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Technical Note

UMTS Technical NoteBy NetTest

ABSTRACT

UMTS (Universal Mobile Telecommunication System) or 3G represents a major leapforward with expectations of faster communication and the capability of combining voiceand data in new ways, to facilitate multi-media and end-to-end broadband services. Atthe same time, UMTS represents a major challenge to vendors and mobile operatorsbecause of the technical complexity and the immense costs involved in theinfrastructure.

The UMTS Technical Note is the latest in the NetTest series of technical notes. Our aimin publishing the technical notes is to provide our customers with clear and accurateinformation on the most relevant technologies. At the same, this technical note is

intended to serve as quick reference guide for the many complex issues surroundingUMTS.

Apart from serving as a quick reference guide and important tool in the day-to-day work,the UMTS technical note also forms part of the material used in the NetTest trainingprograms.

Chapter 1 through 3 dives into the UMTS technology and describes in details thestructure, the network interfaces and protocols, as well as the network functionality, andthe signaling procedures.

Chapter 4 and 5 cover two key aspects in UMTS: security and Quality of Service.

Chapter 6 briefly outlines NetTests offerings within UMTS network monitoring andoptimization to aid our customers face the increasing challenges in a highly competitivemarket place, allowing mobile operators troubleshoot and optimize network and serviceperformance.


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UMTS Technical Note Page 2 of 83

TABLE OF CONTENTS

1. UMTS Network Overview................................................................................................................... 5

1.1 Introduction .......................................................................................................................................... 5

1.2 Standardization .................................................................................................................................... 71.3 The UMTS Releases............................................................................................................................ 7

1.4 The Services on a UMTS Network ...................................................................................................... 8

1.5 The Network Components of a UMTS Network................................................................................. 10

2. UMTS Network Interfaces and Protocols ...................................................................................... 20

2.1 Overview............................................................................................................................................ 20

2.2 General UTRAN Interface Protocols Architecture ............................................................................. 20

2.3 The UTRAN Interfaces....................................................................................................................... 24

2.4 Core Network (CN) Protocols ............................................................................................................ 33

3. UMTS Network Functionality .......................................................................................................... 37

3.1 User Equipment (UE) and Network States ........................................................................................ 37

3.2 Elementary Procedures ..................................................................................................................... 41

3.3 Mobility Management......................................................................................................................... 48

3.4 Radio Resource Management (RRM) ............................................................................................... 53

3.5 CS Service Example: Mobile Terminating (MT) Voice Call................................................................ 59

3.6 PS Service Example: MT Data Connection (Interactive)................................................................... 60

4. UMTS Security and Ciphering ........................................................................................................ 61

4.1 Security .............................................................................................................................................. 614.2 Ciphering............................................................................................................................................ 62

5. Mobile Quality of Service (QoS) ..................................................................................................... 65

5.1 Introduction ........................................................................................................................................ 65

5.2 What is Quality of Service (QoS)?..................................................................................................... 65

5.3 Mechanisms for Delivering QoS ........................................................................................................ 66

6. UMTS Testing ................................................................................................................................... 70

6.1 Hot Spot Expert Analysis Tools .......................................................................................................... 71

6.2 End-to-End Network Monitoring......................................................................................................... 73

7. Terms and Abbreviations ................................................................................................................ 75

8. Websites ........................................................................................................................................... 81

9. References........................................................................................................................................ 82


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TABLE OF FIGURES

Figure 1.1 The evolution of mobile telephony............................................................................................... 5

Figure 1.2 The relationships between GSM (2G), GPRS (2.5G) and UMTS (3G) networks. ...................... 6

Figure 1.3 The 3GPP organizations. ............................................................................................................ 7Figure 1.4 GSM/GPRS/UMTS network architecture. ................................................................................. 10

Figure 1.5 GERAN architecture...................................................................................................................11

Figure 1.6 UTRAN architecture. ................................................................................................................. 12

Figure 1.7 Serving RNC. ............................................................................................................................ 13

Figure 1.9 UMTS network architecture....................................................................................................... 14

Figure 1.10 Core network elements - CS domain. ..................................................................................... 15

Figure 1.11 The signaling gateway function. .............................................................................................. 16

Figure 1.12 Core network elements - PS domain. ..................................................................................... 16

Figure 1.13 The HSS is a superset of the HLR. ......................................................................................... 17

Figure 1.14 The IP Multimedia Subsystem................................................................................................. 18

Figure 2.1 Simplified UMTS structure showing three significant parts....................................................... 20

Figure 2.2 Three protocol stacks connecting the UE with the CN via the UTRAN..................................... 21

Figure 2.3 Control plane UE to PS Core Network (3G-SGSN). ................................................................. 22

Figure 2.4 Control plane UE to CS Core Network (MSC). ......................................................................... 22

Figure 2.5 Circuit and Packet Switched Mobility Management. ................................................................. 23

Figure 2.6 User plane UE to PS Core Network.......................................................................................... 24

Figure 2.7 User plane UE to CS Core Network.......................................................................................... 24Figure 2.8 General structure of the UTRAN interfaces. ............................................................................. 25

Figure 2.9 The Iu interface connects the UTRAN to the CN. ..................................................................... 25

Figure 2.10 The Iu-CS control plane protocol stack. .................................................................................. 26

Figure 2.11 The Iu-PS protocol stack. ........................................................................................................ 28

Figure 2.12 The Iub protocol stack. ............................................................................................................ 29

Figure 2.13 The Iur protocol stack.............................................................................................................. 30

Figure 2.14 Radio interface protocol architecture (service access points marked by circles). .................. 31

Figure 2.15 The MAP protocol stack - on the Gr interface between SGSN and HLR................................ 33

Figure 2.16 MAP services as defined in 3G TS 29.002. ............................................................................ 34

Figure 2.17 Control plane for SGSN-GGSN and SGSN-SGSN interfaces. ............................................... 35

Figure 2.18 Control plane SGSN-MSC/VLR. ............................................................................................. 35

Figure 2.19 User plane for SGSN-GGSN and SGSN-SGSN interfaces. ................................................... 36

Figure 3.1 UE and CN MM states............................................................................................................... 37

Figure 3.2 UE and CN PMM states. ........................................................................................................... 38

Figure 3.3 RRC states. ............................................................................................................................... 39

Figure 3.4 UE state overview...................................................................................................................... 40

Figure 3.5 PDP states................................................................................................................................. 40Figure 3.6 CS Paging Procedure in Iu mode.............................................................................................. 41


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Figure 3.7 CS signaling connection establishment. ................................................................................... 42

Figure 3.8 Signaling connection Release................................................................................................... 43

Figure 3.9 Authentication and security procedure. ..................................................................................... 43

Figure 3.10 CS Service Request and RAB Allocation................................................................................ 44Figure 3.11 PS Service Request and RAB Allocation. ............................................................................... 44

Figure 3.12 PS Service and RAB Release................................................................................................. 45

Figure 3.13 CS Service and Iu Release..................................................................................................... 45

Figure 3.14 CS RAB Allocation................................................................................................................... 46

Figure 3.15 PS RAB Allocation................................................................................................................... 47

Figure 3.16 RAB Release procedure.......................................................................................................... 47

Figure 3.17 Combined GPRS/IMSI Attach procedure with LU................................................................... 49

Figure 3.18 UE initiated combined GPRS/IMSI Detach procedure............................................................ 50

Figure 3.19 LA containing RAs and cells within URA................................................................................. 50

Figure 3.20 UMTS LA/RAU procedure....................................................................................................... 52

Figure 3.21 URA Update. ........................................................................................................................... 53

Figure 3.22 Cell update. ............................................................................................................................. 53

Figure 3.23 Soft handover. Adding and deleting radio resources when moving between connected RNCs.54

Figure 3.24 Soft handover. ......................................................................................................................... 54

Figure 3.25 Before and after hard handover/SRNS relocation and RAU................................................... 55

Figure 3.26 Hard handover and SRNS relocation...................................................................................... 56

Figure 3.27 UMTS to GSM Handover......................................................................................................... 56Figure 3.28 UMTS to GPRS cell relocation................................................................................................ 57

Figure 3.29 CS service: MT voice call. ....................................................................................................... 59

Figure 3.30 PS service: MT data connection (interactive).......................................................................... 60

Figure 4.1 Overview of the security architecture in Rel-4........................................................................... 61

Figure 4.2 Security between networks. ...................................................................................................... 63

