Nokia Siemens Networks LTE
Radio access, rel. RL10,
operating documentation, prerelease
02

LTE/EPC system overview

DN0943898
Issue 01A DRAFT APPROVED
Approval Date 2010-02-28


LTE/EPC system overview

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Table of Contents

This document has 113 pages.

Summary of changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1
Introduction to Nokia Siemens Networks LTE/EPC system. . . . . . . . . . 11

2
Network architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.1
EPS overall architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.1.1
EPS architectures for 3GPP accesses with GTP-based S5 . . . . . . . . . 18

2.1.2
EPS architectures for 3GPP accesses with PMIP-based S5/S8 (IETF variants).
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.1.3
Non-roaming architectures for EPS for non-3GPP accesses . . . . . . . . 20

2.1.4
Roaming architectures for EPS for 3GPP accesses (GTP variants) . . . 21

2.1.5
Roaming architectures for EPS for non-3GPP accesses. . . . . . . . . . . . 23

2.2
Network elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.3
Reference points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.4
Protocol stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.5
LTE architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.5.1
LTE overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.5.2
eNB functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.6
EPC architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

2.6.1
EPC overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

2.6.2
MME functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2.6.3
S-GW functionality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2.6.4
P-GW functionality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2.7
Network elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

2.7.1
Flexi Multiradio BTS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

2.7.2
Flexi Network Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

2.7.3
Flexi Network Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2.8
External interfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.8.1
External interfaces of the Flexi Multiradio BTS . . . . . . . . . . . . . . . . . . . 45

2.8.2
Flexi Network Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.8.3
Flexi Network Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

3
Network and service management . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3.1
Network management architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3.2
Managing the LTE/EPC system with NetAct TM. . . . . . . . . . . . . . . . . . . 49

3.3
Element management tools. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

4
Mobility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4.1
Mobility scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4.2
Mobility anchors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4.3
Inter-eNB handover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

4.4
Inter-RAThandover (3GPP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4.5
Optimized 3GPP2 (HRPD) inter-RAT handover . . . . . . . . . . . . . . . . . . 54

4.6
Roaming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

4.7
Location services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5
Radio resource managementand telecom .. . . . . . . . . . . . . . . . . . . . . 60

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5.1 RRM functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

5.2 State transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

5.3 Connection states for intra-RAT mobilty.. . . . . . . . . . . . . . . . . . . . . . . .64

5.4 Tracking areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66

5.5 Tracking area update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

5.6 Paging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

5.7 Bearer management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70

5.7.1 EPS bearers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70

5.7.2 Quality of service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72

6 Transport and transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

6.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

6.2 IP transport interfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

6.3 Transport switching in eNB.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

6.4 IP transport addressing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

6.5 IP transport QoS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

6.6 IP tunneling mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

6.7 Transport layer reliability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

7 Operability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

7.1 Operability architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

7.2 NetAct ™ at a glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

7.3 NetAct ™ framework. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

7.4 NetAct ™ applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

7.5 Self Organizing Network support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

8 Security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

8.1 Security requirements and methods. . . . . . . . . . . . . . . . . . . . . . . . . . . .86

8.1.1 Security categories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

8.1.2 Security threats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

8.1.3 Security areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

8.1.4 Security features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

8.2 LTE/EPC overall key hierarchy concept. . . . . . . . . . . . . . . . . . . . . . . . .90

8.3 LTE/EPC security architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92

8.4 LTE/EPC plane security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93

8.4.1 C-plane security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

8.4.2 U-plane security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

8.4.3 M-plane security . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .95

8.5 eNB security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96

8.5.1 Secure processing environment of the eNB.. . . . . . . . . . . . . . . . . . . . .96

8.5.2 Security for eNB setup and configuration. . . . . . . . . . . . . . . . . . . . . . . .97

8.6 NetAct security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

8.6.1 User security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

8.6.2 System security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

9 AAA and charging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

9.1 LTE/EPC authentication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

9.2 Authorization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

9.3 Accounting and charging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101

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10 Migration to LTE VoIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
11 Nokia Siemens Networks service solutions . key benefits and customer
values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
12 Nokia Siemens Networks environmental issues . . . . . . . . . . . . . . . . . 111

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List of Figures


Figure 1 LTE/SAE high-level architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Figure 2 LTE air interface technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Figure 3 Architectural evolution of existing 2G/3G networks to LTE. . . . . . . . . . . 15
Figure 4 Smooth migration towards EPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Figure LTE/EPC flat network architecture and direct tunnel . . . . . . . . . . . . . . . 17
Figure 6 Non-roaming architecture for 3GPP accesses within EPS using GTP-

based S5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Figure 7 Non-roaming architecture for 3GPP accesses within EPS using PMIP-

based S5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Figure 8 Roaming architecture for 3GPP accesses within EPS using PMIP-based

S8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Figure 9 Non-roaming architecture with EPS using S5, S2a, S2b . . . . . . . . . . . . 20
Figure Non-roaming architecture with EPS using S5, S2c. . . . . . . . . . . . . . . . . 21
Figure 11 Roaming architecture for 3GPP accesses (GTP-based) - home routed. 21
Figure 12 Roaming architecture for 3GPP accesses (GTP-based) - local breakout

with home operator’s application functions only. . . . . . . . . . . . . . . . . . .22
Figure 13 Roaming architecture for 3GPP accesses (GTP-based) - local breakout

with visited operator’s application functions only . . . . . . . . . . . . . . . . . . 22
Figure 14 Roaming architecture for EPS using S8, S2a, S2b - home routed . . . . . 23
Figure Roaming architecture for EPS using PMIP-based S8, S2a, S2b (chained

