4G Mobile Networks
Long Term Evolution (LTE)
Vladimir Settey
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Cisco Public
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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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Home Location Service Control
Register (HLR) Point (SCP)
• There was wireless ISDN (aka GSM)
Mobility
Mgmt
 Re-define
fixed wireline services (e.g. SS and IN)
Radio
 SMS is a signalling transport rather
than a data
RR’
Resource
BSSAP
Mgmt
 Network transport
based on TDM
RR’
BTSM
BTSM
LAP-Dm
GSM
Radio
LAP-Dm LAP-D
GSM
Radio
© 2010 Cisco and/or its affiliates. All rights reserved.
16/64
kbps
LAP-D
SCCP
MTP/b
16/64
kbps
64/2048
kbps
Mobility
Mgt
service
DTAP
BSSAP
SCCP
MTP/MTPb
64/2048
kbps
MAP
 Voice oriented architecture
INAP
Connection
Mgmt
ISUP
Connection
Mgmt
TUP
Mobile Switching Center +
Visitor Locatio(MSC/VLR)
n Register
BSSMAP
Base Transceiver
System (BTS)
Mobile
Station
Base Station
Controller
(BSC)
TCAP
SCCP
MTP
64 kbps
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• One burst every TDMA frame was sufficient to transport a speech
frame with source rate of 13 kbit/s
• GSM Phase 2 (circa 1996) added Circuit Switched Data support
offering 9.6 kbit/s service
• High Speed CSD consisted in aggregating multiple timeslot for a
single user but resource intensive
Modem Interworking Function (IWF)
Modified V.110
3.1 kHz audio
or
V110 64k UDI
BSC
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MSC
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BTS
Gateway MSC
MSC/VLR
BSC
IP
Packet Control
Unit (PCU)
Gateway GPRS
Support Node
(GGSN)
Serving GPRS
Support Node
(SGSN)
IP
IP
Relay
SNDCP
GTP
SNDCP
LLC
RLC
MAC
GSM
Radio
Relay
GSM
64 kbps
Radio
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Relay
RLC
BSSGP
Nw Services
MAC
64 kbps
L1bis
GTP
LLC
UDP
UDP
BSSGP
IP
L2
IP
L2
Nw Services
L1bis
L1
L1
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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
3G MSC
• More control into the RNC
PSTN
ATM/AAL2
ATM/AAL5
3G RNC
Node B
IP
3G SGSN
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GGSN
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• So hopefully WCDMA got it right on packet services…
Iu-ps
NodeB
Radio Network
Controller (RNC)
Gn/Gp
3G SGSN
GGSN
IP
IP
PDCP
PDCP
GTP-U
GTP-U
GTP-U
GTP-U
RLC
RLC
UDP
UDP
UDP
UDP
MAC
IP
IP
IP
IP
AAL2
AAL2
AAL5
AAL5
L2
L2
ATM
ATM
ATM
ATM
L1
L1
MAC
WCDMA
Radio
Frame
Protocol
WCDMA
Radio
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HLR
MSC-s
MSC-s
Iu-cs
Nb-UP
MAP
INAP
H.248
MGW
BICC or SIP-T
IP
MGW
TCAP
• Still Voice overRTP
CS bearer on the radio access, data
bearer not
SCCP
suitable
Iu-UP (latency,
UDPoverhead)
IP Voice over IP in the Core
AAL2 to transport
• Option
ATM
L1/2
• Introduction of SS7oIP transport
M3UA
SCTPTS 23.205)
(see
IP
L1/2
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HSPA+: Distribute RNC
Removes Drift RNC and
Data plane to NodeHSDPA
B
adds intelligence to the Node B
Iu-ps
Gn
Drift RNC
Serving RNC
Node B
IP
PDCP
Direct Tunnel allows
SGSN to remove itself
from data plane
RLC
MAC
MAC-HS MAC-HS
WCDMA
Frame
Protocol
FP
FP
AAL2/ATM
AAL2
AAL2
L1
L1
WCDMA L1
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3G SGSN
GGSN
IP
PDCP
GTP-U
GTP-U