Figure 5.1 QoS segments........................................................................................................................... 65

Figure 5.2 UMTS QoS architecture. ........................................................................................................... 67

Figure 5.3 QoS attributes and their usage. ................................................................................................ 67

Figure 5.4 Using traffic classes to achieve required QoS. ......................................................................... 68

Figure 5.5 UMTS QoS classes................................................................................................................... 69

Figure 6.1 Test and Measurement is the fast track to detailed information on business metrics............... 70

Figure 6.2 Test phases covered by NetTest hot spot expert analysis tools................................................ 71

Figure 6.3 The InterQuest is a powerful tool with the ability to capture large amounts of data from multiplelinks in both access and core network. ................................................................................... 71

Figure 6.6 MasterQuest is the undisputed leader in GSM and GPRS monitoring and offers the mostcomplete surveillance solution available today. MasterQuest UMTS builds on this platform. 73

Figure 6.7 MasterQuest performs network-wide correlation and monitors end-to-end service delivery

performance............................................................................................................................ 73


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1. UMTS Network Overview

1.1 IntroductionCommunication has always been essential to mankind. When two people meet, they only need their voice tocommunicate, but as the distance increases the need for tools arises. When Alexander Graham Bell invented the

telephone in 1876, a significant step was taken to enable two people to talk together, however far apart they may be that is, as long as they are near a telephone set! For more than a century wire line telephony has been the solutionfor voice communication over distance for most people. Radio based communication systems not depending on awire for network access were developed for special purposes (e.g. military, police, naval and closed car radio nets),

and eventually systems emerged allowing people to communicate via telephones with radio rather than wire lineaccess. They were primarily intended for people driving in cars and were known as mobile telephony systems.

During the early 1980s, the first generation (1G) of mobile telephone systems based on analog technology wasexperiencing rapid growth in many European countries. Each country developed its own system, each incompatiblewith the others in terms of equipment and operation. This led to a wish and a need for a common European mobile

communication system with high capacity and pan-European coverage. The latter implied that the same mobiletelephones could be used in all European countries and that incoming calls would automatically be routed to the

mobile phone independent of location (automatic roaming). In addition it was expected that one single European

market with common standards would lead to cheaper user equipment and vendor-independent network elements.Finally, the use of modern digital technology would result in smaller hand-held devices coupled with improvedfunctionality and quality.

In 1982 the CEPT (Conference of European Posts and Telegraphs) formed a study group called the Groupe Spcial

Mobile (GSM) to study and develop a pan-European public land mobile system the second generation of cellulartelephony (2G). The name of the study group - GSM - was also used for the mobile system. In 1989, GSMresponsibility was transferred from CEPT to the ETSI (European Telecommunication Standards Institute).Originally GSM was only intended for the ETSI member countries. However, many other countries have also

implemented GSM e.g. Eastern Europe, the Middle East, Asia, Africa, the Pacific Basin and North America (witha derivative of GSM called PCS1900). The name GSM now meaning the Global System for Mobile

communication is thus very appropriate.

Figure 1.1 The evolution of mobile telephony.

GSM has been around for a decade and has turned into an overwhelming success, being very widely deployed inmost parts of the world. The system is well suited for voice communication and is also extensively used for Short

Message Service (SMS) information transfer. Circuit switched data services were also covered by the GSM

specification, as the integrated wireless access to voice and data services was one of the goals for the system.However, the offered access speed (max. 9600 baud) has limited the use of the GSM system for data applications.ETSI have defined several solutions to improve the data access of the mobile network often referred to as 2.5G. Thisis to indicate that they represent a step forward compared to GSM, but these systems are still quite tightly connectedto GSM: HSCSD (High Speed Circuit Switched Data), GPRS (General Packet Radio System) and EDGE (Enhanced

Data rates for Global/GSM Evolution).

HSCSD is the simplest enhancement of the GSM system for data: Like GSM it is based on circuit switchedconnections, but a better utilization of the available bandwidth and allocation of more than one time slot perconnection allows higher data rates theoretically up to 57.6 kbps. However, the circuit switched nature of HSCSDmakes it inefficient for data traffic, as this is packet oriented.


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GPRS is designed as a packet data service with a theoretical maximum data rate of approx. 170 kbps. GPRS co-exists with the GSM network, reusing the basic structure of the access network. GPRS is an extension of GSMnetworks with data services carried on the existing radio infrastructure, while the core network is enhanced by apacket overlay with new components and interfaces. GPRS supports combined voice and data services and enables

multimedia services.

EDGE is an enhancement of the GSM/GPRS system using a new air interface modulation technique that allows thebit rate on the air interface to be increased considerably. EDGE will increase the theoretical maximum data rate to384 kbps.

Figure 1.2 The relationships between GSM (2G), GPRS (2.5G) and UMTS (3G) networks.

The UMTS (Universal Mobile Telecommunication System) third generation cellular telephony (3G) is expected

to do more than merely provide better and faster mobile communication. UMTS will also enable combination ofvoice and data services in a new way, for example facilitating multimedia and end-to-end broadband services. Insummary, UMTS will mean the following for operators and their customers:

UMTS for customers:

Worldwide wireless access using a single handset

A wide range of multimedia services with appropriate quality levels

The third generation mobile standard enables mobile users to harness the full power of the Internet through efficienthigh-speed radio transmission, optimized for multimedia communications

UMTS will make the dream of anywhere, anytime communications a reality

UMTS for the operator:

Unification of the diverse wireless access systems we see today into a flexible radio infrastructure

Evolution from earlier "legacy" systems, ensuring global economies of scale and supply while allowing:

- Plenty of scope for product and service differentiation

- Choice of radio access methods and core networks in order to flexibly implement and evolve their systems based onthe regulatory, market or business requirements for each region or country

For operators there is a huge difference in the investment required to provide a 2.5G (GPRS) compared to a 3Gsystem. 2.5G requires relatively small investments for the necessary modifications of the radio access network andadd-on equipment (a packet switched core network) on top of existing GSM networks, while UMTS requires a very

large investment, as most of the network must be created from the ground up. EDGE will also require huge

investments, as a new radio access network will be needed.


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For existing GSM operators, 2.5G technologies will be attractive as they can be implemented based on the operationlicenses operators already have, while UMTS requires new (and in several countries expensive) licenses. For usersGPRS will be a major step forward with new services, while UMTS is mainly an extension of these services. Thusthe success of GPRS and the services it offers will be an important indicator of which services will drive the success

of coming 3G UMTS networks.

1.2 StandardizationOne of the driving forces behind UMTS is the desire to create a truly universal system. This is why thestandardization work has been moved from ETSI to a new organization: Third Generation Partnership Project(3GPP) with the participation of a number of regional and national standardization organizations. Marketconsiderations are handled by an additional partnership the Market Representation Partners (MRP).

Figure 1.3 The 3GPP organizations.

The 3GPP creates a common standard based on the inputs from the participating organizations. The Operator

Harmonization Group (OHG) has been set up to find necessary compromises in the event that the 3GPP is unable toreach agreement. In addition to these bodies, the Third Generation Partnership Project Number 2 (3GPP-2) ensuresthat North American IS-95 radio technology based systems are taken into account.

Even though it is based on existing GSM/GPRS networks, UMTS adds several new components and interfaces tothe core network. The radio access network is also entirely new, based on a new technology, Wideband Code

Division Multiple Access (WCDMA) with better usage of the spectrum than todays GSM, resulting in support forhigher data rates, more capacity and subsequently, more subscribers. Eventually UMTS will cause a completerearrangement of the GSM/GPRS/UMTS core network, as all-IP technology will emerge.

1.3 The UMTS ReleasesIn the standardization of UMTS within the 3GPP, UMTS has been defined in a set of phases or releases. So farthree releases have been defined: UMTS Release 1999 (R99 sometimes also referred to as Release 3/Rel-3),UMTS Release 4 (Rel-4) and UMTS Release 5 (Rel-5). The network architectures figure in section 1.5 indicateshow the releases affect the network. The UMTS releases are the three main deliverables of approved specifications

from 3GPP.

