System Overview

Chapter 2

This chapter is designed to provide the student with an overviewof the system. It addresses system overview components, theirfunctions, features, and required specifications.

OBJECTIVES:Upon completion of this chapter the student will be able to:

describe the network elements and their main functionality.

describe the physical implementation of Ericsson productsused in the network.

understand the philosophy behind a central system foroperation and maintenance.

describe some of the capabilities and features of OSS.

System Survey

EN/LZT 123 3321 R1C

aa nn kkllBB

iioonnaall llyy

ttnneettnnII

2 System Overview

EN/LZT 123 3321 R1C i

2 System OverviewTable of Contents

Topic Page

NETWORK ELEMENTS ......................................................................15MOBILE SERVICES SWITCHING CENTER............................................................... 16GATEWAY ................................................................................................................... 16HOME LOCATION REGISTER ................................................................................... 17VISITOR LOCATION REGISTER................................................................................ 17AUTHENTICATION CENTER...................................................................................... 18EQUIPMENT IDENTITY REGISTER........................................................................... 18BASE STATION CONTROLLER ................................................................................. 18BASE TRANSCEIVER STATION ................................................................................ 18

SYSTEM ARCHITECTURE..................................................................19GENERAL.................................................................................................................... 20SWITCHING SYSTEM................................................................................................. 20BASE STATION SYSTEM ........................................................................................... 21OPERATION AND SUPPORT SYSTEM ..................................................................... 22OTHER NODES POSSIBLY CONNECTED ................................................................ 25

System Survey

ii EN/LZT 123 3321 R1C

aa nn kkllBB

iioonnaall llyy

ttnneettnnII

2 System Overview

EN/LZT 123 3321 R1C 15

NETWORK ELEMENTS

AUC

HLR EIR

SS

BSS

MSC

BSC

BTS

MS

OMC

Switching System

Information transmissionCall connections and information transmission

VLR

Base Station System

PSTN

Figure 2-1. System model.

$EEUHYLDWLRQV

AUC Authentication CenterBSC Base Station ControllerBTS Base Transceiver StationEIR Equipment Identity RegisterHLR Home Location RegisterMS Mobile StationMSC Mobile services Switching CenterOMC Operation and Maintenance CenterVLR Visitor Location Register

The network is divided into three major systems: Switching System (SS) Base Station System (BSS)

System Survey

16 EN/LZT 123 3321 R1C

Operation and Maintenance Center (OMC)

Each of these contain a number of functional units which makeup the entire system. The functional units are parts in the varioushardware units.

The Switching System is responsible for performing callprocessing and subscriber related functions. It includes thefollowing functional units:

Mobile services Switching Center (MSC) Home Location Register (HLR) Visitor Location Register (VLR) Authentication Center (AUC) Equipment Identity Register (EIR)

All radio-related functions are performed in the Base StationSystem (BSS). These include:

Base Station Controller (BSC) Base Transceiver Station (BTS)

The Operation and Maintenance Center (OMC) handles errormessages originating from the network. OMC has access to boththe Switching System (via MSC) and the Base Station System(via BSC).

MOBILE SERVICES SWITCHING CENTERThe 0RELOH VHUYLFHV 6ZLWFKLQJ &HQWHU 06& performs thetelephony switching functions of the system. It controls calls toand from other telephony and data systems, such as the PublicSwitched Telephone Network (PSTN), Integrated ServicesDigital Network (ISDN), Public Land Mobile Network (PLMN),Public Data Networks and, possibly some private networks.

GATEWAYA gateway is a node that interconnects two networks. If a personin the fixed network (PSTN) wants to make a call to a mobilesubscriber, the exchange in PSTN will connect the call to agateway. The gateway function is often carried out in a MSCknown as the *DWHZD\ 06& *06&. All MSCs in thenetwork can work as a gateway.

2 System Overview

EN/LZT 123 3321 R1C 17

HOME LOCATION REGISTERThe +RPH /RFDWLRQ 5HJLVWHU +/5 database stores andmanages all mobile subscriptions belonging to a specificoperator. The HLR is considered the most important databasebecause it stores permanent data about subscribers, includingsubscribers supplementary services, location information, andauthentication parameters. When a person buys a subscription, itis registered in the operators HLR. The HLR can beimplemented with the MSC/VLR or as a stand-alone database.

