Sae epc from a-z

SAE / EPC
from A - Z
INACON GmbH
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Cover design by Stefan Kohler
© 1999 - 2009 INACON GmbH
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• Color Codes in Frame Formats:
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Foreword of the Publisher:
Dear Reader:
Note that this book is primarily a training document because the primary business of
INACON GmbH is the training and consulting market for mobile communications. As
such, we are proud to providing high-end training courses to many clients worldwide,
among them operators like Cingular, Mobilkom Austria, SWISSCOM, T-MOBILE or
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INACON GmbH is not one of the old-fashioned publishers. With respect to time-to-market,
form-factor, homogeneous quality over all books and most importantly with
respect to after-sales support, INACON GmbH is moving into a new direction.
Therefore, INACON GmbH does not leave you alone with your issues and this book
but we offer you to contact the author directly through e-mail (inacon@inacon.de), if
you have any questions. All our authors are employees of INACON GmbH and all of
them are proven experts in their area with usually many years of practical
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The most important assets and features of the book in front of you are:
• Extreme degree of detailed information about a certain technology.
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about virtually every parameter, timer and detail of this technology.
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experiences and real life recordings.
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virtually every page.
Finally, we again like to congratulate you to the purchase of this book and we like to
wish you success in using it during your daily work.
Sincerely,
Gunnar Heine / President & CEO of INACON GmbH

Table of Content
Table of Content
Assessment & Top Level View................................................1
1.1 Why is an Architecture Evolution necessary?...........................2
1.1.1 Integration of E-UTRAN with its new Concepts...........................3
1.1.2 Integration of Non-3GPP RAT's is sub-optimum in Rel. 7
because ..............................................................................................4
1.1.3 Therefore, legacy operators of Non-3GPP-RAT's cannot adopt
the existing 3GPP-CN-Architecture......................................................4
1.2 Important Requirements on SAE according to 3GPP...............6
1.2.1 Coexistence................................................................................7
1.2.2 Service Continuation...................................................................8
1.2.3 Better Performance.....................................................................8
1.2.4 Support of any Radio Access Technology (RAT)......................11
1.2.5 Circuit-switched fallback............................................................12
1.2.6 Management of Access Networks ............................................12
1.2.1 Comprehension Check & Exercise:
Reasons of a System Architecture Evolution?...................................14
1.3 Seamless Mobility Options and their Characteristics..............16
1.3.1 Intra-RAT Mobility.....................................................................17
1.3.2 Inter-RAT Mobility (w/o Optimizations)......................................18
1.3.3 Inter-RAT Mobility (with Optimizations).....................................18
1.4 Architecture Overview............................................................20
1.4.1 Evolved Packet Core in Context................................................20
1.4.1.1 EPC vs. EPS.................................................................................20
1.4.1.2 Non-3GPP Access Networks (trusted / non-trusted).....................21
1.4.2 Zoom into the EPS....................................................................22
1.4.2.1 Functional Overview of Core Network Elements within the EPC. .23
1.4.3 Network Elements and their Functions within the EPC.............24
1.4.3.1 Mobility Management Entity (MME)...............................................24
1.4.3.1.1 Characteristics......................................................................24
1.4.3.1.2 Identification..........................................................................24
1.4.3.1.3 Interfaces & Protocols................................................................26
1.4.3.1.4 Tasks & Functions of the MME.............................................28
1.4.3.1.4.1 NAS-Signaling towards the UE..................................................28
1.4.3.1.4.2 S1-Signaling towards the eNodeB.............................................28
1.4.3.1.4.3 S-GW and P-GW Selection........................................................30
1.4.3.1.4.4 Other Selection Functions..........................................................31
1.4.3.1.4.4 Local Breakout...........................................................................32
1.4.3.1.4.5 IMS and Local Breakout.............................................................32
1.4.3.2 Serving Gateway (S-GW)..............................................................34
1.4.3.2.2 Identification..........................................................................34
1.4.3.2.3 Interfaces & Protocols...........................................................36
© INACON GmbH 1999 - 2009. All rights reserved. Reproduction and/or unauthorized use of this material is prohibited
and will be prosecuted to the full extent of German and international laws. Version Number 2.000 - i -

SAE / EPC from A - Z
1.4.3.2.4 Tasks & Functions of the S-GW............................................38
1.4.3.2.4.1 Packet Routing / Relaying..........................................................38
1.4.3.2.4.2 Legal Interception.......................................................................38
1.4.3.2.4.3 QCI-based Packet Tagging........................................................38
1.4.3.2.4.4 Accounting..................................................................................38
1.4.3.3 PDN Gateway (P-GW or PDN-GW)..............................................40
1.4.3.3.2 Identification..........................................................................40
1.4.3.3.4 Tasks & Functions of the P-GW............................................44
1.4.3.3.4.1 UE IP Address Allocation...........................................................44
1.4.3.3.4.2 QCI-based Packet Tagging........................................................44
1.4.3.3.4.3 Policy Enforcement....................................................................44
1.4.3.3.4.5 Home Agent Function.................................................................45
1.4.3.4 enhanced Packet Data Gateway (ePDG)......................................46
1.4.3.4.2 Identification..........................................................................46
1.4.3.4.4 Tasks & Functions of the ePDG............................................50
1.4.3.4.4.1 ESP-Tunnel Mgmt towards UE's................................................50
1.4.3.4.4.2 QoS-specific Packet Tagging in UL-Direction............................50
1.4.3.4.4.4 MAG-Function for PMIPv6.........................................................50
1.4.3.5 Protocol Stack Architecture on the UE-Side .................................52
Interworking within the EPS-Architecture...........................................54
Operations Overview..............................................................57
2.1 Network Access to the EPC in case of 3GPP-RAT's..............58
2.1.1 E-UTRAN..................................................................................58
2.1.1.1 Related Network Architecture........................................................58
2.1.1.2 Related Network Elements............................................................58
2.1.1.3 Signaling and Important State Changes (EMM, ECM, ESM)........60
2.1.2 GERAN / UTRAN......................................................................62
2.1.2.1.1 Selection of EPC vs. GGSN..................................................62
2.1.2.2 Signaling Procedures (GMM/PMM, SM).......................................64
2.1.1.4 Comprehension Check & Exercise:
Relate E-UTRAN Procedures to GERAN / UTRAN Procedures...............66
2.2 Network Access in case of Non-3GPP RAT's.........................68
2.2.1 Network Discovery and Selection..............................................68
2.2.1.1 Problem Description......................................................................68
2.2.1.2 Interworking with the ANDSF........................................................70
2.2.1.3 Distinction Trusted vs. Non-Trusted Non-3GPP RAT's.................72
2.2.2 Trusted Non-3GPP RAT's.........................................................74
2.2.2.2 Signaling Procedures if EAP and PMIPv6 are used......................76
2.2.2.3 Signaling Procedures if MIPv4 is used..........................................78
2.2.3 Non-Trusted Non-3GPP RAT's.................................................80
2.2.3.2 Signaling Procedures if IKEv2 and PMIPv6 are used...................82
and will be prosecuted to the full extent of German and international laws. Version Number 2.000 - ii -

