GSM Services

Outlines2.1Classification2.2Bearer Services 2.3Teleservices2.4Supplementary Services

2.4.1 Line Identification Services2.4.2Call Offering Services 2.4.3Call Completion Services 2.4.4Multi Party Supplementary Services 2.4.5Closed User Groups (CUG)2.4.6Advice of Charge2.4.7Call Restriction Services

2.5Value Added Services

• Today, GSM is the first digital cellular mobile communication system to enable international roaming and ISDN service characteristics

• GSM is an open standard for services, infrastructure and communication - independent of the individual countries, network operators and producers, and flexible to the requirements of the individual user

• All this has boosted the development of GSM:– Now, over 300 network operators in 130 countries are

offering GSM services. – Over 150 million customers use GSM.– A considerable share of the world-wide

telecommunication market goes to GSM products and -services

• GSM has been designed, above all, for speech communication

• Although the standard also offers data services, their possibilities are limited by a data rate of 9.6 kbps

• To meet the growing demands of increasingly complex data applications, e.g. in the multimedia or Internet sector, higher data rates are necessary

• Therefore, the system's capacity is constantly being enhanced

• One extension of the GSM standard is High Speed Circuit Switched Data (HSCSD)• This innovation gives the bit rates an enormous boost. HSCSD is circuit-switched and

optimizes the existing transmission rates in two respects: – Firstly, a new channel coding method, available in GSM Phase 2+ in single circuit-switched

data, increases the data rate from 9.6 kbps to 14.4 – Secondly, the bundling of up to 4 timeslots can increase the user data rate to 57.6 kbps. This

allows, for example, • Faster e-mail transfer • Faster file transfer, and • Speedier and thus cheaper webbrowsing and data download from the Internet.

• As most of the services used require higher data rates in the downlink than in the uplink, HSCSD really shows an asymmetrical implementation, e.g. 3 timeslots in the downlink and 1 in the uplink

• This also facilitates mobile station design and avoids battery capacity problems

• In contrast to HSCSD, the General Packet Radio Service GPRS is packet-switched instead of circuit-switched

• The radio network resources are only used if data is actually being transmitted • Thus, billing is no longer based on the duration of the call, but on the amount of

transmitted data • Additionally, the type of data service can be charged, for example web browsing or

WAP access • By bundling up to 8 channels, a data rate of up to 171.2 kbps can be achieved, with

up to 8 subscribers per channel • The more subscribers transmit data within a cell, the more the datarate available to

each individual user is reduced• GPRS requires some modifications to the existing GSM infrastructure • Together with HSCSD, GPRS is a further step towards mobile multimedia

• Enhanced Data Rates for Global Evolution (EDGE) is a technology concentrating on the air interface between the mobile and the base station

• Based on a new modulation process, 8 Phase Shift Keying, or 8-PSK, EDGE achieves three times the data rates of HSCSD and GPRS at the air interface

• Furthermore, with EDGE, the subscriber can use all 8 timeslots at the air interface. In contrast to GSM, a digital data unit at the air interface, a symbol, is not just one bit, but three bits

• This technology allows data rates of almost 474 kbps per user • On the other hand, EDGE is very bit error sensitive and requires

careful planning and a sufficient number of base stations

• The Universal Mobile Telecommunications System (UMTS), represents the 3rd generation of mobile communication

• It achieves bit rates of up to 2 Mbit/s if the mobile is static and no other user is transferring any data

• Realistic situations will allow a maximum of 144 or 384 kbps • The introduction of UMTS won't make GSM unnecessary • Simple services like speech will be dealt with by GSM in the future,

whereas high data rate multimedia services and mobile office applications will be handled by UMTS

• UMTS mainly affects the air interface, where a broadband transmission method achieves high transmission speeds

• This requires considerable changes to the network architecture • Thus, especially at the beginning, a close cooperation with the

existing GSM network structure is necessary to guarantee that services are supplied area-wide