GTP-U
GTP-U
RLC
MAC
UDP
UDP
UDP
UDP
IP
IP
IP
IP
AAL5/ATM
L2
L2
L1
L1
Frame
Protocol
AAL2/ATM AAL5/ATM
L2
L1
L1
L1
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Rel-99
Rel-5
Rel-6
Rel-7
Rel-8
WCDMA
HSDPA
HSUPA
MIMO 2x2
64 QAM
HSDPA: Always HSDPA:
on scaling
64 QAM, MIMO
HSDPA:
64 QAM
and MIMO
HSDPA:
16 QAM DL
14.4 Mbps
HSUPA:
5.7 Mbps
DL: Up to
DL: 384 kps
UL: 384 kbps 14.4 Mbps
UL: 384 kbps
2007
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DL:Up to
14.4 Mbps
UL: 5.7 Mbps
2008
HSUPA: 16QAM
Always on
scaling
DL: 28 Mbps
UL: 11 Mpbs
2009
DL: 42 Mbps
UL: 11 Mpbs
2010+
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• Highlighting the growing importance of IP transport
3G MSC-S
IP RAN
w/ ATM PW
or Native IP
Node B
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HLR/HSS
PSTN
SGW
3G MGW
3G RNC
3G SGSN
Core IP
GGSN
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• Evolved Packet System (EPS) is the technology direction for 3GPP
based networks
• Long Term Evolution (LTE) is the next generation 3GPP radio access
network
Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)
• System Architecture Evolution (SAE) is the 3GPP next generation
standard 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 core
Consists 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 improved
latency
Transmission and transition delays <10 & 100ms resp. in unloaded conditions
• Service independent and data-only architecture
Strict data QoS mechanism with no voice dedicated bearer identifictaion
• Always-on model
All registered users have a default bearer established used for signalling
• IP addressing
IPv6 by default with dual stack sessions (IPv4v6)
• Support of alternative access technologies
3GPP and non-3GPP architecture, including possible wireline access
• Local breakout
Part of the traffic may be routed directly in the visited network
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Duplex
FDD and TDD
Channel Bandwidth
1.25 – 20 MHz
Modulation Type
Multiple Access Technique
TDMA Frame Duration
Number of symbols per frame
QPSK, 16-QAM, 64-QAM
DL: OFDMA, UL: SCFDMA
10ms with 1ms subframe
140
Sub-carrier Spacing
15 kHz
Symbol Duration
66.7 us
Cyclic Prefix
Multipath Mitigation
eNB Synchronization
Forward Error Correction
Advanced Antenna Techniques
© 2010 Cisco and/or its affiliates. All rights reserved.
4.69 us, 16.67 us
OFDM / Cyclic Prefix
Frequency (FDD, TDD)
Time (TDD, MBSFN)
1/3 Convolutional and Turbo
MIMO 2x2, 4x4
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Sub-Channel"
(Group of"
Frequencies)"
Sub-Channel"
(Group of"
Frequencies)"
Frequency"
Frequency"
Frequency"
FDMA"
TDMA"
(2G)"
CDMA"
(3G)"
user A
user B
user C
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OFDM"
Time
"
OFDMA"
(LTE & WiMAX)"
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Sub-carrier Spacing
15 kHz
Frequency
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One Resource Element
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3 MHz
5 MHz
10 MHz
1.4 MHz
20 MHz
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256QAM (14% of cell area)
16QAM (18% of cell area)
64QAM (13% of cell area)
QPSK ( 55% of cell area)
 Maximising the bandwidth made available to the users by selecting the
optimum modulation scheme (QPSK, 16QAM, 64QAM, etc.)