Table of Content
2.2.3.3 Signaling Procedures if IKEv2 and DSMIPv6 are used.................84
2.3 Voice Call Establishment........................................................86
2.3.1 IMS-based.................................................................................86
2.3.1.2 Signaling Procedure (SIP, SDP, DIAMETER)...............................88
2.3.2 Circuit-switched Fallback...........................................................90
2.3.2.2 Signaling Procedure for MOC........................................................92
Voice Call Establishment...........................................................................94
2.4 Macro Mobility / Inter-RAT Roaming......................................96
2.4.1 Handover E-UTRAN to Trusted Non-3GPP RAT......................96
2.4.1.2 Signaling Procedure (NBM / PMIPv6 on S2a)...............................98
2.4.2 Handover E-UTRAN to Non-Trusted Non-3GPP RAT...................100
2.4.2.1 Related Network Architecture......................................................100
2.4.1.2 Signaling Procedure (NBM / PMIPv6 on S2b).............................102
Inter-RAT Mobility....................................................................................104
Architectural Details of the EPS..........................................107
3.0 Comprehension Test & Repetition:
Network Interfaces and Protocols..............................................108
3.1 Network Layout and Important Identifiers.............................114
3.1.1 Organization of the E-UTRAN.................................................114
3.1.1.1 Tracking Areas............................................................................115
3.1.1.1.1 TAI and TAI-list...................................................................116
3.1.1.2 E-UTRAN Pool Areas..................................................................116
3.1.2 MME Pool's and MMEI............................................................116
3.1.1.3 S-GW Service Areas...................................................................118
3.1.3 Identifiers of the UE.................................................................120
3.1.3.1 M-TMSI and S-TMSI....................................................................120
3.1.3.2 GUTI............................................................................................122
3.2 Bearer Concept & QoS-Architecture in SAE.........................124
3.2.1 SAE-Bearers, Classification and Policy Enforcement.............124
3.2.2 The QoS-Profile of the SAE-Bearer........................................126
3.2.2.1 GBR - Guaranteed Bit Rate.........................................................127
3.2.2.2 MBR - Maximum Bit Rate............................................................127
3.2.2.3 AMBR - Aggregate Maximum Bit Rate........................................127
3.2.2.4 ARP - Allocation Retention Priority..............................................127
3.2.2.5 QCI-Values and their Meanings..................................................128
3.2.2.6 Mapping between Rel. 8 QoS and earlier Releases...................128
3.2.3 QoS-Architecture with Release 8...................................................130
3.2.3.1 PCRF (Policy and Charging Rules Function)..............................130
3.2.3.2 BBERF (Bearer Binding and Event Reporting Function).............130
3.2.3.3 PCEF (Policy and Charging Enforcement Function)...................130
3.2.3.4 AF (Application Function)............................................................130
3.2.3.5 SPR (Subscription Profile Repository).........................................132
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3.2.3.6 OCS (Online Charging System)..................................................132
3.2.3.7 OFCS (Offline Charging System)................................................132
3.2.4 Bearer Establishment & Authorization - Differences Rel. 8 vs
former Releases...............................................................................134
3.2.5 Relationship and Dependency among the different Bearers...136
Protocol Suite........................................................................139
4.1 The “Mainstream” Protocol Stacks.......................................140
4.1.1 Control Plane / E-UTRAN - EPC.............................................140
4.1.2 User Plane E-UTRAN – EPC (S5/S8 GTP-based)..................142
4.1.3 User Plane E-UTRAN – EPC (S5/S8 PMIPv6/GRE-based)....144
4.2 Generic Protocols within the EPC-Environment...................146
4.2.1 IPv4 and IPv6 and their Differences........................................146
4.2.1.1 Headers and IP-Address Ranges................................................146
4.2.1.2 How to obtain an IP-Address.......................................................148
4.2.1.2.1 IPv4 and DHCP..................................................................148
4.2.1.2.2 IPv6 and “Stateless Autoconfiguration”..............................150
4.2.1.2.3 Real-Life Recording: Stateless Autoconfiguration..............152
4.2.1.3 Fragmentation in IPv4 and IPv6..................................................154
4.2.2 QoS in IP-Networks.................................................................156
4.2.2.1 DiffServ........................................................................................156
4.2.2.1.1 Details of the AF(X,Y) PHB (Assured Forwarding).............158
4.2.2.1.2 Details of the EF PHB (Expedite Forwarding)....................160
4.2.3 SCTP......................................................................................162
4.2.3.1 Important SCTP-Functions..........................................................162
4.2.3.2 Example of an SCTP-Packet.......................................................164
4.2.4 DIAMETER..............................................................................166
4.3 Protocols related to E-UTRA Networks................................168
4.3.1 EPS Mobility Management (EMM)..........................................168
4.3.1.1 Important EMM-Procedures........................................................168
4.3.1.1.1 Common Procedures..........................................................169
4.3.1.1.2 Specific Procedures............................................................169
4.3.1.1.3 Connection Management Procedures................................169
4.3.1.2 State Machine..............................................................................170
4.3.2 EPS Session Management (ESM)..........................................172
4.3.2.1 Important ESM-Procedures.........................................................172
4.3.2.1.1 MME-initiated......................................................................173
4.3.2.1.2 UE-initiated.........................................................................173
4.3.2.2 State Machine..............................................................................174
4.3.3 Radio Resource Control RRC.................................................176
4.3.3.1 Overview......................................................................................176
4.3.3.1.1 Transmission of broadcast information...............................177
4.3.3.1.2 Establish and maintain services.........................................177
4.3.3.1.3 QoS control.........................................................................177
4.3.3.1.4 Transfer of dedicated control information...........................177
4.3.3.2 State Characteristics of RRC.......................................................178
4.3.3.2.1 RRC_IDLE..........................................................................178
4.3.3.2.2 RRC_CONNECTED...........................................................178
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Table of Content
4.3.4 Packet Data Convergence Protocol (PDCP)...........................180
4.3.4.1 Overview......................................................................................180
4.3.4.1.1 RoHC..................................................................................180
4.3.4.1.2 Numbering of PDCP PDU’s................................................180
4.3.4.1.3 In-sequence delivery of PDU’s...........................................180
4.3.4.1.4 Duplicate deletion...............................................................180
4.3.4.1.5 Encryption...........................................................................181
4.3.4.1.6 Integrity Protection..............................................................181
4.3.4.2 Structure of PDCP PDU..............................................................182
4.3.5 The S1-AP Protocol................................................................184
Call Flows & Scenarios.........................................................187
5.1 Attachment through E-UTRAN / new MME..........................188
5.2 Tracking Area Update..........................................................194
5.1.1 Inter MME tracking area update..............................................194
5.1.2 Intra MME tracking area update..............................................195
5.3 PDP Context Establishment.................................................196
5.4 Inter MME Handover............................................................200
and will be prosecuted to the full extent of German and international laws. Version Number 2.000 - v -

Assessment & Top Level View
Chapter 1:
Objectives
Some of your questions that will be answered during this session…
• Why is there a system architecture evolution in the first place?
• Which improvements does SAE yield?
• What are the requirements according to 3GPP?
• Is it possible to obtain just an overview of the new architecture?
• How will the protocol architecture of a typical UE look like?
• Which potential improvements are not covered by the SAE?
1
© INACON GmbH 1999 - 2009. All rights reserved. Reproduction and/or unauthorized use of this material is prohibited - 1 -
and will be prosecuted to the full extent of German and international laws. Version Number 2.000

1.1 Why is an Architecture Evolution necessary?
1
and will be prosecuted to the full extent of German and international laws. Version Number 2.000 - 2 -