The major headlines for each release are:

R99

Defines the UMTS Universal Terrestrial Radio Access Network (UTRAN)

The Radio Network Subsystem (RNS) is added to the existing GSM/GPRS network

The Core Network (CN) is the existing GSM/GPRS network with some enhancements

Rel-4

Rel-4 introduces Media Gateway (MGW), the Mobile Switching Center (MSC) server and the Signaling Gateway (SGW).This allows user data and signaling to be logically separated in the MSC

UTRAN enhancements that include support of even higher data rates, in local areas up to 2 Mbps


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Rel-5

IP Multimedia (IM) Subsystem (IMS) is added

The Home Location Register (HLR) is replaced by/extended to a Home Subscriber Server (HSS)

UTRAN improvements to enable efficient IP-based multimedia services in UMTS

Introduction of IubFlex (allows Radio Network Controllers (RNCs) to connect to more than one set of Node Bs)

Enhancements of Location Services (LCS)

all-IP network will eventually become a reality

Rel-5 will be based on IPv6

The above releases are in the "Frozen" state, which means that revisions are allowed if a correction is needed (i.e.new features are no longer added). A release 6 is planned and more releases are likely to follow: They may coverareas like IMS enhancements, Wireless LAN Integration (WLANI), Internet convergence (regarding protocols andservices), Multimedia Broadcast/Multicast Service (MBMS) and evolution to the network within the PacketSwitched (PS) domain only.

This note will for the most part be based on Rel-4. Other releases will however be mentioned in some cases tohighlight major differences to Rel-4.

1.4 The Services on a UMTS NetworkAs the UMTS network evolves, more and more services will be supported. With UMTS Rel-5 the mobile networkwill support services like those known from the Internet today, e.g. video streaming, Voice over IP (VoIP), videoconferencing and interactive services. The circuit switched part of the network will change and be put on top of apacket-oriented technology (most likely IP), to support higher data rates and to increase flexibility in the network.The packet switched part of the network will not change much, but a new packet domain will be added: the IPMultimedia Subsystem (IMS).

1.4.1 General Services

The basic services provided by UMTS are similar to those known from GSM and ISDN (Integrated Services DigitalNetwork). Using the ITU-T definitions, telecommunication services can be divided into bearer services,

teleservices, and supplementary services. The most basic teleservice supported by UMTS is voice telephony. Aswith all other communications, speech is digitally encoded and transmitted through the network as a digital stream.A variety of data services are offered implemented as packet switched data communication. The Short MessageService (SMS), introduced together with GSM will also be available. Supplementary services are provided on top of

teleservices e.g.:

Call Forwarding/Barring/Waiting/Hold

Three Party Service

Advice of Charge

Caller identification

Closed user groups

1.4.2 Quality of Service

One of the enhancements of 2.5G and 3G networks is the improved support of data communication. To facilitate

this, both GPRS and UMTS have introduced the concept of Quality of Service (QoS) as an integrated part of thesystem. Having an effective QoS mechanism in place enables mobile operators to cost-effectively deliver high-value, differentiated, IP-based applications and services. QoS is discussed in detail in chapter 5.

1.4.3 UMTS Service Capabilities

The way UMTS is defined separates as far as possible the part of the network that makes actual connections fromthe part that maintains services. This facilitates more openness and potential in the market and allows a concept ofseparate providers of contents, service and carriers. Some of these services are listed below.


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1.4.3.1 Location Based Services

The geographic position of the User Equipment (UE) can be given by measuring radio signals. There are manydifferent possible applications for positioning information. The positioning functions may be used internally by theUTRAN for radio system performance optimization, by value-added network services, by the UE itself or through

the network, and by "third party" services. Typical commercial services are:

Traffic information

Fleet management

Follow me

Nearest service

Emergency services

UMTS network planners can also use this information.

Location based services can also be implemented in GSM/GPRS networks where they are based on the signalingbetween the network and the Mobile Station (MS the GSM/GPRS equivalent of the UE).

1.4.3.2 WAP Service

WAP (Wireless Application Protocol) is Internet access optimized for mobile telephony. It will allow the mobileuser to gain access to Internet information and services anywhere anytime, for example e-mail, flight schedules etc.The WAP service capability provides the user with a web-browser that uses a Wireless Markup Language (WML)instead of the HyperText Markup Language (HTML) normally used on the Internet. WML is designed for use withmobile terminals. Gateways in the system will take care of the conversion between the WAP format and the normal

Internet format.

1.4.3.3 Multimedia Messaging Service (MMS)

The Multimedia Messaging Service (MMS) is used for delivering multimedia messages to a UE, from either anotherUE, a fixed point on the Internet or a Value Added Service (VAS) provider. Value-added services could be news,

weather broadcasts, stock exchange information etc. Multimedia messages can contain all types of media in additionto text, e.g. speech, video, audio and still images.

1.4.3.4 CAMEL

The Customized Applications for Mobile networks Enhanced Logic (CAMEL) is a common platform for a numberof services for customers. It provides the UMTS network with Intelligent Network (IN) features like:

Prepaid

Call screening

Supervision

CAMEL allows the necessary information to be exchanged between networks (IN features are normally networkspecific). Traditional IN solutions create circuit switched services. CAMEL will do this and also interact with packetswitched connections.

1.4.4 Virtual Home Environment (VHE)

The VHE is a service concept within UMTS that enables the user to have the same personalized interface to the

network regardless of the network accessed. It requires that networks transfer information on user profiles, charging,services and number portability, which considering the complexity of the networks is not a trivial task. Where theVHE requires network-network communication, the CAMEL will be used.


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1.5 The Network Components of a UMTS Network

Figure 1.4 GSM/GPRS/UMTS network architecture.

The figure above shows some of the subsystems in GSM/GPRS/UMTS networks, as they will evolve with theUMTS releases. On the access network side there is the Base Station Subsystem (the GERAN) for GSM/GPRS andthe RNS (the UTRAN) for UMTS. The CN is based on the GSM/GPRS core network, but as indicated, UMTS Rel-4 and Rel-5 will modify some subsystems and components and add others. This allows existing GSM/GPRS

network operators to benefit from the improved cost-efficiency of UMTS while protecting their 2G investments andreducing the risks of implementation. There are also other entities in the network such as the location services

entities, which are used for location calculation.

The GSM/GPRS/UMTS network interfaces with other Public Land Mobile Networks (PLMNs) including pre Rel-4networks, the PSTN and other IP-based multimedia networks.

1.5.1 Access Network Elements

Two types of access network are defined for GSM/GPRS/UMTS network; the BSS used for GSM, GPRS andEDGE access (the GERAN), and the RNS (the UTRAN) used for WCDMA access.


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1.5.2 The GSM/EDGE Radio Access Network (GERAN) Architecture

The GERAN is the access network defined for GSM, GPRS and EDGE. The GERAN is connected to the GSMPhase 2+ CN either via two legacy interfaces (the A-interface and the Gb interface), or through the Iu interfaces.The interface between the GERAN and the PS domain of the CN (the Iu-PS or the legacy Gb interface) is used forpacket switched data, and the interface between the GERAN and the Circuit Switched (CS) domain of the CN (Iu

CS or the legacy A interface) is used for circuit switched voice or data.

Figure 1.5 GERAN architecture.

1.5.2.1 Base Station Subsystem (BSS)

The BSS or the GERAN is the system of base station equipment (transceivers, controllers, etc.), which isresponsible for communicating with mobile stations in a certain area. The BSS is connected to the MSC through asingle A or Iu-CS interface. Similarly, in PLMNs supporting GPRS, the BSS is connected to the Serving GPRSSupport Node (SGSN) through a single Gb or Iu-PS interface.

The radio equipment of a BSS may support one or more cells. A BSS may consist of one or more base stations.

Where an Abis-interface is implemented, the BSS consists of one Base Station Controller (BSC) and one or moreBase Transceiver Station (BTS). The BTS and the BSC communicate across the Abis interface.

1.5.2.2 Base Transceiver Station (BTS)

The BTS contains the radio transmitters and receivers (transceivers TRX) covering a certain geographical area ofthe GSM network (a base station area consisting of one or more radio cells). The BTS handles the radio linkprotocols with the MS.

1.5.2.3 Base Station Controller (BSC)

The BSC controls a group of BTSs regarding radio channel setup, power control, frequency hopping, and handovers- the transfer of a call in progress from one radio channel to another, typically as a result of an MS moving from onebase station area to another. The BSC is the connection between the mobile station and the MSC.


