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Requirements: MS Word, Internet.Theory: Introduction to GSMGSM is amobile communication modem; it is stands for global system for mobilecommunication (GSM). The idea of GSM was developed at BellLaboratories in 1970.  It is widely used mobile communicationsystem in the world. GSM is an open and digital cellular technologyused for transmitting mobile voice and data services operates at the850MHz, 900MHz, 1800MHz and 1900MHz frequency bands.Featuresof GSM Module:Improved spectrum efficiency International roaming Compatibility with integrated services digital network (ISDN) Support for new services. SIM phonebook management Fixed dialing number (FDN) Real time clock with alarm management High-quality speech Uses encryption to make phone calls more secure Short message service (SMS) The securitystrategies standardized for the GSM system make it the most securetelecommunications standard currently accessible. Although theconfidentiality of a call and secrecy of the GSM subscriber is justensured on the radio channel, this is a major step in achievingend-to- end security.

The GSM network architecture consists of three major subsystems: Mobile Station (MS) Base Station Subsystem (BSS) Network and Switching Subsystem (NSS) The wireless link interface between the MS and the Base Transceiver Station (BTS), which is a part of BSS. Many BTSs are controlled by a Base Station Controller (BSC). BSC is connected to the Mobile Switching Center (MSC), which is a part of NSS.

Figure shows the key functional elements in the GSM network architecture. Thegeneric GSM network architecture is composed of three subsystems asthe Radio Subsystem (RSS), the network and Switching Subsystem (NSS)and the Operation Subsystem (OSS). The subscriber carries the MobileStation, which is part or RSS. TheRSS basically consists of radio specific equipment such as mobilestation (MS), Base Station Subsystem (BSS) to control the radio link.The connection between RSS and NSS is established with A interfacebased on circuit switched PCM·30 system with 2.048 Mbit/s date rate.The chief components of ass are BSS, cellular layout and base stationcontroller (BSC).

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RadioSubstation (RSS)TheRSS consists of the components that are necessary in order toallocate the radio resources to the individual subscribers. Itprincipally consists of the mobile terminals (mobile phone or mobilestation, MS) and the base station subsystem (BSS).BaseStation Subsystem (BSS)TheMobile Station and the Base Station Subsystem communicate across theUm interface, also known as the air interface or radio link. A BSS iscontrolled by a BSC.A BSS maintains radio connections to an MS,coding/decoding of voice and data rate adaptation to/from thewireless network part. There may be many BSS in a GSM network andeach BSS contains several MS.

Base transceiver station (BTS) and abase station controller (BSC) along with the cellular layout. Thesecommunicate across a standardized Abis interface, allowing operationbetween components made by different suppliers.MobileStation (MS)MSis basically mobile equipment (the handset) which comprises all userequipment and software needed for mobile communication and a smartcard called the Subscriber Identity Module (SIM). The MS, whichcontain a SIM, card in the form of a very small chip bside theequipment. TheSubscriber Identity Module (SIM) contains all subscriber informationnecessary for identifying GSM subscriber. Broadly, it holds asubscriber’s International Mobile Subscriber Identity (IMSI),authentication key and algorithm. SIM is independent of the device orhandset In which it is being used because an MS can be identified viaInternational Mobile Equipment Identity (IMEI). As soon as the SIM isinserted into handset, it becomes immediately programmed for use.

Therefore, it can be inserted into any handset. If you have forgottento carry your handset but are carrying your SIM card, it can beinserted in any borrowed phone for use. Without SIM a handset canaccess only emergency services.

Advances in memory and processingcapacity has enabled SIM cards to be programmed to display custommenus for personalized services and therefore, makes it differentfrom conventional cellular phones, Typically, mobile stations havetransmitted power from 2 W to 1W depending upon the cell size, Ifcell size is smaller, the transmitted power will be less.The NSS hasone hardware, Mobile switching center and four software databaseelement: Home location register (HLR), Visitor location Register(VLR), Authentications center (Auc) and Equipment Identity Register(EIR). The MSC basically performs the switching function of thesystem by controlling calls to and from other telephone and datasystems.

It includes functions such as network interfacing and commonchannel signalling.HLR:The HLR isdatabase software that handles the management of the mobilesubscriber account. It stores the subscriber address, service type,current locations, forwarding address, authentication/ciphering keys,and billings information. In addition to the ISDN telephone numberfor the terminal, the SIM card is identified with an InternationalMobile Subscribes Identity (IMSI) number that is totally differentfrom the ISDN telephone number. The HLR is the reference databasethat permanently stores data related to subscribers, includingsubscriber’s service profile, location information, and activitystatus.VLR:The VLR istemporary database software similar to the HLR identifying the mobilesubscribers visiting inside the coverage area of an MSC.

The VLRassigns a Temporary mobile subscriber Identity (TMSI) that is used toavoid using IMSI on the air. The visitor location register maintainsinformation about mobile subscriber thatis currently physically inthe range covered by the switching center. When a mobile subscriberroams from one LA (Local Area) to another, current location isautomatically updated in the VLR. When a mobile station roams intoanew MSC area, if the old and new LA’s are under the control of twodifferent VLRs, the VLR connected to the MSC will request data aboutthe mobile stations from the HLR. The entry on the old VLR is deletedand an entry is created in the new VLR by copying the database fromthe HLR.AuC:The AuCdatabase holds different algorithms that are used for authenticationand encryptions of the mobile subscribers that verify the mobileuser’s identity and ensure the confidentiality of each call.

