106767053 LTE Protocols and Procedures

8/20/2019 106767053 LTE Protocols and Procedures

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LTE Protocols and Procedures Contents

Issue 06 (2006-03-01) Huawei Proprietary and Confidential

Copyright © Huawei Technologies Co., Ltd

i

Contents

1 EPS Architecture ......................................................................................................................... 1-2

1.1 EPS Network Elements ............................................................................................ ..................................... 1-3

1.1.1 User Equipment .................. ................................................................. ................................................ 1-3

1.1.2 Evolved Node B ......................................................................................................... .......................... 1-5

1.1.3 Mobility Management Entity ............................................................................................................... 1-6

1.1.4 Serving Gateway ................................................................................................................... ............... 1-7

1.1.5 Packet Data Network - Gateway .......................................................... ................................................ 1-8

1.2 EPS Interfaces ..................................................................................................................... .......................... 1-9

1.2.1 E-UTRAN Interfaces ..................... ................................................................. ..................................... 1-9

1.2.2 EPC Interfaces ....................... .............................................................. ................................................ 1-9

1.2.3 Additional Network Elements and Interfaces ............................................................. ........................ 1-10

2 EPS Protocols ............................................................................................................................ 2-13

2.1 EPS Signaling.............................................................................................................................................. 2-14

2.2 EPS Protocols ..................................................... ................................................................. ........................ 2-15

2.2.1 NAS Functionality .................................... .............................................................. ........................... 2-15

2.2.2 NAS Concepts and Identities ............................................................... .............................................. 2-16

2.2.3 EMM and ESM .......................................................................................................... ........................ 2-18

2.2.4 NAS States and State Transitions ......................................................... .............................................. 2-20

2.2.5 Uu Interface ................................... ................................................................. ................................... 2-22

2.2.6 Uu Interface - RRC ................................................................... ......................................................... 2-23

2.2.7 Uu Interface - PDCP .......................................................................................................... ................ 2-23

2.2.8 Uu Interface - RLC ................................................................... ......................................................... 2-24

2.2.9 Uu Interface - MAC ............................................................................. .............................................. 2-25

2.2.10 Uu Interface - Physical ............................................................. ........................................................ 2-25

2.2.11 X2 Interface ........................................................ ................................................................. ............. 2-26

2.2.12 X2 Interface - X2 Application Protocol ........................ .............................................................. ..... 2-26

2.2.13 X2 Interface - Stream Control Transmission Protocol ................................................................ ..... 2-27

2.2.14 X2 Interface - GPRS Tunneling Protocol - User ................................................................ .............. 2-27

2.2.15 S1 Interface ........................................................ ................................................................. ............. 2-27

2.2.16 S1 Interface - S1 Application Protocol .......................................................... ................................... 2-28

2.2.17 S1 Interface - SCTP and GTP-U ........................................................ .............................................. 2-28

2.2.18 S11 Interface ................................................................ ................................................................ .... 2-29


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2.2.19 GPRS Tunneling Protocol version 2 - Control ......................................................... ........................ 2-29

2.2.20 S5/S8 Interface .............................................................. ................................................................. .. 2-29

2.2.21 Proxy Mobile IP ............................................................ ................................................................. .. 2-30

2.2.22 S10 Interface ...................................................... ................................................................. ............. 2-30

2.2.23 SGi Interface ...................................................... ................................................................. ............. 2-31

3 LTE/SAE Quality of Service ................................................................................................... 3-32

3.1 EPS Bearer Services and E-UTRA Radio Bearers ...................................................................................... 3-33

3.1.1 QoS in Packet Switched Networks ........................................... ......................................................... 3-33

3.1.2 LTE Bearers .............................................. ................................................................. ........................ 3-33

3.1.3 The Default EPS Bearer ................................................................................................................ ..... 3-35

3.1.4 Dedicated EPS Bearers ........................................ .............................................................. ................ 3-35

3.1.5 EPS QoS Parameters ................................................................. ......................................................... 3-35

3.2 E-UTRA Radio Bearers .................................................................................................................. ............. 3-37

3.2.1 Signaling Radio Bearers ............................................................. ........................................................ 3-37

3.2.2 Data Radio Bearers .............................................................................. .............................................. 3-37

3.2.3 Radio Bearer QoS ................................................................................ .............................................. 3-38

4 Radio Resource Control .......................................................................................................... 4-40

4.1 The RRC Layer ............................................................. ................................................................. ............. 4-41

4.1.2 Services Provided To Upper Layers ................................................................................................... 4-41

4.1.3 Services Expected From Lower Layers .................................... ......................................................... 4-41

4.2 RRC Structure ......................................................................... ............................................................... ..... 4-42

4.3 RRC States ......................................................... ................................................................. ........................ 4-42

4.3.2 Functions .............................................................. ................................................................. ............. 4-43

4.4 RRC Services ..................................................... ................................................................. ........................ 4-45

4.4.1 System Information ......................................................... .............................................................. ..... 4-45

4.4.2 Paging ................................................................. ............................................................... ................ 4-46

4.4.3 RRC Connection Establishment ........................................................... .............................................. 4-47

4.4.4 Initial Security Activation ............................................................................................................. ..... 4-48

4.4.5 RRC Connection Reconfiguration ....................... ................................................................. ............. 4-48

4.4.6 RRC Connection Re-establishment ................................................................. ................................... 4-49

4.4.7 RRC Connection Release .............................................................................................................. ..... 4-50

4.4.8 Radio Link Failure .......................................................................................... ................................... 4-50

4.4.9 Information Transfer ............................................ .............................................................. ................ 4-51

4.4.10 Measurement Configuration ................... ................................................................. ........................ 4-51

4.4.11 Handover Configuration ........................................................... ........................................................ 4-56

4.4.12 Cell Selection ..................................................... ................................................................. ............. 4-56

4.4.13 Cell Reselection ................................................. ................................................................. ............. 4-56

5 Packet Data Convergence Protocol ....................................................................................... 5-58

5.1 PDCP Operation ............................................................ ................................................................. ............. 5-59

5.1.1 Functions .............................................................. ................................................................. ............. 5-59

5.1.2 PDCP Header Compression Profiles .................................................................................................. 5-60


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5.1.3 PDCP Headers ...................................................... ................................................................. ............. 5-61

5.1.4 PDCP ROHC ........................................................ ................................................................. ............. 5-62

5.1.5 PDCP Integrity ..................................................... ................................................................. ............. 5-63

5.1.6 PDCP Ciphering .............................................................. ................................................................. .. 5-64

6 Radio Link Control and Medium Access Control ............................................................. 6-66

6.1 RLC Functions ........................................ ................................................................. ................................... 6-67

6.1.1 Services Provided to Upper Layers ................................................................. ................................... 6-67

6.1.2 Services Expected from Lower Layers ........................................................... ................................... 6-67

