Global System for Mobile Communication

Global System for Mobile Communication

ObjectiveTo learn about evolution of GSM and its basic architecture

Before GSM: Mobile Telephony MilestonesElectric transmission(Graham Bell)1st wirelesstransmissions(Marconi)1st analog cellular networkDigital Technology(1st digital switch)1st public mobile telephone1st GSM communication(digital cellular network)1 0 1 0 1 0 1 0

Why GSM?1982: Europeans thought of GSM1991: GSM brought in operationGSM: A success!

Development of the GSM Standard1982: Groupe Spcial Mobile (GSM) created within CEPT1985: List of recommendations are settled and intensely supported by the industry.1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries: time-scales for the procurement and deployment, compatibly of numbering and routing plans, tariff principles and definition of accounting.

Development of the GSM Standard1990: The GSM specifications for the 900 MHz are frozen. Specifications start for the 1800 MHz GSM systems. GSM stands as "Global System for Mobile communications"1991: First system trial are running.

Development of the GSM Standard1992: Official commercial launch of GSM service in Europe.1993: -The GSM-MoU has 62 signatories in 39 countriesworldwide. In addition 32 applicants in 19 others countries.-GSM network are operational in Europe.-First commercial services also start outside Europe.-One million subscribers to GSM networks.

GSM Specifications12 SERIESOPERATION ANDMAINTENANCE01 SERIESGENERAL02 SERIESSERVICE ASPECTS03 SERIESNETWORK ASPECTS04 SERIESMS-BSS INTERFACE ANDPROTOCOLS05 SERIESPHYSICAL LAYER ON THERADIO PATH.06 SERIESSPEECH CODINGSPECIFICATIONS07 SERIESTERMINAL ADAPTERSFOR MOBILE STATIONS11 SERIESEQUIPMENT AND TYPEAPPROVAL SPECIFICATIONS10 SERIESSERVICE INTERWORKING09 SERIESNETWORKINTERWORKING08 SERIESBSS TO MSC INTERFACES

GSM BenefitsDigital AdvantagesWorldwide marketOpen systemTechnology low costHigh resistance to interferencesTransmission data rateRoaming Transmission SecurityAdvantages of the GSM standard

GSM ServicesTelephonyEmergency CallsShort Message: Point to PointShort Message: Cell BroadcastData Services

Mobile Data Technology Evolutionthroughput kbps10 k100 k64 k1 M2 M1 k19981999200020012002timeframeEDGEUMTS GPRSHSCSD9.6SMS14.4circuitpacketGPRS = General Packet Radio ServiceHSCSD = High Speed Circuit Switched DataEDGE = Enhanced Data rate for Gsm EvolutionUMTS = Universal Mobile Telecomunication System

Supplementary ServicesNumber IdentificationCall BarringCall ForwardingCall WaitingCall CostMulti-party Call

GSM Frequency

GSM Frequency

Basic Network Overview

Traffic/SignalingTrafficSignalingbla bla bla... RING ! riiiiingNetwork

Network OverviewBSCMSCBTSOMC-ROMC-SMSBSSNSSPSTNOSS

Mobile Station+SIM Card+BatteryHandsetbattery2Wjmhfodkgdjipjf153454Mobile Station=

The SIM-Card Functions25 mm15 mmMicrochip with storeduser informationCredit Card SizePermanent data:-Unique mobile subscriber identity through IMSI number,-Authentication parameter Ki,-Authentication algorithm A3,-Generating encryption key Kc algorithm A8.Removable data:- Temporary Mobile Subscriber Number,- Location Area Identification. SIM-Card

Subscriber IdentificationNatureInternational Mobile Subscriber Identity

Conformity with E212Mobile Station - Integrated Services Digital Network Nb

Similar to ISDN, Conformity with E164/E213Nb. digits32max 101 to 32 to 4total max 15*This code does not identify a geographical areabut an operatorFormatMCCMNCMSINH1 H2 x x x ......... x x xCCNDCSNM1 M2 x x x x x x x xMeaningMobileCountryCodeMobileNetworkCodeMobile SubscriberIdent. NbH1 H2 = Identity of HLR within the home PLMNCountryCode(where subscription has been made)NationalDestinationCode *Mobile Subscriber(national definition)M1 M2 = nbr of logical HLRNational Significant Mobile NumberIdentify a PLMN worldwideIdentify the subscriber of a PLMN