HLR Redundancy

When a single HLR fails, all subscribers with records in thatHLR will not be able to roam or receive calls. HLRRedundancy can prevent such a loss of subscriber activity. Thisfeature is achieved by having an additional HLR node for eachHLR node in the network.

HLR Redundancy provides protection against disaster situationssuch as fire at an HLR site. At the same time, it will giveprotection against Signaling failures towards an HLR and willalso lower the lack of availability caused by HLR restarts.

With this feature, the subscriber can make and receive calls evenin disastrous situations like an earthquake with little or nochange in network continuity or functionality.

The HLR Redundancy feature, allows failure to be invisible tothe network and the subscriber. A mated HLR is introduced insuch a way that subscribers and load are shared in normaloperation, and when one HLR fails, the other picks up all trafficnormally routed to the pair.

VISITOR LOCATION REGISTERThe 9LVLWRU /RFDWLRQ 5HJLVWHU 9/5 database containsinformation about all mobile stations currently located in theMSC service area. VLR contains temporary subscriberinformation needed by the MSC to provide service for visitingsubscribers. The VLR can be seen as a distributed HLR. TheEricsson VLR is always integrated in the MSC. When a mobilestation roams into a new MSC service area, the VLR connectedto that MSC requests and stores data about the mobile stationfrom the HLR. If the mobile station makes a call at another time,the VLR will already have the information needed for call set-up.

System Survey

18 EN/LZT 123 3321 R1C

AUTHENTICATION CENTERA database called the $XWKHQWLFDWLRQ &HQWHU $8& isconnected to the HLR. The function of the AUC is to providethe HLR with authentication parameters and ciphering keys.Both provide system security. The AUC protects networkoperators from fraud.

EQUIPMENT IDENTITY REGISTERThe (TXLSPHQW ,GHQWLW\ 5HJLVWHU (,5 database containsmobile equipment identity information which helps to blockcalls from stolen, unauthorized, or defective mobile stations. Forexample, mobile equipment reported stolen can be barred fromthe network.

BASE STATION CONTROLLERThe %DVH 6WDWLRQ &RQWUROOHU %6& provides all the radio-related functions. It is a high capacity switch that providesfunctions including handover, cell configuration data, andchannel assignment. A number of BSCs are served by a MSC.

BASE TRANSCEIVER STATIONThe %DVH 7UDQVFHLYHU 6WDWLRQ %76 handles the radiointerface to the mobile station. The BTS is the radio equipment(transceivers and antennas) needed to serve each cell in thenetwork. A group of BTSs are controlled by a BSC.

2 System Overview

EN/LZT 123 3321 R1C 19

SYSTEM ARCHITECTURECME 20 is the Ericsson implementation of the GSM 900 andand GSM 1800, and CMS 40 is the Ericsson implementation ofGSM 1900.

*06&

Figure 2-2. Ericsson GSM networks system model.

$EEUHYLDWLRQV

AUC Authentication CenterBGW Billing GatewayBSC Base Station ControllerDTI Data Transmission InterfaceEIR Equipment Identity RegisterGMSC Gateway MSCHLR Home Location RegisterILR Interworking Location RegisterMIN Mobile Intelligent Node

System Survey

20 EN/LZT 123 3321 R1C

MS Mobile StationMSC Mobile services Switching CenterMXE Message CenterOSS Operation and Support SystemRBS Radio Base StationSOG Service Order GatewayVLR Visitor Location Register

GENERALAll Ericsson GSM networks are cellular mobile telephonysystems based on the GSM specification. They are based onEricssons latest AXE switching system technology. This meansthat all features and services implemented in AXE over the yearsare standard. In addition, Ericsson GSM networks will utilizefuture AXE developments.

Software development is carried out in stages, creating aplatform where functionality improves with time. The fact thatthe AXE system is module makes it possible to makemodifications, additions and deletions without affecting existingsystem operations.

Hardware development follows the increasing performancerequirements and state-of-the-art technology. With the open-ended structure of AXE architecture, new hardware (forexample, processors and line terminals), are being introducedcontinuously.