The objective of this section is to point out why there is a system
architectural evolution necessary in the first place.
[3GTS 22.278]
1.1.1 Integration of E-UTRAN with its new Concepts
• IP-centric setup
At the end of the day, E-UTRAN is only there to provide powerful IP-bearers to
the users.
Consequentially, the offering of voice services over E-UTRAN is only possible as
VoIP. This means a hard cut compared to previous 3GPP-technologies and
illustrates the reasoning behind the considerations of circuit-switched fallback.
to be continued on the next page
• Abbreviations of this Section:
CN Core Network RAT Radio Access Technology (e.g.
GERAN, UTRAN, ...)
E-UTRAN Evolved UMTS (Universal Mobile
Telecommunication System)
Terrestrial Radio Access Network
SAE System Architecture Evolution
e2e End-to-End UE User Equipment
GAN Generic Access Network UMAN Unlicensed Mobile Access Network
GERAN GSM EDGE Radio Access Network UTRAN UMTS (Universal Mobile
IP Internet Protocol (RFC 791) VoIP Voice over IP
LTE Long Term Evolution (of UMTS) WiMAX Worldwide Interoperability for
Microwave Access (IEEE 802.16)
QoS Quality of Service
1

• Low Latency Requirements
• E-UTRAN imposes specific maximum latencies to be achieved for state
changes within the E-UTRAN control plane (e.g. from RRC-idle to RRC-connected)
and, even more important, during the traversal of user data
through the user plane.
• In that respect, for the control plane state change latencies of app. 50 ms are
the target.
• User data shall be delayed by no more than 5 ms in the ideal case when
traversing through E-UTRAN. Note that this value does not take into
account latencies within the EPC or beyond!"Packet-switched only"
requires a serious QoS-integration with respect to e2e-integration and
service differentiation
The full-scale integration of QoS is a precondition for the operation of any carrier-grade
services over E-UTRAN. If different services of the same or different users
cannot be distinguished and differently treated, based e.g. on their latency
requirements, then E-UTRAN will probably fail.
• Amendment of network controlled bearer management -> instead of UE-managed
only as in Rel. 6
This important change relieves the UE from the responsibility to request the
establishment of real-time bearers and allows the network, esp the PCRF to take
care of this function.
1.1.2 Integration of Non-3GPP RAT's is sub-optimum in Rel. 7 because ...
• Mobility between 3GPP-RAT and Non-3GPP-RAT does almost not exist
At the current time, the major difference between former approaches (Rel. 6 ) and
SAE with respect to macro-mobility, is the definition of so called optimized
handover procedures for certain access network combinations (cdma2000 <=> E-UTRAN).
Without optimization, at the current time SAE pretty much relies on the capability
of the UE to operate two simultaneous radio links to enable seamless roaming
between different access network types (e.g. WiFi => cdma2000)
• In Rel. 6 and 7, non-3GPP-RAT's are conceptually treated as "alien"
technologies to be amended to existing 3GPP-RAT's
There is no possibility in Rel 6 and 7 to consider specifics of foreign access
networks when interconnecting them to a 3GPP-network. Therefore, this
interconnection is merely done on AAA-level with a transparent IPsec-tunnel
between the UE and through that access network towards the 3GPP-network.
1.1.3 Therefore, legacy operators of Non-3GPP-RAT's cannot adopt the existing
3GPP-CN-Architecture
• Which is very critical for those operators who want to adopt LTE / E-UTRAN
in addition to their already existing Non-3GPP-RAT's (e.g. cdma2000 /
WiMAX)
Consider an operator who has no 3GPP-access networks in operation at this time
but who intends to use LTE (E-UTRAN) in the future. Without an evolved system
architecture those operators would have to operate two core networks in parallel;
one for E-UTRAN and the other one for their legacy access networks. This in turn
is not feasible because of the high OPEX.
1

• Which would be quite beneficial as 3GPP provides proven "off-the-shelf"
solutions
The number of 3GPP core networks exceeds by far any other implementation in
the market. Their price and stability prospers quite a bit from the related volume
of scales effects.
The other possibility has clearly been shown during recent years in the WiMAX-area:
The IEEE had only defined the air interface and therefore, a core network
and all protocols and procedures were missing. It was finally the WiMAX-forum
that jumped in and filled out those gaps but it took years and a considerable
expenses which have to be settled among less shoulders.
Room for your Notes:
AAA Authentication, Authorization and
Accounting
PCRF Policy and Charging Rules Function
(3GTS 23.203)
e2e End-to-End RAT Radio Access Technology (e.g.
GERAN, UTRAN, ...)
EPC Evolved Packet Core (3GTS 23.401)
(Rel. 8 onwards)
RRC Radio Resource Control
IEEE Institute of Electrical and Electronics
Engineers
IPsec Internet Protocol / secure (RFC
4301)
UE User Equipment
LTE Long Term Evolution (of UMTS) UTRAN UMTS (Universal Mobile
OPEX Operational Expenditure WiFi Wireless Fidelity (www.wi-fi.org)
WiMAX Worldwide Interoperability for
1

1.2 Important Requirements on SAE according to 3GPP
The objective of this section is to start the listing of requirements on SAE as
stated by 3GPP.
1

1.2.1 Coexistence
• With legacy architectures
We will illustrate that the SAE-core architecture is suited to interconnect to all
kinds of other network architectures.
• Equal Support of IPv4and IPv6
The majority of the UE's will probably support both, IPv4 and IPv6.
DL Downlink QoS Quality of Service
RAT Radio Access Technology (e.g.
GERAN, UTRAN, ...)
GSM Global System for Mobile
Communication
I-WLAN Interworking WLAN (Wireless Local
Area Network) (3GTS 23.234)
UE User Equipment
IPv4 Internet Protocol (version 4) UTRAN UMTS (Universal Mobile
IPv6 Internet Protocol (version 6) WLAN Wireless Local Area Network (IEEE
802.11)
1

1.2.2 Service Continuation
• Upon Change of RAT
The indicated interruption time appears to be rather high and unsuitable for real-time
services.
• Upon Change between circuit-switched and packet-switched radio access
This requirement relates particularly to the VCC feature as specified in 3GTS
23.206 and 3GTS 24.206.
1.2.3 Better Performance
• Lower latency
• Process higher data rates
• Better security
• QoS and service differentiation
[3GTS 22.278 (8), 3GTR 23.882]
1

3GTR 3rd Generation Technical Report RAT Radio Access Technology (e.g.
GERAN, UTRAN, ...)
3GTS 3rd Generation Technical
Specification
VCC Voice Call Continuity (3GTS 23.206)
1

1.2 Important Requirements on SAE according to 3GPP
The objective of this section is to continue the listing of requirements on SAE
as stated by 3GPP.
1

1.2.4 Support of any Radio Access Technology (RAT)
• Existing and future
• 3GPP and non-3GPP
• Trusted and non-trusted
This distinction is new with SAE whereas in prior releases every non-3GPP
access network was considered as “non-trusted”. We will elaborate further later in
this book.
3GPP Third Generation Partnership Project
(Collaboration between different
standardization organizations (e.g.
ARIB, ETSI) to define advanced
mobile communications standards,
responsible for UMTS)
NSP Network Service Provider
ANDSF Access Network Discovery and
Selection Function (3GTS 24.302)
GERAN, UTRAN, ...)
BS Base Station (IEEE 802.16) SAE System Architecture Evolution
UTRAN UMTS (Universal Mobile
EPS Evolved Packet Switched WiMAX Worldwide Interoperability for
GERAN GSM EDGE Radio Access Network
1