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• Downlink
Physical 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)
• Uplink
Physical Random Access Channel (PRACH)
Physical Uplink Shared Channel (PUSCH)
Physical Uplink Control Channel (PUCCH)
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3GPP Access
SWx (DIAMETER)
HSS
S12 (GTP-U)
UTRAN
SGSN
GERAN
Rx+ (DIAMETER)
S3
(GTP-C)
MME
S1-MME
(S1-AP)
E-UTRAN
eNodeB
PCRF
S6a
(DIAMETER)
S4 (GTP-C, GTP-U)
S10
(GTP-C)
S1-U
(GTP-U)
UE
S11
(GTP-C)
Gxc
Gx (DIAMETER)
SGW
S5/8 (PMIPv6, GRE)
S5/8 (GTP-C, GTP-U)
Gxa
Gxb
S6b
(DIAMETER)
PGW
AAA
SGi
Operator’s
IP Services
(e.g. video, IMS)
SWm
(DIAMETER)
S2a
(PMIPv6, GRE
MIPv4 FACoA)
S2b
(PMIPv6,
GRE)
SWa
ePDG
SWn S2c
Trusted
Non-3GPP
IP Access
UE
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Untrusted
Non-3GPP
IP Access
STa (RADIUS,
DIAMETER)
UE
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3GPP Access
SWx (DIAMETER)
HSS
S12 (GTP-U)
UTRAN
SGSN
GERAN
Rx+ (DIAMETER)
S3
(GTP-C)
MME
S1-MME
(S1-AP)
E-UTRAN
UE
eNodeB
PCRF
S6a
(DIAMETER)
S4 (GTP-C, GTP-U)
S10
(GTP-C)
S1-U
(GTP-U)
S11
(GTP-C)
Gxc
Gx (DIAMETER)
SGW
S5/8 (PMIPv6, GRE)
S5/8 (GTP-C, GTP-U)
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
Gxb
S6b
(DIAMETER)
PGW
AAA
SGi
Operator’s
IP Services
(e.g. video, IMS)
SWm
(DIAMETER)
S2a
(PMIPv6, GRE
MIPv4 FACoA)
S2b
(PMIPv6,
GRE)
SWa
ePDG
SWn S2c
Trusted
Non-3GPP
IP Access
UE
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Gxa
Untrusted
Non-3GPP
IP Access
STa (RADIUS,
DIAMETER)
UE
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3GPP Access
SWx (DIAMETER)
HSS
S12 (GTP-U)
UTRAN
SGSN
GERAN
Rx+ (DIAMETER)
S3
(GTP-C)
MME
S1-MME
(S1-AP)
E-UTRAN
UE
eNodeB
PCRF
S6a
(DIAMETER)
S4 (GTP-C, GTP-U)
S10
(GTP-C)
S1-U
(GTP-U)
S11
(GTP-C)
Gxc
Gx (DIAMETER)
SGW
S5/8 (PMIPv6, GRE)
S5/8 (GTP-C, GTP-U)
Home Subscriber Services (HSS)
Centralised database holding user profile:
• Interacts with MME for user
authentication and profile download
• Stores current location information (e.g.
assigned MME, Serving SGW)
• One or more subscription profiles
containing IMSI, QoS, Services, etc.
Gxb
S6b
(DIAMETER)
PGW
AAA
SGi
Operator’s
IP Services
(e.g. video, IMS)
SWm
(DIAMETER)
S2a
(PMIPv6, GRE
MIPv4 FACoA)
S2b
(PMIPv6,
GRE)
SWa
ePDG
SWn S2c
Trusted
Non-3GPP
IP Access
UE
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Gxa
Untrusted
Non-3GPP
IP Access
STa (RADIUS,
DIAMETER)
UE
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3GPP Access
SWx (DIAMETER)
HSS
S12 (GTP-U)
UTRAN
SGSN
GERAN
Rx+ (DIAMETER)
S3
(GTP-C)
MME
S1-MME
(S1-AP)
E-UTRAN
UE
eNodeB
PCRF
S6a
(DIAMETER)
S4 (GTP-C, GTP-U)
S10
(GTP-C)
S11
(GTP-C)
S1-U
(GTP-U)
Gxc
Gx (DIAMETER)
SGW
S5/8 (PMIPv6, GRE)
S5/8 (GTP-C, GTP-U)
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 towards
PDNGW (GTP or PMIPv6)
Gxb
S6b
(DIAMETER)
PGW
AAA
SGi
Operator’s
IP Services
(e.g. video, IMS)
SWm
(DIAMETER)
S2a
(PMIPv6, GRE
MIPv4 FACoA)
S2b
(PMIPv6,
GRE)
SWa
ePDG
SWn S2c
Trusted
Non-3GPP
IP Access
UE
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Gxa
Untrusted
Non-3GPP
IP Access
STa (RADIUS,
DIAMETER)
UE
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3GPP Access
SWx (DIAMETER)
HSS
S12 (GTP-U)
UTRAN
SGSN
GERAN