Mobile Identification IMEIType ApprovalCodeTACFACSNRSPFinal AssemblyCodeSerial number(SPare)

MS ClassmarkRevision level (Phase 1, 2, 2+)RF powerEncryption algorithm (A5/1,A5/2)Frequency (900/1800/1900)Short messageClassmarkClassGSM900GSM1800GSM1900Power classes12345

8 W*5 W 2 W**0.8 W1 W**0.25 W4 W1 W**0.25 W4 W*Typical value for car mounted**Typical value for handheld

BSS ArchitectureOMC-RRadioInterfaceA InterfaceAter InterfaceAbis InterfaceNSSBSSOMN InterfaceMSMS

BTSBTS

BTSRadioInterface

BSS Functionality

BSC

BTS

BSS Configuration

Transcoder

NSS ArchitectureMSCMSCAuCEIRVLRHLRPSTN

MSC FunctionalityCall ProcessingOperation and MaintenanceInterworkingBilling

HLR FunctionalitySubscriber ID: MSISDN and IMSICurrent Subscriber VLRSupplementary ServicesSubscriber StatusAuthentication Key and AUC Functionality

VLR FunctionalityMobile StautsLocation Area IdentityTMSIMSRN

EIR FunctionalityWhite ListedGrey ListedBlack Listed

AUC Functionality

OMC Functionality

1876: The telephone was introduced to the public at the Centennial Exposition of the United States in Philadelphia. Alexander Graham Bell was able to transmit speech electrically, in one direction only, over a copper wire circuit of several hundred feet in length. This speaking telegraph was quickly perfected for adequate two-way communication and was offered for business and residential service the following years. Within a short time there were thousands, then tens of thousand, and soon hundreds of thousand of paying customers.

End of the 19th century: While the struggle to search for the ways to utilize the copper wire transmission facility more and more efficiently, a young German scientist named Heinrich Rudolf Hertz discovered a strange and wonderful phenomenon: from an electric spark there seemed to emanate invisible waves of force which could be captured at a distant location by a suitably constructed receiving device. Hertzs own experiments extended only a few yards.

1897: Guglielmo Marconi shows the first wireless transmission over 15 km in Bristol. A few years later(1901), G. Marconi transmitted these waves overseas, and began to call it Radio.

1946: The first public mobile telephone service was introduced in twenty five American cities. Each system used a single, high-powered transmitter and large tower in order to cover distances of over 50 km in a particular market. Nevertheless these early FM push-to-talk telephone systems of the late 1940s used 120 kHz of RF bandwidth in a half duplex mode (only one person on the telephone call could talk at a time), even though the actual telephone-grade speech because of the kHz of baseband spectrum. The large RF bandwidth was needed because of the difficulty in mass producing tight RF filters and low-noise, front-end receiver amplifiers.

1970: A.Pinet introduced in France the first digital switch.

1982: The first commercial cellular system was turned on in Chicago.

1992: GSM, the first fully digital cellular system, was introduced on in Germany and in France.1982:CEPT decides to establish a "Groupe Spcial Mobile" (the initial origin of the Term GSM) in to develop a set of common standards for a future pan-European Cellular Mobile Network.1984:Establishment of three Working Parties to define and describe GSM features:the radio interface,transmission and signaling protocols,interfaces and network architecture.1985, 1986: Discussion and adoption of a list of recommendations to be generated by the Group Spcial Mobile. A so-called permanent nucleus is established to continuously coordinate the work, which is intensely supported by industry delegates. Thinking over a radio transmission prototype.1987:The first Memorandum of Understanding (MoU) is prepared during mid-1987 and signed by 13 European countries in September 1987. Apart from the drafting of the technical specifications within the ad-hoc working groups, European public telecommunication operators worthy recognized the cooperation for commercial and operational aspects. The MoU serves as an adequate forum for discussion on pure operational matters. Its main purposes is to provide a framework for all the necessary measures to be taken by the signatories together to ensure the opening of a commercial service in their respective countries by 1991.The network operators plan the progressive implementation of the networks in each country so that transport routes between the countries of signatories could be brought early into the coverage of the respective systems.1988:Validation and trials, especially the radio interface, show that GSM will work.With the establishment of the European Telecommunication Standards Institute (ETSI), Groupe Spcial Mobile becomes a technical committee:GSM is embodied into European Telecommunications Standards,GSM stands as "Global System for Mobile Communication" grant.1991:First system-trial are running at Telecom 91 exhibition.The GSM Recommendations comprise:more than 130 single documents;include more than 5,000 pages.The GSM MoU of 1987 was later signed by more operators and amended by 1991 to accept members from non CEPT operators countries thus extend its scope to spread cooperation agreements with non-signatory bodies.1993:Aside the GSM-MoU has 62 members (signatories) in 39 countries worldwide; and in addition 32 potential members (observers, applicants) in 19 other countries.GSM networks are operational in Denmark, Finland, France, Greece, Ireland, Italy, Luxembourg, Norway, Portugal, Sweden, Switzerland, United kingdom.The end of 1993 shows one millions subscribers to GSM networks, however more than 80% of them are to be found in Germany alone.

