3G Architecture

UMTS Architecture and Element Functionalities

TM51102EN03GLA3A3 © 2010 Nokia Siemens Networks

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Contents

1 Introduction 3 2 User equipment 9 2.1 Architecture 10 2.2 Terminal Equipment 12 2.3 Mobile Termination 12 2.4 UICC 12 3 UTRAN 15 3.1 Node B 16 3.2 Radio Network Controller 18 4 Core Network 21 4.1 General Architecture for UMTS R.99 22 4.2 UMTS R.4 Architecture 36 5 Transport Technologies 43 5.1 ATM 44 5.2 IP 58 6 Exercises 75 7 Solution 79



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© 2010 Nokia Siemens Networks 2



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1 Introduction


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A Universal Mobile Telecommunications System (UMTS) network can be visualized from different angles, such as from the point of view of the user plane, control plane, or the function of each subsystem. In this module we will look at UMTS from the latter angle, where the focus is on the different network elements within the network.

The UMTS network architecture can be divided into four subsystems:

• User Equipment

• Radio Access Network

• Core Network including the network elements for service groups

• Network Management Subsystem.

This separation will allow modularity in the composition of networks. The objective is to be able to combine any 3G CN with any 3G RAN. In addition, technical enhancements and updates of individual modules will be able to be introduced more easily, quicker and at less expensively due to the separation of functions.

Each subsystem can be further divided into separate technologies. For example, the RAN (Radio Access Network) is compromised of different air interface technologies, such as GSM EDGE Radio Access Network (GERAN), UMTS Terrestrial Radio Access Network (UTRAN) and future solutions such as WLAN, 1ExTREME and 4G.

The core network is today clearly divided into:

• Circuit Switched (CS) domain.

• Packet Switched (PS) domain.

The network elements of the circuit switched domain are offering CS bearer services. They are inherited from GSM: MSC/VLR and GMSC. The packet switched domain is responsible to offer PS bearer services. Based on GPRS core network elements, the PS bearer services are currently non-real time services. But standards are on the way to enhance this infrastructure, so that also real-time services can be served via the PS domain transmission infrastructure.

The CS and PS domains share some network elements. These common CS and PS domain network elements are the HLR, AC, and EIR.

A set of service platforms was specified in GSM. These are now – in an enhanced version – also available in UMTS. Network elements for service groups include CAMEL, text telephony, Location Based Services (LBS) network elements. As can be seen service provisioning is partly located in the core network and contains all the service-enabling platforms that support the multitude of 3G services that an operator can offer.



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IP/ATM Backbone

PSTN/ISDN

Other PLMN

Ext. IP Networks

GSM BSC MSS Gateway Control Server (GCS)

HLR

IN/SCE APSE

RNCWCDMA

MGW

SGSNGGSN

MGW

A

A

Iu-CS

BICC CS-2, SIP-T

H.248

Iu-PS

Fig. 1 Mobile general architecture


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The UMTS specifications stipulated that the new air interface and system capabilities should reuse the existing 2G systems, such as GSM and GPRS.

Therefore, it is envisaged that operators can quickly rollout network once the equipment is available. The standards dictate the configuration of the open interfaces and the function of each subsystem; however, the implementation is vendor or operator specific. This has led into much more modular network architecture than we find in today's GSM networks. NSN fully supports open interfaces. The network elements are designed to be modular and are built in the manner that the functions can mature and evolve from new developments.

Each year, the UMTS specifications are upgraded to support continuing functionality in the network. The next version of the specifications is known as UMTS Release 4 followed UMTS Release 5, Release6 and further.

UMTS Release 4 will focus among others on having a specified IP or ATM Telephony Core. The focus of Release 5 is to have IP Multimedia Subsystem.



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TS 23.002:Network Architecture

CS Domain

PS Domain

Entities commonto the CS & PS Domain

GSM BSS

UTRAN

UE

RANRadio Access Network

CNCore Network

TS 23.060:GPRS

Entities commonto the CS & PS Domain

Network Management Subsystem

ExternalNetworks

Enhanced GSM

Core Networks

UMTS Architecture

Fig. 2 UMTS network architecture


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2 User equipment


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2.1 Architecture

The UE has a substructure. It consists of the Universal Integrated Circuit Card (UICC), which communicates with the Mobile Equipment (ME). The UICC is a smart card, like the SIM card in GSM, and contains subscriber-specific information. It is prepared and sold by the operator of a UMTS Network. The ME is an end system which is independent of the subscription. This clear division between subscriber-specific and subscriber-independent elements allows for the sale and purchase of end systems and subscriptions separately. Early mobile Telecommunication Networks did not make this distinction. It was introduced in GSM and is considered to be one of the factors contributing to its success.

Traditionally, the UE is a single piece of equipment, i.e. a single ME containing a UICC; when 3GPP started work on UMTS, this was a tacit assumption. Increasingly, however, UEs can consist of several networked MEs, e.g. all of the mobile devices of a subscriber, sharing the same UICC.

The ME is composed of the Terminal Equipment (TE) and the Mobile Termination (MT) which we will explain below.



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UE

UICCMobile Equipment (ME)

Terminal Equipment

(TE)

Mobile Termination (MT)

TAF

Access Network

Cu

R

Uu

User Equipment

Fig. 3 UE architecture form


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2.2 Terminal Equipment

The TE can be a specialized UMTS mobile phone. In principle, however, it can be any end system, e.g. a laptop. The TE manages the end system hardware such as display, camera, microphone, etc. It runs the applications, and performs session control by communicating with a peer TE at the other end of the communication session.

2.3 Mobile Termination

The MT terminates the radio transmission, performs radio resource control, deals with security on the radio link and supports mobility and QoS for data received from the TE. It can be integrated with the TE in a mobile phone. However, it can also be a separate card that—together with the UICC—is included in a laptop to make it UMTS capable. In this case the MT contains a Terminal Adaptation Function (TAF) that allows it to interface with the TE. A MT can also support multiple TEs simultaneously, all on the basis of the same UICC, in other words on the basis of a single subscription. In this way Personal Area Networks (PANs) can be supported.

2.4 UICC

This section discusses the UICC, a core concept in 3G Networks, in more detail. The UICC is a smart card, typically of a size 25mm*15mm. It is bought together with the subscription and inserted into the end system, e.g. mobile phone. In fact, the UICC normally resembles the SIM card for GSM that most readers are likely to have come across. The UICC, however, is more general than a SIM card: the SIM card holds subscriber-specific data for precisely one technology, namely GSM. The UICC, by contrast, may hold subscriber-specific data—so called applications—for several technologies: it may hold a SIM application for GSM, a Universal Subscriber Identity Module (USIM) application for UMTS and an IP Multimedia Services Identity Module (ISIM) application for IMS usage, all on the same physical UICC. This way, the user may access GSM, and UMTS including IMS, all with one UE.

A UICC application identifies a user, and, most importantly, identifies how to charge this user. Without it, only emergency calls are possible. AUICC application also contains the secret keys that allow for subscriber authentication. This information is also available on the network side. It is stored, of course, in the HLR.