1.2.5 Circuit-switched fallback
• In that case, the UE performs a combined attach through E-UTRAN to the EPC
and the EPC updates the circuit-switched core network of the 2G/3G radio
resources.
• This way, the UE can remain reachable for incoming voice calls and will be paged
by the EPC.
• Likewise, the UE can establish mobile originating sessions. More details will be
provided later
[3GTS 23.272].
1.2.6 Management of Access Networks
• ANDSF
More details about the ANDSF will be provided later.
• Access network sharing
• Access network sharing has been introduced to 3GPP with Rel. 6 [3GTS
23.251]. It enables a network operator to share their access network
resources with other network operators who only need to deploy core
network portions.
• Which parts of the core network need to be deployed depends on whether
the MOCN or GWCN configuration for access network sharing has been
selected.
• However, for the LTE/SAE-case, only the MOCN option makes sense and
can be deployed.
[3GTS 23.882 (7.17.1)]
• Load sharing among access networks
• Auto configuration
The term “cells” includes femto cells which in turn may be also used as home base
stations.
[3GTS 22.278 (Annex A)]
1

3G 3rd Generation ... GWCN GateWay Core Network configuration
LTE Long Term Evolution (of UMTS)
Specification
MOCN Multi-Operator Core Network
UE User Equipment
(Rel. 8 onwards)
1

Reasons of a System Architecture Evolution?
Question No 1: Please state the three most important characteristics of the
envisaged system architecture compared to today's technology and architecture
from your perspective.
1

1

1.3 Seamless Mobility Options and their Characteristics
The objectives of this section are to illustrate the different variations of
mobility and how they are implemented as part of the SAE.
Key points of this section are that:
1. Which mobility options are supported by a UE is communicated through
the UE mobility capabilities [3GTS 24.302 (8.2.1.1)].
2. Inter-RAT mobility involves a considerable transition and interruption time,
if there are no specific optimizations in place and if the UE cannot operate
two radio links simultaneously.
Image Description
• The image depicts two overlapping rectangles, one red and the other one yellow.
• The red rectangle represents intra-RAT mobility in idle mode (without radio link)
as well as in connected mode (radio link exists).
• Similarly, the yellow rectangle shall illustrate inter-RAT mobility in idle mode
(without radio link) as well as in connected mode (radio link exists).
1

• The area in the middle of both rectangles (joined area) indicates the special case
of optimized inter-RAT mobility procedures.
[3GTS 23.402 (4.1.3)]
1.3.1 Intra-RAT Mobility
• Intra-RAT mobility is always provided through technology-specific procedures.
• For instance, the GSM recommendations describe precisely the tasks of the
mobile station and the network to enable the seamless mobility of the mobile
station in idle and dedicated mode.
• Intra-RAT mobility is frequently called micro-mobility.
DSMIPv6 Dual Stack Mobile IPv6 PMIPv6 Proxy Mobile IPv6 (RFC 5213)
GERAN, UTRAN, ...)
GERAN GSM EDGE Radio Access Network SAE System Architecture Evolution
Communication
UE User Equipment
HBM Host Based Mobility UTRAN UMTS (Universal Mobile
NBM Network Based Mobility WiMAX Worldwide Interoperability for
1

1.3.2 Inter-RAT Mobility (w/o Optimizations)
• Generically, inter-RAT mobility is frequently called macro-mobility. This process
relates to the change of the radio access technology e.g. from WiFi to E-UTRAN.
• Typically, inter-RAT mobility makes use of IP-based mobility techniques like
CMIP or PMIP. CMIP represents what is referred to as HBM in the image while
PMIP relates to NBM.
Irrespective of whether HBM or NBM is applied, it is always the UE in case of
inter-RAT mobility w/o optimizations that decides autonomously which RAT is
used and whether a switch of the RAT is applicable. Therefore, the difference
between NBM and HBM is that HBM requires additional protocols in the UE and
NBM requires additional protocols in the EPC.
• If the user shall experience interruption-free services during a change of the RAT
w/o optimizations, then the UE must support the operation of two simultaneous
radio links: One with the former RAT and one with the new RAT. Only after the
latter one has been successfully established, the old radio link may be released.
1.3.3 Inter-RAT Mobility (with Optimizations)
• Optimizations always relate to additional specifications that govern mobility
related information exchange between the UE and the network.
• This information exchange typically only occurs while a radio link exists and
relates to the transfer of measurement data and handover information.
• Therefore, optimized inter-RAT mobility can only be specified individually
between two specific access network types (e.g. E-UTRAN <=> cdma2000
[3GTS 23.402 (9)] or GERAN <=> UTRAN).
• In our image we illustrated various different examples of optimized inter-RAT
mobility options all of which can be found in the orange colored overlap between
the yellow and the red rectangle.
• Optimizations lead to a considerable reduction of the transition and disruption
times during inter-RAT changes and, very importantly, they avoid that the UE is
required to operate two simultaneous radio links if these interruption times shall
be avoided.
Question No 2: Please add the aforementioned consequences to the image at the
two empty bullets.
SAE does not yet cover any mobility between GAN and E-UTRAN.
Question No 3: Which enhancements (if any) does SAE yield over Rel. 7
considering the aforementioned statements?
1

CMIP Client Mobile IP NBM Network Based Mobility
PMIP Proxy Mobile IP
(Rel. 8 onwards)
GERAN, UTRAN, ...)
GAN Generic Access Network SAE System Architecture Evolution
GERAN GSM EDGE Radio Access Network UE User Equipment
HBM Host Based Mobility UTRAN UMTS (Universal Mobile
IP Internet Protocol (RFC 791) WiFi Wireless Fidelity (www.wi-fi.org)
1

1.4 Architecture Overview
1.4.1 Evolved Packet Core in Context
The objective of this section is to depict the EPC as new network cloud in
context to the legacy and new network clouds.
Image Description
• The image is split into two parts: in the upper part, the image illustrates the legacy
network parts and clouds which already exist with 3GPP Rel. 6 and 7.
• These network parts and clouds are illustrated in gray color.
• In the lower part, the new network clouds with Rel. 8 are depicted. They have
been colorized to provide for a better distinction from the legacy network clouds.
• I-WLAN IP access from non-3GPP non-trusted access network may be achieved
either directly (lower option) or through the packet-switched core network domain
(upper option).
1.4.1.1 EPC vs. EPS
The two terms EPC and EPS can be distinguished as illustrated:
• The EPC represents the core component of the EPS.
• The EPS contains the EPC and the E-UTRAN (LTE) access network. However, it
does not contain the other access networks.
[3GTS 23.401, 3GTS 23.402]
1

1.4.1.2 Non-3GPP Access Networks (trusted / non-trusted)
• In the legacy part (gray) the image illustrates the so called non-3GPP non trusted
access networks which have been supported by 3GPP-recommendations since
Rel. 6.
• New with Rel. 8 and SAE are the so called trusted non-3GPP access networks.
Those trusted non-3GPP access networks comply to an EPC-operator's security
requirements [3GTS 33.402 (4.2)] and are therefore granted direct access to the
EPC. More details are provided in chapter 2.
Whether a non-3GPP access network is trusted or untrusted is ...
1. either pre-configured in the UE or ...
2. the UE learns the trust relationship during EAP-AKA authentication through
that access network from its home-PLMN.
3. Yet another option is that the selected access network does not at all support
EAP-AKA authentication in which case the UE determines that it camps on
an untrusted non-3GPP access network.
The major difference for the UE with respect to the trust relationship of the selected
non-3GPP access network is that in "untrusted case" the UE must establish an
IPsec-tunnel through IKEv2 with an ePDG in the EPC [3GTS 33.402 (8)].
The illustrated IPsec-tunnel through the non-3GPP trusted access network is only
necessary in case the S2c-interface is used and it comes without interface name.
AKA Authentication and key agreement
(3GTS 33.102)
IKEv2 Internet Key Exchange protocol /
version 2 (RFC 4306)
4301)
EAP Extensible Authentication Protocol
(RFC 3748)
LTE Long Term Evolution (of UMTS)
EAP-AKA Extensible Authentication Protocol
method for 3rd generation
Authentication and Key Agreement
(RFC 4187)
PLMN Public Land Mobile Network
(Rel. 8 onwards)
EPS Evolved Packet Switched UE User Equipment
I-WLAN Interworking WLAN (Wireless Local
Area Network) (3GTS 23.234)
1