6.1.3 Functions .............................................................. ................................................................. ............. 6-67

6.2 RLC Modes and Formatting ................................................................ ........................................................ 6-68

6.2.1 Transparent Mode ................................................ ................................................................. ............. 6-68

6.2.2 Unacknowledged Mode ....................................... .............................................................. ................ 6-68

6.2.3 Acknowledged Mode ...................................................... .............................................................. ..... 6-69

6.2.4 TMD PDU ............................................................ ................................................................. ............. 6-70

6.2.5 UMD PDU ................................................................................................................. ........................ 6-71

6.2.6 AMD PDU ................................................ ................................................................. ........................ 6-72

6.2.7 RLC Timers .......................................................... ................................................................. ............. 6-75

6.2.8 Configurable Parameters ............................................................ ........................................................ 6-75

6.3 MAC Functions ............................................................. ................................................................. ............. 6-75

6.4 MAC Architecture ......................................................................................... .............................................. 6-76

6.5 MAC Formatting ........................................................... ................................................................. ............. 6-77

6.5.1 MAC Headers ...................................................... ................................................................. ............. 6-77

6.5.2 MAC Subheaders ............................................................ ................................................................. .. 6-78

6.5.3 Random Access Process ............................................................. ........................................................ 6-81

7 X2/S1 Interface and Protocols ................................................................................................ 7-84

7.1 X2AP Functions and Procedures ......................................................... ........................................................ 7-85

7.1.2 Functions of the X2 Application Protocol ....................................................... ................................... 7-85

7.1.3 X2 Elementary Procedures ......................................................... ........................................................ 7-86

7.1.4 Message Formatting ........................................................................................................... ................ 7-87

7.1.5 X2 Basic Mobility Procedures - Handover Preparation ........................................................ ............. 7-88

7.1.6 X2 Load Indication .............................................. .............................................................. ................ 7-92

7.1.7 X2 Resource Status Reporting ............................................................. .............................................. 7-94

7.1.8 X2 Setup ................................................... ................................................................. ........................ 7-95

7.1.9 X2 eNB Configuration .................................................................................................................. ..... 7-96

7.2 S1AP Functions and Procedures ............. ................................................................. ................................... 7-97

7.2.1 S1AP Functions ............................................................... ................................................................. .. 7-98

7.2.2 S1AP Elementary Procedures ................... ................................................................. ........................ 7-99

7.2.3 S1 Setup ..................................................................................................................... ...................... 7-101

7.2.4 eNB and MME Configuration Update ................................................. ............................................ 7-103

7.2.5 NAS Transport .......................................................................... ....................................................... 7-103

7.2.6 Initial Context Setup ............................................ .............................................................. .............. 7-105


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7.2.7 E-RAB Establishment ................................................................................................................... ... 7-107

7.2.8 S1 Handover..................................................................................................................................... 7-109

7.2.9 Path Switch .......................................................... ................................................................. ........... 7-114

7.2.10 Handover Cancel ........................................................... ................................................................. 7-116

7.2.11 Status Transfer ............................................................... ................................................................. 7-117

7.2.12 UE Context Release ................................................................................................ ....................... 7-117

7.2.13 Reset ........................................................ ................................................................. ...................... 7-118

7.2.14 Location Reporting Control ......... ................................................................. ................................. 7-118

7.2.15 Overload ............................................................. ................................................................. ........... 7-119

7.2.16 Direct Information Transfer ................................................................................................ ........... 7-119

7.2.17 Paging ................................................................ ................................................................ ............ 7-120

7.3 User Plane GTP Functions and Procedures .............................................................. ................................. 7-120

7.3.1 GTP Tunnels ........................................................ ................................................................. ........... 7-120

7.3.2 GTPv1-U Header ...................................... ................................................................. ...................... 7-121

7.3.3 Extension Header ............................................................ ................................................................. 7-122

7.3.4 Handling of Sequence Numbers ........................................................... ............................................ 7-123

7.3.5 GTPv1-U Procedures ................................................................ ....................................................... 7-123

7.3.6 Path Management ............................................................ ................................................................. 7-123

7.3.7 UDP header and Port Numbers ....................................................................... ................................. 7-126

8 Mobility in LTE ...................................................................................................................... 8-127

8.1 X2 Handover ...................................................... ................................................................. ...................... 8-128

8.1.1 Handover Phases ............................................................. ................................................................. 8-128

8.1.2 X2 Based Handover with Lossless PDCP ....................................................... ................................. 8-128

8.1.3 Data Forwarding .................................................. ................................................................. ........... 8-132

8.2 S1 Handover ....................................................... ................................................................. ...................... 8-133

8.2.1 Inter MME and S-GW Handover ......................................................... ............................................ 8-133

8.2.2 S1 Status Transfer ........................................................................................... ................................. 8-135

8.3 Inter RAT Handover ................................................................ ................................................................ .. 8-136

8.3.1 E-UTRAN to UTRAN Handover... ................................................................. ................................. 8-136

8.3.2 UTRAN to E-UTRAN Handover.................................................................... ................................. 8-137

9 Glossary ................................................................................................................................... 9-138


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Figures

Figure 1-1 LTE Reference Architecture ....................................... ............................................................... ....... 1-3

Figure 1-2 User Equipment Functional Elements ......................................................... ..................................... 1-4

Figure 1-3 Evolved Node B Functional Elements .............................................................................................. 1-5

Figure 1-4 MME Functional Elements ............................................................................................................... 1-7

Figure 1-5 S-GW Functional Elements ......................................................................... ..................................... 1-8

Figure 1-6 PDN-GW Functional Elements.............. ................................................................. .......................... 1-8

Figure 1-7 E-UTRAN Interfaces ...................................................................................................... .................. 1-9

Figure 1-8 EPC Architecture and Interfaces ....................................................... .............................................. 1-10

Figure 1-9 Additional Network Elements and Interfaces .............................................. ................................... 1-11

Figure 2-1 NAS and AS Control Plane ............................................................... .............................................. 2-14

Figure 2-2 NAS and AS User Plane .............................................................................. ................................... 2-15

Figure 2-3 NAS Protocol stack................................ ................................................................ ......................... 2-16

Figure 2-4 NAS Identities ............................ ................................................................. ................................... 2-17

Figure 2-5 TA and TA List ............................................................. ................................................................. .. 2-18

Figure 2-6 NAS States and State Transtions............................................................................. ........................ 2-21

Figure 2-7 Network Attach ............................................................ ................................................................. .. 2-22

Figure 2-8 Uu Interface Protocols ................................................................................. ................................... 2-23

Figure 2-9 Main RRC Functions .............................................................................................. ........................ 2-23

Figure 2-10 PDCP Functions ......................................................... .............................................................. ..... 2-24

Figure 2-11 RLC Modes and Functions .................................................. ......................................................... 2-25

Figure 2-12 Medium Access Control Functions .................................................................................. ............. 2-25