PMIP-based S8-S2a/b) - home routed . . . . . . . . . . . . . . . . . . . . . . . . . .23
Figure 16 Roaming architecture for EPS using S8, S2c - home routed . . . . . . . . . 24
Figure 17 Roaming architecture for EPS using S8, S2a, S2b - home routed . . . . . 25
Figure 18 Roaming architecture for EPS using S5, S2c -local breakout . . . . . . . . 25
Figure 19 Uu user plane protocol stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Figure Uu control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Figure 21 S1-U user plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Figure 22 X2 user plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Figure 23 S5/S8 user plane protocol stack (GTP variant). . . . . . . . . . . . . . . . . . . .30
Figure 24 S5/S8 user plane protocol stack (IETF variant) . . . . . . . . . . . . . . . . . . .30
Figure S1-MME control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . .31
Figure 26 X2 control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Figure 27 S5/S8 control plane protocol stack (GTP variant). . . . . . . . . . . . . . . . . . 31
Figure 28 S5/S8 control plane protocol stack (IETF variant) . . . . . . . . . . . . . . . . . 31
Figure 29 S10 control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Figure S11 control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Figure 31 S6a control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Figure 32 S13 control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Figure 33 SBc control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Figure 34 S4 user plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Figure S12 user plane protocol stack.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Figure 36 S3 control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Figure 37 S4 control plane protocol stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Figure 38 Functional split between radio access and core network . . . . . . . . . . . . 35
Figure 39 E-UTRAN and EPC with S1-flex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
Figure Flexi Multiradio BTS site solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

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Figure 41 Flexi Multiradio BTS site solution for the 2TX MIMO in a 3-sector configu


ration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Figure 42 Flexi Multiradio RRH 60 W.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Figure 43 Flexi Network Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Figure 44 Flexi Network Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 45 External interfaces of the Flexi Multiradio BTS . . . . . . . . . . . . . . . . . . . 45
Figure 46 External interfaces of the Flexi Network Server. . . . . . . . . . . . . . . . . . . 46
Figure 47 External interfaces of the Flexi Network Gateway . . . . . . . . . . . . . . . . . 47
Figure 48 LTE/EPC network management architecture. . . . . . . . . . . . . . . . . . . . . 48
Figure 49 Mobility scenarios for LTE/EPC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Figure 50 Mobility anchor point. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Figure 51 Inter-eNB handover with X2 interface. . . . . . . . . . . . . . . . . . . . . . . . . . 53
Figure 52 Inter-eNB handover without X2 interface.. . . . . . . . . . . . . . . . . . . . . . . 53
Figure 53 3GPP inter-RAT handover.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Figure 54 Architecture for optimized LTE-HRPD mobility . . . . . . . . . . . . . . . . . . . 55
Figure 55 Roaming scenario with home routed traffic . . . . . . . . . . . . . . . . . . . . . . 56
Figure 56 Roaming scenario for local breakout with home operator\'s application func


tions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Figure 57 Roaming scenario for local breakout with visited operator\'s application

functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Figure 58 EMM state transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Figure 59 ECM state transitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Figure 60 Intra-RAT mobility in ECM-IDLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Figure 61 Intra-RAT mobility in ECM-CONNECTED. . . . . . . . . . . . . . . . . . . . . . . 66
Figure 62 Multiple-TA registration concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Figure 63 LTE/EPC EPS high level bearer model. . . . . . . . . . . . . . . . . . . . . . . . . 70
Figure 64 LTE/EPC service data flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Figure 65 Example of E-UTRAN transport topologies. . . . . . . . . . . . . . . . . . . . . . 75
Figure 66 Tunnels in the LTE/EPC network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Figure 67 LTE/EPC Operation and maintenance concept. . . . . . . . . . . . . . . . . . . 77
Figure 68 NetAct ™ OSS evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Figure 69 SON architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Figure 70 LTE/EPC key hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Figure 71 LTE/EPC security architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Figure 72 LTE/EPC plane security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Figure 73 C-plane security architecture for LTE/EPC . . . . . . . . . . . . . . . . . . . . . . 94
Figure 74 U-plane security architecture for LTE/EPC . . . . . . . . . . . . . . . . . . . . . . 95
Figure 75 M-plane security architecture for LTE/EPC . . . . . . . . . . . . . . . . . . . . . . 96
Figure 76 Layered security association structure of the LTE/EPC. . . . . . . . . . . . . 99
Figure 77 LTE/EPC AKA procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Figure 78 Retrieval of LTE authorization information. . . . . . . . . . . . . . . . . . . . . . 100
Figure 79 EPC charging - 3GPP access - nonroaming. . . . . . . . . . . . . . . . . . . . 101
Figure 80 EPC charging - 3GPP access - roaming, home routed traffic . . . . . . . 102
Figure 81 EPC charging - 3GPP access - roaming with local breakout. . . . . . . . 102
Figure 82 LTE/EPC architecture with PS & CS domains completely separated . 104
Figure 83 LTE/EPC architecture CS fallback. . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Figure 84 Single radio voice call continuity (SR-VCC) principle . . . . . . . . . . . . . 106
Figure 85 LTE/EPC SR-VCC architecture for 3GPP accesses . . . . . . . . . . . . . . 106

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Figure86 LTE/EPC SR-VCC architecture for 1xRTT. . . . . . . . . . . . . . . . . . . . . .107
Figure 87 LTE/EPC architecture with All-IP network deploying LTE. . . . . . . . . . . 108


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List of Tables

Table 1 Summary of customer benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table 2 Mobility scenarios and anchor points . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Table 3 LCS requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Table 4 Scope of RRM functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Table 5 QoS scheme for LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Table 6 Standard QCI characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Table 7 Description of security keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Table 8 Security termination points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

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Summary of changes LTE/EPC system overview

Summary of changes

Issue History

Issue
Number
Date of Issue Reason for Update
1-0 Draft 2009-05-04 Preliminary version for pre-P3 deliveries.

Details
All

.
New document.
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1


Introduction to Nokia Siemens Networks
LTE/EPC system

g This document provides an overview of the LTE/EPC system. Functions and

features are described without respect to the system releases when they will actually

be available. This information can be found in the Nokia Siemens Networks LTE

roadmap.

Nokia Siemens Networks expects five billion people to be connected to the Internet by
2015. Wireless access plays a major role in realizing this target. Wireless networks will
be used to extend broadband penetration beyond the reach of wireline networks. Evolution
of terminals and networking technology coupled with Internet access as a global
phenomenon are allowing advanced operators to report polynomial growth in mobile
data usage already now.