1.4.2 Zoom into the EPS
The objectives of this section are to:
1.Illustrate the inner structure of the EPC and the E-UTRAN.
2. Point out the "one-to-many" nature of the interconnections within the EPS.
Image Description
• The image depicts another time the two network clouds EPC and E-UTRAN and
illustrates the physical interconnections (black lines) of the various network
elements to the two IP-backbone networks.
[3GTS 23.401 (5.3.2)]
1

1.4.2.1 Functional Overview of Core Network Elements within the EPC
• The MME or Mobility Management Entity takes care of various control plane
functions like mobility management and session management.
• The S-GW or Serving Gateway is the peer of the MME within the user plane and
its functions evolve around packet data routing and forwarding.
• The PDN-Gateway has similar functions as the Serving Gateway but it remains
the anchor during a packet data connection even if MME and S-GW. It is feasible
to assume that GGSN's will typically be upgraded into PDN-GW's.
S-GW and PDN-GW may easily be integrated into a single box in order to save
hardware and latency. A combination of MME and S-GW is probably less appealing
because the MME is a very slim hardware box.
• The ePDG is required to interconnect non-trusted non-3GPP networks to the
EPC. Its functions evolve around tunnel termination towards the UE and the non-trusted
non-3GPP access network.
MME Mobility Management Entity (3GTS
23.401) (Rel. 8 onwards)
eNB Enhanced Node B PDN Packet Data Network
(Rel. 8 onwards)
PDN-GW Packet Data Network Gateway (part
of EPC)
ePDG evolved Packet Data Gateway (3GTS
23.402)
EPS Evolved Packet Switched S-GW Serving Gateway (3GTS 23.401)
GGSN Gateway GPRS Support Node UE User Equipment
IP Internet Protocol (RFC 791) UTRAN UMTS (Universal Mobile
1

1.4.3 Network Elements and their Functions within the EPC
1.4.3.1 Mobility Management Entity (MME)
1.4.3.1.1 Characteristics
The objective of this section is to illustrate the most important characteristics
of the MME.
Image Description
• The MME is a network element that takes care of control plane tasks.
• The MME may physically be part of an SGSN or S-GW or it may be setup as a
stand-alone network element.
• MME's are typically organized in pool areas (S1Flex) to provide for load balancing
among the MME's which belong to the same pool. All eNodeB's which belong the
related E-UTRAN pool areas shall have access to the MME's belonging to this
MME-pool area(s).
[3GTS 23.002 (4.1.4.1), 3GTS 23.401 (4.4.2)]
1.4.3.1.2 Identification
• Each MME is identified by using an MME Group ID (MMEGI), and an MME Code
(MMEC). Both parameters together form the MMEI [3GTS 23003 (19.4.2.4)].
1

Specification
MMEC MME Code
MMEGI MME Group Identity
(Rel. 8 onwards)
MMEI MME Identity
GW Gateway SGSN Serving GPRS Support Node
ID Identity UTRAN UMTS (Universal Mobile
1

1.4.3.1.3 Interfaces & Protocols
The objectives of this section are to illustrate the MME, its interfaces towards
other network elements and the protocol stacks used on these interfaces.
Image Description
• The green color used for the interfaces indicates the control plane relationship of
a protocol or an interface.
[3GTS 23.401 (5.1)]
1

DIAMETER Successor of the RADIUS protocol MME Mobility Management Entity (3GTS
MSC Mobile Services Switching Center
EIR Equipment Identity Register MSC-S MSC-Server
EMM EPS Mobility Management (3GTS
24.301)
NAS Non-Access-Stratum
eNB Enhanced Node B S1-AP S1 Application Part
EPC Evolved Packet Core (3GTS
SCTP Stream Control Transmission
Protocol (RFC 2960)
ESM EPS Session Management (3GTS
24.301)
SGSN Serving GPRS Support Node
GTP GPRS Tunneling Protocol (3GTS
29.060)
TCP Transmission Control Protocol
GTP-C GTP Control Plane UDP User Datagram Protocol (RFC 768)
GW Gateway UTRAN UMTS (Universal Mobile
HSS Home Subscriber Server [3GTS
23.002]. HSS replaces the HLR
with 3GPP Rel. 5
1

1.4.3.1.4 Tasks & Functions of the MME
1.4.3.1.4.1 NAS-Signaling towards the UE
The objective of this section is to illustrate the MME as peer of the eNodeB
and the UE for different signaling tasks.
The MME and the UE use the physical resources of the LTE-Uu-interface and the
S1-interface to exchange NAS-signaling [3GTS 24.301] which relates to EMM and
ESM.
1.4.3.1.4.2 S1-Signaling towards the eNodeB
• MME and eNodeB use the S1-AP-protocol for various tasks as stated in the
image.
[3GTS 36.413]
1

Specification
24.301)
NAS Non-Access-Stratum
24.301)
S1-AP S1 Application Part
LTE Long Term Evolution (of UMTS) UE User Equipment
1

1.4.3.1.4.3 S-GW and P-GW Selection
The objective of this section is to illustrate the responsibility of the different
network elements to select specific entities inside their pools to become
responsible for a certain UE.
Image Description
• Is is the eNodeB that selects the MME out of an MME-pool.
• The selection of the S-GW is done based on O&M-constraints.
Nevertheless, if the possibility is there to select an S-GW which is integrated with
the selected P-GW, the MME shall prefer this choice.
• The selection of the P-GW is either predefined through a decision of the HSS of
the registering UE or the MME may apply route optimizing decisions, e.g. by
selecting a local P-GW in the V-PLMN in case of roaming.
The aforementioned route optimization is frequently called local breakout
[3GTS 23.882 (7.2)]
[3GTS 23.401 (4.3.8)]
1

1.4.3.1.4.4 Other Selection Functions
• In addition to the aforementioned selection functions the MME is also responsible
to select the new MME in case of a handover with MME-change.
• Besides, the MME will select the SGSN in case of inter-RAT handovers to GSM
or UMTS, if the packet-switched core network in the 2G/3G-domain supports the
IuFlex-feature.
Specification
GERAN, UTRAN, ...)
Communication
23.002]. HSS replaces the HLR with
3GPP Rel. 5
UE User Equipment
UMTS Universal Mobile Telecommunication
System
O&M Operation and Maintenance V-PLMN Visited PLMN
1

1.4.3.1.4.4 Local Breakout
The objective of this section is to explain the term "local breakout".
Key point of this section is to bear in mind that local breakout basically
relates to "route optimization" in case of roaming.
It is obvious that local breakout will save latency and bandwidth, because the blue
link to the server is essentially shorter than the red link.
1.4.3.1.4.5 IMS and Local Breakout
• Local breakout is particularly interesting in case of roaming and IMS-access.
• In that case, it may be desirable to allow the user data traffic to "breakout" locally
in the V-PLMN whereas the SIP-signaling must in any case be routed to the IMS
in the H-PLMN (according to the IMS-rules).
[3GTR 23.882 (7.2)]
1