Rx+ (DIAMETER)
S3
(GTP-C)
MME
S1-MME
(S1-AP)
E-UTRAN
UE
eNodeB
PCRF
S6a
(DIAMETER)
S4 (GTP-C, GTP-U)
S10
(GTP-C)
S1-U
(GTP-U)
S11
(GTP-C)
Gxc
Gx (DIAMETER)
SGW
S5/8 (PMIPv6, GRE)
S5/8 (GTP-C, GTP-U)
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)
Gxb
S6b
(DIAMETER)
PGW
AAA
SGi
Operator’s
IP Services
(e.g. video, IMS)
SWm
(DIAMETER)
S2a
(PMIPv6, GRE
MIPv4 FACoA)
S2b
(PMIPv6,
GRE)
SWa
ePDG
SWn S2c
Trusted
Non-3GPP
IP Access
UE
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Gxa
Untrusted
Non-3GPP
IP Access
STa (RADIUS,
DIAMETER)
UE
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3GPP Access
SWx (DIAMETER)
HSS
S12 (GTP-U)
UTRAN
SGSN
GERAN
Rx+ (DIAMETER)
S3
(GTP-C)
MME
S1-MME
(S1-AP)
E-UTRAN
eNodeB
PCRF
S6a
(DIAMETER)
S4 (GTP-C, GTP-U)
S10
(GTP-C)
S1-U
(GTP-U)
S11
(GTP-C)
Gxc
Gx (DIAMETER)
SGW
S5/8 (PMIPv6, GRE)
S5/8 (GTP-C, GTP-U)
UE
Policy&Charging Rule Function (PCRF)
User and application-aware policy decision point:
• Interacts with PGW to enforce per
session or per flow policies
• Gets event notification from PGW
(mobilty and/or traffic related)
• Interacts with application for admission
control and policy definitiion
• Supports roaming capabilities
Gxb
S6b
(DIAMETER)
PGW
AAA
SGi
Operator’s
IP Services
(e.g. video, IMS)
SWm
(DIAMETER)
S2a
(PMIPv6, GRE
MIPv4 FACoA)
S2b
(PMIPv6,
GRE)
SWa
ePDG
SWn S2c
Trusted
Non-3GPP
IP Access
UE
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Gxa
Untrusted
Non-3GPP
IP Access
STa (RADIUS,
DIAMETER)
UE
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3GPP Access
SWx (DIAMETER)
HSS
S12 (GTP-U)
UTRAN
SGSN
GERAN
Rx+ (DIAMETER)
S3
(GTP-C)
MME
S1-MME
(S1-AP)
E-UTRAN
eNodeB
PCRF
S6a
(DIAMETER)
S4 (GTP-C, GTP-U)
S10
(GTP-C)
S1-U
(GTP-U)
S11
(GTP-C)
Gxc
Gx (DIAMETER)
SGW
S5/8 (PMIPv6, GRE)
S5/8 (GTP-C, GTP-U)
UE
Enhanced Packet Data Gateway (ePDG)
Support for untrusted non-3GPP access
• EPC point of attachment for user
accessing over other non-owned access
• Terminates IPSec tunnel from UE
established with IKEv2 & EAP-AKA
• Supports network-based IP mobility
towards the selected PGW (PMIPv6)
Gxb
S6b
(DIAMETER)
PGW
AAA
SGi
Operator’s
IP Services
(e.g. video, IMS)
SWm
(DIAMETER)
S2a
(PMIPv6, GRE
MIPv4 FACoA)
S2b
(PMIPv6,
GRE)
SWa
ePDG
SWn S2c
Trusted
Non-3GPP
IP Access
UE
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Gxa
Untrusted
Non-3GPP
IP Access
STa (RADIUS,
DIAMETER)
UE
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HSS
S6a
EPS AKA via S6a
(Auth Vectors)
Challenge and keys
exchange
MME
E- UTRAN
RRC Integrity and ciphering
Mutual Authentication
NAS Integrity/Ciphering
eNB
U-Plane Ciphering
UE
• 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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HSS
MME
PCRF
S1-MME
UE
eNodeB
S-GW
Evolved Packet Core (EPC)
Evolved UTRAN (E-UTRAN)
NAS
RRC
PDCP
RRC
PDCP
S1-AP
SCTP
S1-MME
36.413
NAS
S1-AP
SCTP
RLC
MAC
RLC
IP
IP
MAC
L2
L2
OFDMA
OFDMA
L1
L1
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PDN-GW
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HSS
PCRF
MME
S1-U
UE
S5/S8
eNodeB
Evolved Packet Core (EPC)
Evolved UTRAN (E-UTRAN)
IP (user)
PDCP
RLC
PDCP
RLC
GTP-U
UDP
MAC
MAC
IP
L2
OFDMA
OFDMA
L1
© 2010 Cisco and/or its affiliates. All rights reserved.