• Bit rates between 300 and 9,600bps can be chosen according to data terminal equipment and the interference situation of the air interface

• With HSCSD, the data rate may increase to 57.6 kbps • All Bearer Services are handled as circuit-switched services between the

mobile data equipment and the NSS requiring a permanent link between the involved components

• A converter, called Packet Assembler-Disassembler or PAD, is used to adapt these signals to the packet-switched mode in public data networks, e.g. the Internet

• With GPRS, a total packet-switched transmission is provided between all data terminal equipment at a maximum bit rate of 171.2 kbps

• Teleservices provide voice and non-voice services • Voice services include normal speech telephony and emergency calls • Non-voice services include the Short Message Service, for example, that is

the sending, receipt and broadcast of short messages • Short messages can be received at any time, even during a call, and are

transmitted over signalling channels • Whereas normal short messages are stored temporarily in the Short

Message Service Center SMSC, with Cell Broadcast they are stored in the Base Station Controller BSC

• The fax services, also referred to as Group 3 facsimile, provide automatic fax service between a mobile fax and a fax machine within a PSTN, or between 2 mobile fax terminals, each with its own MSISDN at a maximum speed of 9.6 kbps

• Supplementary Services can be controlled by the subscriber as well as by the network

• There are two groups of services – First, there are those services which are

provided by the service provider and made available to a customer

– Then there are the services which are invoked by a customer. The desired service is, for example, activated by a customer pressing a particular key, as is the case with line identification

• The supplementary services subdivide into several types

• The Line Identification Services include the Calling Line Identification Presentation (CLIP), that is the display of the caller's number on the called party's mobile station

• Using Calling Line Identification Restriction (CLIR), the calling party can restrict its call number, so it cannot be identified by the called party

• COLP, for identification of the called party by the caller, and Connected Line Identification Restriction

• COLR, if the called party does not want to be identified by the caller

• Call Offering Services are services which allow a customer to forward incoming calls to other target numbers

• Call Forwarding Unconditional CFU ensures that all incoming calls are diverted to a number specified by the customer, independent of the conditions of the call

• Call Forwarding on mobile Subscriber Busy CFB diverts calls only if the called subscriber is making a call and the line is busy

• Supported by the Optimal Routing Service SOR - a GSM Phase 2+ feature -calls are routed directly to the subscriber's current location

• Call Completion Services allow the customer to postpone incomingcalls which he is currently not able to accept, as well as to hold calls while simultaneously making another call

• Call Waiting CW notifies the customer of an incoming call when no traffic channel is available, and the customer is engaged in an active or held call

• The Call Holding Service HOLD permits the customer to interrupt communication on the active call for another call, without losing the connection to the first call

• Multi Party Services, also called conferencing services, allow the customer to communicate with more than one party simultaneously

• The Multi Party Service can be initiated if a customer is in control of at least one active call and one call on hold

• After it has been initiated, parties an be added, disconnected or separated

• Thus the subscriber initiating the service can add more parties to the Multiparty Call and exclude others from conversation

• Closed User Group (CUG) gives a particular group of customers the opportunity to communicate with each other in PLMN or ISDN networks

• The members of a Closed User Group can't communicate with subscribers outside the group

• If desired, one or more subscribers in this group can be authorisedto call subscribers outside, or to receive calls from them

• Emergency calls are not subject to the restrictions of this service

• The service Advice of Charge (AOC) is a supplementary service that allows a mobile subscriber who uses services to receive service-related billing details

• With Reverse Charging, on the other hand, a called subscriber can be charged for certain calls

• For this purpose, each individual call is analyzed and evaluated• Reverse Charging is activated at request by the calling subscriber,

and must be permitted by the called subscriber • At present, Reverse Charging is not implemented in GSM networks

• There are basically two categories of Call Restriction Services: one refers to outgoing calls, and the other to incoming calls. The service offers several possibilities, such as – Barring all outgoing and incoming calls – Barring all outgoing international calls