Figure 2-13 Physical Layer Functions ......................................................................................................... ..... 2-26

Figure 2-14 X2 Interface Protocols .......................................................................................... ........................ 2-26

Figure 2-15 S1 Interface Protocols ........................................................... ........................................................ 2-28

Figure 2-16 S11 Interface Protocols ............................................................................................................ ..... 2-29

Figure 2-17 S5/S8 Interface Protocols ................................................................ .............................................. 2-30


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Figure 2-18 S10 Interface Protocols ......................................................... ........................................................ 2-31

Figure 2-19 SGi Interface Protocols ......................................................... ........................................................ 2-31

Figure 3-1 QoS Packet Scheduling ........................................................... ........................................................ 3-33

Figure 3-2 LTE Bearers ............................................................................................................ ........................ 3-34

Figure 3-3 Service Data Flows ................................................................ ......................................................... 3-34

Figure 3-4 Default and Dedicated EPS Bearers ............................................................ ................................... 3-35

Figure 3-5 Signaling Radio Bearers ................................................................... .............................................. 3-37

Figure 3-6 Data Radio Bearers ................................................................................................ ......................... 3-38

Figure 3-7 E-RAB QoS Parameters to the eNB ............................................................ ................................... 3-38

Figure 3-8 E-UTRA E-RAB QoS ................................................................................................................ ..... 3-39

Figure 4-1 RRC Interaction with Lower Layers ............................................................ ................................... 4-41

Figure 4-2 eNB Structure .............................................................................................. ................................... 4-42

Figure 4-3 RRC States ........................................................ ................................................................. ............. 4-43

Figure 4-4 E-UTRA RRC State Interaction ........................................................ .............................................. 4-44

Figure 4-5 Mobility Procedures between E-UTRA and CDMA2000 ............................................................ .. 4-45

Figure 4-6 MIB and SIB1 Parameters ........................................................................... ................................... 4-45

Figure 4-7 LTE SIBs .................................... ................................................................. ................................... 4-46

Figure 4-8 RRC Paging ................................................................ ................................................................ .... 4-47

Figure 4-9 RRC Connection .......................................................... .............................................................. ..... 4-47

Figure 4-10 RRC Security Mode Command ....................................................................................... ............. 4-48

Figure 4-11 RRC Connection Reconfiguration ............................. ................................................................. .. 4-49

Figure 4-12 RRC Connection Reestablishment ............................................................. ................................... 4-50

Figure 4-13 RRC Connection Release..................... ................................................................. ........................ 4-50

Figure 4-14 Information Transfer ............................................................. ........................................................ 4-51

Figure 4-15 Measurement Configuration ................ ................................................................. ........................ 4-52

Figure 4-16 Measurement Object ............................................................. ........................................................ 4-53

Figure 4-17 Report Configuration ............................................................ ........................................................ 4-53

Figure 4-18 Periodical Reporting ................................................................................................................ ..... 4-54

Figure 4-19 Event Based Trigger (Event A3) ................................................................................................ ... 4-54

Figure 4-20 Event A3 Example ........................................................................................................ ................ 4-56

Figure 5-1 PDCP Functions ........................................................... ................................................................. .. 5-59

Figure 5-2 PDCP Data PDU for SRB ................................................................. .............................................. 5-61

Figure 5-3 User Plane PDCP Data PDU with Long PDCP SN (12 bits) .......................................................... 5-61


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Figure 5-4 User Plane PDCP Data PDU with Short PDCP SN (7 bits) ....................................................... ..... 5-62

Figure 5-5 PDCP Control PDU for PDCP Status Report ................................................................. ................ 5-62

Figure 5-6 PDCP Control PDU for Interspersed ROHC Feedback Packet .............................. ........................ 5-62

Figure 5-7 ROHC Feedback .......................................................... .............................................................. ..... 5-63

Figure 5-8 Derivation of MAC-I .............................................................................................. ........................ 5-64

Figure 5-9 Count Value ........................................................................... ......................................................... 5-64

Figure 5-10 PDCP Ciphering .................................. .............................................................. ........................... 5-64

Figure 6-1 RLC Modes ....................................................... ................................................................. ............. 6-67

Figure 6-2 Transparent Mode RLC .............. ................................................................. ................................... 6-68

Figure 6-3 Unacknowledged Mode RLC ...................................................................... ................................... 6-68

Figure 6-4 Acknowledged Mode RLC ......... ................................................................. ................................... 6-70

Figure 6-5 RLC UMD 5bit SN (No Length Indicators) ................ .............................................................. ..... 6-71

Figure 6-6 RLC UMD 10bit SN (No Length Indicators) .............. .............................................................. ..... 6-71

Figure 6-7 RLC UMD with 2 Length Indicators .............................................................................................. 6-72

Figure 6-8 RLC AMD with no Length Indicators ......................... .............................................................. ..... 6-73

Figure 6-9 RLC AMD with Odd Number of Length Indicators .................................................................. ..... 6-73

Figure 6-10 RLC AMD PDU Segment......... ................................................................. ................................... 6-74

Figure 6-11 AMD Segmentation ........................................ .............................................................. ................ 6-74

Figure 6-12 RLC Status PDU ........................................................ .............................................................. ..... 6-75

Figure 6-13 MAC Structure (UE Side).................................................... ......................................................... 6-76

Figure 6-14 MAC Header .............................................................. ................................................................. .. 6-77

Figure 6-15 MAC Subheaders ................................................................. ......................................................... 6-78

Figure 6-16 Timing Advance Parameter ............................................................. .............................................. 6-79

Figure 6-17 Short BSR and Truncated BSR MAC Control Element .............................................................. .. 6-79

Figure 6-18 Long BSR MAC Control Element ................................................................................................ 6-79

Figure 6-19 Power Control Headroom ........................................................................................................ ..... 6-80

Figure 6-20 Power Headroom Control Element ............................................................ ................................... 6-80

Figure 6-21 Random Access RRC Signaling Procedure .......................................................... ........................ 6-81

Figure 6-22 Random Access Response .............................. ................................................................. ............. 6-82

Figure 6-23 Backoff Indicator ................................................................. ......................................................... 6-83

Figure 7-1 X2 Control and User Plane ............................................................................................................. 7-85

Figure 7-2 X2 Handover Request ............................................................. ........................................................ 7-89

Figure 7-3 X2 Handover Preparation Failure ...................................................................................... ............. 7-90


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Figure 7-4 X2 SN Status Transfer ............................................................ ........................................................ 7-91

Figure 7-5 X2 UE Context Release .......................................................................................... ........................ 7-92

Figure 7-6 X2 Handover Cancel ............................................................... ........................................................ 7-92

Figure 7-7 X2 Load Indication .................................................................................................................... ..... 7-93

Figure 7-8 X2 Uplink Interference .............................................................................................................. ..... 7-93