One important feature is that the UICC is inaccessible to the user. The identifier and secret keys can only be manipulated by the operator who is selling the UICC. The UICC thus creates a secure environment (for the operator) which is essential to many commercial applications. One could speculate that the UICC will prove to be one of the key assets for UMTS operators when it comes to 4G and in competition with other mobile Communication Networks.



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Technically, UICC applications contain the following data:

• USIM [3GPP 31.102]:

o Identifier

International Mobile Subscriber Identity (IMSI), this is a unique identifier of the subscription. The IMSI is a number which is only used within the UMTS Network. It is not used as an identifier with regard to the outside.

(Packet) Temporary Mobile Subscriber Identity (P-TMSI/TMSI), these are the temporary identifiers of a subscription. For security reasons, temporary identifiers are used instead of the IMSI after the UE is attached to the network. The P-TMSI is used for the PS Domain, the TMSI for the CS Domain.

Mobile Station International ISDN number (MSISDN). This is the phone number under which this subscription can be reached. At the same time, the MSISDN is the publicly known identifier – called public identifier - of a subscription…

The identifier information is mirrored in the HLR. o Secret keys. This information is mirrored in the HLR. o Current location—the UE thus replicates the information about location that is

also kept in the network (SGSN, MSC and RNC). o Miscellaneous information such as preferred language, the list of preferred

networks (e.g. the Home Network), etc. o SMS, MMS, etc.

• SIM information is the GSM equivalent to the USIM data above.

Additionally, the UICC contains an address book. The UICC includes a CPU that allows it to access and process the information above, e.g. to perform authentication on the basis of the secret keys.


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3 UTRAN


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3.1 Node B

One or more Node B’s are controlled and addressed by an RNC. A Node B is a physical unit for implementation of the UMTS radio interface. It is converting the physical transmission of the data from fixed network transmission (ATM based) to WCDMA transmission.

As a central transmission and reception site, it serves on or more UMTS cells. It is serving one UMTS cell in case of an omni cell with 360º service or, for example, 2, 3, or 6 sector cells with 180º 120º and 60º service respectively.

The Node B is connected: via Iub interface to its controlling RNC via Uu interface to the UEs.



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RNCRadio Network

Controller

NodeB

RNSRadio

NetworkSub

system

UTRAN

Iub

RNC

NodeB

NodeB

NodeB

UEUu

• Support of 1or several cells• “WCDMA Transmission”• ATM Termination• Forward Error Correction FEC• Radio Interface Measurements

(Quality & Strength)

NodeB

Omni-Cell

Sector-Cell

NodeB

Sector-Cell

Sector-Cell

Fig. 20 (TM2201EU04TM_0002 The UMTS Network, 41)

Node B

Fig. 4 Node B


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3.2 Radio Network Controller

The UMTS Terrestrial Radio Access Network (UTRAN) is sub-divided into Radio Network Subsystems RNS. The Radio Network Controller (RNC) is the central controlling unit of a RNS. It is controlling itself and all the Node Bs of the RNS.

The RNC is connected via the following ATM based interfaces:

• Iub interface: to connected the Node Bs

• Iur interface: to neighboring RNCs

• Iu interface: to the Core Network CN

Due to different protocol stacks, the Iu interface can be sub-divided into an Iu –ps interface and an Iu-cs interface.

The Iu-ps interface is used for data and signaling transmission to the PS domain of the CN, the Iu-cs interface is used for data exchange with the CS domain.

The main task of the RNC is to perform Radio Resource Management RRM for all UEs in its service area. Therefore, it can be compared to the GSM BSC.

Different to the GSM BSC, it is 100% autonomously responsible for all RRM decisions. RRM means to be that the RNC is responsible for signaling with the UEs via Radio Resource Control (RRC) protocol, it is deciding about the allocation of resources, Handover to other cells and release of resources.

The RNC is holding the RRC connection to the UEs as long as data have to be transmitted. It is storing the UEs location information to transmit the data to the right location. The location information can be requested by the CN for Location Based Services. It is responsible for reliable transmission over the radio interface, performing Backward Error Correction in acknowledged mode.

It is responsible for Ciphering/De- Ciphering and Integrity Check.



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RNCRadio Network

Controller

NodeB

RNSRadio

NetworkSub

system

UTRANIu(CS)

Iub

Iur

RNC

NodeB

NodeB

Iub

NodeB

SGSN

UE

IWF/ TC

MSC /VLR

Iu(PS)

Uu

PSDomain

CSDomain

• 100% autonomously RRM(e.g. Radio Resource Control, Access Control,

Admission Control, Handover Control,…)

• (De-)Ciphering & BEC (Layer 2 tasks)• storing UEs location information• RNS-Control (RNC & Node B’s)• ATM Switching

(Iu, Iur & Iub: ATM Interfaces)

• „WCDMA specific tasks“

Radio Network

Controller

Fig. 5 Radio Network Controller


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4 Core Network


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4.1 General Architecture for UMTS R.99

The UMTS networks are based on GSM Phase 2+ Core Networks. This approach safeguards the investments made by today's GSM network operators and reduces the 3G implementation risks. The UMTS Terrestrial Radio Access

Network (UTRAN) is connected to the enhanced Phase 2+ Core Network (CN) via Iu interface. The GERAN and UTRAN can be connected to the same CN. The GSM Mobile Station (MS) is connected to the GERAN via GSM radio interface Um, the UMTS User Equipment (UE) to UTRAN via UMTS radio interface Uu. Important note: In order to allow a smooth evolution, some network elements are used in the 2G and 3G context, such as the MSC. In this material, it will be normally called MSC. If a specific reference to the second or third generation is required, it will be called 2G-MSC and 3G-MSC, respectively. The same is true for the SGSN.

CS Domain The CS Domain of the UMTS CN consists of the following functions:

MSC: Mobile Services switching Center

GMSC: Gateway MSC

SMS-GMSC: Short Message Service Gateway MSC

SMS-IWMSC: Short Message Service Interworking MSC

VLR: Visitor Location Register

TC/IWF: Transcoding & Interworking Function PS Domain The PS Domain of the UMTS CN consists of the following functions:

GGSN: Gateway GPRS Support Node

SGSN: Serving GPRS Support Node

CGF: Charging Gateway Function

BG: Border Gateway Function Entities common to the CS & PS Domain HLR: Home Location Register

AUC: Authentication Center

EIR: Equipment Identity Register



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PSTN

X.25

ISDN

IP

IWF/TC

GMSC

GGSN

MSC /VLR

SGSN

HLR AuCEIRCSEUTRAN

TRAU

BSC

BTS

RNC

BTS

Node B(n x BTS)

RNC

Node B(n x BTS)

Node B(n x BTS)

UE

SMS-GMSCSMS-IWMSC SM-SC

CGF BillingSystem

CS Domain

PSDomain

GSM BSS

Iu(CS)

Iu(PS)

Iub

Iur Ga

Gd

Gn

GcGr

GfCAP

CAP

E

FC/D

Gi

Uu

A

Abis

GbUm

UMTS Network Summary (Rel. ’99)

Fig. 6 UMTS R.99 Core Network


TM51102EN03GLA3


4.1.1 Common Elements

IN Service :

The term Intelligent Network (IN) stands for IN solutions with INAP protocol (only in home PLMN) as well as for the CAMEL solution for international roaming.