3GTR 3rd Generation Technical Report IMS Internet Protocol Multimedia Core
Network Subsystem (Rel. 5 onwards)
IP Internet Protocol (RFC 791)
(Rel. 8 onwards)
H-PLMN Home PLMN SIP Session Initiation Protocol (RFC
3261)
3GPP Rel. 5
V-PLMN Visited PLMN
1

1.4.3.2 Serving Gateway (S-GW)
of the S-GW.
[23.002 (4.1.4.2.1), 23.401 (4.4.3.3)]
Image Description
• The S-GW represents the user plane side of the MME
• Although the S-GW is logically a separate network element from the PDN-GW ,
the two network elements may physically be integrated into a single network
element (e.g. to save on latency).
• S-GW's are typically organized into S-GW pools to provide for load balancing
among the S-GW's which belong to the same service area.
• All eNodeB's which belong the related E-UTRAN pool areas shall have access to
the S-GW's belonging to this S-GW service area.
• An S-GW has no EPS-specific identifiers and is identified by means of IP-addresses
and URL's.
1

S-GW Serving Gateway (3GTS 23.401)
EPS Evolved Packet Switched SGSN Serving GPRS Support Node
URL Uniform Resource Locator (RFC
1738)
PDN Packet Data Network UTRAN UMTS (Universal Mobile
1

The objectives of this section are to illustrate the S-GW, its interfaces
towards other network elements and the protocol stacks used on these
interfaces.
Image Description
• The green color of an interface indicates the control plane relationship of a
protocol or an interface. Likewise, orange color indicates user plane relationship.
Note that on S5 and S8 interface it is an operator choice to implement either GTP
or PMIPv6 together with GRE. Irrespective of this choice, the S-GW must support
GTP on various other interfaces like for example towards MME, eNodeB or RNC.
[3GTS 23.401 (5.1), 23.402 (5.1)]
1

DIAMETER Successor of the RADIUS protocol MME Mobility Management Entity (3GTS
(3GTS 23.203)
eNB Enhanced Node B PDN Packet Data Network
GRE Generic Routing Encapsulation
(RFC 2784)
PMIPv6 Proxy Mobile IPv6
29.060)
RNC Radio Network Controller
GTP-C GTP Control Plane S-GW Serving Gateway (3GTS 23.401)
GTP-U GTP User Plane SCTP Stream Control Transmission
Protocol (RFC 2960)
H-PLMN Home PLMN SGSN Serving GPRS Support Node
HSGW HRPD Serving Gateway (cdma2000
term)
IP Internet Protocol (RFC 791) UDP User Datagram Protocol (RFC 768)
1

1.4.3.2.4 Tasks & Functions of the S-GW
The objective of this section is to illustrate the tasks and functions of the S-GW.
1.4.3.2.4.1 Packet Routing / Relaying
1.4.3.2.4.2 Legal Interception
1.4.3.2.4.3 QCI-based Packet Tagging
When the S-GW receives IP-packets in uplink or downlink direction it will check the
related QCI-value based on the relationship of the packet to a certain service data
flow and handle the packet accordingly, e.g. relay it to the responsible GTP-tunnel or
GRE-tunnel.
1.4.3.2.4.4 Accounting
[3GTS 23.401 (4.4.3.2), 23.402 (4.3.3.2)]
1

Specification
GRE Generic Routing Encapsulation (RFC
2784)
QCI QoS Class Identifier
29.060)
S-GW Serving Gateway (3GTS 23.401)
1

1.4.3.3 PDN Gateway (P-GW or PDN-GW)
of the P-GW.
Image Description
• The home agent function is only applicable if the UE accesses the P-GW through
one of the interfaces S2a, S2b or S2c.
• A P-GW is identified by means of IP-addresses and URL's.
• In addition and by means of specific DNS-resolution, a P-GW is logically identified
through APN's which refer to a specific service (PDN-access) that a given P-GW
can provide (see section 2.1.2.1.1).
[23.002 (4.1.4.2.2), 23.401 (4.3.3.3), 23402 (4.4.3.3)]
1

APN Access Point Name (Reference to a
GGSN)
P-GW Packet Data Network Gateway (part
of EPC)
DNS Domain Name System PDN-GW Packet Data Network Gateway (part
of EPC)
IP Internet Protocol (RFC 791) UE User Equipment
URL Uniform Resource Locator (RFC
1738)
1

The objectives of this section are to illustrate the P-GW, its interfaces
interfaces.
Image Description
• The image reuses the color codes from chapter 2. The green color indicates the
control plane relationship of a protocol or an interface. Likewise, orange color
indicates user plane relationship.
• The ESP-tunnel over S2c has been established using EAP-AKA over IKEv2.
• The protocol layer “Application” comprises among others http, SIP, RTP (with
voice or video).
[3GTS 23.401 (5.1), 23.402 (5.1)]
DSMIPv6
1

Accounting
MIPv4 Mobile IP Version 4
DIAMETER Successor of the RADIUS protocol NAT Network Address Translation (RFC
1631)
DSMIPv6 Dual Stack Mobile IPv6 P-GW Packet Data Network Gateway (part
of EPC)
(RFC 4187)
(3GTS 23.203)
(Rel. 8 onwards)
ESP Encapsulating Security Payload
(RFC 4303)
PMIPv6 Proxy Mobile IPv6 (RFC 5213)
2784)
RTP Real-time Transport Protocol (RFC
3550, RFC 3551)
29.060)
Protocol (RFC 2960)
GTP-C GTP Control Plane SGi Reference Point in LTE
GTP-U GTP User Plane SIP Session Initiation Protocol (RFC
3261)
IMS Internet Protocol Multimedia Core
Network Subsystem (Rel. 5
onwards)
UDP User Datagram Protocol (RFC 768)
IPv4 Internet Protocol (version 4) V-PLMN Visited PLMN
1

1.4.3.3.4 Tasks & Functions of the P-GW
The objective of this section is to present the tasks and functions of the P-GW.
1.4.3.3.4.1 UE IP Address Allocation
1.4.3.3.4.2 QCI-based Packet Tagging
• The P-GW performs this task as part of the classification and according to the
installed QoS-policy.
• Based on the installed DL-TFT, the QCI is determined and traffic handling rules
are determined.
1.4.3.3.4.3 Policy Enforcement
• Traffic shaping: Delay data packet transmission until resources become available.
• Traffic policing: Discard packet if no resources to transmit them are available.
1

Question No 4: Why does the P-GW perform legal interception and the S-GW and,
as you will see, the ePDG, too?
1.4.3.3.4.5 Home Agent Function
[3GTS 23.401 (4.4.3.3), 23.402 (4.3.3.3)]
Specification
DL Downlink QCI QoS Class Identifier
DSMIPv6 Dual Stack Mobile IPv6 QoS Quality of Service
GW Gateway S-GW Serving Gateway (3GTS 23.401)
IP Internet Protocol (RFC 791) TFT Traffic Flow Template
LMA Local Mobility Anchor (RFC 5213) UE User Equipment
of EPC)
1