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1.5.2.4 GSM Mobile Station (MS)

The GSM MS consists of the mobile equipment (the terminal) and the Subscriber Identity Module (SIM) card. TheSIM provides personal mobility, providing user access to subscribed services irrespective of a specific terminal. TheInternational Mobile Equipment Identity (IMEI) uniquely identifies the mobile equipment. The SIM card contains

the International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system, a secret key for

authentication, and other information. The IMEI and the IMSI are independent, thereby allowing personal mobility.The MS communicates with the GSM network via the radio interface (Um Interface).

In relation to UMTS the MS must operate in one of the following two modes:

A mode based on A/Gb interfaces between BSS and CN e.g. for:

- pre-Release 4 terminals

- Rel-4 terminals when connected to a BSS with no Iu interface towards the CN

A mode based on Iu-CS and Iu-PS between BSS and CN for:

- Rel-4 terminals when connected to a BSS with Iu interfaces towards the CN

1.5.3 Universal Terrestrial Radio Access Network (UTRAN) ArchitectureUMTS R99 saw the introduction of a new radio access network, the UTRAN. The UTRAN is based on WCDMAtechnology, introduced in order to achieve a better bandwidth efficiency compared to the techniques used inGSM/GPRS. The UTRAN is connected via the Iu to the GSM Phase 2+ CN; the interface between UTRAN and thePS domain of the CN (IuPS) is used for packet switched data, and the interface between UTRAN and the CSdomain of the CN (IuCS) is used for circuit switched data. There is actually a third domain, the BroadCast (BC)

domain, which can used to broadcast a short message to a given geographical area (service area, being one ormore cells). The interface to the BC domain is called Iu-BC. It is not shown in the figure in section 1.5.2 and willnot be described further here.

1.5.3.1 Radio Network Subsystem (RNS)

The UTRAN consists of one or more RNSs connected to the CN via the Iu interfaces. Each RNS consists of a RNCand one or more Node Bs. The Node Bs are connected to the RNCs via the Iub interface. The Node Bs provide radio

access (i.e. antennas) to the network. The RNCs of each RNS can be interconnected via the Iur interface

Figure 1.6 UTRAN architecture.


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1.5.3.2 The Radio Network Controller (RNC)

Each RNC has responsibility for and control over the radio resources of a set of cells. The RNC is equivalent to aGSM/GPRS BSC but is more self-controlled. A RNC may have different roles in the UTRAN network:

Controlling RNC

- Each RNC is responsible for the resources of its set of cells and the Node Bs in its RNS. In this role the RNC is calledthe Controlling RNC (CRNC)

Serving RNC

- For each connected UE the RNCs may have an additional role: A Serving RNC (SRNC) providing radio resources tothe connected UE. The SRNC terminates the Iu towards the CN

Figure 1.7 Serving RNC.

Drift RNC

- In order to minimize the effect of handovers, RNCs may have a third role: A Drift RNC (DRNC). A DRNC provides(lends) resources to a SRNC for a specific UE. The DRNC will normally also act as a SRNC (or DRNC) for other UEs

Figure 1.8 Drift RNC.


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1.5.3.3 The Node B

The Node B handles the transmission and reception of signals in one or more cells, similar to GSM BTS. The NodeB is also responsible for the inner loop power control. Please refer to section 3.5 for more information on powercontrol.

1.5.3.4 User Equipment (UE)

The UE is equivalent to the GSM MS, i.e. it is the terminal through which the users access the network. The UEconsists of the mobile equipment (the terminal) and a Universal Service Identity Module (USIM). The mobileequipment is uniquely identified by the IMEI. In order to allow future enhancements, the terminal equipment shouldhave an Application Programming Interface (API). The USIM provides personal mobility, providing the user withaccess to subscribed services. Unlike the GSM SIM card, the USIM card may hold a number of profiles. Eachprofile will have a specific purpose. It can be used to adjust the available services to the capabilities of the terminal

into which the USIM card is installed. Both the user and the network can adjust the profiles.

1.5.4 Core Network Elements

Figure 1.9 UMTS network architecture.

The CN is logically divided into a CS domain and a PS domain. In addition, a set of databases (Registers) is usedfor storage of information needed by the system. The different entities in the domains are described below.


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1.5.5 Core Network Elements Circuit Switched (CS) Domain

Figure 1.10 Core network elements - CS domain.

1.5.5.1 Mobile Switching Center/Gateway Mobile Switching Center (MSC/GMSC)

The central component of the CS domain in the CN is the MSC. The MSC is an exchange, which performs all the

switching and signaling functions for MSs located in a geographical area designated as the MSC area. The maindifference between an MSC and an exchange in a fixed network is that the MSC has to take into account the impact

of the allocation of radio resources and the mobile nature of the subscribers, which means it performs proceduressuch as:

Procedures required for the location registration

Procedures required for handover

The MSC/GMSC constitutes the interface between the radio system and the fixed networks. The MSC performs allnecessary functions in order to handle the circuit switched services to and from the mobile stations. The MSC isresponsible for call control (setup, routing, control and termination of the calls), management of inter-MSC

handover and supplementary services, and for collecting charging/accounting information. The MSC is connected tothe location and equipment registers and to other MSCs in the same network.

The GMSC acts as the gateway to other mobile networks and the public-switched networks (telephone network,ISDN and data networks).

In order to obtain radio coverage of a given geographical area, a number of base stations are normally required; i.e.each MSC would thus have to interface several base stations. In addition several MSCs may be required to cover a

country.

1.5.5.2 Media Gateway/Mobile Switching Center (MGW/MSC) Server

To enable bearer-independent (and thus enabling all-IP based networks) CS network architecture in Rel-4, the MSCis split into an MGW for transport of user data and an MSC server for signaling. The MSC server mainly comprises

the Call Control (CC) and mobility control parts of an MSC. The split into MGW and MSC server also results in amore independent environment for service creation. The new CAMEL features benefit from this concept when the

service control gets independent from the switching fabric.


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MGW is the PSTN/PLMN transport termination point and interfaces UTRAN with the CN over Iu. The MGW mayterminate bearer channels from a circuit switched network and media streams from a packet network (e.g. RTP(Real-time Transport Protocol) streams in an IP network).

1.5.5.3 Signaling Gateway (SGW)

A SGW converts signaling (both ways) at transport level between the SS7 based transport of signaling used in pre-Rel 4 networks, and the IP based transport of signaling possibly used in post-R99 networks (i.e. between SigtranSCTP/IP and SS7 MTP). The SGW does not interpret the application layer (e.g. MAP, CAP, BICC, ISUP) messagesbut may have to interpret the underlying SCCP (Signaling Connection Control Part) or SCTP (Stream ControlTransmission Protocol) layer to ensure the correct routing of the signaling. The SGW will be necessary to obtain an

all-IP UMTS network.

The signaling gateway function may be implemented as a stand-alone entity or inside another entity.

Figure 1.11 The signaling gateway function.

1.5.6 Core Network (CN) Elements Packet Switched (PS) Domain

Figure 1.12 Core network elements - PS domain.


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1.5.6.1 Serving GPRS Support Node (SGSN)

The SGSN acts as a packet switch and router in the PS domain of the CN. The SGSN controls the access of the MSto the network and routes packets to the right BSC/RNC. It performs Mobility Management (MM) functions similarto the MSC in the CS domain of the CN such as location registration, Routing Area Updates (RAUs) and paging.

The SGSN also handles security functions such as authentication and ciphering (between the MS/UE and the

SGSN).

1.5.6.2 Gateway GPRS Support Node (GGSN)

The GGSN acts as a packet router in the PS domain of the CN and is the gateway between the mobile IP packet

routing of the GPRS/UMTS network and the fixed IP routing of the Internet. It transfers packets between the IPmultimedia networks and the appropriate SGSN, which currently serves the MS/UE. If the MS changes the SGSNduring ready mode, the GGSN is used as a data packet buffer. The GGSN stores subscriber data for active MSs/UEsand performs security functions such as firewall and screening.

1.5.7 Core Network (CN) Elements Registers

1.5.7.1 Home Location Register (HLR)

The HLR is an independent core network element up to and including Rel-4. In Rel-5 the HLR is replaced by theHSS (Home Subscriber Server see next section), which is a superset of the HLR. The HLR contains all the

administrative information of each subscriber registered in the particular network, information on permittedservices, and the current location of the mobile. The location of the mobile is typically in the form of the signalingaddress of the Visitor Location Register (VLR) associated with the MS. There is logically one HLR per network,although it may be implemented as a distributed database.