The IN platform provides the operators the tools for creating completely new services as well as full access to modify existing one, even on a subscriber basis.

The highly scalable intelligent network platform offers the possibility to efficiently introduce and operate value adding intelligent services. The best example for this is the prepaid service in Mobile Network. Not only prepaid services can be built based on Mobile Network, but also are Virtual Private Network (VPN), Freephone, premium rate, split charging, and many more.

Home Location Register :

The Home Location Register (HLR) is a database in charge of the management of the mobile subscribers. There may be one or more HLRs in GSM PLMN

The HLR is always associated with an Authentication Center (AC). It participates in different procedures, for e.g.:

• It sends all necessary data to the VLR.

• It supports the call setup in case of Mobile Termination Call (MTC) by sending routing information to the Gateway MSC (Interrogation).

• It transmits the security parameters from AuC to VLR on request.

An HLR contains different semi-permanent mobile subscriber data, e.g.:

• IMSI: International Mobile Subscriber Identity

• MSISDN: Mobile Station International ISDN number

• Packet Data Protocol (PDP) address(es), e.g. IP address

• Services: Bearer Services (BS), Tele Services (TS), Supplementary Services(SS)

• A list of all the group IDs a service subscriber is entitled to use to establish voice group or broadcast calls

• CAMEL Subscriber Information(s)

• Service Restrictions (e.g. roaming limitations)

Additionally, the HLR contains different temporary information of the mobile subscriber, e.g.:

• VLR and SGSN addresses

• Mobile station Roaming Number



25

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• SMS flags

The organization of the subscriber data is outlined in GSM 23.008


GMSC

GGSN

MSC /VLR

SGSN

HLR AuC

CS Domain

PS Domain

C

GrGc

Subscriber data (Examples):• Semi-permanent Data: MSISDN, IMSI, Services

(BS, TS, SS), QoS Profile, CSI, Service Restrictions,..• Temporary Data: VLR / SGSN address, MS Non-Reachable flag, MSRN, SMS flags,..

• Subscriber Registration• Storing/Managementsubscriber profiles

• Deliver profiles to VLR/SGSN• Storing Location Information• (VLR / SGSN)• MTC: Deliver Routinginformation to GMSC / GGSN

• Associated with AuC

• Storing „secret Keys“(counterpart: USIM) &Security Algorithm

• Generating Security Parameter(GSM: Triples; UMTS: Quintets)

• Deliver Parameter to VLR / SGSN (via HLR)

• Associated with HLR

BS: Bearer ServiceTS: Tele ServiceSS: Supplementary ServiceCSI: CAMEL Subscription InformationQoS: Quality of ServiceIMSI: International Mobile Subscriber IdentityMSISDN: Mobile Station ISDN NumberMSRN: Mobile Station Roaming Number

D

HLR

Home Location RegisterAuC

Authentication Center

Fig. 7 Home Location Register and Authentication Centre


TM51102EN03GLA3


Authentication Center :

The Authentication Center (AuC) is responsible to store the secret Keys of the subscribers and the security algorithm, which are necessary for the generation of the GSM and UMTS security parameters. On request of the VLR respectively the SGSN the AuC generates the security parameters. They are delivered via HLR to VLR/SGSN to enable Authentication, Ciphering and Integrity Check.

The AuC is connected only with the HLR via the non-standardized interface H. The HLR requests data for authentication and cipher setting from the AuC. The HLR can store this data, and makes it available to the VLR and SGSN on demand. The data delivered from the AuC is used for:

• Mutual authentication of the SIM-card (via IMSI) and the serving PLMN

• Delivering a key to check the communication integrity over the radio path between the user equipment and the VPLMN

• Ciphering over the radio path between the user equipment and the RNC.

The AuC is responsible to store the secret Keys of the subscribers and the security algorithm, which are necessary for the generation of the GSM and UMTS security parameters. On request of the VLR respectively the SGSN the AuC generates the security parameters. They are delivered via HLR to VLR/SGSN to enable Authentication, Ciphering and Integrity Check.

Equipment Identity Register :

Equipment Identity Register (EIR) optional database is used to verify the International Mobile

Equipment Identity (IMEI) numbers. The EIR is organized in three lists:

1. Black list

2. Grey list

3. White list The black list holds IMEIs, which are forbidden in the PLMN. The grey list holds IMEIs under supervision by law enforcement agencies, and the white list holds IMEIs, which are allowed to access the PLMN.

A mobile phone can be also classified as to be unknown in the EIR. The interface F connects the EIR with the VLR, while the Gf interface links it with the SGSN.

The EIR is connected to:

• The SGSN via Gf interface

• The VLR via F interface



27

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• Storing IMEIs(counterpart: ME)on White / Gray / Black List• Performing IMEI Checkon VLR / SGSN request

• optional network functionMSC /VLR

SGSN

EIR

CS Domain

PS Domain

F

Gf

IMEIInternational

Mobile stationEquipment

Identity

EIR

Equipment Identity Register

Fig. 8 Identity Equipment Register


TM51102EN03GLA3


4.1.2 Circuit Switched UMTS Network Element

MSC Server

The MSC-Server is responsible for all call control tasks of the MSC and VLR. Its tasks include the:

• Call control of mobile originated and mobile terminated calls in the CS domain

• The VLR functionality. For all subscribers in the MSC-Server supply area, it holds temporarily the subscriber profile, location information, identities, etc.

• Interaction with the CS-MGW. The MSC-Server determines the QoS parameters required for the subscriber’s application. It is then the responsibility of the CS-MGW to make the bearer available. The interaction between MSC-Server and CS-MGW is done via an open interface, based on the ITU-T H.248 standard.

• Termination of UE-network and network-network signaling. The UE-network signaling is done via the Iu-CS interface. For the network-network signaling, signaling protocols such as the BICC (Bearer Independent Call Control) protocol can be used.

• CDR collection.

The MSC Server is connected to other network elements via the following interfaces:

• A-interface: to the GSM Base Station Controller BSC

• D-interface: to the HLR

• F-interface: to the EIR

• Gs-interface: to the SGSN

• Iu CS-interface: to the RNC

• Mc-interface: to the CS-MGW for separation between call control and bearer control. The ITU standard H.248 respectively its IETF standard equivalent Media Gateway Control (MEGACO) is used on Mc.

• Nc-interface: to GMSC Server for Bearer-Independent Call Control (BICC)

GMSC Server

The GMSC-Server adopts the call control tasks of the GMSC. Its tasks include:

• Interrogation of the HLR

• Termination of network-network signaling

• Interaction with the CS-MGW

• CDR collection

The GMSC Server is connected to other network elements almost the same as MSC-Server.



29

Short Message Service Gateway MSC (SMS-GMSC)

The SMS-GMSC acts as an interface between an external Short Message Service Center SMS-SC and the PLMN, to allow short message to be delivered to MS/UE from the Service Center.

The choice of which MSCs can act as SMS Gateway MSCs is a network operator matter (e.g. all MSCs or some designated MSCs)

Short Message Service Interworking MSC (SMS-IWMSC)

The SMS interworking MSC acts as an interface between the PLMN and a SMS-SC to allow short messages to be submitted from MS/UE to the SMS-SC.