With a view to taking the next step up the evolutionary ladder beyond HSPA, 3GPP
Release 8 has standardized a technology called Long Term Evolution/System Architecture
Evolution (LTE/SAE). It is designed to

.
make the most of scarce spectrum resources:
Deployable with bandwidths ranging from 1.4 MHz to 20 MHz, LTE/SAE provides up
to four times the spectral efficiency of HSDPA Release 6.
.
afford users an experience on par with today’s best residential broadband access:
LTE/SAE delivers peak user data rates ranging up to 173 Mbps and reduces latency
to as low as 10 ms.
.
leverage flat all-IP network architecture and a new air interface to significantly cut
per-Mbyte costs, with later product innovations potentially improving performance
even further:
For instance a 4x4 Multiple Input/Multiple Output (MIMO) scheme will boost
downlink rates up to 326 Mbps.
System approach

Based on these performance targets 3GPP is defining the air interface, network architecture,
and system interfaces. All services are packet-based; that is, VoIP serves to
implement voice. Figure 1 shows an LTE/SAE network’s high-level architecture.

LTE/SAE does not entail a circuit-switched domain. 3GPP envisages fully IP-based
transmission. The IP backbone network supports guaranteed QoS on demand with a
very simplified, but backward compatible QoS concept. Carrier-grade Ethernet is used
where possible; in particular to connect the evolved node B (eNB), the LTE’s base
station.

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Access Core Switching & Transport
Service Control and DataBases
eNB
IMS PCRF HSS/AAA
S-GW P-GW
MME
Internet
Figure 1 LTE/SAE high-level architecture

In the following, the Nokia Siemens Networks solution of the LTE/SAE architecture is
referred to as Nokia Siemens Networks LTE/EPC (Long Term Evolution/Evolved Packet
Core) system.

Simplified network architecture

Today’s WCDMA core network architecture for the PS domain comprises SGSN and

GGSN. The radio network architecture comprises Node B and RNC.
The Nokia Siemens Network LTE/EPC system is streamlined to optimize network performance,
maximize data throughput, and minimize latency. Rather than four nodes
(Node B, RNC, SGSN, GGSN), the LTE/EPC system comprises a far simpler configuration
of just eNB, two logical user plane entities, Serving Gateway and PDN Gateway,
collectively called the S-GW/P-GW, and one control plane entity (MME). Gateway functions
may be provided in common or separate physical nodes. All entities are connected
by standardized interfaces to support multi-vendor configurations. Transport is fully IP-
based. Because the access network operates without a central controller (BSC, RNC),
base stations (eNBs) interconnect and connect directly to the S-GW/P-GW and MME to
exchange control and user information. This approach entails fewer interfaces and
minimal complexity caused by protocol conversion and content mapping.

High-performance air interface

The LTE air interface differs markedly from legacy technology. Advanced applied
Orthogonal Frequency Division Multiplexing (OFDM) technologies achieve performance
and savings goals based on low total cost of ownership.

Figure 2 summarizes the technological approach to the projected air interface. Many
orthogonal OFDM sub-carriers may be allocated according to carrier bandwidth available
in the downlink. The uplink employs a single carrier FDMA technology (SC-FDMA)
to preclude high peak-to-average power ratios, thereby streamlining the RF design and
extending the battery life of the terminals.

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scalable Hybrid ARQ 64 QAM Fast Link Adaptation

NACK
Rx Buffer
ACK
Combined
decoding
2
1
2
1
Modulation
Short TTI =1 ms
Transmission time interval
DL: OFDMA UL: SC-FDMA
Channel RXTX
RXTX
Available bandwidth
...
Frequency
OFDM
symbols
Sub-carriers
... Guard
intervals
Time Advanced Scheduling
Time & Frequency
(Frequency Selective Scheduling)
Figure 2 LTE air interface technology

OFDM allows for improved interference control, advanced scheduling techniques and
ease of implementation of Multiple Input Multiple Output (MIMO) concepts. MIMO
antenna technology and higher order modulation (64QAM), combined with fast link
adaptation methods, maximize spectral efficiency. In principle, operators do not need to
acquire new spectrum. The LTE air interface is designed to operate in the same
spectrum as, and in parallel with, the legacy WCDMA/HSPA air interface, for example
on a separate carrier. The system’s flexible spectrum allocation (including scalable
bandwidth) allows carriers to be spread across any suitable spectrum licensed for 2G or
3G operation. Deployable in spectrum bands with bandwidths of 1.4, 3, 5, 10, 15, and
20 MHz, LTE offers unique spectrum flexibility. The small 1.4 and 3.0 MHz bandwidths
are optimized for GSM and CDMA re-farming, where operators might not initially be able
to free up more bandwidth.

Customer benefits

The introduction of LTE provides the following key benefits to operators compared with
existing 3G deployments:

. Maximized use of allocated frequency bands
LTE provides high aggregate data rates per cell and supports flexible frequency
bandwidths and in particular allows re-farming of 2G spectrum.

. Reduced cost of ownership
LTE has a simpler architecture: it has fewer nodes and fewer node types, and is
entirely IP based. It also uses IP transport allowing the use of cheap equipment and
infrastructure. The ability to run voice and data services on a unified infrastructure
will also have an impact on reducing costs.

. Competitive mobile broadband packet access
LTE is optimized for broadband IP packet access providing the high bandwidth (100
Mbps DL/50 Mbps UL) and low latency required. It supports seamless and lossless
low latency handover and provides sophisticated QoS to support important real-time
applications such as voice, video and real-time gaming. LTE can support terminal
speeds of 150-350 km/s and cell ranges of up to 100 km.

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.
Superior inter-technology mobility
The LTE/EPC combination provides seamless mobility with other 3GPP access
systems (UMTS, GPRS), with 3GPP2/cdma2000 and, where possible, with non3GPP
(for example WLAN).

Table 1 summarizes the main customer benefits.