The HLR provides functionality like:

Support to PS domain entities such as the SGSN and GGSN, through the Gr and Gc interfaces. It is needed to enablesubscriber access to the PS domain services

Support to CS domain entities such as the MSC/MSC server and GMSC/GMSC server, through the C and D interfaces. Itis needed to enable subscriber access to the CS domain services and to support roaming to legacy GSM/UMTS CSdomain networks

1.5.7.2 Home Subscriber Server (HSS)

Figure 1.13 The HSS is a superset of the HLR.

In UMTS Rel-5 the HSS replaces the HLR. The HSS is a superset of the HLR and contains all the functionality ofthe HLR plus additional functionality to support the IM functionality of the IMS (please refer to section 1.5.8).

The HSS is an entity common to the PS and CS domains. The HSS is the master database for a given user andcontains the subscription related information to support the network components handling calls/sessions, forexample support to the call control servers in order to complete routing/roaming procedures by solving

authentication, authorization, naming/addressing resolution and location dependencies.

A UMTS Network may contain one or several HSSs, depending on the number of mobile subscribers, the capacity

of the equipment, and the organization of the network.


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The HSS consists of the following functionalities:

IM functionality to provide support to control functions of the IMS such as the Call State Control Function (CSCF). It isneeded to enable subscriber access to the IM CN subsystem services

The subset of the HLR functionality required by the PS domain

The subset of the HLR functionality required by the CS domain, if it is desired to enable subscriber access to the CSdomain or to support roaming to legacy GSM/UMTS CS domain networks

The HSS contains the following user-related information:

User identification, numbering and addressing information

User security information

- Network access control information for authentication and authorization

User location information at inter-system level

- The HSS supports the user registration, and stores inter-system location information, etc.

User profile information (i.e. parameter settings for specific purposes)

1.5.7.3 Visitor Location Register (VLR)

The VLR contains selected administrative information from the HLR, necessary for call control and provision of the

subscribed services, for each mobile currently located in a Location Area (LA) controlled by the VLR. Each time anMS performs roaming in a new LA, the VLR covering that LA informs the HLR about the new location of thesubscriber. The HLR subsequently informs the VLR about the services to which the subscriber has access. The VLRalso controls the assignment of TMSI.

The HLR and the VLR, together with the MSC, provide the call routing and roaming capabilities of the network. In

most implementations the VLR is integrated with the MSC, and with UMTS Rel-4 it will be a part of the MSCserver.

1.5.7.4 Authentication Center (AuC)

The AuC is a protected database that contains the individual subscriber-identification keys (also contained in SIM),and provides the subscriber data to HLR and VLR (via HLR) used for authentication and encryption of calls.

1.5.7.5 Equipment Identity Register (EIR)

The EIR is a database that contains a list of all valid mobile equipment on the network, and in which each MS isidentified by its IMEI. An IMEI is marked as invalid if the mobile has been reported stolen or is not type approved.

1.5.8 IP Multimedia Subsystem (IMS)

Figure 1.14 The IP Multimedia Subsystem.


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The IMS is the major difference between UMTS Rel-4 and Rel-5. The IMS comprises all CN elements for provisionof multimedia services. IM services are based on a session control capability defined by the Internet EngineeringTask Force (IETF). IM services, along with multimedia bearers, utilize the PS domain - possibly including anequivalent set of services to the relevant subset of CS Services.

The IMS enables PLMN operators to offer multimedia services to their subscribers based on and built upon Internetapplications, services and protocols. 3GPP has no intention of standardizing such services within the IMS. Theintention is that these services will be developed by PLMN operators and third party suppliers, including those inthe Internet space, using the mechanisms provided by the Internet and the IMS. The IMS should enable theconvergence of, and access to, voice, video, messaging, data and web-based technologies for the wireless user, and

combine the growth of the Internet with the growth in mobile communications.

The specific functional elements of the IMS are described below.

The CSCF which can have three roles:

- Proxy-CSCF (P-CSCF) is the first contact point for the UE within the IMS. The Policy Control Function (PCF) is alogical entity of the P-CSCF

- Interrogating-CSCF (I-CSCF) is the contact point within an operators network for all IMS connections destined to a

user of that particular network operator

- Serving-CSCF (S-CSCF) performs the session control services for the UE

The Media Gateway Control Function (MGCF) performs protocol conversion between ISUP (ISDN User Part) and the IMScall control protocols (e.g. ISUP/SIP (Session Initiation Protocol) conversion)

The Multi Resource Function (MRF) performs multiparty call and multimedia conferencing functions

The IP Multimedia Media Gateway (IM-MGW) terminates bearer channels from a switched circuit network and mediastreams from a packet network. The IM-MGW may support media conversion, bearer control and payload processing(e.g. codec, echo canceller, conference bridge)


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2. UMTS Network Interfaces and Protocols

2.1 OverviewThe figure below gives a simplified view of the UMTS architecture. It splits UMTS in 3 significant parts: The UE,the access network (UTRAN) and the CN.

Figure 2.1 Simplified UMTS structure showing three significant parts.

The information that flows through the UTRAN is logically split into two parts:

The access stratum - being information required for the interaction between the UE and the UTRAN

The Non Access Stratum (NAS) - being information transferred between the CN and the UE across the UTRAN

The reason for this split is a desire to make the information transfer between CN and UE independent of the radiohandling in the UTRAN.

2.2 General UTRAN Interface Protocols ArchitectureThe UTRAN interface protocols consists of 3 parallel protocol stacks:

The control plane which amongst other things conducts the signaling that enables the transport of user data

The user plane is where the user data are actually transported

The Transport Network Control Plane (TNCP)

- The transport channels in the user plane are dynamic. The TNCP makes it possible to establish and remove transportchannels on a given UTRAN interface


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Figure 2.2 Three protocol stacks connecting the UE with the CN via the UTRAN.

2.2.1 Control Plane

The control plane is used for signaling between the UE and the network. The control plane includes an (upper layer)application protocol (RANAP/RNSAP/NBAP) and a (lower layer) signaling bearer for transporting the applicationprotocol messages.

The application protocol is used for things like setting up bearers (i.e. Radio Access Bearer (RAB) or radio link) inthe radio network layer, controlling different transmission resources and handover). In the three-plane structure thebearer parameters in the application protocol are not directly tied to the user plane technology; they are generalbearer parameters. The control plane protocols include a mechanism for transparent transfer of NAS messages.

The lower layer the signaling bearers - for application protocol, is a part of the transport network user plane. The

control actions required for setting up the signaling bearers are Operations & Maintenance (O&M) actions.

2.2.2 User Plane

The user plane includes the data streams and the data bearers for the data streams. The data streams arecharacterized by one or more frame protocols specified for that interface. The user plane protocols implement the

radio access bearer service, i.e. carries the user data through the access stratum.

The lower layer the data bearers - in the user plane is a part of the transport network user plane. The transportnetwork control plane directly controls the data bearers in transport network user plane during real-time operation.

2.2.3 Transport Network Control Plane (TNCP)

Many of the bearers in the UTRAN network are dynamically created as required (in the form of an ATM virtualcircuit), and closed afterwards. The TNCP handles this.

The TNCP does not have a radio network layer. It includes the ALCAP protocols needed to set up the transport

bearers (data bearer) for the user plane and the signaling bearer for the ALCAP protocols. The TNCP allows theapplication protocol in the radio network control plane to be independent of the data bearer technology in the userplane.

When the TNCP is used, a control plane application protocol signaling transaction triggers the ALCAP protocol toset up of the data bearer. The ALCAP protocol is specific for the user plane technology used. ALCAP is however

not used for all types of data bearers. If there is no ALCAP signaling transaction, the TNCP is not needed at all. Thisis the case when pre-configured data bearers are used.


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The signaling bearer for ALCAP is always set up by O&M actions and it may or may not be of the same type as thesignaling bearer for the application protocol.

2.2.4 End-to-End View of UTRAN Protocols

Figure 2.3 Control plane UE to PS Core Network (3G-SGSN).

Figure 2.4 Control plane UE to CS Core Network (MSC).