The choice of which MSCs can act as SMS Interworking MSCs is a network operator matter (e.g. all MSCs or some designated MSCs).


MSC /VLR

SGSN

CSDomain

PSDomain

E

Gd

SM-SCShort MessageService Center

SMS-GMSCSMS Gateway MSC

SMS-IWMSCSMS Interworking MSC

all or some designatedMSCs can act as

SMS-GMSC/IWMSC(Network operator

dependent)

TS 23.002

ExternalNetworks

SMS-GMSC

SMS-IWMSC

Fig. 9 SMS-GMSC & SMS-IWMSC


TM51102EN03GLA3


Visitor Location Register

The Visitor Location Register (VLR) is responsible to aid the MSC with information on the subscriber, which are temporarily in the MSC service area. Therefore, in praxis it is always associated with an MSC.

The VLR request the subscriber profiles of subscriber with activated MS/UE it he MSC service area from the Home Location Register (HLR) and stores them temporarily. Temporarily means as long as the subscriber is not registered in a new MSC/VLR, even if he deactivated the MS/UE.

VLR stores temporary data, e.g. information on the subscriber's current location (the Location Area), the state of activation (Attached/Detached).

Furthermore, the VLR is responsible for the initiation of security functions, e.g. the Authentication procedure, the start of ciphering and the TMSI re-allocation. Examples of subscriber data in the VLR:

• MSISDN: Mobile Subscriber ISDN No.

• IMSI: International Mobile Subscriber Identity

• TMSI: Temporary Mobile Subscriber Identity

• LMSI: Local Mobile Subscriber Identity

• MSRN: Mobile Station Roaming Number

• LAI: Location Area Identity

• Authentication Parameter

• The identity of the SGSN where the MS has been registered



31

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* e.g. Authentication, Authorization, Cipher & Integrity Start

MainVLRtasks:

• storing Subscriber profiles• Mobility Management• storing Location Information• controlling

Security Features*

for all UEs in MSC AreaVLR as „MSCs Data Base“:

• Subscriber Profile,e.g. IMSI, MSISDN,

Services (TS, BS, SS),..

• Temporary Subscriber Datae.g. LMSI, TMSI, MSRN,

Security Parameter, Location Information, IMSI attach/detach,..

VLRMSCB

HLR

D• Location Updates• Subscriber Profiles → VLR• Security Parameter

(via HLR → VLR)• Interrogation

(MSRN via HLR to GMSC)

• Location Updates• Subscriber Profiles → VLR• Security Parameter

(via HLR → VLR)• Interrogation

(MSRN via HLR to GMSC)AuC

TS: Tele ServicesBS: Bearer ServicesSS: Supplementary ServicesMSRN: Mobile Station Roaming Number

IMSI: International Mobile Subscriber IdentityLMSI: Local Mobile Subscriber IdentityTMSI: Temporary Mobile Subscriber Identity

VLR

Visitor Location Register

Fig. 10 Visitor Location Register


TM51102EN03GLA3


Transcoding Function TC

The Transcoding TC function is used to perform conversion between standard ISDN 64 kbit/s speech transmission and the UMTS Adaptive Multi-Rate (AMR) speech codec (Specs: 26-series).

The AMR speech coder is a single integrated speech codec with eight source rates from 4.75 kbit/s to 12.2 kbit/s, and a low rate background noise encoding mode. The speech coder is capable of switching its bit-rate every 20 ms speech frame upon command (TS 26.071). Different to GSM, in UMTS the Transcoding function is not part of the Radio Access Network RAN. It has been defined as part of the UMTS Core Network CN. Some optimization procedures allow it be passed through, without transcoding, in the case of UE to UE communication for example, when double-transcoding would be performed for nothing.

Interworking Function

The “classical” Core Network CN interface (e.g. A-G) are all Time Division Multiplexed TDM based (E1/T1). Different to this, the Iu interface between UTRAN and the UMTS CN is ATM-based. An Interworking Function (IWF) is necessary for conversion between TDM-based and ATM-based interfaces.

Remark: IWF and TC function can be stand-alone network elements or be integrated into the UMTS MSC, depending on the manufacturers / network operators decision / demands.



33

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IWF/

TC

TRAU

MSC

Iu(CS)

AB

TCTranscoding

BlaBlaBla

BlaBlaBla

RANRadio Access

Network

CNCore Network

• CN function in UMTS:part of MSC or standalone N.E.

• Conversion of Speech Data (CN ⇔ RAN):using AMR speech codec

• CN: 64 kbit/s (ISDN)• RAN: 4.75 – 12.2 kbit/s (AMR)

AMR: Adaptive MultiRate

FGs

E

C

• Interworking: TDM ↔ ATM• all „classical“ CN-Interfaces (A-G):

TDM based (E1/T1 ≈ PCM30/PCM24)• Iu(CS): ATM based

IWF

4.75 – 12.2 kbit/s 64 kbit/s (ISDN)

UTRAN CN

TC

Transcoding

&

IWF

InterWorkingFunction

VLR

BSC

RNC

Fig, 11 Transcoding and Interworkng Function


TM51102EN03GLA3


4.1.3 Packet Switched Network Element

Serving GPRS Support Node

The Serving GPRS Support Node (SGSN) constitutes an interface between the radio access network and the core network. It is responsible to perform all necessary functions to handle packet switched services to and from the mobile phone. SGSN performs following task:

• Network Access Control

Authentication is one aspect of network access control. Hereby, the network is checking the validity of the subscriber’s USIM and the USIM is checking the validity of the network (SGSN). Only if both sides determine a successful authentication, network services can be used.

Then the subscriber is requesting a service, the Authorization process makes sure, that the subscriber is allowed to use the requested service. The services, the subscriber is authorized to use may depend on his location. Other important tasks of network access control are the collection of Charging Data Records

(CDR) and Operator Determined Barring.

• Mobility Management

Similar to the MSC, the SGSN is responsible for the mobility management, which includes procedures like routing area update and paging.

Packet Routing and Transfer

Its tasks include the classical packet switching aspects, such as relaying, routing, address translation, encapsulation, and tunneling. In contrast to the 2G-SGSN, a 3G-SGSN is not responsible for ciphering and user data compression.

Gateway GPRS Support Node

The Gateway GPRS Support Node (GGSN) constitutes the interface between the PLNM and external packet data networks (PDN). Similar to the SGSN, it is responsible for the PS service provisioning. GGSN performs following task:

• Network Access Control

Two main network access control tasks are performed with a GGSN: It is responsible for screening, i.e. the operator can determine, which type of packets is allowed to be transmitted via a GGSN. Some manufacturers have outsourced this function into a separate firewall. The GGSN is also responsible for charging data generation.

• Mobility Management

The mobility management tasks include HLR inquiries in case of a mobile terminated call.



35

• Packet Routing and Transfer

Packets have to be routed. The GGSN is responsible to relay them from one link to another, determine the next route with the help of routing tables. The GTP protocol is used between the GGSN and SGSN/RNC. The user data is encapsulated to be transparently transmitted between the GGSN and RNC. This is called tunneling.

Border Gateway Function

Roaming is possible for packet switched services. Hereby, user data and signaling information is transmitted between the two PLMN via the interface Gp.