Operator benefits Subscriber benefits
. reduced complexity, flat IP based packet-only
architecture lower operator CAPEX and OPEX
. interworking with legacy systems as an integral
part of service continuity
. scalable bandwidth allows flexible deployment with
limited spectrum
. significant improvements in spectral efficiency and
data performance for multimedia services
. economies of scale leveraging existing assets
meaning rapid availability for the mass market
. enriched user experience with real time, interactive
services and seamless connectivity
. broadband mobility at a decreasing cost
. wide variety of devices and services

Table 1 Summary of customer benefits

Network evolution and migration

Nokia Siemens Networks is committed to providing a smooth evolutionary path for every
operator, following a roadmap that factors each operator’s installed base and strategy
into the equation (see Figure 3):

.
3G operators with a deployed WCDMA/HSPA network can migrate directly to
LTE/EPC. Migrating to the flat network architecture of Internet High Speed Packet
Access (I-HSPA) may also be beneficial because it accommodates LTE/EPC’s flat
IP-based network architecture while supporting legacy WCDMA/HSPA handsets.
The operator can thus enjoy the transport and network scaling benefits immediately,
and easily upgrade the network to LTE/EPC later.
.
3G operators who have deployed I-HSPA have flat network architecture similar to
LTE/EPC in place, and can thus cost-efficiently introduce LTE/EPC.
.
Operators running 2G networks (GSM/GPRS) can introduce LTE/EPC directly or
via one of the above WCDMA/HSPA paths, depending on their timetables for introducing
mobile broadband services and the spectrum they have available. Because
LTE supports bands as small as 1.4 MHz, spectrum may be re-farmed smoothly and
gradually from GSM to LTE.
.
CDMA operators can introduce LTE/EPC networks directly, or follow one of the
above paths. GSM/EDGE may be a good choice for strategies more immediately
focused on voice centric business. The same applies to Greenfield operators.
Operators opting to take the I-HSPA path can capitalize on the ecosystem of HSPA
terminals, benefit from the flat architecture today, and quickly optimize mobile broadband
performance.
.
Operators with TD-SCDMA networks, which are currently deployed in China only,
will probably migrate directly to LTE, preferably using the TDD mode of LTE.
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Leverage existing handset base
Exploit core network synergies

Enabling flat broadband architecture GSM/WCDMAhandset base
WCDMA/
HSPA
I-HSPA
GSM/
(E)GPRS
LTE
TD SCDMA
CDMA
Figure 3 Architectural evolution of existing 2G/3G networks to LTE

Network deployment

For 3GPP operators, the Nokia Siemens Networks EPS solution enables optimized
steps from 2G/3G legacy infrastructure to reach the target EPS architecture as illustrated
in Figure 4:

1.
Introduction of direct tunnel between RNC and GGSN (HSPA R7):
2.
Introduction of RNC functionality and direct tunnel between NB and GGSN (I-HSPA
R7)
3.
Introduction of EPC (LTE R8)
4.
Upgradeability of legacy SGSN with MME functionality
5.
Upgradeability of legacy GGSN with P-GW functionality
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NB
RNC
GGSN
SGSN
NB
RNC
GGSN
HSPA R6 HSPA R7
Direct tunnel
Control plane User plane Capacity expansions
Direct
tunnel
Direct
tunnel
Direct
tunnel
GGSN
SGSN
HSPA R7
Internet HSPA
SGSN
NB with
RNC funct.
P-GW
S-GW
MME
LTE R8
eNB
Figure 4 Smooth migration towards EPS

Nokia Siemens Networks LTE/EPC product portfolio

The LTE/EPC system comprising the logical entities eNB, S-GW, P-GW, and MME is
realized by the following Nokia Siemens Networks products:

. Flexi Multiradio BTS LTE
eNB functionality is supported as the evolution of the Nokia Siemens Networks Flexi
Multiradio BTS. Nokia Siemens Networks’ LTE eNB is based on the Flexi Multiradio
BTS. The same Flexi Multiradio System and RF Modules are used for
WCDMA/HSPA and for LTE. With downloadable LTE SW, the Flexi Multiradio BTS
operates in LTE SW mode, to become the Flexi Multiradio BTS LTE. From a BTS
site installation and hardware point of view, Flexi Multiradio BTS LTE enables operators
to build BTS sites using modules, without the requirement for a specific BTS
cabinet.

. Flexi Network Server
MME functionality is supported as the evolution of the Nokia Siemens Networks

SGSN product.

. Flexi Network Gateway
S-GW/P-GW functionality is supported as the evolution of Nokia Siemens Networks
ISN product.

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Network architecture

2 Network architecture

Long Term Evolution (LTE) is a 3GPP project that provides extensions and modifications
of the UMTS system to allow implementing a high data rate, low latency and packet
optimized radio access networks. Service Architecture Evolution (SAE) is an associated
3GPP project working on 3GPP core network evolution. The focus is on the packet
switched domain assuming that both data and voice services will be supported over the
same packet switched network.

Nokia Siemens Networks’ LTE/SAE solution, known as the Nokia Siemens Networks
LTE/EPC system, applies flat network architecture as illustrated in Figure 5. The radio
network consists of a single node, the evolved Node B (eNB). In the core network
Mobility Management Engine (MME) takes the role of SGSN in current GPRS networks.
MME is a control plane element allowing user plane traffic bypass over a direct tunnel.
Different gateway elements in EPC take the role of GGSN providing connectivity to
operator service networks and the Internet.

There are two gateway functions, which may or may not co-exist within a single gateway
element:

.
Serving Gateway (S-GW), the user plane (U-plane) gateway to the E-UTRAN
.
Packet Data Network Gateway (P-GW), the user plane (U-plane) gateway to the
PDN (e.g. the Internet or the operator\'s IP Multimedia Subsystem (IMS))
Direct tunnel
Interne t
S-GW/P-GWMMeNB M E
Figure 5 LTE/EPC flat network architecture and direct tunnel

LTE/EPC provides decreased cost per transmitted bit. This is achieved by:

.
advanced modulation techniques that allow optimized use of radio frequency
.
flat architecture that minimizes the number of network elements and optimize the
use of the transmission network
.
capability to serve high quality, low latency real-time traffic allowing both voice and
data services to be provided over a single all-IP network
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LTE/EPC system overview

2.1 EPS overall architecture
The Evolved Packet System (EPS) is made up of the Evolved UTRAN (E-UTRAN),
Evolved Packet Core (EPC) and connectivity to legacy 3GPP access and non-3GPP
access systems.