Figure 7-9 Downlink RNTP .................................................................................................. ........................... 7-93

Figure 7-10 X2 Resource Status Request .................................................................................................... ..... 7-94

Figure 7-11 X2 Resource Status Update............................................................. .............................................. 7-95

Figure 7-12 X2 Setup Request ..................... ................................................................. ................................... 7-96

Figure 7-13 eNB Configuration Update .............................................................................................. ............. 7-97

Figure 7-14 S1 Control and User Plane .............................................................. .............................................. 7-98

Figure 7-15 S1 Setup Request .......................................................................................................... .............. 7-102

Figure 7-16 S1 Setup Response ................................................................ ...................................................... 7-102

Figure 7-17 S1 Initial UE Message .......................................................................................... ...................... 7-104

Figure 7-18 S1 Downlink and Uplink NAS Transport .................................................. ................................. 7-104

Figure 7-19 S1 Initial Context Setup Request ............................................................... ................................. 7-106

Figure 7-20 Initial Context Setup Response ................................................................................................ ... 7-107

Figure 7-21 S1 E-RAB Setup Request ............................................................... ............................................ 7-108

Figure 7-22 S1 E-RAB Setup Response ......................................................................................................... 7-108

Figure 7-23 E-RAB Release Indication .......................................................................................................... 7-109

Figure 7-24 Requirement for S1 Handover Procedures............................................................ ...................... 7-110

Figure 7-25 S1 Handover Required .......................................................... ...................................................... 7-111

Figure 7-26 S1 Handover Command ....................................................... ....................................................... 7-112

Figure 7-27 S1 Handover Request ............... ................................................................. ................................. 7-113

Figure 7-28 Handover Request Acknowledge ................................................................................................ 7-114

Figure 7-29 Handover Notify ........................................................................................................... .............. 7-114

Figure 7-30 S1 Path Switch Request ................................................................................................ .............. 7-115

Figure 7-31 Path Switch Request Acknowledge ................................................................................. ........... 7-116

Figure 7-32 Handover Cancel ....................................................... .............................................................. ... 7-116

Figure 7-33 UE Context Release .............................................................. ...................................................... 7-117

Figure 7-34 UE Context Release Request ........................................................................................... ........... 7-118

Figure 7-35 S1 Reset .......................................................... ................................................................. ........... 7-118

Figure 7-36 S1 Trace Start ............................................................. ......................................错误未定义书签


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Figure 7-37 Location Report Control ............................................................................................................. 7-119

Figure 7-38 Overload Start ............................................................ ................................................................. 7-119

Figure 7-39 Paging .................................................................................. ....................................................... 7-120

Figure 7-40 GTP Tunnel ..................................................... ................................................................. ........... 7-121

Figure 7-41 GTPv1-U Header ................................................................. ....................................................... 7-121

Figure 7-42 GTP Extension Header .............................................. .............................................................. ... 7-122

Figure 7-43 GTP Echo Procedure.................................................. .............................................................. ... 7-124

Figure 7-44 Supported Extension Headers Notification ........................................................... ...................... 7-125

Figure 7-45 End Marker Procedure .................................................................................................. .............. 7-125

Figure 8-1 Handover Phases .......................................................... .............................................................. ... 8-128

Figure 8-2 X2 Based Handover with Lossless PDCP.................... .............................................................. ... 8-129

Figure 8-3 Mobility Control Information .................................................................................................... ... 8-130

Figure 8-4 X2AP SN Status Transfer ............................................................................ ................................. 8-131

Figure 8-5 S1 Based Inter MME/S-GW Handover ............................................ ............................................ 8-133

Figure 8-6 S1 Based Inter MME/S-GW Handover Continued ............................................................ ........... 8-134

Figure 8-7 S1 Based Inter MME/S-GW Handover Continued ............................................................ ........... 8-135

Figure 8-8 E-UTRAN to UTRAN Handover ................................ ................................................................ . 8-136

Figure 8-9 E-UTRAN to UTRAN Handover Continued .......................................................... ...................... 8-137


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1-1

Tables

Table 1-1 UE Categories ..................................................... ................................................................. ............... 1-4

Table 2-1 NAS EMM and ESM Procedures ....................................................... .............................................. 2-19

Table 3-1 QCI Attributes .............................. ................................................................. ................................... 3-36

Table 5-1 Supported Header Compression Protocols and Profiles ...................................................... ............. 5-60

Table 6-1 RLC PDU Formats .................................. .............................................................. ........................... 6-70

Table 6-2 FI Field Interpretation ............................................................... ........................................................ 6-72

Table 6-3 LCID Coding for DL-SCH ....................................................................................... ........................ 6-77

Table 6-4 LCID Coding for UL-SCH ....................................................................................... ........................ 6-78

Table 6-5 Power Headroom Report Mapping ................................................................ ................................... 6-80

Table 6-6 Uplink Grant ....................................................... ................................................................. ............. 6-82

Table 7-1 Mapping between X2AP Functions and X2AP EPs ..... ............................................................... ..... 7-86

Table 7-2 Class 1 Elementary Procedures ............................................... ......................................................... 7-86

Table 7-3 S1AP Class 1 Elementary Procedures ................ ................................................................. ............. 7-99

Table 7-4 S1AP Class 2 Elementary Procedures ................ ................................................................. ........... 7-100

Table 7-5 Messages in GTP-U ................................................................. ....................................................... 7-123


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1EPS Architecture

About This Chapter

The following table lists the contents of this chapter.

Section

1.1 EPS Network Elements

1.2 EPS Interfaces


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1-3

1.1 EPS Network Elements

The term EPS (Evolved Packet System) relates to the Evolved 3GPP Packet SwitchedDomain. In contrast to the 2G and 3G networks defined by the 3GPP, LTE can be simplydivided into a flat IP based bearer network and a service enabling network. The former can be

further subdivided into the E-UTRAN (Evolved - Universal Terrestrial Radio Access Network)

and the EPC (Evolved Packet Core) where as support for service delivery lies in the IMS (IPMultimedia Subsystem). This reference architecture can be seen in Figure 1-1

Figure 1-1 LTE Reference Architecture

UEeNB

E-UTRAN EPC

S-GW

MME

PDN-GW

IMS

HSS Video ASCSCF

eNB

Whilst UMTS is based upon WCDMA technology, the 3GPP developed new specifications

for the LTE air interface based upon OFDMA (Orthogonal Frequency Division MultipleAccess) in the downlink and SC-FDMA (Single Carrier - Frequency Division Multiple Access)in the uplink. This new air interface is termed the E-UTRA (Evolved - Universal Terrestrial

Radio Access).

1.1.1 User Equipment

Like that of UMTS, the mobile device in LTE is termed the UE (User Equipment) and is

comprised of two distinct elements; the USIM (Universal Subscriber Identity Module) and the

ME (Mobile Equipment).