The data has to pass Border Gateways (BG) in each PLMN. The BG interfaces the PLMN and external, inter-PLMN backbone networks. Based on the roaming agreement between two operators, border gateways can perform mutual authentication of each other before a secure connection is established between them and data flows pass via them.

Charging gateway Function

Both SGSN and GGSN generate Charging Data Records (CDR). The CDRs routed via the CGF to the billing system. The interface Ga is used between SGSN/GGSN and Charging Gateway Function (CGF). CGF is responsible to:

• Manage reliable CDRs

• Act as intermediate storage for CDRs

• Pre-processing of CDRs before forwarding them to the billing centre.


TM51102EN03GLA3


4.2 UMTS R.4 Architecture

UMTS networks are designed to offer a wide range of multimedia services. A consequence of more variable services is that the core network must offer more efficient and flexible transport options than the Release 99 network does.

Therefore the UMTS Core Network CS domain is a central aspect of Release 4 modification (TS 23.002). The intention of these modifications is a separation of the call control from the transport the user data. A wide range of bearers must be made available in the core and radio access network to make these new services available for the subscriber. Today’s exchanges and MSCs are optimized for voice transport. An MSC is responsible for:

• Bearer control and bearer management

• Call control

• Service provisioning

With so many different tasks combined in one network element, any modification is costly and time consuming. With a traditional MSC it is very hard for operators to react fast to changing demand in the market. More flexible solutions are required.

Beginning with UMTS Release 4, call control and bearer control and management are separated. The separation of planes is done in the UMTS Release 4 circuit switched domain.

The UMTS Release 99 network elements MSC/VLR, and GMSC are substituted by the network entities MSC-Server, GMSC-Server and CS-MGW (Circuit Switched – Media Gateway).



37

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PSTN/ISDN

Bearer Level

Call ControlLevel

GERAN

UTRAN

Applications and Services

Mc (H.248/MEGACO)Mc

CAPCAP

Nb (e.g. ATM, IP)

Nc (e.g. BICC)

AIu

CD

Iu

A

MEGACO: IETF Media Gateway Control protocolH.248: ITU protocol for Media Gateway ControlBICC: Bearer Independent Call ControlCDR: Call Data RecordsMGW: Media Gateway

PS Domainunchanged

compared to R`99

PS Domainunchanged

compared to R`99

R`4TS 23.002

(G-)MSC Server:• Call Control• Mobility Management• MGW Control• VLR functionality• CDRs• (HLR-Interrogation)

MGW:• Bearer Control• Transmission Resource Management• Data Format Conversion• Transcoding

MSC GMSC

HLR

CS-MGW CS-MGW

UMTS CN R`4

CS Domain

Fig. 12 UMTS Core Network R.4 CS domain


TM51102EN03GLA3


The CS-MGW is responsible for bearer control. Its functions include:

• Bearer control: The requirements for the bearer control are set in the (G)-MSC-Server. The CS-MGW gets this information via an open interface. The CS-MGW must determine, whether it can make bearers available in accordance to the QoS parameters set.

• Bearer channel termination: The different transmission technologies may be in use, e.g. ATM and IP over Ethernet. The ATM bearer then ends in the MGW and the IP bearer begins at the MGW for user data transport.

• Media conversion and payload processing: If the CS-MGW is interfacing UTRAN, voice information must be processed. E.g. voice may be transmitted with 64 kbps in the core network, but for the radio interface, 12.2 kbps speech is required. The UMTS specific voice codec is found in the MGW. The same is true for conference bridges, echo cancellers, etc.

• Mobile specific functions: A CS-MGW must support mobility specific functions, such as SRNC relocation and handover procedures.

The CS MGW can also be connected to other networks such as PSTN and PLMN using the following interfaces:

• A-interface: to the GSM Base Station Controller BSC

• Iu-CS interface: to the RNC

• Nb-interface: to other MGW. Different options are possible on Nb for user data transfer and bearer control signaling (e.g. ATM, IP).



39

4.2.2 Mobile Switching Center Server

Mobile Switching Centre Server (MSC server) concept offers common core network for the GSM and the UMTS subscribers. Release 99 introduces the UTRAN network. NSN's 3G-MSC offers connections both towards the GSM Base Station Subsystem (BSS) and towards the WCDMA-based UMTS Terrestrial Radio Access Network (UTRAN).

When the network architecture based on UMTS Release 4 is introduced, the user and control planes are separated in the network. This means that the 3G-MSC evolves to the direction where the MSC's switching functions are brought to the Media Gateway (MGW) product and the MSC evolves to an MSS-like product.

The MSS product provides call control logic for terminals that use circuit switched logic. MSS mainly comprises the call control and mobility control parts of a GSM/UMTS MSC. The MSS is responsible for the control of mobile originated and mobile terminated circuit switched calls. It terminates the user-network signaling and translates it into the relevant network – network signaling. The MSS also contains a VLR to hold the mobile subscribers' service data and CAMEL related data. MSS

controls the parts of the call state that pertain to connection control for media channels in a MGW.

The MSC server connects to the Media Gateway using the H.248 protocol (MEGACO). The physical connection between the MSC server and Media Gateway (MGW) is Ethernet. The interface between two MGWs performs bearer control and transport through the ATM backbone by using several ATM Adaptation Layer protocols (AAL1, AAL2, and AAL5) or the IP backbone.

The functionality of the MSC server can be divided into two roles: Visited MSS (VMSS) and Gateway MSS.

• VMSS contains VLR and controls the MGW that is connected towards the (BSS and UTRAN) radio networks.

• Gateway MSS functionality is to control the MGW that is performing interworking between packet core network and the external PSTN/ISDN network.

The NSN product that performs the Gateway MSS functionality is called Gateway

Control Server (GCS).


TM51102EN03GLA3


4.2.3 Camel Service Environment CSE

For the introduction of CAMEL services, some network elements have to be enhanced and new functional entities have to be introduced (TS 23.078):

• GSM Service Control Function (gsmSCF): functional entity that contains the CAMEL service logic to implement Operator-Specific Services OSS. It interfaces e.g. with the gsmSSF, the gprsSSF and the HLR.

• GSM Service Switching Function (gsmSSF): functional entity that interfaces the MSC/GMSC to the gsmSCF. The concept of the gsmSSF is derived from the IN SSF, but uses different triggering mechanisms because of the nature of the mobile network.

• GPRS Service Switching Function (gprsSSF): functional entity that interfaces the SGSN to the gsmSCF.

• Home Location Register HLR: for subscribers requiring CAMEL support, the HLR stores different types of CAMEL Subscriber Information CSI (e.g. O-CSI for Mobile Originating Calls, T-CSI for Mobile Terminating Calls). The O-CSI is sent to VLR at Location Update, on data restoration of if the O-CSI is updated by administrative action. The O/T-CSI is sent to the GMSC when the HLR responds to a request for routing information.

• MSC/VLR or SGSN: VLR or SGSN store the different CSI information as part of the subscriber data for subscribers roaming in the MSC/VLR or SGSN area. MSC or SGSN monitor the call states and communicate (internally) with gsmSSF for further proceeding.