EPS solutions for 3GPP accesses are typically selected by operators, who want to introduce
EPS as smooth evolution to their existing 2G/3G infrastructure. EPS solutions for
non-3GPP accesses are typically selected by operators, who want to maximize the
deployment of generic, non-3GPP protocols and minimize the deployment of 3GPP
specific protocols.

The EPS architecture has three key aspects which address the performance requirements
for LTE/EPC:

.
reduction of the number of network elements on the data path compared to
GPRS/UMTS
.
streamlining of RAN functionality by providing it in a single node
. separation of the control and user plane network elements (MME and S-GW).
There are different architecture reference models specified in 3GPP TS 23.402:
.
EPS architectures for 3GPP accesses with GTP-based S5
.
EPS architectures for 3GPP accesses with PMIP-based S5/S8 (IETF variants)
.
Non-roaming architectures for EPS for non-3GPP accesses
.
Roaming architectures for EPS for 3GPP accesses (GTP variants)
.
Roaming architectures for EPS for non-3GPP accesses
2.1.1 EPS architectures for 3GPP accesses with GTP-based S5
The GTP based (with GTP S5 reference point) EPS solution for 3GPP accesses is typically
selected by operators, who want to introduce EPS as smooth evolution to their exisating
2G/3G infrastructure.

SGi
S12
S3
S1-MME
Gx
S6a
Rx
S10
S11
S5
GTP
Serving
Gateway
PDN
Gateway
S1-U
S4
2G/3G
MME
Operator\'s IP
Services
(e.g. IMS, PSS etc.)
PCRF
HSS
E-UTRAN
SGSN
3GPP Access
Figure 6 Non-roaming architecture for 3GPP accesses within EPS using GTP-
based S5

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Network architecture

2.1.2
EPS architectures for 3GPP accesses with PMIP-based S5/S8 (IETF
variants)
The IETF based (with PMIPv6 S5/S8 reference point) EPS solution for 3GPP accesses
is typically selected by operators, who want to maximize the deployment of generic,
IETF defined protocols and minimize the deployment of 3GPP specific (e.g. GTP) protocols.


The IETF variant can be deployed for both 3GPP and non-3GPP accesses.

SGi
S12
S3
S1-MME
Gx
S6a
Rx
S10
S11
S5
PMIP
Serving
Gateway
PDN
Gateway
S1-U
S4
2G/3G
MME
Operator\'s IP
Services
(e.g. IMS, PSS etc.)
PCRF
HSS
E-UTRAN
SGSN
3GPP Access
Gxc
Figure 7 Non-roaming architecture for 3GPP accesses within EPS using PMIP-
based S5

SGi
S12
S3
S1-MME
Gx
S6a
Rx
S10
S11
S8
S1-U
S4
2G/3G
MME
HSS
SGSN
3GPP Access
VPLMN
HPLMN
Operator\'s IPServices
(e.g. IMS, PSS etc.)
Serving
Gateway E-UTRAN
PDN
Gateway
hPCRF
Gxc
vPCRF
S9
Figure 8 Roaming architecture for 3GPP accesses within EPS using PMIP-based
S8

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2.1.3 Non-roaming architectures for EPS for non-3GPP accesses
The following considerations apply to interfaces where they occur in Figure 9, Figure 10
Figure 14, Figure 15, Figure 16, Figure 17, and Figure 18:

.
S5 can be GTP-based or PMIP-based.
.
Gxc is used only in the case of PMIP variant of S5 or S8.
.
Gxa is used when the Trusted non-3GPP Access network is owned by the same
operator.
.
Gxa is terminated in the Trusted non-3GPP Accesses if supported.
.
S2c is used only for DSMIPv6 bootstrapping and DSMIPv6 De-Registration (Binding
Update with Lifetime equals zero) when the UE is connected via 3GPP access.
Dashed lines are used in Figure 10, Figure 15 and Figure 18 to indicate this case.
g SWu shown in Figure 9 also applies to architectural reference models in Figure 10
and Figure 14 to Figure 18, but is not shown for simplicity.

SGi
Gx
S2b
SWn
Operator\'s
IP Services
(e.g. IMS, PSS etc.)
SWm
SWx
SWa
HPLMN
S6b
Rx
Gxb
S2a
Gxa
STa
Gxc
S5
S6a
3GPP
Access
Serving
Gateway
SWu
HSS
PCRF
PDN
Gateway
Trusted
Non-3GPP
IP Access
Untrusted
Non-3GPP
IP Access
ePDG 3GPP AAA
Server
UE
Non-3GPP
Networks
Figure 9 Non-roaming architecture with EPS using S5, S2a, S2b

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SGi
Gx
S2c
SWn
Operator\'s
IP Services
(e.g. IMS, PSS etc.)
SWm
SWx
SWa
HPLMN
S6b
Rx
Gxb
S2c
Gxa
STa
Gxc
S5
S6a
3GPP
Access
Serving
Gateway
HSS
PCRF
PDN
Gateway
Trusted
Non-3GPP
IP Access
Untrusted
Non-3GPP
IP Access
ePDG 3GPP AAA
Server
UE
S2c
S2c
S2c
Non-3GPP
Networks
Figure 10 Non-roaming architecture with EPS using S5, S2c

2.1.4 Roaming architectures for EPS for 3GPP accesses (GTP variants)
SGi
S12
S3
S1-MME
Gx
S6a
Rx
S10
S11
S8
S1-U
S4
2G/3G
MME
HSS
SGSN
3GPP Access
VPLMN
HPLMN
Operator\'s IPServices
(e.g. IMS, PSS etc.)
Serving
Gateway E-UTRAN
PDN
Gateway
PCRF
Figure 11 Roaming architecture for 3GPP accesses (GTP-based) -home routed

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SGi
S12
S3
S1-MME S6a
Rx
S10
S11
S5
GTP
S1-U
S4
2G/3G
MME
HSS
SGSN
3GPP Access
VPLMN
HPLMN
Serving
Gateway E-UTRAN PDN
Gateway
hPCRF
Gx
vPCRF
S9
Visited Operator
PDN
Home Operator\'s IP
Services
Figure 12 Roaming architecture for 3GPP accesses (GTP-based) - local breakout
with home operator’s application functions only