1.4.3.4 enhanced Packet Data Gateway (ePDG)
of the ePDG.
Image Description
• The ePDG is an enhanced PDG as defined in Release 6. Please recall that a
PDG usually was physically broken down into two parts: one inside the GGSN
and one inside the TTG [3GTS 23.234].
• The selection of an ePDG through the UE occurs either through static
configuration or dynamically [3GTS 23.402 (4.5.4)].
• An ePDG has no EPS-specific identifiers and is identified by means of IP-addresses
and URL's.
[3GTS 23.402 (4.3.4)]
1

Specification
PDG Packet Data Gateway
EPS Evolved Packet Switched TTG Tunnel Termination Gateway
GGSN Gateway GPRS Support Node UE User Equipment
IP Internet Protocol (RFC 791) URL Uniform Resource Locator (RFC
1738)
MAG Mobile Access Gateway (RFC 5213)
1

The objectives of this section are to illustrate the ePDG, its interfaces
interfaces.
Image Description
• The image reuses the color codes from chapter 2. The green color indicates the
control plane relationship of a protocol or an interface. Likewise, orange color
indicates user plane relationship. The black lines represent physical links which
are used to piggyback the SWu-interface.
• The ESP-tunnel over S2c has been established using EAP-AKA over IKEv2.
• The Gxb-interface as depicted in the image is currently not specified.
[3GTS 23.401 (5.1), 23.402 (5.1)]
1

Accounting
2784)
AKA Authentication and key agreement
(3GTS 33.102)
DIAMETER Successor of the RADIUS protocol IP Internet Protocol (RFC 791)
(RFC 3748)
(3GTS 23.203)
(RFC 4187)
Protocol (RFC 2960)
ePDG evolved Packet Data Gateway
(3GTS 23.402)
ESP Encapsulating Security Payload
(RFC 4303)
UDP User Datagram Protocol (RFC 768)
1

1.4.3.4.4 Tasks & Functions of the ePDG
The objective of this section is to present the tasks and functions of the
ePDG.
1.4.3.4.4.1 ESP-Tunnel Mgmt towards UE's
The allocated IP-address is just relayed by the ePDG. It stems from the P-GW.
1.4.3.4.4.2 QoS-specific Packet Tagging in UL-Direction
1.4.3.4.4.4 MAG-Function for PMIPv6
[3GTS 23.402 (4.3.4)]
1

Specification
of EPC)
23.402)
ESP Encapsulating Security Payload (RFC
4303)
GW Gateway UE User Equipment
IP Internet Protocol (RFC 791) UL Uplink
MAG Mobile Access Gateway (RFC 5213)
1

1.4.3.5 Protocol Stack Architecture on the UE-Side
The objective of this section is to illustrate the protocol stack architecture of
the UE with SAE.
Key point of this section is that the UE becomes merely an IP-bearer
provider which shall pick the optimum modem under all circumstances.
1

CC Call Control PHY Physical Layer
DSMIPv6 Dual Stack Mobile IPv6 RAT Radio Access Technology (e.g.
GERAN, UTRAN, ...)
RLC Radio Link Control
24.301)
RR Radio Resource Management
24.301)
GERAN GSM EDGE Radio Access Network RTP Real-time Transport Protocol (RFC
3550, RFC 3551)
HTTP HyperText Transfer Protocol (RFC
2616)
SDP Session Description Protocol (RFC
2327, RFC 3266, RFC 3264)
4301)
SIP Session Initiation Protocol (RFC
3261)
IPv4 Internet Protocol (version 4) SMTP Simple Mail Transfer Protocol (RFC
2821)
IPv6 Internet Protocol (version 6) SRTP Secure RTP (RFC 3711)
MAC Medium Access Control TCP Transmission Control Protocol
MIPv4 Mobile IP Version 4 UDP User Datagram Protocol (RFC 768)
MM Mobility Management UE User Equipment
MSRP Message Session Relay Protocol
(draft-ietf-simple-message-sessions-
XX)
PDCP Packet Data Convergence Protocol
1

Interworking within the EPS-Architecture
The objective of this section is to illustrate how E-UTRAN and EPC inter-operate
during Internet access and during inter-eNodeB handover.
• Let us assume that the illustrated UE establishes a connection to E-UTRAN and
the EPC at time T1.
• The connection is established towards eNodeB No1 which selects MME No2 for
that session.
• The MME No2 selects the Serving Gateway No 2 for the user plane.
• Serving Gateway No2 establishes a link towards PDN-Gateway No 2.
• PDN-Gateway No 2 uses the firewall at the edge of the PLMN to relay user data
packets to the example http-server on the external IP-network.
Question No 5: Please use orange and green pens to add the EPS-specific
interfaces and their names (e.g. S5) to the image. Draw the green and orange
lines along the black lines to relate physical links to logical interfaces.
1

Question No 6: Let us assume that the UE changes the serving eNodeB at time
T2 from eNodeB No1 to eNodeB No2. In our example, the related handover
procedure shall be an X2-based handover w/o Serving-Gateway relocation
[3GTS 23.401 (5.5.1.1.2)]. Please add the related X2-interface to the image using
again the orange and green pens.
Question No 7: In the aforementioned case there was no Serving Gateway
relocation. What is your opinion under which circumstances will MME and/or
Serving Gateway be changed?
eNB Enhanced Node B MME Mobility Management Entity (3GTS
(Rel. 8 onwards)
PDN Packet Data Network
23.402)
EPS Evolved Packet Switched UE User Equipment
1

Lessons Learned / Conclusions
1

Operations Overview
Chapter 2:
Operations Overview
Objectives
Some of your questions that will be answered during this session…
• How does the network access and attachment work for the different RAT's?
• How does the UE prioritize different available access networks and access
network types?
• How can a UE which is attached to the EPC, establish a voice call?
• How does inter-RAT mobility work while the UE is attached to the EPC?
• What are the most important differences between host and network based
mobility in that respect?
2

2.1 Network Access to the EPC in case of 3GPP-RAT's
2.1.1 E-UTRAN
2.1.1.1 Related Network Architecture
The objective of this section is to indicate the network infrastructure which is
involved when a UE registered to the EPC through E-UTRAN.
Question No 8: Please draw a line around all network parts which together form
the EPS.
2.1.1.2 Related Network Elements
• The PCRF or Policy Control and Charging Rules Function replaces and combines
the PDF and the CRF which were used prior to Release 7. In that respect, the
PCRF takes care of QoS-authorization and charging rules enforcement.
• The HSS is an enhanced HLR which does not only store all subscriber data
records but which can also talk IP and DIAMETER.
2

3GPP Third Generation Partnership
Project (Collaboration between
different standardization
organizations (e.g. ARIB, ETSI) to
define advanced mobile
communications standards,
3GPP Rel. 5
Accounting
CRF Charging Rules Function MME Mobility Management Entity (3GTS
DIAMETER Successor of the RADIUS protocol PCRF Policy and Charging Rules Function
(3GTS 23.203)
PDF Policy Decision Function (Part of the
IP Multimedia Subsystem)
EPS Evolved Packet Switched PLMN Public Land Mobile Network
HLR Home Location Register QoS Quality of Service
GERAN, UTRAN, ...)
UE User Equipment
SGi Reference Point in LTE UTRAN UMTS (Universal Mobile
Operations Overview
2