PDN-GW
S-GW
S1-U
36.414
GTP-U GTP-U PMIP
UDP
UDP GRE
IP
IP
L2
L2
L1
L1
S5/S8
29.274
(GTP)
29.275
(PMIPv6)
IP (user)
PMIP GTP-U
UDP
GRE
IP
L2
L1
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HSS
PCRF
MME
X2
UE
eNodeB
Evolved Packet Core (EPC)
Evolved UTRAN (E-UTRAN)
X2-AP
SCTP
IP
L2
X2-C
36.423
L1
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PDN-GW
S-GW
X2-AP
GTP-U
SCTP
UDP
IP
IP
L2
L2
L1
L1
GTP-U
X2-U
36.424
UDP
IP
L2
L1
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HSS
PCRF
MME
S6a
Gx
UE
eNodeB
Evolved Packet Core (EPC)
Evolved UTRAN (E-UTRAN)
DIAMETER
SCTP
IP
L2
L1
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S6a
29.272
PDN-GW
S-GW
DIAMETER
DIAMETER
SCTP
SCTP
IP
IP
L2
L2
L1
L1
DIAMETER
Gx
29.212
SCTP
IP
L2
L1
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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 IP
address (either IPv4 or IPv6)
• PDN types IPv4, IPv6 and IPv4v6 are supported
• /64 IPv6 prefix allocation via IPv6 Stateless Address autoconfiguration
according to RFC 4862, if IPv6 is supported (Mandatory)
• IPv6 parameter configuration via Stateless DHCPv6 according to
RFC 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 the
IPv6 prefix and Interface Identifier to the MME or to the SGSN. The MME
or the SGSN forwards the IPv6 Interface Identifier to the UE.”
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• Idle Mode Mobility procedures
UE Initial Attach
Periodic Location Update / Inter- and intra-RAT reselection
UE Detach
• Active Mode Mobility
Intra-RAT Intra- and inter-area handover
Inter-RAT handover
• RRC States
RRC-IDLE
RRC-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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MME
3G UE
S-GW
P-GW
HSS
1. Attach Request
2. Identity Req/Rsp
3. UE Authentication (EAP-AKA) and Ciphering Start
4. User Profile Download
5. Bearer Request
6. Bearer Request
PCRF
Bearer Authorisation
(inc. IP @, policy)
9. Bearer Accept
8. Bearer Accept
10. Attach Accept/Complete
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3G UE
Old RNC
1. HO Preparation
Target RNC
Old SGSN
2. Relocation Required
Target SGSN
GGSN
3. Fwd Reloc Req
4. Relocation Request
5. RAB establishment at target NodeB
6. Relocation Request Ack
8. Relocation Command
7. Fwd Reloc Ack
9. Reconfig Radio
10. SRNS Context Transfer
11. Relocation Detected
12. Relocation Detected
13. Update PDP Req
14. Policy Ctrl
(optional)
15. Update PDP Ack
Relocation Completion including Radio resource release at Old RNC and RAU procedure
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3G UE
Old eNB
Target eNB
MME
Old S-GW
Target S-GW
P-GW
Established 2-way Bearer
1. HO prep and exec
Fwd Data
DL Data
2. Path Switch Req
3. Create Session Req
4. Modify Bearer Req
5. Policy Ctrl
7. Create Session Resp
6. Modify Bearer Ack
8. Path Switch Resp
9. Release
10. Delete Session Req/Resp
Established 2-way Bearer
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3G UE
Old MME
1. HO preparation
Target MME
2. Fwd Reloc Req
Old S-GW
Target S-GW
P-GW
3. Create Session Req/Resp
4. HO prep at Target eNB
5. Create Indirect TunnelReq/Resp
6. Fwd Reloc Resp
7. Create Indirect TunnelReq/Resp
9. HO Command
8. HO Command
10. eNB context transfer
11. HO Notify
12. Reloc Complete Req/Resp
13. Update Session Req
14. Modify Bearer Req
15. Policy Ctrl
17. Update Session Resp
Relocation Completion including radio resource release at Old