SGi
S12
S3
S1-MME S6a
Rx
S10
S11
S5
GTP
S1-U
S4
2G/3G
MME
HSS
SGSN
3GPP Access
VPLMN
HPLMN
Serving
Gateway E-UTRAN PDN
Gateway
hPCRF
Gx
vPCRF
S9
Visited Operator\'s IP
Services
Figure 13 Roaming architecture for 3GPP accesses (GTP-based) - local breakout
with visited operator’s application functions only

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2.1.5 Roaming architectures for EPS for non-3GPP accesses
SGi
Gx
S2b
SWn
SWm
SWx
SWa
VPLMN
Non-3GPP
Networks
S6b
Rx
Gxb
S2a
Gxa
STa
Gxc
S6a
3GPP
Access
HSS
hPCRF
Trusted
Non-3GPP
IP Access
Untrusted
Non-3GPP
IP Access
3GPP AAA
Proxy
HPLMN
vPCRF
3GPP AAA
Server
SWd
ePDG
S8
Serving
Gateway
PDN
Gateway
Operator\'s
IP Services
(e.g. IMS, PSS etc.)
S9
Figure 14 Roaming architecture for EPS using S8, S2a, S2b - home routed

SGi
Gx
S2b
SWn
SWm
SWx
SWa
VPLMN
Non-3GPP
S6b
Rx
Gxb
Gxa
STa
Gxc
S6a
3GPP
Access
HSS
hPCRF
Untrusted
Non-3GPP
IP Access
3GPP AAA
Proxy
HPLMN
vPCRF
3GPP AAA
Server
SWd
ePDG
S8
PDN
Gateway
Operator\'s
IP Services
(e.g. IMS, PSS etc.)
S9
Trusted
Non-3GPP
IP Access
S2a - PMIP
Serving
Gateway
Networks

Figure 15
Roaming architecture for EPS using PMIP-based S8, S2a, S2b (chained
PMIP-based S8-S2a/b) - home routed

g Chained S2a/S2b and S8 used when VPLMN has business relationship with Non3GPP
Networks and S-GW in VPLMN includes local non-3GPP Anchor.

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LTE/EPC system overview

The following are some additional considerations for the use of Gxc:

.
Gxc is used only in the case of PMIP-based S8 and for 3GPP access.
.
Gxc is not required for Trusted Non-3GPP IP Access; Gxa is used instead to signal
the QoS policy and event reporting.
SGi
Gx
SWn
SWm
SWx
SWa
VPLMN
Non-3GPP
Networks
S6b
Rx
Gxb
Gxa
STa
Gxc
S6a
3GPP
Access
HSS
hPCRF
Trusted
Non-3GPP
IP Access
Untrusted
Non-3GPP
IP Access
3GPP AAA
Proxy
HPLMN
vPCRF
3GPP AAA
Server
SWd
ePDG
S8
Serving
Gateway
Operator\'s
IP Services
(e.g. IMS, PSS etc.)
S9
UES2c
S2c
S2c
PDN
Gateway
Figure 16 Roaming architecture for EPS using S8, S2c -home routed

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SGi
Gx
S2b
SWn
SWm
SWx
SWa
VPLMN
Non-3GPP
Networks
S6b
Rx
Gxb
S2a
Gxa
STa
Gxc
S6a
3GPP
Access
HSS
hPCRF
Trusted
Non-3GPP
IP Access
Untrusted
Non-3GPP
IP Access
3GPP AAA
Proxy
HPLMN
vPCRF
3GPP AAA
Server
SWd
ePDG
S8
Serving
Gateway
PDN
Gateway
Operator\'s
IP Services
(e.g. IMS, PSS etc.)
S9
Figure 17 Roaming architecture for EPS using S8, S2a, S2b - home routed

Rx
S5
SGi
SWn
SWm
SWx
SWa
VPLMN
Non-3GPP
Networks
S6b
Rx
Gxb
Gxa
STa
Gxc
S6a
3GPP
Access
HSS
hPCRF
Trusted
Non-3GPP
IP Access
Untrusted
Non-3GPP
IP Access
HPLMN
vPCRF
3GPP AAA
Server
SWd
ePDG
Serving
Gateway
Operator\'s
IP Services
(e.g. IMS, PSS etc.)
S9
Visited network IP
services or proxies
to home network
services or PDN
S2c
UE
S2c S2c
3GPP AAA
Proxy
PDN
Gateway
S2c
Figure 18 Roaming architecture for EPS using S5, S2c - local breakout

g The two Rx instances in Figure 16 and Figure 18 apply to different application functions
in the HPLMN and VPLMN

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2.2


Network elements

The following new network elements are introduced for LTE/EPC:

. Mobility Management Entity (MME)
is the control plane (C-plane) functional element in EPC. The MME manages and
stores UE context, generates temporary identities and allocates them to UEs,
authenticates the user, manages mobility and bearers, and is the termination point
for Non-Access Stratum (NAS) signaling.

. Serving Gateway (S-GW)
is the user plane (U-plane) gateway to the E-UTRAN. The S-GW serves as an
anchor point both for inter-eNB handover and for intra-3GPP mobility (i.e. handover
to and from 2G or 3G. It is also responsible for packet forwarding, routing, and buffering
of downlink data for UEs that are in LTE-IDLE state.

. Packet Data Network Gateway (P-GW)
is the user plane (U-plane) gateway to the PDN (e.g. the Internet or the operator\'s
IP Multimedia Subsystem (IMS)). The P-GW is responsible for policy enforcement,
charging support, and user\'s IP address allocation. It also serves as a mobility
anchor point for non-3GPP access.

. Evolved NodeB (eNB)
is the only node within E-UTRAN providing the air interface to UE.
The eNB is responsible for radio transmission to and reception from UE. This
involves providing functionality for management of the radio resources (including
admission control), radio bearer control, scheduling of user data, and control signaling
over the air interface. Additionally, eNB performs ciphering and header compression
over the air interface.

The legacy network elements of interest to LTE/EPC are the following:

. Serving GPRS Support Node (SGSN)
is responsible for the transfer of packet data between the Core Network and the
legacy 2G/3G RAN. For LTE/EPC this node is only of interest from the perspective
of inter-system mobility management.

. Home Subscriber Server (HSS)
is the IMS Core Network entity responsible for managing user profiles, performing
the authentication and authorization of users. The user profiles managed by HSS
consist of subscription and security information as well as details on the physical
location of the user.