The ME supports a number of functional entities including:

RR (Radio Resource) - this supports both the Control Plane and User Plane and in sodoing, is responsible for all low level protocols including RRC (Radio Resource Control),

PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium

Access Control) and the PHY (Physical) Layer.

EMM (EPS Mobility Management) - is a Control Plane entity which manages themobility management states the UE can exist in; LTE Idle, LTE Active and LTE

Detached. Transactions within these states include procedures such as TAU (TrackingArea Update) and handovers.


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ESM (EPS Session Management) - is a Control Plane activity which manages theactivation, modification and deactivation of EPS bearer contexts. These can either be

default EPS bearer contexts or dedicated EPS bearer contexts.

Figure 1-2 User Equipment Functional Elements

UE

EPS Mobility & EPS

Session Management

IP Adaptation

FunctionRadio Resource

Control

Plane

User

Plane

EPS Session Management

Bearer Activation

Bearer ModificationBearer Deactivation

Radio Resource

RRC, PDCP, RLC, MAC &

PHY Layer Protocols

EPS Mobility Management

Registration

Tracking Area UpdateHandover

In terms of the Physical Layer, the capabilities of the UE may be defined in terms of thefrequencies and data rates supported. Devices may also be capable of supporting adaptive

modulation including QPSK (Quadrature Phase Shift Keying), 16QAM (16 Quadrature

Amplitude Modulation) and 64QAM (Quadrature Amplitude Modulation).

In terms of the radio spectrum, the UE is able to support several scalable channels including;1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz whilst operating in FDD (Frequency

Division Duplex) and/or TDD (Time Division Duplex). Furthermore, the UE may also

support advanced antenna features such as MIMO (Multiple Input Multiple Output).

Table 1-1 UE Categories

UE Category MaximumDownlinkData Rate

Number ofDownlinkData Streams

MaximumUplinkData Rate

Support forUplink64QAM

1 10.3Mbit/s 1 5.2Mbit/s No




5 302.8Mbit/s 4 75.4Mbit/s Yes


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1-5

1.1.2 Evolved Node B

In addition to the new air interface, a new base station has also been specified by the 3GPP

and is referred to as an eNB (Evolved Node B). These, along with their associated interfacesform the E-UTRAN and in so doing, are responsible for:

RRM (Radio Resource Management) - this involves the allocation to the UE of the physical resources on the uplink and downlink, access control and mobility control.

Date Compression - is performed in both the eNB and the UE in order to maximize the

amount of user data that can be transferred on the allocated resource. This process isundertaken by PDCP.

Data Protection - is performed at the eNB and the UE in order to encrypt and integrity

protect RRC signaling and encrypt user data on the air interface.

Routing - this involves the forwarding of Control Plane signaling to the MME and User

Plane traffic to the S-GW (Serving - Gateway).

Packet Classification and QoS Policy Enforcement - this involves the “marking” of

uplink packets based upon subscription information or local service provider policy. QoS(Quality of Service) policy enforcement is then responsible for ensuring such policy isenforced at the network edge.

Figure 1-3 Evolved Node B Functional Elements

eNB

Radio Resource

Management

DataCompression

Data ProtectionRouting

Packet

Classification

and QoS Policy

Enforcement

Security in LTE is not solely limited to encryption and integrity protection of information passing across

the air interface but instead, NAS encryption and integrity protection between the UE and MME alsotakes place. In addition, IPSec may also be used to protect user data within both the E-UTRAN and

EPC.

eNB Identities

In addition to the UE identities already discussed, there are a number of specific identitiesassociated with the eNB. These include:

TAI (Tracking Area Identity) - is a logical group of neighboring cells defined by the

service provider in which UEs in LTE Idle mode are able to move within withoutneeding to update the network. As such, it is similar to a RAI (Routing Area Identity)

used in 2G and 3G packet switched networks.

ECGI (E-UTRAN Cell Global Identifier) - is comprised of the MCC, MNC and ECI(Evolved Cell Identity), the later being coded by each service provider.


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Femto Cells

In order to improve both network coverage and capacity, the 3GPP have developed a new typeof base station to operate within the home or small business environment. Termed the HeNB(Home Evolved Node B), this network element forms part of the E-UTRAN and in so doing

supports the standard E-UTRAN interfaces. However, it must be stated that HeNBs do notsupport the X2 interface.

The architecture may include an HeNB-GW (Home Evolved Node B - Gateway) whichresides between the HeNB in the E-UTRAN and the MME / S-GW in the EPC in order toscale and support large numbers of base station deployments.

1.1.3 Mobility Management Entity

The MME is the Control Plane entity within the EPC and as such is responsible for the

following functions:

NAS Signaling and Security - this incorporates both EMM (EPS Mobility Management)

and ESM (EPS Session Management) and thus includes procedures such as TrackingArea Updates and EPS Bearer Management. The MME is also responsible for NASsecurity.

S-GW and PDN-GW Selection - upon receipt of a request from the UE to allocate a

bearer resource, the MME will select the most appropriate S-GW and PDN-GW. Thisselection criterion is based on the location of the UE in addition to current load

conditions within the network.

Tracking Area List Management and Paging - whilst in the LTE Idle state, the UE istracked by the MME to the granularity of a Tracking Area. Whilst UEs remain within the

Tracking Areas provided to them in the form of a Tracking Area List, there is norequirement for them to notify the MME. The MME is also responsible for initiating the

paging procedure. Inter MME Mobility - if a handover involves changing the point of attachment within the

EPC, it may be necessary to involve an inter MME handover. In this situation, the

serving MME will select a target MME with which to conduct this process.

Authentication - this involves interworking with the subscriber’s HSS (Home SubscriberServer) in order to obtain AAA (Access Authorization and Accounting) information with

which to authenticate the subscriber. Like that of other 3GPP system, authentication is based on AKA (Authentication and Key Agreement).


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1-7

Figure 1-4 MME Functional Elements

NAS Signaling

and Security

S-GW andPDN-GW

Selection

Tracking Area ListManagement and

Paging

Inter MME

Mobility

Authentication

MME

1.1.4 Serving Gateway

The S-GW terminates the S1-U Interface from the E-UTRAN and in so doing, provides the

following functions:

Mobility Anchor - for inter eNB handovers, the S-GW acts as an anchor point for theUser Plane. Furthermore, it also acts as an anchor for inter 3GPP handovers to legacy

networks - GPRS and UMTS.

Downlink Packet Buffering - when traffic arrives for a UE at the S-GW, it may need to be buffered in order to allow time for the MME to page the UE and for it to enter the

LTE Active state.

Packet Routing and Forwarding - traffic must be routed to the correct eNB on thedownlink and the specified PDN-GW on the uplink.

Lawful Interception - this incorporates the monitoring of VoIP (Voice over IP) and other packet services.