41

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AuC

Gn

E

MSC/VLR

GSM Service Switching Function• interfaces MSC/VLR to gsmSCF• derived from IN SSF

• stores CAMEL Subscription Information CSI

GPRS Service Switching Function• interfaces SGSN to gsmSCF

GSM Service Control Function:

contains CAMELservice logic for

Operator-SpecificServices

MSC/VLR & SGSN:store CSI as part ofsubscriber profile

MSC/VLR & SGSN:store CSI as part ofsubscriber profile

CSDomain

PSDomain

gsmSSF gsmSSF

GMSC

gsmSCF

IN HLR

gprsSSF

SGSN GGSN

CSE

CAMEL Service

Environment

Fig. 13 CAMEL Services


TM51102EN03GLA3




43

5 Transport Technologies


TM51102EN03GLA3


5.1 ATM

The basic functioning of Asynchronous Transfer Mode (ATM) can be compared to an inner city street with separate lanes for different traffic types. For example there can be one or more lanes for normal traffic, maybe reserved lanes for bus traffic and finally bicycle lanes all with different properties and resource needs.

ATM, also known as cell relay, is a fast packet switching and multiplexing technology. ATM was developed as part of the work on broadband ISDN to support a universe of services (for example, voice, data and video over public network).

ATM is a connection-oriented, error-detecting protocol. ATM does not offer error correction. Error correction is the responsibility of end user nodes. Minimizing error correction in intermediate nodes provides the advantages of increased speed of switching and elimination of associated delay.

ATM provides efficient support for transmission of bursty wideband services and offers an integrated solution to voice (circuit mode as well as packet voice), data, and video. ATM provides quality of service (QoS) guarantee and reliability even when resources are shared and thus ATM provides the benefit of sharing network resources and predictable network behavior based on packet switching technology.

ATM utilizes statistical multiplexing to take advantage of the inherently bursty nature of applications. For a group of bursty connections, less bandwidth can be reserved than if bandwidth reservation would be based on the peak rate of the connections. Achieved transmissions cost savings are considerable.

The fundamental strategy behind ATM is to split the information into small fixed-size units, called 'cells', that are easy to handle. The fixed size of the cell allows efficient switching. ATM networks allow statistical multiplexing (that is, multiplexing of many connections with variable rate characteristics), which altogether reduces the overall bandwidth requirements.



45

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Voice

Video

Data

Adaptation X

Adaptation Y

Adaptation ZS

WIT

CH

Services Adaptation Layer ATM Layer Physical Layer

ATM Cells

ATM Principle

Fig. 14 Asynchronous Transfer Mode


TM51102EN03GLA3


5.1.1 ATM cell

The user traffic is split and delivered in fixed length packets called ATM cells. The size of the cell is 53 bytes, which is divided into a 5-byte header and a 48-byte payload field. The ATM cell is relayed based on a label in the header: Virtual Channel Identifier (VCI) and Virtual Path Identifier (VPI).



47

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Header

5 bytes

Payload

48 bytes

53 bytes

ATM Cell

Fig. 15 ATM cell structure


TM51102EN03GLA3


There are two formats of an ATM cell (depending on the type of the interface):

• ATM UNI (User-Network Interface) cell that is used for communication between ATM endpoints and ATM switches.

• ATM NNI (Network-Node Interface) cell that is used for communication between ATM switches.

For ATM interfaces in 3G networks, User-Network Interface (UNI) refers to the interface between terminal equipment and a network termination where access protocols apply. The interface between a RNC and a WCDMA BTS is seen as an UNI interface.

Network-Node Interface (NNI) is the interface between two network nodes like a RNC and an MGW.

The figure shows the specified ATM interfaces between network elements in a 3G network.



49

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ATM is employed

UE BS

BS

BS

RNC

RNC

MGW MSC

SGSN GGSN

Uu Iub Iu-CS A

Iur

Iu-PS

Gn

Iub

IubUNI

UNI

NNI

NNI

NNI

NNI

ATM Interfaces

B

Gi

Fig. 16 ATM interface in 3G network


TM51102EN03GLA3


There is a slight difference between the first byte of the UNI and NNI header. The NNI header does not include the Generic Flow Control (GFC) field. Instead the NNI header has a Virtual Path Identifier (VPI) field that occupies the first 12 bits, allowing larger trunks between public ATM switches.



51

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53

52

…

8

7

Payload

6

HEC5

CLPPTVCI4

VCI3

VCIVPI2

VPIGFC1

12345678

Pay

load

(48

byt

es)

Hea

der

(5 b

ytes

)

53

52

…

8

7

Payload

6

HEC5

CLPPTVCI4

VCI3

VCIVPI2

VPI1

12345678

User Network Interface

(UNI)

Network Network Interface

(NNI)

GFC Generic Flow Control

VPI Virtual Path Identifier

VCI Virtual Channel Identifier

PT Payload Type

CLP Cell Loss Priority

HEC Header Error Control

ATM Cell

Fig. 17 Basic ATM cell format


TM51102EN03GLA3


Generic Flow Control (GFC)

Provides local functions, such as identifying multiple stations that share a single ATM interface. This field is typically not used and is set to its default value.

Virtual Path Identifier (VPI)

In conjunction with the VCI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination.

Virtual Channel Identifier (VCI) In conjunction with the VPI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination.

Payload Type (PT) Indicates in the first bit whether the cell contains user data or control data. If the cell contains user data, the second bit indicates congestion, and the third bit indicates whether the cell is the last in a series of cells that represent a single AAL5 frame.

Cell Loss Priority (CLP) Indicates whether the cell should be discarded if there is congestion in the network. If the CLP bit equals 1, the cell should be discarded in preference to cells with the CLP bit equal to zero.

Header Error Control (HEC) Calculates the checksum only on the header itself. The network instantly discards any cell that fails the header error check.



53

5.1.2 ATM connection

ATM is a connection-oriented technique. The end-to-end route is defined through the network at the beginning of the connection setup and the route remains the same throughout the connection. ATM cells are routed on the same route to both directions. This guarantees that the cells arrive in the receiving end in the same order they were sent. Furthermore, cell delay variation is also minimized and since routes are known it is possible to predict link behavior.

• ATM virtual connection

Virtual connections (VC) are used for providing connectivity between communicating endpoints. There are two types of ATM connections:

• Virtual Channel Connection (VCC)

• Virtual Path Connection (VPC).

Each ATM cell contains a label in its header to explicitly identify the VC, to which the cell belongs. This label consists of two parts: Virtual Channel Identifier (VCI) and Virtual Path Identifier (VPI).

Virtual Channel Connection (VCC) is a logical connection in ATM.

Virtual Channel Identifier (VCI) identifies a particular VC link under a given VPC. A specific value of a VCI is assigned each time a VC is switched in the network. Hence, it has only local meaning.

Virtual Path Connection (VPC) is a logical grouping of VCCs having the same endpoints. Thus, all the cells flowing in a single VPC are switched together. Virtual paths are used for bundling a number of virtual channels into a higher bandwidth stream routed through ATM switches. That is, cross-connection and switching can be done on a higher level and not on individual VCC level.

Virtual Path Identifier (VPI) identifies a group of VC links at a given reference point that share the same VPC. A specific value of a VPI is assigned each time a VP is switched in the network.

Transmission path is a bundle of VPs. The following figure shows the relation among VCs, VPs and a transmission path.