. Policy Charging and Rules Function (PCRF)
is responsible for brokering QoS policy as well as on the and charging policy applied
on a per-flow basis.

. Authentication, Authorization and Accounting function (AAA)
is responsible for relaying authentication and authorization information to and from
non-3GPP access network connected to EPC.

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Network architecture

2.3 Reference points
The EPS reference points as specified in [TS36.300], [TS23.401] and [TS23.402]

include:
S1-MME Control plane reference point between E-UTRAN and MME
S1-U User plane reference point between E-UTRAN and the S-GW
X2 Control and user plane reference point between two E-UTRAN nodes
S2 Group of reference points between P-GW and non-3GPP access

network (e.g. WLAN, cdma2000), used for control and mobility support
for non-3GPP access interworking

S3
Reference point between MME and SGSN, used for user and bearer
information exchange for inter-3GPP access network mobility

Gn
Reference point between pre-release 8 SGSN and MME/P-GW

Gp
Reference point between pre-release 8 SGSN and P-GW in roaming
scenario

S4
Reference point between S-GW and release 8 SGSN, used for U plane
tunnelling and related mobility support as S GW is anchor point for
3GPP handover

S5
Reference point between S-GW and P-GW but not crossing a PLMN
boundary, used for U plane tunnelling and tunnel management and for
S-GW relocation. S5 includes both GTP and IETF variants

S6a
Reference point between MME and HSS, used for transfer of subscription
and authentication data

S6b
Reference point between P-GW and 3GPP AAA Server/proxy for
mobility related authentication and retrieval of mobility/QoS related
parameters

Gx
Reference point between P-GW and the PCRF, used to transfer QoS
policy and charging rules: Note that Gxc is reference point between SGW
and PCRF to transfer QoS policy and charging rules, if IETF variant
is utilized for S5/S8

S8
Roaming reference point between S-GW and P-GW across a PLMN
boundary, used for U-plane tunnelling and tunnel management and SGW
relocation; similar to S5

S9
Reference point between the vPCRF and the hPCRF, used to transfer
QoS policy and charging rules; similar to S7

S10
Reference point between MMEs, used for information transfer e.g.
during MME relocation

S11
Reference point between MME and S-GW, used for control information
such as EPS bearer management

S12
Reference point between S-GW and the UTRAN, used for U-plane tunnelling
when Direct Tunnel is established

S13
Reference point between MME and EIR to enable UE identity check

SGi
Reference point between P-GW and PDN, based on the UMTS Gi

STa
Reference point between trusted non-3GPP access and 3GPP AAA
Server/Proxy to carry out AAA procedures

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SWa Reference point between untrusted non-3GPP access and 3GPP AAA
Server/Proxy to carry out AAA procedures
SWd Reference point between 3GPP AAA Server and 3GPP AAA Proxy
SWx Reference point between 3GPP AAA Server and HSS for transfer of
authentication data
Rx Reference point between PCRF and AF in the PDN, based on the Rx
interface of UMTS

g There are several variants of the S2 reference point. The S2a is for trusted non3GPP
access networks and the S2b is for un-trusted ones. The S2c extends to the
UE for both types of access network. There are also multiple variants of Gx reference
point.

Gx is used for transfer of policy and charging information from PCRF to P-GW. Gxa
is used for transfer of policy and charging information from PCRF to trusted non3GPP
access. Gxc is used for transfer of policy and charging information from PCRF
to S-GW in case IETF variant of S5/S8 is utilized.


There are 3GPP (GTP) and IETF (PMIP) variants of the S5 and S8 reference points.
The protocol over the S1-U will be GTP-U.
The protocols over the S3, S4, S5 reference points are based on GTP. The protocol


used over the S5-PMIP reference point is based on Proxy Mobile IP version 6
(PMIPv6).
(link not active)
For details about the corresponding interfaces see the LTE/EPC interfaces description.

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2.4 Protocol stacks
The protocol stacks for the control and user plane of the most important reference points
of the LTE/EPC system are illustrated in the following figures:

. Radio protocol architecture
. Figure 19 Uu user plane protocol stack
. Figure 20 Uu control plane protocol stack
. EPS protocol architecture
. Figure 21 S1-U user plane protocol stack
. Figure 22 X2 user plane protocol stack
. Figure 23 S5/S8 user plane protocol stack (GTP variant)
. Figure 24 S5/S8 user plane protocol stack (IETF variant)
. Figure 25 S1-MME control plane protocol stack
. Figure 26 X2 control plane protocol stack
. Figure 27 S5/S8 control plane protocol stack (GTP variant)
. Figure 28 S5/S8 control plane protocol stack (IETF variant)
. Figure 29 S10 control plane protocol stack
. Figure 30 S11 control plane protocol stack
. Figure 31 S6a control plane protocol stack
. Figure 32 S13 control plane protocol stack
. Figure 33 SBc control plane protocol stack
. Protocol architecture for interfaces for legacy 3GPP interworking
. Figure 34 S4 user plane protocol stack
. Figure 35 S12 user plane protocol stack
. Figure 36 S3 control plane protocol stack
. Figure 37 S4 control plane protocol stack
UE

eNB

S-GW

IP
PDCP
RLC
MAC
PHY
PDCP
RLC
MAC
PHY
GTP-U
UDP
IP
L1/L2
GTP-U
UDP
IP
L1/L2
NAS
RRC
PDCP
RLC
MAC
PHY

LTE-Uu S1-U

Figure 19 Uu user plane protocol stack

UE

eNB
LTE-Uu S1-MME
RRC
PDCP
RLC
MAC
SCTP
PHY
S1-AP
L1/L2
IP
MME

NAS
S1-AP
SCTP
IP
L1/L2

Figure 20 Uu control plane protocol stack

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UE

IP
PDCP
RLC
MAC
PHY

eNB
PDCP
RLC
MAC
PHY
GTP-U
UDP
IP
L1/L2
S-GW
GTP-U
UDP
IP
L1/L2
LTE-Uu S1-U

Figure 21 S1-U user plane protocol stack

eNB

eNB


GTP-U
UDP
IP
L1/L2

GTP-U
UDP
IP
L1/L2

X2

Figure 22 X2 user plane protocol stack

S-GW

P-GW


GTP-U
UDP
IP
L1/L2

GTP-U
UDP
IP
L1/L2

S5/S8

Figure 23 S5/S8 user plane protocol stack (GTP variant)