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At the top of the control plane, NAS control messages are carried. These messages are used for GPRS MobilityManagement/Session Management and Mobility Management/Call Control (GMM/SM, respective MM/CC):GMM/SM and MM/CC are described in 3GPP TS 24.008. Figure 2.5 summarizes the MM/GMM/SM/CCfunctionality:

Circuit Switched Packet Switched

Mobility Management (MM) GPRS Mobility Management (GMM)

Registration

IMSI detach indication

Location updating

Security

Authentication

Identity

TMSI reallocation

Connection management

CM service

Abort

Miscellaneous

MM information/status

Attach and Detach

P-TMSI reallocation

Authentication and ciphering

Identity request/ response

Routing area update

GMM Status/ Information

Service Request/Accept/Reject

Circuit-mode connections Call Control (CC) GPRS Session Management (SM)

Call establishment

Alerting

Call proceeding/confirmed

Connect/ connect acknowledge

Progress

Setup

Call information phase

Modify

User information

Call clearing

Disconnect

Release/ release complete

Supplementary service control

Facility

Hold

Retrieve

Miscellaneous

Congestion control

Notify

DTMF handling

Status

Activate Packet Data Protocol (PDP) context

Activate Secondary PDP Context

Request PDP context activation

Modify PDP context request

Deactivate PDP context

SM Status

Figure 2.5 Circuit and Packet Switched Mobility Management.

SMS supports the mobile-originated and mobile-terminated Short Message Service (SMS) as described in 3GPP TS23.040. Information on the access stratum protocol layers is given in the description of protocols for the specific

interfaces.


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Figure 2.6 User plane UE to PS Core Network.

Figure 2.7 User plane UE to CS Core Network.

2.3 The UTRAN InterfacesFor the UTRAN, four interfaces are defined: two internal (Iur and Iub) and two external (Iu and Uu). Each interfacecarries both user data and signaling. This document focuses on the control plane protocols (signaling).


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2.3.1 General UTRAN Interface Protocols Architecture

The protocols on each of the UTRAN interfaces have a general structure as shown below.

Figure 2.8 General structure of the UTRAN interfaces.

Each protocol stack is divided into an upper layer (the radio network layer) and a lower layer (the transport networklayer). The upper layers are used for applications and information that go beyond a particular interface, while thelower layer ensures and conducts the transport of information on a particular interface.

2.3.2 Iu Interface

The Iu interface connects the UTRAN to the CN. The Iu interface is split up in three functional types of interfaces.The Iu interface towards the CS domain is called Iu-CS. The Iu interface towards the PS domain is called Iu-PS.The last core network domain is the BC domain and the interface towards that is the Iu-BC. The Iu-BC is notcovered by this document. The UTRAN is responsible for all radio-related aspects including mobility of a UE inconnected mode on cell level.

Figure 2.9 The Iu interface connects the UTRAN to the CN.


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The CN is responsible for the end user service related aspects, including keeping track of the UE in idle mode onlocation/routing area level.

The Iu interface supports a common set of RAB services that are offered by UTRAN to the CN nodes, regardless of

their type.

2.3.3 Iu-CS Protocol Stack

Figure 2.10 The Iu-CS control plane protocol stack.

The Iu-CS control plane protocol stack consists of a signaling bearer layer, the transport network layer, and anapplication protocol on the radio network layer.

The broadband Signaling System No. 7 is used as signaling bearer for the Radio Access Network ApplicationProtocol (RANAP). This means that SCCP is used by RANAP. Both connectionless and connection orientedprocedures are used. Message Transfer Part 3b (MTP3b) is used by SCCP. SSCF-NNI and SSCOP and AAL5 areinterface protocols between ATM and SS7 protocols.

2.3.3.1 The Radio Access Network Application Protocol (RANAP) Layer

The RANAP encapsulates and carries higher-layer signaling, handles signaling between the 3G-SGSN and UTRAN,

and manages the GTP connections on the Iu interface.


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RANAP provides UTRAN specific control/signaling including:

The overall management of the RAB such as setup, release and maintenance

Transport of NAS information between UE and CN, like MM and broadcast information

Paging requests to the UE

UE location information

Error handling

Overload handling

Iu connection management

The RANAP is specified in 3G TS 25.413.

2.3.3.2 The Signaling Bearer Layer

The signaling bearer layer consists of several protocol layers:

The SCCP provides connectionless and connection oriented services for the higher layer. Connections are made on amobile-by-mobile basis. SCCP is defined in ITU-T Recommendation Q.716

MTP3b provides functions like message routing, signaling link management, load sharing, changeover and changebackbetween links. MTP3b is defined in ITU-T Recommendation Q.2210

Service Specific Co-ordination Function (SSCF-NNI). SSCF maps the requirements of the layer above to therequirements of SSCOP. SSCF-NNI is defined in ITU-T Recommendation Q.2140

Service Specific Connection Oriented Protocol (SSCOP) provides mechanisms for the establishment and release ofconnections and the reliable exchange of information between signaling entities. SSCOP is defined in ITU-TRecommendation Q.2110

ATM Adaptation Layer (AAL5) adapts the upper layer protocol to the requirements of the lower ATM cells. AAL5 isdefined in ITU-T Recommendation I.363.5

Together the SSCF, the SSCOP and the AAL5 are also known as the Signaling ATM Adaptation Layer NetworkNode Interface (SAAL-NNI).

The signaling bearer layers below RANAP are defined in 3G TS 25.412.

2.3.4 Iu-PS Protocol Stack

The Iu-PS protocol stack is slightly different from the Iu-CS protocol stack. The operator has two stacks to choosefrom for signaling: The operator can use the same stack as for Iu-CS, or the alternative IP over ATM based stack,

using M3UA (a special MTP3 adaptation protocol for use over IP), the SCTP and IP.


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Figure 2.11 The Iu-PS protocol stack.

The figures in section 2.2.4 show the relation between the Iu-PS protocol stacks and the protocol stacks on otherUMTS interfaces.

2.3.4.1 The GPRS Tunneling Protocol for the User Plane (GTP-U)

This protocol tunnels user data between UTRAN and the 3G-SGSN, and between the GPRS Support Nodes (GSNs)in the backbone network. GTP must encapsulate all PDP Protocol Data Units (PDUs). GTP is specified in 3G TS29.060. The GTP-U is defined by the same recommendation as the GTP-C protocol layer mentioned in section2.4.2. However, different messages defined in the recommendation are used for the control plane (GTP-C) and the

user plane (GTP-U) applications.

2.3.4.2 The User Datagram Protocol/Internet Protocol (UDP/IP)

UDP/IP are the backbone network protocols used for routing user data and control signaling.

2.3.5 Iub Interface

The Iub interface is used by the CRNCs (or DRNCs) to request the setting up, adding or deleting of radio links inthe Node Bs. It is also used by the DRNC to perform radio resource admission control and hardware resource

control.


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2.3.6 Iub Protocol Stack

Figure 2.12 The Iub protocol stack.

The signaling bearer used by Node B Application Part (NBAP) comprises of SSCF-UNI on top of SCCOP andAAL5. Together the three signaling bearer layers are called the Signaling ATM Adaptation Layer (SAAL). Thefigures in section 2.2.4 show the relation between the Iub protocol stacks and the protocol stacks on other UMTSinterfaces.

2.3.6.1 The Node B Application Part (NBAP) Protocol Layer

The NBAP protocol, specified in 3G TS 25.433, is used on the Iub interface. Here it provides UTRAN specificcontrol/signaling e.g.:

Handling and control of the measurements, performed by the UE

Management of radio links and of common channel and resources

Synchronization

Error handling

2.3.6.2 User Plane Radio Network Layer Protocols

The user plane radio network layer on the Iub interface consists of a number of protocols. The structure reflects theway the information is organized on the air interface, i.e. the data streams that are carried across the Uu interface.These protocols are listed on the following page.


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Detailed information on these channels is, however, outside the scope of this document:

Common Packet CHannel Framing Protocol (CPCH FP)

Uplink Shared CHannel Framing Protocol (USCH FP)

Downlink Shared CHannel Framing Protocol (DSCH FP)

Paging CHannel Framing Protocol (PCH FP)

Forward Access CHannel Framing Protocol (FACH FP)

Random Access CHannel Framing Protocol (RACH FP)

Dedicated Transport CHannel Framing Protocol (DCH FP)

2.3.7 Iur Interface

The Iur interface is used by the SRNCs to request the setting up, adding or deleting of radio links in the DRNCs. Italso supports handover and synchronization. In order to minimize the equivalent of the inter-BSC handovers knownfrom GSM/GPRS, the Iur is used to enable inter-RNC soft handover. This is again to hide radio network functionsfrom the CN and in particular to avoid ping-pong effects, for example, UEs frequently changing back and forth

between two cells, on the CN.