2.1.1.3 Signaling and Important State Changes (EMM, ECM, ESM)
The objective of this section is to illustrate on top level how a UE attaches to
the EPC through E-UTRAN, obtains an IP-address and sets up the so called
"default EPS-bearer".
Image Description
• The image depicts the communication between UE and MME which is happening
during the initial attachment and default EPS-bearer establishment.
• In that respect, the image uses the orange background color to indicate that the
RRC- and S1-bearers are required for the related EMM-message exchange.
• On the right and left hand side, the image also depicts in half-transparent way the
related state changes of ECM, EMM and ESM.
Typically, during attachment the UE also obtains an IP-address from the EPC or
rather, to be more precise, from the PDN-GW which is behind the MME. Therefore,
the ESM-state change is piggybacked on top of the EMM-procedure attachment.
The ESM-messages are embedded into the related EMM-messages.
[3GTS 23.401 (5.3.2), 3GTS 24.301 (5.5.1)]
2

Specification
3GPP Rel. 5
ECM EPS Connection Management (3GTS
24.301)
24.301)
eNB Enhanced Node B PDN-GW Packet Data Network Gateway (part
of EPC)
(Rel. 8 onwards)
EPS Evolved Packet Switched S1-AP S1 Application Part
24.301)
UE User Equipment
29.060)
Operations Overview
2

2.1.2 GERAN / UTRAN
The objective of this section is to illustrate the network architecture which is
applied if a UE attaches to the EPC through GERAN or UTRAN.
2.1.2.1.1 Selection of EPC vs. GGSN
• The SGSN will base its decision of whether to select a route to the GGSN or to
the EPC (and consequently to a PDN-GW) on the APN which it receives from the
HSS and the UE.
Note that with Rel. 8 and the introduction of the EPC, a new format for the APN-operator
identifier has been defined:
"apn.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org" [3GTS 23.060 (19.4.2.2.3)]
• This operator identifier is typically constructed by the SGSN autonomously or
received from the HSS together with the APN-network identifier. The UE usually
only provides the APN-network identifier.
2

The optional S12-interface (user plane only) is used only if the direct tunnel
functionality [3GTS 23.060 (15.6)] is supported by the SGSN. in this case, there is
a direct data link established between RNC and Serving Gateway. Note that this
feature already existed with Rel. 7.
Question No 9: Based on which criteria does the SGSN select the way to the EPC
rather than to the GGSN?
GGSN)
MNC Mobile Network Code
(Rel. 8 onwards)
(3GTS 23.203)
GERAN GSM EDGE Radio Access Network PDN Packet Data Network
GGSN Gateway GPRS Support Node PDN-GW Packet Data Network Gateway (part
of EPC)
3GPP Rel. 5
RNC Radio Network Controller
MCC Mobile Country Code [ITU-T E.212] UE User Equipment
Operations Overview
2

2.1.2.2 Signaling Procedures (GMM/PMM, SM)
The objective of this section is to illustrate on top level how a UE attaches to
the EPC through GERAN or UTRAN, using the legacy packet-switched core
network.
The SGSN needs to perform a DNS-query to resolve the APN to either the GGSN or
to the EPC.
In case of PMIP, the related messages are PMIPv6: Proxy Binding Update and Proxy
Binding Ack [3GTS 23.402 (5.2)]
[3GTS 23.060 (6.5), (9.2.2.1A)]
The direct tunnel is established to reduce the latency within the user plane. This
direct tunnel uses the S12-interface but, as illustrated, it is optional.
2

Specification
GGSN)
DNS Domain Name System PDP Packet Data Protocol
(Rel. 8 onwards)
PMIP Proxy Mobile IP
GERAN GSM EDGE Radio Access Network PMIPv6 Proxy Mobile IPv6 (RFC 5213)
GGSN Gateway GPRS Support Node PMM Packet Mobility Management
GMM GPRS Mobility Management RNC Radio Network Controller
29.060)
GW Gateway SM Session Management (3GTS 23.060,
3GTS 24.008)
3GPP Rel. 5
UE User Equipment
MAP Mobile Application Part (3GTS
29.002)
Operations Overview
2

Relate E-UTRAN Procedures to GERAN / UTRAN Procedures
The objective of this section is to compare and relate the just described E-UTRAN
procedures to the GERAN/UTRAN procedures.
Question No 10: Please fill in the missing procedures and correspondence arrows
into the image.
2

Operations Overview
RAN Radio Access Network
GERAN GSM EDGE Radio Access Network RRC Radio Resource Control
GMM GPRS Mobility Management SM Session Management (3GTS 23.060,
3GTS 24.008)
PDP Packet Data Protocol UTRAN UMTS (Universal Mobile
PMM Packet Mobility Management
2

2.2 Network Access in case of Non-3GPP RAT's
2.2.1 Network Discovery and Selection
2.2.1.1 Problem Description
The objective of this section is to illustrate that the UE may encounter long
delays or sub-optimum service during network selection because of the
variety of access networks available
2

AP Access Point (IEEE 802.11, 802.16) RAT Radio Access Technology (e.g.
GERAN, UTRAN, ...)
BS Base Station (IEEE 802.16) UE User Equipment
BTS Base Transceiver Station UTRA UMTS (Universal Mobile
Terrestrial Radio Access
eNB Enhanced Node B WiFi Wireless Fidelity (www.wi-fi.org)
Communication
WiMAX Worldwide Interoperability for
Operations Overview
2

2.2.1.2 Interworking with the ANDSF
The objective of this section is to provide an overview as to how the UE
interacts with the ANDSF.
Key point of this section is that 3GPP uses OMA-defined protocols for the
solicited transfer of supported access network information to the UE.
The location of the UE can be conveyed most simply as CI or through GPS / A-GPS.
The trust relationship between an access network and the H-PLMN network operator
is not conveyed to the UE by the ANDSF.
[3GTS 22.278 (7.16), 3GTS 23.402 (4.8), 3GTS 24.302 (6.8)]
2

Operations Overview
H-PLMN Home PLMN
Specification
OMA Open Mobile Alliance
(http://www.openmobilealliance.org/)
CI Cell Identity UE User Equipment
GPS Global Positioning System
2

2.2.1.3 Distinction Trusted vs. Non-Trusted Non-3GPP RAT's
The objective of this section is to illustrate how the UE distinguishes between
trusted and non-trusted non-3GPP radio access networks.
Key point of this section is that a trusted non-3GPP access network must
use EAP-AKA when authenticating the UE.
The UE shall fall back to non-trusted operation if the trust relationship between the
access network and the H-PLMN network operator cannot be determined [3GTS
24.302 (6.2.4)].
Question No 11: Please add to the image the distinguishing criteria between
trusted and non-trusted non-3GPP access networks.
2

The trust relationship of an access network is ultimately decided upon by the H-PLMN
network operator.
The UE either possesses pre-configured trust relationship information or the trust
relationship between access network and H-PLMN is conveyed to the UE during the
EAP-AKA-based access authentication.
[3GTS 24.302 (4.1), (6.2)]
Specification
H-PLMN Home PLMN
Accounting
(RFC 3748)
(RFC 4187)
(Rel. 8 onwards)
GERAN, UTRAN, ...)
23.402)
UE User Equipment
Operations Overview
2

2.2.2 Trusted Non-3GPP RAT's
The objective of this section is to indicate the network infrastructure which is
involved when a UE registers to the EPC through a trusted non-3GPP
access network.
The S101- and S103-interfaces are only applicable if the trusted non-3GPP access
network is a cdma2000 network. In that case, these two interfaces are used for
handover optimization.
[3GTS 23.402 (6)]
2

Specification
Accounting
(Rel. 8 onwards)
GERAN, UTRAN, ...)
3GPP Rel. 5
UE User Equipment
Operations Overview
2

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