• Or– Barring all incoming calls except those coming from the country of the

home network • The calls can be barred manually by the subscriber, or by network

configuration

• Value Added Services are supplied by the respective Service Provider or network operator, and can be transmitted either via a normal telephone call or via SMS

• These services offer the supplier a further opportunity - apart from price - to attract customers

• Value Added Services are, for example: – Information on cultural events or traffic announcements via Cell Broadcast – Reservation of a hotel, a flight or a hire car – Help in the event of a car breakdown – Information services – Medical advice – Ticket reservation – Sports news – Delivery services, like sending flowers to a particular person and many more

• The Base Station Subsystem BSS provides the connection between the mobile stations and the Network Subsystem NSS

• The NSS forwards user signals to other mobiles via the BSS or subscribers in the Public Switched Telephone Network (PSTN), andprovides necessary customer data

• The Operation & Maintenance Subsystem (OMS) monitors BSS and NSS performance, and remotely debugs occurring faults in the network elements

• Additional components such as interface elements to data networks, the Short Message Service Center or the Voice Mail System complete the GSM system architecture

• The Base Station Subsystem ensures as complete a network coverage as possible and includes a large number of structurally organised radio cells

• It consists of the following elements: – The Base Transceiver Station – The Base Station Controller – The Transcoder

• The central element of one cell of this kind is a transmitting and receiving unit known as a Base Transceiver Station (BTS).

• This makes the connection to the mobile station via the air interface and controls the transceiver (TRX)

• The transceiver, the central functional unit of the BTS, maintains calls to a maximum of 8 mobile stations via one frequency pair each

• The BTS is also responsible for the monitoring of the signal quality and the encoding and modulation of useful signals

• Via the A-bis interface, it forwards calls, signals and control information destined for the OMS and the NSS to the Base Station Controller (BSC)

• The Base Station Subsystem forwards the signals to the Network Subsystem (NSS) where speech and circuit-switched data are controlled and forwarded to other networks if necessary

• The NSS provides data relevant to security and mobility • The speech signals processed by the transcoder reach the Mobile

Services Switching Center (MSC) via the A interface • The MSC serves as a digital exchange for the forwarding of

messages, connecting mobile subscribers with each other or with subscribers in other networks such as the Public Switched Telephone Network, the ISDN network, or data networks.

• The GSM network is monitored and controlled from a central point. This is the Operation and Maintenance Center (OMC)

• The OMC has the following tasks: – 1. The Fault Management system analyses alarms from the BSS elements.

When faults occur, they are eliminated when necessary via software command or in situ by technicians.

– 2. The Configuration Management function installs the software when new BSS network elements are implemented, manages hardware inventory lists, and changes operation parameters, for example for radio frequencies of a BTS.

– 3. The Software Management system feeds in new software or updates and manages the software inventory lists

• For dealing with customer support and supplying certain services, GSM includes a number of additional components

• The Administration & Billing Center ABC transfers customer data to the appropriate registers of the NSS and into the AUC and the HLR

• The Administration Center is connected to the Personalization Center for SIM Cards (PCS) via an interface

• This makes it possible to disable the SIM card if necessary and protect it from abuse

• The so-called Call Detail Records are used in the Billing Center for bill preparation

• In GSM, the Public Land Mobile Network (PLMN) is a cellular network with a hierarchical structure

• The smallest unit is the radio cell, which the BTS supplies with frequencies, or, in other words, radio channels

• It provides the network coverage. Several radio cells are put together to form administrative areas controlled by a BSC

• Various areas controlled by one BSC each form a location area controlled by a VLR

• It is also possible for a Location Area to cover one BSC only, or even one cell, if reasonable. If a mobile phone subscriber changes to a new Location Area, a Location Update takes place automatically, so the location of the subscriber is known to the network via a VLR linked to the MSC