GTP/PMIP Support - if PMIP (Proxy Mobile IP) is used on the S5/S8 Interfaces, theS-GW must support MAG (Mobile Access Gateway) functionality. Furthermore, support

for GTP/PMIP chaining may also be required.


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Figure 1-5 S-GW Functional Elements

Mobility Anchor

Downlink

Packet

Buffering

Packet Routing

and Forwarding

Lawful

Interception

GTP/PMIP

Support

S-GW

1.1.5 Packet Data Network - GatewayThe PDN-GW is the network element which terminates the SGi Interface towards the PDN(Packet Data Network). If a UE is accessing multiple PDNs, there may be a requirement for

multiple PDN-GWs to be involved. Functions associated with the PDN-GW include:

Packet Filtering - this incorporates the deep packet inspection of IP datagrams arriving

from the PDN in order to determine which TFT (Traffic Flow Template) they are to beassociated with.

Lawful Interception - as with the S-GW, the PDN-GW may also monitor traffic as it

passes across it.

IP Address Allocation - IP addresses may be allocated to the UE by the PDN-GW. This is

included as part of the initial bearer establishment phase or when UEs roam betweendifferent access technologies.

Transport Level Packet Marking - this involves the marking of uplink and downlink

packets with the appropriate tag e.g. DSCP (Differentiated Services Code Point) basedon the QCI (QoS Class Identifier) of the associated EPS bearer.

Accounting - through interaction with a PCRF (Policy Rules and Charging Function), thePDN-GW will monitor traffic volumes and types.

Figure 1-6 PDN-GW Functional Elements

Packet Filtering

Lawful

Interception

IP Address Allocation

Transport

Level Packet

Marking

Accounting

PDN-GW


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1-9

1.2 EPS Interfaces

1.2.1 E-UTRAN Interfaces

As with all 3GPP technologies, it is the actual interfaces which are defined in terms of the protocols they support and the associated signaling messages and user traffic that traversethem. Figure 1-7 illustrates the main interfaces in the E-UTRAN.

Figure 1-7 E-UTRAN Interfaces

E-UTRAN EPC

X2

Uu

S-GW

MMEeNB

eNB

S1-MME

S1-MMES1-U

S1-U

Uu Interface

The Uu Interface supports both a Control Plane and a User plane and spans the link betweenthe UE and the eNB / HeNB. The principle Control Plane protocol is RRC (Radio Resource

Control) while the User Plane is designed to carry IP datagrams.

X2 Interface

The X2 interface interconnects two eNBs and in so doing supports both a Control Plane and

User Plane. The principle Control Plane protocol is X2AP (X2 Application Protocol).

S1 Interface

The S1 interface can be subdivided into the S1-MME interface supporting Control Plane

signaling between the eNB and the MME and the S1-U Interface supporting User Plane traffic between the eNB and the S-GW. The principle Control Plane protocol is S1AP (S1

Application Protocol).

1.2.2 EPC Interfaces

Figure 1-8 illustrates the fundamental architecture of the EPC and in so doing identifies the

key interfaces which exist between the network elements. It should be stated however that

there exists additional interfaces which link the EPC with the IMS and legacy 3GPP / Non3GPP architectures.


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Figure 1-8 EPC Architecture and Interfaces

EPC

S1-MME

S1-U

S11

S5/S8

S-GW

SGi

PDN-GW

MME

MME

S10

1.2.3 Additional Network Elements and Interfaces

In addition to the network elements, interfaces and associated protocols discussed so far, the

EPC connects with numerous other nodes and networks. These are illustrated in Figure 1-9.


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1-11

Figure 1-9 Additional Network Elements and Interfaces

EPC

S11

S5/S8

S10

MME

MME

SGSN

RNC

PCRF

HSS

EIR

S6a

S101

S2a

Gx

ePDG

S2bS103

S12

S4

S3

S13

CDMA

2000

CDMA

2000

TrustedNon 3GPPIP Access

UntrustedNon 3GPPIP Access

PDN-GW

Wn

S-GW

These include, but are not limited to the:

HSS (Home Subscriber Server) - this can be considered a “master” database within thePLMN. Although logically it is considered as one entity, the HSS in practice is made up

of several physical databases depending upon subscriber numbers and redundancyrequirements. The HSS holds variables and identities for the support, establishment and

maintenance of calls and sessions made by subscribers. It is connected to the MME via

the S6a Interface which uses the protocol Diameter.

PCRF (Policy and Charging Rules Function) - this supports functionality for policycontrol through the PDF (Policy Decision Function) and charging control through the

CRF (Charging Rules Function). As such, it provides bearer network control in terms ofQoS and the allocation of the associated charging vectors. The PCRF downloads this

information over the Gx Interface using the Diameter protocol.

ePDG (evolved Packet Data Gateway) - which is used when connecting to Untrusted

Non 3GPP IP Access networks. It provides functionality to allocate IP addresses inaddition to encapsulating / de-encapsulating IPSec (IP Security) and PMIP tunnels. Itconnects to the PDN-GW via the S2b Interface.

RNC (Radio Network Controller) - which forms part of the 3GPPs UTRAN (UniversalTerrestrial Radio Access Network), the RNC connects to the S-GW to support the

tunneling of User Plane traffic using GTP-U. The interface linking these network

elements is the S12 Interface.

SGSN (Serving GPRS Support Node) - this forms part of the 3GPPs 2G and 3G packetswitched core domain. It connects to both the MME and S-GW in order to support


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packet switched mobility and uses the GTPv2-C and GTP-U protocols respectively. TheSGSN connects to the MME via the S3 Interface and the S-GW via the S4 Interface.

EIR (Equipment Identity Register) - this database enables service providers to validate a

particular IMEI (International Mobile Equipment Identity) against stored lists. It

connects to the MME via the S13 Interface and uses the Diameter protocol for messagetransfer.


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LTE Protocols and Procedures 2 EPS Protocols



2-13

2 EPS ProtocolsAbout This Chapter

The following table lists the contents of this chapter.

Section

2.1 EPS Signaling

2.2 EPS Protocols


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2 EPS Protocols LTE Protocols and Procedures



Issue 06 (2006-03-01)

2.1 EPS Signaling

The connectivity between the UE and the EPS can be split into a Control Plane and a UserPlane. Both of these can further split into the NAS (Non Access Stratum) and AS (AccessStratum). The Access Stratum consist of the protocols and signaling involved with the

E-UTRAN, i.e. maintain both the air interface and S1 interfaces. In contrast, the Non Access

Stratum, as its name suggests, is not part of the Access Stratum and is defined as higher layersignaling and traffic (IP datagrams).

Control Plane

Figure 2-1 illustrates the concept of NAS and AS signaling, i.e. the Control Plane. It is worth

noting that the NAS signaling is effectively transparent to the E-UTRAN. Access Stratumsignaling provides a mechanism to deliver NAS signaling, as well as the lower layer signaling

required to setup, maintain and manage the connections. The X2 interfaces are also part ofthis methodology and as such it also is part of Access Stratum signaling.