Virtual paths help to reduce the control cost by grouping connections that share common paths through the network into a single unit. Network management actions can then be applied to a small number of groups of connections instead of a large number of individual VCC connections.


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Virtual Path Connections (VPCs) have many advantages:

Simplified network architecture

Network transport functions can be separated into those related to individual logical connections (VCC) and those related to a group of logical connections (VPC).

Increased network performance and reliability

The network deals with fewer, aggregated entities.

Segregation of traffic

A form of priority control can be implemented by segregating traffic types requiring different quality of service (QoS).



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VC

VC

Transmission Path

VP

VP

Virtual Channel and Virtual Path

Fig. 18 Relation between transmission path


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Reduced processing and short connection setup time

Much of the work is done when the VPC is set up. By reserving capacity on a VPC in anticipation of later call arrivals, new VCCs can be established by executing simple control functions at the end points of the VPC; no call processing is required at transit nodes. Thus, the addition of new VCCs to an existing VPC involves minimal processing which decreases the connection setup delay.

Enhanced network services

The VPC is used internally in the network but is also visible to the end user. Thus, the user may define closed user groups or closed networks of VC bundles.

• Network elements involved in transport

• The following are the definitions of the network elements involved in the transport of user plane information (from ITU-T I.311):

• VP cross-connect is a network element, which connects VP links. It translates VPI (not VCI) values and is directed by management plane functions − not by control plane functions.

• VC cross-connect is a network element, which connects VC links. It terminates VPCs and translates VCI values and is directed by management plane functions − not by control plane functions.

• VP-VC cross-connect is a network element that acts both as a VP cross-connect and as a VC cross-connect. It is directed by management plane functions − not by control plane functions.

• VP switch is a network element that connects VP links. It translates VPI (not VCI) values and is directed by control plane functions.

• VC switch is a network element that connects VC links. It terminates VPCs and translates VCI values and is directed by control plane functions.

• VP-VC switch is a network element that acts both as a VP switch and as a VC switch. It is directed by control plane functions.

• Routing functions of virtual channels are done at a VC switch/cross-connect. This routing involves translation of the VCI values of the incoming VC links into the VCI values of the outgoing VC links.



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VC Switch / Cross Connect

VP Switch / Cross Connect

VPI 1

VPI 4

VPI 1 VPI 3 VPI 2

VPI 5

VPI 3

VPI 2

VCI 21VCI 22

VCI 21VCI 22

VCI 21VCI 22

VCI 24

VCI 23

Endpoint

of VPC

Fig. 19 VC and VP switch


VP Switch / Cross Connect

VPI 1VCI 21VCI 22

VPI 2VCI 23VCI 24

VPI 3VCI 25VCI 24 VPI 6

VCI 21VCI 22

VPI 5VCI 25VCI 24

VPI 4VCI 23VCI 24

Fig. 20 VP switching


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5.2 IP

Nowadays, engineers are aiming for the convergence of the whole network (from Radio Access to Core) by trying to make what we call “all IP” network. IP is becoming an important transport technology in telecommunication networks as it has too many advantages.

Because of its widespread use and relatively easy implementation, the usage of TCP/IP protocols is, in practice, supported by every WAN and LAN technology used today.

Today TCP/IP protocols are developed and standardized by the Internet Engineering Task Force (www.ietf.org). IETF membership is free and there is no subscription fee for documents.

Although TCP/IP can be mapped and explained with the classical layered OSI-protocol model, there are some differences. There are, for example, no session or presentation layers defined, but the functionality of these is built directly into application layer protocols.

Most data communication uses the client - server model. In this model, a client sends a request to a server that maybe located on another network somewhere on the Internet. The server processes the client’s request and sends a reply to the client. In order for the requests and replies to be understood, the client and the server must speak the same language.



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Client

Service Request

Service Reply

ServerCommunicationNetwork

Fig. 21 Client/Server mode


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5.2.1 IP networks

Internet Protocol (IP) is a layer-3 protocol that is used to carry data over different types of network. IP works in connectionless packet mode; that is, data is transported to the destination without the establishment of a connection between the source and the destination similar to a postal system. Each packet will have an address for both sender and receiver, which is referred to as an IP address. There are two types of IP address: private IP addresses and public IP addresses. Public IP addresses are globally unique in that all IP packets in a public network will have unique IP sender and receiver addresses.



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Street BStreet A Crossing

#1 #2 #2 #3

Host 1 Host 2 Host 2 Host 3

Router

Network A Network B

Fig. 22 Addressing in IP network


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IP is used as the interconnection protocol in the Internet. The use of unique addresses means that every machine connected to the Internet can send packets to any other machine connected to the Internet, assuming this has not been denied for security reasons. Each packet will have an address for the sender and the receiver. Large deliveries may be divided or fragmented into several smaller packets to help transportation. The network does not guarantee when and how the packets will arrive. It is referred to as a best effort network.



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IP Network C

IP Network B

IP Network A

Internet

Router 2

Router 1

Router 3

Fig. 23 IP network example


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5.2.2 IP routing

Any IP device that can forward IP packets (which have a destination address other than its own) to other IP devices is called a router. The process of selecting the best data link and next hop on the route to the right destination network is called routing.



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L1

L2

IP

TCP/UDP

Application

L1

L2

IP

L1’

L2’

IP’Relay

Routing is the process of selecting the next destination using routing table.

Router:• Layer 3 “switch”

• Decides where to transmit the IP packet next, after analyzing the IP header information.

• Depends on data link and physical layer, segmentation or reassembly may be necessary.

Router

Router

Fig. 24 Router and its tasks


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Routing can be either static or dynamic. In static routing the router will have a fixed routing table, which includes the destination IP networks and corresponding next hops. In dynamic routing, the routers exchange information on the destination IP networks and corresponding next hops. This dynamic information is exchanged via routing protocols like the OSPF (Open Shortest Path First), the RIP (Routing Information Protocol), the IGRP (Interior Gateway Routing Protocol) and the BGP (Border Gateway Protocol).

5.2.3 Components in IP networks

Domain name server

The Domain Name System (DNS) is an application layer protocol, which is used to convert difficult-to-remember 32-bit IP addresses to more easily remembered symbolic names, and vice versa. An example of a DNS is gprs.ntc.nsn.com which maps to the IP address 192.168.0.1.

The conversion from the symbolic name to the IP address is done in DNS servers. A DNS server is a database containing IP addresses and corresponding symbolic names. A single DNS cannot store the information on all address-name pair.

As shown in the figure, the host has to translate the IP address for gprs.ntc.nsn.com. For this, the following steps are performed:

1. The host sends a DNS query to its local DNS server, asking for the IP address of gprs.ntc.nsn.com.

2. The local DNS server does not know the answer, because it only has a database of the local users. It forwards the query to a predefined root level DNS server. The root level DNS server replies with a list of IP addresses to .com -level DNS servers.

3. The local DNS server sends the query to the .com DNS servers. The .com DNS server replies with a list of IP addresses of the nsn.com -level DNS servers.

4. The local DNS server sends the query to one of the nsn.com DNS servers, which replies with a list of the addresses of ntc.nsn.com -level DNS servers.