2.3.8 Iur Protocol Stack

Figure 2.13 The Iur protocol stack.

The transport network layer part of the control plane protocols for the Iur are the same as those for Iu-PS. Again theoperator has a choice between two stacks. The radio network layer in the Iur protocol stack consists of the RadioNetwork Subsystem Application Part (RNSAP) protocol.


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2.3.8.1 The Radio Network Subsystem Application Part (RNSAP) Protocol Layer

The RNSAP protocol is used on the Iur interface, where it provides UTRAN specific control/signaling e.g.:

Relocation of SRNC

Transport of NAS information between the UE and the CN, like MM and broadcast information

Paging requests to the UE

Management of transport channel resources (radio and physical links)

Soft handovers

The RNSAP is specified in 3G TS 25.423.

2.3.9 Uu Interface

Figure 2.14 Radio interface protocol architecture (service access points marked by circles).

The Uu interface is the air interface between the UE and the UMTS network. The figures in section 2.2.4 show therelation between the Iub protocol stacks and the protocol stacks on other UMTS interfaces.


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2.3.9.1 The Radio Resource Control (RRC) Protocol Layer

The RRC protocol, specified in 3G TS 25.331, is used between the UTRAN (the RNC) and the UE. It providesfunctionality including:

Broadcast of information

Management of:

- RRC connection between the UE and UTRAN (establishment, release, maintenance)

- Radio Bearers (establishment, release, reconfiguration)

- RRC connection radio resources (assignment, release, reconfiguration)

Mobility functions for the RRC connection

Control of requested QoS

Handling of UE measurement reports

Outer loop power control (please refer to section 3.4.3.2)

Control of ciphering

Paging

RRC message integrity protection

Timing advance (Timing Division Duplex (TDD) mode)

2.3.9.2 The Packet Data Convergence Protocol (PDCP) Layer

The PDCP specified in 3G TS 25.323 is used in the user plane between the UTRAN (the RNC) and the UE. Itprovides functionality including:

Compression and decompression of header in IP data streams (e.g. TCP/IP and RTP/UDP/IP headers for IPv4 and IPv6)

Transfer of user data between PDCP service users

2.3.9.3 The Radio Link Control (RLC) Protocol LayerThe RLC protocol is used for RLC connections between the UTRAN (the RNC) and the UE. There is one RLCconnection for each Radio Bearer (RB). The RLC protocol provides functionality including:

Segmentation and reassembly of long upper layer PDUs

Concatenation of short upper layer PDUs

Transfer of user data including error correction and flow control

In-sequence delivery of upper layer PDUs

Sequence number checking

Detection and recovery of protocol errors

Ciphering

The RLC protocol is specified in 3G TS 25.322.

2.3.9.4 The Medium Access Control (MAC) Protocol Layer

The MAC protocol is just above the physical layer. It is used between the UTRAN (the RNC) and the UE. Itprovides functionality including:

Mapping between logical channels and transport channels

Selection of appropriate transport format for each transport channel depending on instantaneous source rate

Handling of priority between data flows of one UE and between UEs

Multiplexing/demultiplexing of upper layer PDUs to and from the actual physical layer transport channels

The MAC protocol is specified in 3G TS 25.321.


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2.4 Core Network (CN) ProtocolsThis section discusses protocol stacks for all relevant interfaces in the CN, both the CS domain and the PS domain.Again the focus will be on the control plan protocols (signaling).

2.4.1 The Mobile Application Part (MAP) Protocol

Figure 2.15 The MAP protocol stack - on the Gr interface between SGSN and HLR.

The MAP protocol (or a fraction of it) is used on a number of interfaces in the CN. TCAP, SCCP, MTP3, and MTP2are transport protocol layers defined in Signaling System No. 7. The same protocols are used to support MAP in CSPLMNs.

Figure 2.16 on the following page shows the services and functionality supported by the MAP protocol.


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Services and Functionality Supported by the MAP Protocol

Mobility

Location management services

Paging and search

Access management services

Handover services

Authentication management services

Security management services

International mobile equipment identitiesmanagement services

Subscriber management services

Identity management

Fault recovery services

Subscriber information services

Call Handling

Send routing information service

Provide roaming number service

Resume call handling service

Group call service

Provide SIWFS number

SIWFS signaling modify

Set reporting state service

Status report service

Remote user free service

Immediate Service Termination (IST) services

Supplementary Services Related

Register/erase/activate/deactivate/interrogate/invokesupplementary services

Password services

Unstructured supplementary services support

Register/erase CC entry service

Short Message Service Management

Send-routing-info-for-SMS service

Forward SMS

Report SM delivery status service

Ready for SM service

Alert service center service

Inform service center service

Send info for SMS service

Network-Requested PDP Context Activation

Send routing info for GPRS service

Failure report service

Note MS present for GPRS service

Location Service Management (LCS)

Send routing info for LCS service

Provide subscriber location service

Subscriber location report service

Operation and Maintenance

Subscriber tracing services

Other operation and maintenance services

Figure 2.16 MAP services as defined in 3G TS 29.002.

2.4.1.1 Interfaces using the MAP Protocol

SGSN HLR (the Gr interface):

The MAP protocol supports signaling exchange with the HLR, as defined in 3G TS 29.002, with enhancements for GPRS,see 3G TS 23.060

SGSN EIR (the Gf interface):

The MAP protocol supports signaling between the SGSN and the EIR, as described in sub clause "Identity CheckProcedures" 3G TS 23.060

SGSN - SMS-GMSC or SMS-IWMSC (the Gd interface): The MAP protocol supports signaling between the SGSN and SMS-GMSC or SMS-IWMSC, as described in sub clause

"Point-to-point Short Message Service" 3G TS 23.060

GGSN HLR (the Gc interface):

This optional signaling path allows a GGSN to exchange signaling information with an HLR. There are twoalternative ways of implementing this signaling path:

If an SS7 interface is installed in the GGSN, the MAP protocol can be used between the GGSN and an HLR

If an SS7 interface is not installed in the GGSN, any GSN with an SS7 interface installed in the same PLMN as the GGSN,can be used as a GTP-to-MAP protocol converter to allow signaling between the GGSN and an HLR


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2.4.2 GSN GSN Control Plane

Figure 2.17 Control plane for SGSN-GGSN and SGSN-SGSN interfaces.

GTP-C

- This protocol tunnels signaling messages between SGSNs and GGSNs (Gn), and between SGSNs in the backbonenetwork (Gp). GTP-C is used for location management and MM and is specified in 3G TS 29.060

UDP

- This protocol transfers signaling messages between GSNs

2.4.3 SGSN - MSC/VLR

Figure 2.18 Control plane SGSN-MSC/VLR.


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Base Station System Application Part+ (BSSAP+)

- A subset of BSSAP procedures supports signaling between the SGSN and MSC/VLR, as described in 3G TS 29.018.The requirements for the lower layers are specified in 3G TS 29.016

2.4.4 GSN GSN User Plane

Figure 2.19 User plane for SGSN-GGSN and SGSN-SGSN interfaces.

GTP-U

- This protocol tunnels user data between SGSNs and GGSNs (Gn), and between SGSNs in the backbone network (Gp).GTP is specified in 3G TS 29.060. The GTP-U is defined by the same recommendation as the GTP-C protocol layermentioned in section 2.4.2. However, different messages defined in the recommendation are used for the controlplane (GTP-C) and the user plane (GTP-U) applications

UDP

- This protocol transfers user data between GSNs


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3. UMTS Network FunctionalityThis chapter provides an overview of the basic control signaling and node interworking.

The UE, the UTRAN and the CN operate in a number of states. Each state is characterized by the activity level andthereby the resource requirements. In UMTS the changing resource requirements are supported by dynamic

allocation of resources. This gives better utilization of resources, reduced interference and extended battery life formobiles. The states also define the CN behavior towards the UE, for example terminate or reject an incoming call ifthe UE is turned off, idle or already active.

A set of elementary procedures controls the state changes and allocation of resources as required. MobilityManagement (MM) and Radio Resource Management (RRM) such as handovers enable the UE to move seamlessly

around in the network.

One of the characteristics of UMTS is that elementary procedures can be combined in different ways to implement acomplete service. The specifications also enable the same thing to be done in several ways.In addition to describing the elementary procedures, MM and RRM, examples are used to explain the generalsignaling procedures for a number of services. The detail level is selected to provide a functional overview.