Figure 2-1 NAS and AS Control Plane

UE

E-UTRAN EPC

S-GW

MME

PDN-GWeNB

Non AccessStratum

Signaling

Access

StratumSignaling

User Plane

The User Plane focuses on the delivery of IP datagrams to and from the EPC, namely the

S-GW and PDN-GW. Figure 2-2 illustrates this concept.


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2-15

Figure 2-2 NAS and AS User Plane

UE

E-UTRAN EPC

S-GW

MME

PDN-GWeNB

Non AccessStratum IP

Datagrams

AccessStratum

Transport

In the case of the User Plane the higher layer NAS is an IP datagram. This effectively is

delivered between the UE and the PDN-GW, with the eNB and S-GW acting as lower layer

relaying devices.

2.2 EPS Protocols

2.2.1 NAS Functionality

The Non Access Stratum (NAS) protocols are used for signaling exchange between the UEand the Mobility Management Entity (MME).

NAS sits on top of RRC layer in the UE and S1AP of the MME. All NAS messages are

carried by RRC and SIAP messages in radio interface and S1-MME interface respectively.

The NAS signaling is identified as EPS Mobility Management (EMM) and EPS SessionManagement (ESM).

The EMM Protocol signaling is related to UE mobility and security procedures. The ESM

protocol handles signaling related to the default and dedicated user plane bearers.


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Figure 2-3 NAS Protocol stack

RLC

MAC

PHY

PDCP

RRC

eNBUE

Uu

NAS

Non Access Stratum

RLC

MAC

PHY

PDCP

RRC

IP

L1/L2

SCTP

S1AP

IP

L1/L2

SCTP

S1AP

NAS

MME

S1

2.2.2 NAS Concepts and Identities

Tracking Area

The NAS layer makes use of Tracking Area (TA) for mobility management. The Tracking

Area is the same concept as GSM/UMTS concept of Routing Area, it is an operator definedgroup of cells. The MME is aware of the location of an attached UE at the TA or TA list level

through the TA Update procedure. The TA is typically the area within which the UE is pagedfor incoming calls.

Tracking Area Identity (TAI) is a cell configuration.

TAI = MCC + MNC + TAC, where

TAI : Tracking area identity

MCC : Mobile Country Code

MNC : Mobile Network Code

TAC : Tracking Area Code

As an operator option, there may also be MME Pool (MME Group) areas defined. An MMEPool Area is defined as an area within which a UE may be served without need to change theserving MME. An MME Pool Area is served by one or more MMEs in parallel. MME poolAreas are a collection of complete Tracking Areas. MME Pool Areas may overlap each other,

as seen in Figure 2-4


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2-17

Figure 2-4 NAS Identities

MME 1

T A 3

T A 4

T A 1

T A 2

T A 5

T A 6

T A 7

M

ME 2

MME

1

MME 1

MME 2

MME G r o u

pA

MME G

r o u pB

MME G r o u p C

P L MN

G U T I

S - T M S I

U E C on t e x t


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GUTI

The EPC uses the IMSI number as the permanent user identifier (or rather, USIM identifier).As in the legacy core Network a temporary identifier is also used, for subscriber identityconfidentiality reasons, in place of the IMSI whenever possible. The temporary identifier in

the EPS is called the Globally Unique Temporary Identity (GUTI).

The use of the GUTI is very similar to the use of the legacy TMSI (CS domain) and PTIMSI

(PS domain) numbers. There is a difference however: the GUTI explicitly links with theMME pool Area concept.

GUTI = MCC + MNC + MMEGI + MMEC + M-TMSI, where

MMEGI: MME Group Identifier (16 bit)

MMEC: MME Code (8 bit)

M-TIMSI : M- Temporary Mobile Subscriber Identity（32 bit）

The GUTI is allocated when the UE performs initial registration (Attach) with an MME. The

GUTI is then typically changed whenever the UE performs some EMM procedure, such as TAupdate. The S-TMSI is a shortened version of the GUTI that uniquely identifies the user with

an MME Group. The S-TMIS ,rather than the complete GUTI, is used within most NASmessages.

Tracking Area List

In order to avoid frequent TA updating, the MME may order the UE to keep multiple TAswhich is called TA List of a UE.

UE only updates the TA information to MME when it moves to a TA not in its TA list.

Figure 2-5 TA and TA List

TA 1

Cell 1 Cell 2 Cell 3 Cell 4

TA2

Cell 5 Cell 6 Cell 7 Cell 8

UE1 UE 2

List (TA1， TA2) List ( TA2)

2.2.3 EMM and ESM

The NAS signaling between the UE and the EPC is identified as EMM or ESM. Table 2-1

illustrates the main EMM and ESM signaling procedures.


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2-19

Table 2-1 NAS EMM and ESM Procedures

EMM Procedures ESM Procedures

Attach Default EPS Bearer Context Activation

Detach Dedicated EPS Bearer Context Activation

Tracking Area Update EPS Bearer Context Modification

Service Request EPS Bearer Context Deactivation

Extended Service Request UE Requested PDN Connectivity

GUTI Reallocation UE Requested PDN Disconnect

Authentication UE Requested Bearer Resource Allocation

Identification UE Requested Bearer Resource Modification

Security Mode Control ESM Information Request

EMM Status ESM Status

EMM Information

NAS Transport

Paging

EMM Procedures

The key EMM procedures include:

Attach - this is used by the UE to attach to an EPC (Evolved Packet Core) for packetservices in the EPS (Evolved Packet System). Note that it can be also used to attach to

non-EPS services.

Detach - this is used by the UE to detach from EPS services. In addition, it can also be

used for other procedures such as disconnecting from non-EPS services.

Tracking Area Updating - this procedure is always initiated by the UE and is used for the

various purposes. The most common include normal and periodic tracking area updating.

Service Request - this is used by the UE to get connected and establish the radio and S1

bearers when uplink user data or signaling is to be sent.

Extended Service Request - this is used by the UE to initiate a Circuit Switched fallback

call or respond to a mobile terminated Circuit Switched fallback request from thenetwork.

GUTI Reallocation - this is used to allocate a GUTI (Globally Unique TemporaryIdentifier) and optionally to provide a new TAI (Tracking Area Identity) list to a particular UE.

Authentication - this is used for AKA (Authentication and Key Agreement) between the

user and the network.

Identification - this is used by the network to request a particular UE to provide specificidentification parameters, e.g. the IMSI (International Mobile Subscriber Identity) or the

IMEI (International Mobile Equipment Identity).


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Security Mode Control - this is used to take an EPS security context into use, andinitialize and start NAS signaling security between the UE and the MME with the

corresponding NAS keys and security algorithms.

EMM Status - this is sent by the UE or by the network at any time to report certain error

conditions. EMM Information - this allows the network to provide information to the UE.