One important question was how far GSM should go in its specification work; that is, to what degree the system had to be specified so as to be identical in all countries, and how much could be left to the operators and suppliers to agree upon.Clearly, without identical air interfaces in all networks, the subscribers are not going to have free roaming between network. This was considered to be the absolute minimum degree of standardization, and these equipment were favored. One might have seen it as advantageous to specify everything in the system, including the hardware and the mobile station and even other parts of the system. It was agreed upon that there would be no attempt to specify the system in such detail. Basically, only the functional interfaces between the majors buildings blocks would be specified. This approach had several advantages, perhaps the most important of which is that for each major building block, the principle of functional specifications offers each operator, and thus the customer, the opportunity to purchase whatever make of equipment he wants, thus setting the stage for maximum competition between manufacturers. For instance the fact that an operator has purchased an exchange from a certain supplier does not force him to go on buying equipment from the same supplier.Standardized electrical interfaces as well as protocols are provided for both the fixed network and subscriber equipment. These include standardized rate adaptations compatible with conventional ISDN (Integrated Services Digital Network) definitions.The features and benefits expected in the GSM were:superior speech quality (equal to or better than the existing analog cellular technology),low terminal and services costs,a high level of security (confidentiality and fraud prevention),international roaming (under one subscriber directory number),support of low power hand-portable terminals,variety of new services and network facilities.It was a logical consequence of the prevailing reality that a measure of Inter-working compatibility with the services offered by other existing telecommunication networks was sought. In particular, the basis for the services in GSM standard can be found in the ISDN concept.

Up to V10* the data services were limited to 9.6 kbps.A new service has been standardized in ETSI to reach 14.4 kbps user rate (AUIR) on one TS. This enhancement is a part of a global strategy aimed at offering higher data rates.This new data rate is the result of a new channel coding on the radio interface. The BSS provides two modes:transparent data service,non transparent data service, using RLP protocol between MS and IWF.

The network can carry two types of information:Traffic: it concerns all the user to user information. It can be voice as well as data.Signaling: the network also requires to carry information for its own working. Their purposes are numerous: traffic data routing, maintenance, security... These data are usually not visible from users point of view.There exists several signaling types:PTS (Per-Trunk Signaling): signaling and voice component are transmitted on the same facility. PTS requires the voice component to be completely built, even if the call cant be completed.CCS (Common Channel Signaling): two separate paths are used for information transfer (one for traffic, another for all-related signaling information). Thus, CCS allows the voice component to be built separately which allows resources to be saved. For instance, no voice facilities would be assigned to the call if the dialed number is busy.

GSM works with CCS(#7)