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16. Modify Bearer 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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1
UTRAN /
GERAN
IuCS / A
Incoming SMS
MSC
SGs
2
SMS is delivered via SGs interface
MME
S1-MME
CSFB UE
E-UTRAN
S6a
HSS
S11
S1-U
Serving/
PDN GW
• During EPC attach, CSFB UE’s are also attached over SGs to MSC
• MME maintains mapping of TA to LA to determine appropriate MSC to
establish SGs association with
• SMS can be delivered/sent without FallBack to legacy radio (SGs interface
includes SMS payload capability)
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1
4 UE Responds to paging –
incoming call terminated via
standard 2G/3G procedures
IuCS / A
UTRAN /
CSFB UE
GERAN
Incoming Call – delivered to VMSC which
has SGs association for this subscriber
MSC
SGs
2
3
UE retunes to 2G/3G RAT on receipt
of page
UE is paged via the SGs interface
MME
S1-MME
CSFB UE
E-UTRAN
S6a
HSS
S11
S1-U
Serving/
PDN GW
• 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 or
other circumstances)
• This capability (Roaming Retry) requires upgrades on GMSC, VMSC
and HLR. Introduces further termination latency.
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1
UTRAN /
GERAN
IuCS / A
IuPS / Gb
SGSN
(SR-VCC)
IMS (HPLMN)
Subscriber has already registered
into IMS following EPC attach
MSC Server
(SR-VCC)
SCC AS
Sv
S3
MME
TAS
Mg
ISC
I/S-CSCF
Cx
S6a
IP-SM-GW
HSS
MGCF
Mw
P-CSCF
S11
S1-MME
2
SR-VCC
UE
UE Originates
Call
E-UTRAN
S1-U
Serving/
PDN GW
SGi
(Gm from UE)
• 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
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IMS (HPLMN)
3
SR-VCC UE
2
NewUTRAN
call leg/
established
GERAN
IuCS / A
IuPS / Gb
1
UE retunes to 2G/3G SGSN
RAT during active call (SR-VCC)
MSC Server
(SR-VCC)
SCC AS performs
bearer management
and tears down original
SCC AS
leg
Sv
S3
MME
Mg
IP-SM-GW
ISC
I/S-CSCF
Cx
S6a
TAS
HSS
MGCF
Mw
P-CSCF
S11
S1-MME
SR-VCC UE
E-UTRAN
S1-U
Serving/
PDN GW
SGi
(Gm from UE)
• SCC AS performs leg management – hides mobility events from other IMS
application servers
• SR-VCC only works in one direction – LTE  2G/3G
• Requires upgrades on legacy MSC infrastructure
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CSFB
VoIMS
End-User Services
Re-use legacy implementation
OneVoice (IR.92) provides baseline. All
operator proprietary services and extensions
must be ported to IMS.
Regulatory
Re-use legacy implementation
National regulatory services must be
implemented in IMS.
Service Differentiation
Restricted to only services deliverable from
legacy core.
IR.92 services can be blended with other IMS
services such as presence, RCS, rich
messaging.
End-user Experience
Significant post-dial delay. Retuning from
CS back to LTE may take some time –
impact to data services.
No retuning required to access CS equivalent
services. Still industry concerns regarding SRVCC latency.
Complexity
Medium – CS core requires upgrades for
SGs interface and also to support Roaming
Retry.
High – Significant new network infrastructure
required. SR-VCC extremely complex.
Intensive service porting to ensure full legacy
parity.
Cost
Unknown – upgrades must come from
existing CS vendors. Believed that legacy
vendors are using this to their advantage
to seek premium.
High – large investment required for new
infrastructure. However, diverse range of
vendors opens door for innovative deals/
solutions.
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Thank you.