profile Download
5. Attach Accept/Complete
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3G UE MME S-GW HSS
1. Attach Request
2. Identity Req/Rsp
3. UE Authentication (EAP-AKA) and Ciphering Start
4. User Profile Download
5. Bearer Request
10. Attach Accept/Complete
PCRF
P-GW
6. Bearer Request
Bearer Authorisation
(inc. IP @, policy)
8. Bearer Accept9. Bearer Accept
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13. Update PDP Req
3G UE Old RNC Old SGSN GGSN
2. Relocation Required
5. RAB establishment at target NodeB
1. HO Preparation
Target RNC Target SGSN
3. Fwd Reloc Req
6. Relocation Request Ack
4. Relocation Request
7. Fwd Reloc Ack8. Relocation Command
9. Reconfig Radio
10. SRNS Context Transfer
12. Relocation Detected
15. Update PDP Ack
11. Relocation Detected
Relocation Completion including Radio resource release at Old RNC and RAU procedure
14. Policy Ctrl(optional)
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3. Create Session Req
3G UE MME Old S-GW
2. Path Switch Req
Target S-GW P-GWOld eNB Target eNB
Fwd Data
1. HO prep and exec
Established 2-way Bearer
DL Data
4. Modify Bearer Req
6. Modify Bearer Ack
5. Policy Ctrl
7. Create Session Resp
8. Path Switch Resp
9. Release10. Delete Session Req/Resp
Established 2-way Bearer
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3G UE Old S-GW
8. HO Command
Target S-GW
3. Create Session Req/Resp
P-GWOld MME Target MME
1. HO preparation
14. Modify Bearer Req
16. Modify Bearer Resp
15. Policy Ctrl
5. Create Indirect TunnelReq/Resp
4. HO prep at Target eNB
7. Create Indirect TunnelReq/Resp
6. Fwd Reloc Resp
9. HO Command
2. Fwd Reloc Req
11. HO Notify
10. eNB context transfer
13. Update Session Req
17. Update Session Resp
Relocation Completion including radio resource release at Old
eNB and Session and Fwd tunnel tear down at old MME/SGW
12. Reloc Complete Req/Resp
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The EPS architecture (3GPP Rel 8)is the first 3GPP all-IP architecture Voice and SMS are still
the cash cows for mobile operators
Migration is critical
User experience must be preserved
CSFB is the interim solution recommended by NGMN IMS is the target solution for Telephony and Multimedia Services OneVoice IMS profile simplifies implementation for VoLTE NGMN and OneVoice initiatives reduce risk of industry fragmentation SMS typically required before voice due to EU regulatory requirements
for data roaming services
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During EPC attach, CSFB UEs are also attached over SGs to MSC MME maintains mapping of TA to LA to determine appropriate MSC toestablish SGs association with SMS can be delivered/sent without FallBack to legacy radio (SGs interface
includes SMS payload capability)
S1-MME
SGs
S11
S6a
IuCS / A
S1-UCSFB UE E-UTRAN
Serving/
PDN GW
MME
UTRAN /
GERANMSC
HSS
Incoming SMS1
SMS is delivered via SGs interface2
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Additional complexity / upgrades required on CS core to support use-case where the MSC sending Page is different to MSC receiving Page
response (i.e. TA to LA mapping is inaccurate due to cell breathing orother circumstances)
This capability (Roaming Retry) requires upgrades on GMSC, VMSCand HLR. Introduces further termination latency.
S1-MME
SGs
S11
S6a
IuCS / A
S1-UCSFB UE E-UTRAN
Serving/PDN GW
MME
CSFB UEUTRAN /GERAN
MSC
HSS
Incoming Call delivered to VMSC whichhas SGs association for this subscriber
1
UE is paged via the SGs interface2
UE retunes to 2G/3G RAT on receipt
of page
3
UE Responds to paging incoming call terminated viastandard 2G/3G procedures
4
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To enable mid-call mobility, S-CSCF anchors call at SCC AS TAS provides end-user services (e.g. IR.92) MGCF provides breakout to PSTN or other CS networks
ISC
Mw
S1-MME
Sv
S11
Mg
SGi(Gm from UE)
S6a
IuCS / A
IuPS / Gb
S3
S1-U
Cx
IMS (HPLMN)
P-CSCF
SR-VCC UE E-UTRANServing/PDN GW
MME
UTRAN /GERAN
MSC Server(SR-VCC)
SGSN(SR-VCC)
I/S-CSCF
HSS
TASSCC AS IP-SM-GW
MGCF
Subscriber has already registeredinto IMS following EPC attach
UE OriginatesCall
1
2
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SCC AS performs leg management hides mobility events from other IMSapplication servers
SR-VCC only works in one direction LTE 2G/3G Requires upgrades on legacy MSC infrastructure
ISC
Mw
S1-MME
Sv
S11
Mg
SGi
(Gm from UE)
S6a
IuCS / A
IuPS / Gb
S3
S1-U
Cx
IMS (HPLMN)
P-CSCF
SR-VCC UE E-UTRANServing/
PDN GW
MME
SR-VCC UEUTRAN /
GERAN
MSC Server
(SR-VCC)
SGSN
(SR-VCC)
I/S-CSCF
HSS
TASSCC AS IP-SM-GW
MGCF
UE retunes to 2G/3GRAT during active call
1
New call legestablished
2
SCC AS performsbearer managementand tears down original
leg
3
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CSFB VoIMS
End-User Services Re-use legacy implementation OneVoice (IR.92) provides baseline. Alloperator proprietary services and extensions
must be ported to IMS.
Regulatory Re-use legacy implementation National regulatory services must beimplemented in IMS.
Service Differentiation Restricted to only services deliverable fromlegacy core.
IR.92 services can be blended with other IMSservices such as presence, RCS, rich
messaging.
End-user Experience Significant post-dial delay. Retuning fromCS back to LTE may take some time
impact to data services.
No retuning required to access CS equivalentservices. Still industry concerns regarding SR-
VCC latency.
Complexity Medium CS core requires upgrades forSGs interface and also to support Roaming
Retry.
High Significant new network infrastructurerequired. SR-VCC extremely complex.
Intensive service porting to ensure full legacyparity.
Cost Unknown upgrades must come fromexisting CS vendors. Believed that legacy
vendors are using this to their advantageto seek premium.
High large investment required for newinfrastructure. However, diverse range of
vendors opens door for innovative deals/solutions.
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Thank you.