SWITCHING SYSTEMMSCs in all Ericsson GSM networks are based on AXEtechnology including modularity. Gateway MSC works as anincoming transit exchange for PLMN. This function is a part ofMSC.

In all Ericsson GSM networks, VLR is always built in to MSC.This makes signaling between the two nodes over the networkunnecessary. Internal signaling can be used, which decreases thesignaling load over the network.

HLR can be implemented with MSC/VLR or implemented as astand-alone node.

AUC and EIR are implemented either as stand-alone nodes or asa combined AUC/EIR node. AUC and EIR are developed by

2 System Overview

EN/LZT 123 3321 R1C 21

Sema Group Telecom Division in Great Britain and are based onstandard industry hardware from Digital.

The DWD 7UDQVPLVVLRQ ,QWHUIDFH 7, is a hardwareplatform implementing the GSM InterWorking Function (IWF)for data communications (bearer and fax teleservices.) DTI isimplemented on the AXE 10 platform integrated in theMSC/VLR. In previous releases, this function is implementedwith an external GIWU (GSM Interworking Unit.) By beingintegrated into the AXE platform, the DTI does not needseparate Operations and Maintenance facilities.

,QWHUZRUNLQJ/RFDWLRQ5HJLVWHU ,/5 is a new product thatcurrently exists in CMS 40 network only. ILR makes inter-system roaming possible, meaning that you can roam in both anAMPS network and a PCS network. ILR consists of an AMPSHLR and a PCS VLR.

BASE STATION SYSTEMBSC in all Ericsson GSM networks is also based on AXEtechnology. It can be implemented as a stand-alone node orintegrated with MSC/VLR.

Ericsson terminology used for BTS is Radio Base Station(RBS). Ericsson GSM networks for 900 and 1800 Mhz has twobasic series of base stations; RBS 200 and RBS 2000 while theEricsson GSM networks for 1900Mhz only uses RBS 2000.

Both series offer products for indoor installations; RBS 200(GSM 900), RBS 205 (GSM 1800) and RBS 2202 as well asoutdoor installations; RBS 203 and 204(GSM 900), RBS 2101and RBS 2102. The latter two being a mini and a compactversion in the 2000 series.

System Survey

22 EN/LZT 123 3321 R1C

OPERATION AND SUPPORT SYSTEMOperation and Support System (OSS) is Ericssonsimplementation of OMC. OSS offers the customer cost effectivesupport for centralized, regional and local operations andmaintenance activities required by a cellular network. OSS is thefunctional entity from which the network operator monitors andcontrols the system. OSS in all Ericsson GSM networks is basedon an application in the product family TMOS, Ericsson'ssystem for Telecommunications Management and OperationsSupport.

OSS can be viewed as a two-level management function. Forcentralized control of a network, the installation of a 1HWZRUN0DQDJHPHQW&HQWHU10&, with subordinate 2SHUDWLRQDQG0DLQWHQDQFH&HQWHUV20&; is advantageous. NMC staff canconcentrate on system-wide issues, whereas local personnel ateach OMC can concentrate on short-term, regional issues. TheOMC and NMC functionality can be combined in the samephysical installation or implemented at different locations.

The OSS is designed as a coherent management system used tosupport a number of other network elements. These are:

Mobile Switching Center (MSC) Base Station Controller (BSC) Visitor Location Register (VLR) Home Location Register (HLR) Equipment Identity Register (EIR) Authentication Center (AUC) mobile Intelligent Network nodes (IN)

2 System Overview

EN/LZT 123 3321 R1C 23

Operation and Support System

NMC

OMC OMC

MIN

MSCBSC

BTS

HLR

AUC /EIR

Figure 2-3. OSS provides for central supervision of all networkelements.

A Base Transceiver Stations (BTSs) are supported through BSCas well.

Other Ericsson certified nodes, MXE (Message Center) forexample; can also be supported.

If mobile Intelligent Network nodes (IN) are available in thesystem these can be supported to some extent.