A GSM system is basically designed as a combination of three major subsystems: the Network SubSystem (NSS), the radio subsystem called the Base station SubSystem (BSS), and the Operation SubSystem (OSS).The Network SubSystem (NSS) includes the equipment and functions related to end-to-end-calls, management of subscribers, mobility, and interfaces with the fixed network (PSTN). It is built on the switch of the system called Mobile-services Switching Center (MSC).The Base station SubSystem (BSS) includes the equipment and functions related to the management of the connection on the radio path. It mainly consists of Base Transceiver Stations (BTS) communicating with the Mobile Station (MS) and one Base Station Controller (BSC) managing the flow of information between the BTSs and the MSC.The Operation SubSystem (OSS) mainly contains Operation and Maintenance Center for NSS (OMC-S) and Operation and Maintenance Center devoted to the BSS (OMC-R). It is connected to all equipment in the switching system and to the BSC (BTSs are not connected to the OSS). Any mobile network or PLMN (Public Land Mobile Network) is related to a public fixed network, commonly to the PSTN (Public Switched Telephone Network).The Mobile Station (MS) is composed of three parts:the handset includes the radio equipment (receiver-transmitter) and the Man-Machine Interface (MMI),the SIM card (Subscriber Identity Module-card): this smart card allows the identification of any subscriber (not only of his equipment) by the network. In particular, he can borrow any mobile without changing anything from the network point of view since he keeps the same SIM-card,the battery.The SIM-Card is a removable smart card, the size of a credit card, and contains an integrated circuit chip with a microprocessor, random access memory, and read-only memory.Many MSs use the SIM-Card which can be snapped out of the credit card SIM, if required.When a mobile users want to make a call, they insert their SIM-Card and provide their Personal Identity Number (PIN), which is compared with a PIN stored within the SIM-CARD. The PIN can also be permanently bypassed by the subscribers if authorized by the service provider. Disabling the PIN code simplifies the call setup but reduces the protection of the user's account in the event of a stolen SIM-CARD.The International Mobile Subscriber Identity (IMSI) is the primary identification of the subscriber within the GSM network and is permanently assigned to him.

The Mobile Subscriber ISDN Number (MSISDN) is the number that the calling party dials in order to reach the GSM subscriber. It is used by the land networks to route calls toward an appropriate GSM network. MSISDN is stored in HLR.Stored inside the Mobile Equipment.Used to replace IMSI or TMSI when both are unavailable (example: Emergency calls without SIM-Card) or when required by the network (for maintenance).Can be used for EIR database updating (when existing):TAC = 6 digits describing the type of equipment,FAC = 2 digits for identification of the factory,SNR = 6 digits for the serial number of the device.The type of MS must be given to the NSS at the beginning of each new connection, because this type can change between calls. The subscriber may insert this SIM-Card into another Mobile Equipment (ME).The classmark of each MS can contain up to five parameters:revision level,RF power capability,encryption algorithm: A5/1, A5/2,frequency capability: P-GSM (2 x 25 MHz), E-GSM (2 x 35 MHz), R-GSM (2 x 4 MHz), GSM 1800, GSM 1900,short message capability.This classmark is sent when the system establishes the radio link between MS and the Base Transceivers Stations.The power class information is the maximum power the MS is able to transmit and is used by the network for several procedures: selection, power control, handover.

The Base Station SubSystem (BSS) is a set of equipment (aerials, transceivers and a controller) that is viewed by the Mobile Switching Center through a single A interface as being the entity responsible for communicating with mobile telephones or Mobile Stations (MSs) in a certain area.The radio equipment of a BSS may be composed of one or more cells, such a BSS may contain one or more Base Transceiver Stations (BTSs).The interface between the BSC and the BTSs is called an Abis interface.The BSS includes two types of equipment:the Base Transceiver Station (BTS functionally includes also the TRAU) in contact with the mobile stations through the radio interface,the BSC, the latter being in contact with the Mobile Switching Center.A BSS contains only one Base Station Controller (BSC).The function split is basically between a transmission equipment, the BTS, and the BSC. BSCs of a same area are connected to a switch. In a GSM system this switch is called MSC (Mobile Switching Center). MSCs are connected to each others.Usually, each MSC is associated to four databases.The Visitor Location Register (VLR) memorizes information about the subscribers physically present in a geographic area. If a subscriber leaves this area, this information is stored in the VLR of another MSC. Each Home Location Register (HLR) is related to a precise number of subscribers. The information present in a subscribers HLR are quite similar to these contained in the VLR of the area where he is but, here, this information is static. Thus the VLR stands for a copy of the HLR more easily available (the VLR and the MS are in the same area). They are always linked, since the HLR memorizes the identity number of the VLR where it can find its subscriber.Authentication Center (AuC): Radio channel use sets a problem of communication safety. In particular operators have to pay attention to the fraudulent resources use. Therefore the network is provided with a system of user authentication. The Equipment Identity Register (EIR) is a list of all the Mobile Equipment: it contains valid and invalid mobile equipment.When a communication comes from the PSTN to a given subscriber, it enters the network in the MSC that contains the subscribers HLR. This MSC is called GMSC (Gateway MSC).