3.1 User Equipment (UE) and Network StatesWhen the UMTS UE is turned on, it will enter IDLE mode. It will start the cell search mechanism scanning the

UMTS band for a cell with broadcast information matching the list of allowed PLMNs. When a suitable cell isfound, the UE will camp on this cell and request initial access to the UTRAN to attach to the network and enter the

CONNECTED state. Once attached the UE will be known/registered to the network and can access the servicesoffered. This mode of operation is also known as Camping on UTRAN Cell.

Multimode UEs are able to operate on existing GSM/GPRS networks in addition to the UMTS network. When no

UMTS network is available, the UE may operate on a GSM/GPRS cell. This mode of operation is also known asCamping on GSM/GPRS Cell.

The UE may also feature intersystem handovers and Location Updates (LUs).

The following state descriptions apply when the UE is camping on UTRAN cell.

3.1.1 Circuit Switched (CS) Mobility Management (MM) States

In CS mode the UE and CN operate in three states as shown below, similar to GSM behavior.

Figure 3.1 UE and CN MM states.


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When the UE is turned on and performs an IMSI Attach it goes from MM-DETACHED to MM-CONNECTED andthen to MM-IDLE, when the IMSI Attach is successfully completed. In MM-IDLE state the UE is registered in theCN by Location Area (LA) but not registered in the UTRAN.

When a call is started or when performing location updating the UE goes back to MM-CONNECTED until

completion of the call/transaction.

When the IMSI Detach is performed the state is changed to MM-DETACHED. In MM-CONNECTED state the UEwill be registered in the UTRAN by cell ID and in the CN by the Iu connection ID.

3.1.2 Packet Switched Mobility Management (PMM) States

In PS mode the UE and CN operate in three states as shown below.

Figure 3.2 UE and CN PMM states.

When the UE performs a GPRS Attach, it goes from PMM-DETACHED to PMM-CONNECTED, and then to

PMM-IDLE when the GPRS Attach is successfully completed and the signaling connection is released.In PMM-IDLE state the UE is registered in CN by Routing Area (RA) but not registered in the UTRAN.

When a new service is requested or when performing Routing Area Updates (RAUs) it goes back to PMM-CONNECTED until completion of the service/transaction. In PMM-CONNECTED state the UE will be registeredin the UTRAN by cell ID and in the CN by the Iu connection ID.

When the PS Detach is performed the state is changed to PMM-DETACHED.


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3.1.3 Radio Resource Control (RRC) Service States

Figure 3.3 RRC states.

Depending on the type of connection and the traveling speed, the UE may be in one of several different states. Thisis handled by the RRC states, controlled by the RNC. InIdle mode the UE has no active connections. In Connected

mode the UE may be in one of four RRC states: The Cell_ FACH(Forward Access CHannel) state is used for communication over common channels with limited

bandwidth, e.g. IMSI Attach and LU

The Cell_DCH(Dedicated CHannel) state is used for communication over allocated dedicated channels like voice

call and data transmission. In this state the UTRAN will perform handovers for CS QoS and Cell Update for PSQoS

The Cell_PCH(Paging CHannel) and URA_PCHstates are used when there is no data to send. The UE will onlylisten to the Paging Channel thus minimizing battery load. In the Cell PCH state the UE will perform CellUpdates whereas in the URA_PCH state the UE performs the less frequent UTRAN Registration Area (URA)

Updates. (Refer to section 3.3.3 for descriptions of locations.) The advantage of the latter is increased powersavings and the sacrifice is that paging is required. E.g. URA_PCH is preferred to Cell_PCH when the UE ismoving at high speed to minimize frequency of location updating procedures

3.1.4 UE State Overview

Figure 3.4 summarizes the UE and RRC states. The location of the UE will be known by the network in varyingresolution. Depending on the actual state the UE will be registered in different databases and with differentaccuracy. Based on the state and the type of active connection either the UE or the UTRAN will select which cell tocamp on. Refer to section 3.3.3 for descriptions of locations.


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UE State RRC State UE Known in UE Registered in UE RegistrationAccuracy

Cell Selected by

PMM-DETACHED - HLR IMSI, last LA/RA -

PMM-IDLE LA/RA CN LA/RA, UE, LA/RA Update

PMM-CONNECTED Cell_FACH Cell CN,UTRAN

Iu connectionURA

UE, Cell Update

Cell_DCH Cell CN,

UTRAN

Iu connection

Cell

UE, Cell Update (PS) or

UTRAN Handover (CS)

Cell_PCH Cell CN,

UTRAN

Iu connection

URA

UE, Cell Update

URA_PCH URA UTRAN URA UE, URA Update

Figure 3.4 UE state overview.

3.1.5 Packet Data Protocol (PDP) States

A PS subscription contains the subscription of one or more PDP addresses. Each PDP address is described by one ormore PDP contexts in the UE, the SGSN, and the GGSN. Every PDP context exists independently in one of twoPDP states. The PDP state indicates whether data transfer is enabled for that PDP address or not. All PDP contextsof a subscriber follow the same PMM state for the IMSI of that subscriber.

Figure 3.5 PDP states.

3.1.5.1 INACTIVE State

In the INACTIVE state the data service for a certain PDP address of the subscriber is not active. The PDP context

contains no routing or mapping information to process PDP data transfer related to that PDP address. No data can betransferred. A change in location of a UE causes no update for the PDP context in INACTIVE state even if thesubscriber is PS Attached.

The UE initiates the movement from INACTIVE to ACTIVE state by initiating the service request procedure withPDP Context Activation.


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3.1.5.2 ACTIVE State

In ACTIVE state, the PDP context for the PDP address in use is activated in the UE, SGSN and GGSN. The PDPcontext contains mapping and routing information for transferring PDP PDUs for that particular PDP addressbetween the UE and the GGSN.

An active PDP context for a UE is moved to INACTIVE state by initiating the service release procedure with PDPContext Deactivation. All active PDP contexts for a UE are moved to INACTIVE state when the PMM statechanges to IDLE or PMM-DETACHED.

3.2 Elementary ProceduresSignaling and transport resources are established and released dynamically on request based on the required QoS foroptimal utilization of resources. In UMTS different services with different QoS will share the radio resources. Thus,all procedures are usually wrapped in signaling connection and RAB establishment, modifications and release.

3.2.1 Paging

The paging procedure is used by the CN to indicate to the UE that it needs to terminate a transaction, e.g. anincoming call or data.

UMTS uses two different types of paging procedures depending on whether a connection to the same CN domainexists or not. Paging Type I is the normal way to use paging. It is used to a UE in IDLE mode to establish asignaling connection for termination of the new transaction. It is sent to those LAs/RAs where the UE has last

reported its location. Paging Type II is used when the UE already has a connection to one CN domain and anotherconnection has to be established to the same CN domain. As it is sent to mobiles with an active connection only, it issent directly to one UE.

When a UE is both IMSI- and GPRS-attached in a network that operates in mode I, the MSC/VLR executes pagingfor circuit switched services via the SGSN.

Figure 3.6 CS Paging Procedure in Iu mode.

3.2.2 Signaling Connection Establishment

To establish a signaling connection from the UE to the CN, an RRC connection needs to be established from the UEto the UTRAN (RNC), and an Iu connection from the UTRAN to the CN. Separate signaling connections areestablished from the UE to each of the CN domains as required.

The RRC connection establishment procedure is initiated by the UE creating an AAL2 link connection between the

RNC and the Node B, and then a WCDMA Physical Dedicated Channel between the Node B and the UE, and iscompleted using this combined Signaling Radio Bearer (S-RB) to establish the RRC connection.


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When the RRC connection has been established, the transaction reasoning procedure is performed.The transaction reasoning procedure is used by the UE to indicate to the CN what type of transaction is requested.The Iu connection is initiated by the UE establishing the Iu signaling bearer and the Iu control plane connection.

The signaling connection can subsequently be used for transparent NAS signaling between the UE and the CN.

Figure 3.7 CS signaling connection establishment.

3.2.3 Signaling Connection ReleaseWhen the transaction is completed and the signaling connection is no longer required, it will be released by theRNC.

The release procedure is initiated by releasing RRC connection starting with the WCDMA Physical DedicatedChannel and the S-RB. Then releasing the Iu control plane connection and the Iu signaling bearer completes therelease.

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