OSS management areas are based on TelecommunicationManagement Network (TMN). TMN is a model for managementof telecommunication networks. The most important parts are:

Configuration Management

Fault Management

Performance Management

Configuration ManagementIn OSS, the actual cellular network is shown in a Graphical CellDisplay (GCD). The operation and maintenance staff have the

System Survey

24 EN/LZT 123 3321 R1C

ability to zoom in on specific regions of the network to get amore detailed picture of, for example; a cell. They point andclick on a selected part of the screen to zoom in.

Figure 2-4. Graphical Cell Display.

Fault ManagementThe operator can monitor their complete network by using the1HWZRUN6WDWXV3UHVHQWDWLRQ shown in the figure below.. If afailure occurs in the network, one or more alarms are activatedand forwarded to OMC. Different icons are used to show theseverity of the alarm. One icon is used to show critical situationswhile another icon is used to show warnings.

2 System Overview

EN/LZT 123 3321 R1C 25

Figure 2-5. Network Status Presentation Map showing icon fordifferent types of alarms.

Performance ManagementIn order to plan for future use of the cellular network, eachoperator must check the performance of the network. It ispossible for an operator to collect and receive statistics based onboth short-term and long-term measurements.

OTHER NODES POSSIBLY CONNECTED

Message center0HVVDJH FHQWHU 0;( is the node used for handling ShortMessage Service (SMS), cell broadcast, voice mail and fax mail.These services are optional, therefore the node is optional anddoes not belong to the basic system structure.

System Survey

26 EN/LZT 123 3321 R1C

Mobile Intelligent Network Node0RELOH,QWHOOLJHQW1HWZRUN1RGH0,1 is the node used forhandling the mobile IN services (Intelligent Network). MIN isbased on the AXE platform, and comprises much of theexperiences from intelligent network in fixed telephony.

Service Order GatewayOperators administrative systems, normally called a CustomerAdministration Systems (CAS); are very complex. Theseadministrative systems are often very inflexible, and lead to highnetwork adaptation costs.

The 6HUYLFH 2UGHU *DWHZD\ 62* is a product enablingCustomer Administrative Systems to exchange information withEricssons network elements containing service information.With SOG, Ericsson provides a better solution for supplyingcustomer administrative systems with interfaces for serviceorders. New nodes will be supported in future releases.

The Service Order Gateway provides a remote interface to thenetwork elements. It combines functionality for management ofsubscriptions in the Home Location Register (HLR) and theAuthentication Center (AUC) with administration of equipmentin the Equipment Identity Register (EIR).

SOG receives message requests from CAS in the form ofCustomer Service Orders (CSO). SOG interprets the datacontent, manipulates the data and delivers appropriateinformation to the relevant network elements in the form ofNetwork Service Orders (NSO).

2 System Overview

EN/LZT 123 3321 R1C 27

MCMSC

SOGSOG

HLRHLR

I/F

CustomerCustomerAdm.Adm.SystemSystem

OSS/OMCOSS/OMC

AUCAUC EIREIR MINMIN

Figure 2-6. Service Order Gateway (SOG).

Billing GatewayThe %LOOLQJ *DWHZD\ %*: collects billing information, orCall Data Records (CDRs), in files from the network elementsand immediately forwards these to post-processing systems thatuse the files as input. Billing Gateway acts as a billing interfaceto all network elements in an Ericsson network. The flexibleinterface of BGW supports adaptation to new types of networkelements as well. Internal alarms are forwarded to OSS at anOMC.

Most often, the BGW is located in connection to the customeradministration and billing systems and is handled by theadministrative organization.

Figure 2-7 shows some of the billing information possible tosort out from a specific call.

System Survey

28 EN/LZT 123 3321 R1C

isBillable

isRoaming

Roaming

Non-Roaming

Unbillable

Non-Roaming

Roaming

MSCStockholm

MSCMalmoe

Figure 2-7. Billing information.

To summarize, an operator uses the BGW to FROOHFW billinginformation from the network and the SOG to VHQG serviceorder information to different network elements.

Collection = BGW, Billing Gateway

HLRHLR

I/F

CustomerAdm.System

MSCMSC

SOGSOG

Provisioning = SOG, Service Order Gateway

MSCMSC

BGWBGW

AUCAUC EIREIR

Figure 2-8. Gateway products for billing information and serviceorders.