Transport of NAS messages - this is to carry SMS (Short Message Service) messages inan encapsulated form between the MME and the UE.

Paging - this is used by the network to request the establishment of a NAS signaling

connection to the UE. Is also includes the Circuit Switched Service Notification

ESM Procedures

The key ESM procedures include:

Default EPS Bearer Context Activation - this is used to establish a default EPS bearer

context between the UE and the EPC.

Dedicated EPS Bearer Context Activation - this is to establish an EPS bearer context

with specific QoS (Quality of Service) and TFT (Traffic Flow Template) between the UE

and the EPC. The dedicated EPS bearer context activation procedure is initiated by thenetwork, but may be requested by the UE by means of the UE requested bearer resource

allocation procedure.

EPS Bearer Context Modification - this is used to modify an EPS bearer context with a

specific QoS and TFT.

EPS Bearer Context Deactivation - this is used to deactivate an EPS bearer context or

disconnect from a PDN by deactivating all EPS bearer contexts to the PDN.

UE Requested PDN Connectivity - this is used by the UE to request the setup of a

default EPS bearer to a PDN.

UE Requested PDN Disconnect - this is used by the UE to request disconnection from

one PDN. The UE can initiate this procedure to disconnect from any PDN as long as it isconnected to at least one other PDN.

UE Requested Bearer Resource Allocation - this is used by the UE to request anallocation of bearer resources for a traffic flow aggregate.

UE Requested Bearer Resource Modification - this is used by the UE to request a

modification or release of bearer resources for a traffic flow aggregate or modification ofa traffic flow aggregate by replacing a packet filter.

ESM Information Request - this is used by the network to retrieve ESM information, i.e. protocol configuration options, APN (Access Point Name), or both from the UE during

the attach procedure.

ESM Status - this is used to report at any time certain error conditions detected uponreceipt of ESM protocol data.

2.2.4 NAS States and State Transitions

There are separate protocol state machines for the EMM protocol and ESM protocol.

EMM protocol state machine relates to whether the UE is properly registered in the networkor not and whether there exists an active NAS Signaling Connection between the UE and

MME or not. The ESM protocol state machine deals exclusively with the existence or not of

EPS bearers.


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2-21

EMM protocol state machine contains two sets of states: EMM states and ECM states(EPSConnection Management). The UE is either “EMM REGISTERED” OR “EMM

DEREGISTERED”, i.e. attached or not. The ECM states are only relevant in the EMM

REGISTERED state and reflect whether there is an active NAS Signaling Connectionestablished (ECM Connected) or not (ECM Idle).

The NAS signaling Connection is required for any exchange of NAS message with the

exception of the very messages that triggers the establishment of the NAS SignalingConnection itself (e.g. Attach Request or Paging).

Figure 2-6 NAS States and State Transitions

ESM ACTIVE

PDN Contents:

IP Adress， APN, QoS Paramters

S5 IP address & TEIDS11 IP address & TEID(S1-U IP address & TEID)

Data Transfer Possible when ECMconnected

One Default BearerZero, one or more Dedicated Bearer

EMM REGISTERED

MME context:IMSI, GUTI, Talist

IP address, Security association

ECM IDLENo NAS Signaling ConnectionTracking Area Updates

ECM CONNECTEDNAS Signaling Connection

Data transfer possible

NAS ConnectionRelease

NAS ConnectionEstablishment

ESM INACTIVENo PDN context

EMM DEREGISTEREDNo MME context

EPS BearerEstablishment

Last EPS BearerReleased

Attach Detach

The ESM states are quite straightforward: when at least one (default) bearer is established the

UE is in the “ESM Active” state, otherwise it is in the “ESM Inactive” state. The ESMsignaling needed to establish a bearer requires that the UE is properly registered in the

network. It therefore naturally follows that the UE must be in the EMM registered statewhenever it is ESM Active.

It also follows that there must be a NAS Signaling connection present during the ESM

signaling phase when a bearer is being established, i.e. the UE is then ECM connected.However, there is no requirement to keep the NAS Signaling Connection active for the

lifetime of the EPS bearer. Hence the UE may very well be ECM Idle while being ESM

Active. This makes sense, since the UE may be attached for days, weeks or even months onthe end.


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The NAS states (MME related states) are aligned with the RRC states (eNodeB related states).A UE in RRC Idle state is, from the MMEs point of view, in the NAS state ECM Idle. Paging

or a request from higher layers to transmit uplink data or signaling will cause a transition from

RRC Idle to RRC Connected, causing also a transition from ECM Idle to ECM Connected.This is not shown in Figure 2-6.

Figure 2-7 Network Attach

eNBUERRC CONNECTION

AUTHENTICATION

MME

EMM: EPS ATTACH REQUESTESM: PDN CONNECTIVITY REQUEST

SECURITY MODE

EMM: EPS ATTACH ACCEPT

ESM: ACTIVE DEFAULT EPSBEARER CONTEXT REQUEST

EMM: EPS ATTACH COMPLETE

ESM: ACTIVE DEFAULT EPSBEARER CONTEXT ACCEPT

Enter state

ECM_CONNECTED

Enter state

EMM_REGISTEREDESM_ACTIVE

2.2.5 Uu Interface

The Uu Interface supports both a Control Plane and a User plane and spans the link between

the UE and the eNB / HeNB. The principle Control Plane protocol is RRC in the AccessStratum and EMM (EPS Mobility Management)/ ESM (EPS Session Management) in the

Non Access Stratum. In contrast, the User Plane is designed to carry IP datagrams. However, both Control and User Planes utilize the services of the lower layers, namely PDCP (PacketData Convergence Protocol), RLC (Radio Link Control) and MAC (Medium Access Control),

as well as the PHY (Physical Layer).


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2-23

Figure 2-8 Uu Interface Protocols

RLC

MAC

PHY

PDCP

RRC

RLC

MAC

PHY

PDCP

IP

Control Plane eNBUE

Uu

User Plane

EMM and ESM Non Access Stratum

Access Stratum

2.2.6 Uu Interface - RRC

The main air interface control protocol is RRC (Radio Resource Control). For RRC messages

to be transferred between the UE and the eNB it uses the services of PDCP, RLC, MAC andPHY. Figure 2-9 identifies the main RRC functions. In summary, RRC handles all the

signaling between the UE and the E-UTRAN, with signaling between the UE and Core Network, i.e. NAS (Non Access Stratum) signaling, being carried by dedicated RRC

messages. When carrying NAS signaling, RRC does not alter the information but instead, provides the delivery mechanism.

Figure 2-9 Main RRC Functions

eNB

RLC

MAC

PHY

PDCP

RRC

NAS Signaling

System InformationPLMN and Cell Selection

Admission Control

Security Management

Cell ReselectionMeasurement Reports

Handovers and Mobility

Documents

106767053 LTE Protocols and Procedures