5. The local DNS server then forwards the query to one of the ntc.nsn.com DNS servers. The ntc.nsn.com - level DNS server replies with an IP address corresponding to the gprs.ntc.nsn.com DNS name.

6. The local DNS server forwards the reply to the original host.



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Local DNS Server

Root DNS Server

.com DNS Server

.nsn.com DNS Server

.ntc.nsn.com DNS Server

gprs.ntc.nsn.com?

1

23

4

5

6

gprs = 192.168.0.15192.168.0.15

Client Host

DNS

Fig. 25 Operation in DNS


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Dynamic Host Configuration Protocol

The Dynamic Host Configuration Protocol (DHCP) is used to provide automatic network configuration information from the DHCP server to the DHCP client.

From the IP point of view, the important configuration parameters that a client needs to know are the IP address, netmask, and the default gateway. This means that IP addresses are not assigned permanently to any client, but instead they are allocated from a pool of addresses assigned to a DHCP server. In order to avoid ‘ghost’ users using IP addresses they no longer need, the given IP addresses and the other parameters are associated with a lease time. This lease time can be configured to be from few to several days. Before the lease expires, the client has to try to renew the lease. The client must stop using the IP address if the lease expires.



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DHCP Server

Host

(DHCP Client)

Remote Access Server

(DHCP Client)

Remote Host

DHCP Offer (A)

IP Address : 192.168.0.51

Netmask : 255.255.255.0

Gateway : 192.168.0.1

Lease Time : 5 hours

DHCP Offer (B)

IP Address : 192.168.0.52

Netmask : 255.255.255.0

Gateway : 192.168.0.1

Lease Time : 30 minutes

DHCP

Fig. 26 Operations in DHCP


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Virtual Private Network

A Virtual Private Network (VPN) is a method of securely communicating between a VPN client, such as a user, and the user’s organization's network over a public non-secure network such as the Internet. The VPN concept has been around for some time. The concept of VPN was initially used in telephone networks. Only recently have they become popular due to the prevalence of the Internet and advances in security technologies.

Nowadays many companies use Internet-based VPNs because it is more cost effective than using private networks. Companies use the Internet as a virtual backbone for creating a secure virtual link between their corporate offices and remote offices.

VPN uses a variety of encryption and security mechanisms to make the virtual link secure and to prevent hackers or eavesdroppers from accessing or modifying the data without being detected. VPNs use a technique known as tunneling to transport encrypted data over the Internet. Tunneling involves encapsulating one protocol such as IPX, AppleTalk, or IP, encrypting it, and then encapsulating it into IP datagrams. Tunneling offers the advantage of obscuring the original network layer protocol.

As shown in the figure, the following steps are performed to create a VPN connection:

1. A VPN client dials up to the NAS –Network Access Server, located at the ISP using a Point-to-Point Protocol (PPP) through a PSTN or wireless connection.

2. The NAS communicates with the security server to identify the VPN client.

3. The NAS initiates a communication link using a tunneling protocol over the Internet to the VPN client's organization gateway.

4. The organization’s gateway decides either to accept or reject the established tunnel from the ISP's NAS.

5. The organization gateway queries the organization security server to confirm the tunnel.

6. Once the tunnel is accepted by the organization gateway, the ISP's NAS logs the acceptance/ traffic.

7. The organization gateway exchanges information such as PPP with the VPN client and assigns the client an IP address. is created between the VPN client and the organization gateway to tunnel the data.



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Internet

VPN Client

Security Server

NAS

Company

Gateway

Company

Security Server

1

2 63

4

5

7

ISP

Company

VPN

Fig. 27 Architecture of VPN


TM51102EN03GLA3


Firewalls

A firewall is a system that controls access to and from an insecure external network to the local network of an organization. Firewalls are often implemented at a point where the local network of an organization connects to an external network such as the Internet. This is often the weakest point since it is vulnerable to an attack.

A firewall at this point will allow all the packets leaving and entering the local network to be examined thoroughly. The examination of packets is defined by the control access policy defined in the security policy of the network. Any packets observed by the firewall to come from an insecure source are discarded. As a result, the risk of an attack on the network is reduced.



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Firewall

Secure Private Network

Internet

Firewall

Fig. 28 Placement of the firewall


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75

6 Exercises


TM51102EN03GLA3


Exercise 1

What is the first technology that was newly implemented in the UMTS network?

FDMA

WCDMA

FDD

TDD

Exercise 2

What is the NE that makes the ATM/TDM adaption to the MSC interfaces in the R.99?

TC

IWF

MSC

RNC

Exercise 3

Which of these information is not kept in the USIM?

IMSI

MSISDN

TMSI

Subscriber services

Exercise 4

Where the Ciphering/Deciphering task is handled in the UMTS Network?

Node B

RNC

MGW

MSC



77

Exercise 5

The Iur interface is used between 2 RNCs. What is the purpose of this interface?

There is no use for this interface

It is used for soft handovers

It is used to transfer software files

It is used for redundancy

Exercise 6

Which information is stored in the EIR?

IMSI

MSISDIN

IMEI

K

Exercise 7

Which NEs are responsible for Mobility Management?

RNC

Node B

MSS

SGSN

Exercise 8

Which NE is newly implemented in the UMTS R.4?

GGSN

RNC

MGW

HSS

Exercise 9

What are the tasks of the MSS?

Switching the CS traffic

Call setup and release

Generating charging data

Control the MGWs


TM51102EN03GLA3


Exercise 10

What is the smallest entity used in ATM networks?

Cell

Packet

Time slot

Frame

Exercise 11

Which NE in IP network that provide IP addresses to hosts?

DNS

Router

DHCP Server

Firewall



79

7 Solution


TM51102EN03GLA3


Exercise 1

What is the first technology that was newly implemented in the UMTS network?

FDMA

WCDMA

FDD

TDD

Exercise 2

What is the NE that makes the ATM/TDM adaption to the MSC interfaces in the R.99?

TC

IWF

MSC

RNC

Exercise 3

Which of these information is not kept in the USIM?

IMSI

MSISDN

TMSI

Subscriber services

Exercise 4

Where the Ciphering/Deciphering task is handled in the UMTS Network?

Node B

RNC

MGW

MSC



81

Exercise 5

The Iur interface is used between 2 RNCs. What is the purpose of this interface?

There is no use for this interface

It is used for soft handovers

It is used to transfer software files

It is used for redundancy

Exercise 6

Which information is stored in the EIR?

IMSI

MSISDIN

IMEI

K

Exercise 7

Which NEs are responsible for Mobility Management?

RNC

Node B

MSS

SGSN

Exercise 8

Which NE is newly implemented in the UMTS R.4?

GGSN

RNC

MGW

HSS

Exercise 9

What are the tasks of the MSS?

Switching the CS traffic

Call setup and release

Generating charging data

Control the MGWs


TM51102EN03GLA3


Exercise 10

What is the smallest entity used in ATM networks?

Cell

Packet

Time slot

Frame

Exercise 11

Which NE in IP network that provide IP addresses to hosts?

DNS

Router

DHCP Server

Firewall

3G Architecture

Documents

umts network architecture

different network elements

ps domain network elements

services lbs network

radio network controller

gprs core network elements

introduction umts architecture

ran radio access network