TheAuC holds the authentication and encryption keys for all thesubscribers in both the home and visitor location register.EIR:The EIR isanother database that keeps the information about the identity ofmobile equipment such the International mobile Equipment Identity(IMEI) that reveals the details about the manufacturer, country ofproduction, and device type. This information is used to preventcalls from being misused, to prevent unauthorised or defective MSs,to report stolen mobile phones or check if the mobile phone isoperating according to the specification of its type.Whitelist:This listcontains the IMEI of the phones who are allowed to enter in thenetwork.Blacklist:This list onthe contrary contains the IMEI of the phones who are not allowed toenter in the network, for example because they are stolen.

Grey list:This listcontains the IMEI of the phones momentarily not allowed to enter inthe network, for example because the software version is too old orbecause they are in repair. IWF-InterworkingFunction: It is asystem in the PLMN that allows for non speech communication betweenthe GSM and the other networks. The tasks of an IWF are particularlyto adapt transmission parameters and protocol conversions. Thephysical manifestations of an IWF may be through a modem which isactivated by the MSC dependent on the bearer service and thedestination network. The OSS (Operational Support Systems) supportsoperation and maintenance of the system and allows engineers tomonitor, diagnose, and troubleshoot every aspect of the GSM network.GSM offersmuch more than just voice telephony. Contact your local GSM networkoperator to the specific services that you can avail.GSM offersthree basic types of services:Telephony services or teleservices Data services or bearer services Supplementary services TeleservicesThe abilitiesof a Bearer Service are used by a Teleservice to transport data.

These services are further transited in the following ways:VoiceCallsThe most basicTeleservice supported by GSM is telephony. This includes full-ratespeech at 13 kbps and emergency calls, where the nearestemergency-service provider is notified by dialing three digits.Videotextand FacsmileAnother groupof teleservices includes Videotext access, Teletex transmission,Facsmile alternate speech and Facsmile Group 3, Automatic FacsmileGroup, 3 etc.ShortText MessagesShortMessaging Service (SMS) service is a text messaging service thatallows sending and receiving text messages on your GSM mobile phone.In addition to simple text messages, other text data including news,sports, financial, language, and location-based data can also betransmitted.

BearerServicesData servicesor Bearer Services are used through a GSM phone. to receive and senddata is the essential building block leading to widespread mobileInternet access and mobile data transfer. GSM currently has a datatransfer rate of 9.6k. New developments that will push up datatransfer rates for GSM users are HSCSD (high speed circuit switcheddata) and GPRS (general packet radio service) are now available.SupplementaryServicesSupplementaryservices are additional services that are provided in addition toteleservices and bearer services. These services include calleridentification, call forwarding, call waiting, multi-partyconversations, and barring of outgoing (international) calls, amongothers.

A brief description of supplementary services is given here:Conferencing : It allows a mobile subscriber to establish a multiparty conversation, i.e., a simultaneous conversation between three or more subscribers to setup a conference call. This service is only applicable to normal telephony.

Call Waiting : This service notifies a mobile subscriber of an incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call. Call Hold : This service allows a subscriber to put an incoming call on hold and resume after a while. The call hold service is applicable to normal telephony. Call Forwarding : Call Forwarding is used to divert calls from the original recipient to another number. It is normally set up by the subscriber himself.

It can be used by the subscriber to divert calls from the Mobile Station when the subscriber is not available, and so to ensure that calls are not lost. Call Barring : Call Barring is useful to restrict certain types of outgoing calls such as ISD or stop incoming calls from undesired numbers. Call barring is a flexible service that enables the subscriber to conditionally bar calls. Number Identification : There are following supplementary services related to number identification: Calling Line Identification Presentation : This service displays the telephone number of the calling party on your screen.

Calling Line Identification Restriction : A person not wishing their number to be presented to others subscribes to this service. Connected Line Identification Presentation : This service is provided to give the calling party the telephone number of the person to whom they are connected. This service is useful in situations such as forwarding’s where the number connected is not the number dialled. Connected Line Identification Restriction : There are times when the person called does not wish to have their number presented and so they would subscribe to this person.

Normally, this overrides the presentation service. Malicious Call Identification : The malicious call identification service was provided to combat the spread of obscene or annoying calls. The victim should subscribe to this service, and then they could cause known malicious calls to be identified in the GSM network, using a simple command. Advice of Charge (AoC) : This service was designed to give the subscriber an indication of the cost of the services as they are used. Furthermore, those service providers who wish to offer rental services to subscribers without their own SIM can also utilize this service in a slightly different form.

AoC for data calls is provided on the basis of time measurements. Closed User Groups (CUGs) : This service is meant for groups of subscribers who wish to call only each other and no one else. Unstructured supplementary services data (USSD) : This allows operator-defined individual services.Conclusion: Thus we have studied a case study on GSM architecture.