S-GW

P-GW


Tunneling
layer
IPv4/IPv6
L1/L2

Tunneling
layer
IPv4/IPv6
L1/L2

S5/S8

Figure 24 S5/S8 user plane protocol stack (IETF variant)

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UE

NAS
RRC
PDCP
RLC
MAC
PHY

eNB
RRC
PDCP
RLC
MAC
PHY
S1-AP
SCTP
IP
L1/L2
NAS
S1-AP
SCTP
IP
L1/L2
MME
LTE-Uu S1-MME

Figure 25 S1-MME control plane protocol stack

eNB

eNB


X2-AP
SCTP
IP
L1/L2

X2-AP
SCTP
IP
L1/L2

X2

Figure 26 X2 control plane protocol stack

S-GW

P-GW


GTP-C
UDP
IP
L1/L2

GTP-C
UDP
IP
L1/L2

S5/S8

Figure 27 S5/S8 control plane protocol stack (GTP variant)

S-GW

P-GW


PMIPv6
IPv4/IPv6
L1/L2

PMIPv6
IPv4/IPv6
L1/L2

S5/S8

Figure 28 S5/S8 control plane protocol stack (IETF variant)

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MME

MME

GTP-C
UDP
IP
L1/L2


GTP-C
UDP
IP
L1/L2

S10

Figure 29 S10 control plane protocol stack

S-GW

MME


GTP-C
UDP
IP
L1/L2

GTP-C
UDP
IP
L1/L2

S11

Figure 30 S11 control plane protocol stack

MME

HSS


DIAMETER
TCP/SCTP
IP
L1/L2

DIAMETER
TCP/SCTP
IP
L1/L2

S6a

Figure 31 S6a control plane protocol stack

MME

EIR


DIAMETER
TCP/SCTP
IP
L1/L2

DIAMETER
TCP/SCTP
IP
L1/L2

S13

Figure 32 S13 control plane protocol stack

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eNB

MME

CBC

S1-AP
STCP
IP
L1/L2

SBc-AP
STCP
IP
L1/L2
S1-AP
STCP
IP
L1/L2
Interworking
SBc-AP
STCP
IP
L1/L2

S1-MME SBc

Figure 33 SBc control plane protocol stack

S-GW

SGSN


GTP-U
UDP
IP
L1/L2

GTP-U
UDP
IP
L1/L2

S4

Figure 34 S4 user plane protocol stack

S-GW

UTRAN


GTP-U
UDP
IP
L1/L2

GTP-U
UDP
IP
L1/L2

S12

Figure 35 S12 user plane protocol stack

MME

SGSN


GTP-C
UDP
IP
L1/L2

GTP-C
UDP
IP
L1/L2

S3

Figure 36 S3 control plane protocol stack

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S-GW

SGSN

GTP-C
UDP
IP
L1/L2


GTP-C
UDP
IP
L1/L2

S4

Figure 37 S4 control plane protocol stack

2.5 LTE architecture
The Nokia Siemens Networks Long Term Evolution (LTE) architecture is compliant with

3GPP specification [TS 36.300].
The LTE performs the following key functions in the operator LTE RAN network (see
eNB functionality):


. handling terminals compliant to 3GPP
. managing radio resources
2.5.1 LTE overview
The LTE network architecture is composed of only one network element which provides
the air interface to UE. eNBs can be connected to each other via the X2 interface and
connected to MMEs and S-GWs via the S1 interface.

Functional split

The functional split between LTE RAN and Core fully implements radio functionality in
the eNB as illustrated in Figure 38. The new functionalities compared with HSPA are
Radio Link Control (RLC) Layer, Radio Resorce Control (RRC) and Packet Data Convergence
Protocol (PDCP) functionalities.

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......
..............................
..................................................
................................
............................................
............................
....................
..................................................
..............................................
......
......................
..................................
........................
......
....................................
............
....................................
........
........
....................
..........
................................
................................................
........
......
......
......
........
Figure 38 Functional split between radio access and core network

S1 flexibility

A single eNB can connect to multiple MMEs and multiple S-GWs. This ability provides
flexibility and reliability and is referred to as S1-flex. The eNB connection options are
illustrated in Figure 39.

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LTE_Uu S1

S5/S8a
S1-U
S10
EUTRAN EPC
eNB
eNB
S11
S1-MME
S10
S11
S11
S1-U
S1-MME
P-GW
X2
X2
MME
S-GW
eNB
MME
S-GW
Figure 39 E-UTRAN and EPC with S1-flex

2.5.2 eNB functionality
The eNB includes the majority of the LTE system functionality. The functions are very
similar to the HSPA part of a traditional Radio Network Controller but scaled down to the
scope of one eNB. Thus the complexity and related cost of the system are minimized.

The eNB hosts the following functions:

Physical layer (L1/PHY)

. PHY procedures, e.g. power control
. Channel coding, modulation, resource element and antenna mapping, (I)FFT
Data link layer (L2)

. PDCP: IP header compression (RoHC)
. Ciphering
. RLC: RLC segmentation
. Automatic Repeat Request (ARQ)
. MAC: MAC multiplexing
. Hybrid Automatic Repeat Request (HARQ)
. Packet Scheduling
Network layer (L3)

. Radio Resource Control
. Radio Bearer Control
. Radio Admission Control
. Idle and Connected Mode Mobility Controll
. Packet Scheduling
. Inter-cell Interference Coordination
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Network architecture

2.6

2.6.1

.
Load Balancing
.
Inter-RAT RRM
.
Scheduling and transmission of
.
Paging messages
.
Broadcast information
Network related functions

.
Routing of U-plane to S-GW
.
Uplink QoS support at transport and bearer level
EPC architecture

The Nokia Siemens Networks Evolved Packet Core (EPC) architecture is compliant with

3GPP specifications [TS23.401] and [TS23.402].
The EPC performs the following key functions in the operator LTE/EPC network (see
MME functionality, S-GW functionality, P-GW fun