GSM Introduction

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The global system for mobile communications (GSM) is a set of recommendations and specifications for a digital cellular telephone network (known as a Public Land Mobile Network, or PLMN). These recommendations ensure the compatibility of equipment from different GSM manufacturers, and interconnectivity between different administrations, including operations across international boundaries The GSM network is comprised of the following components: Network Elements The GSM network incorporates a number of network elements to support mobile equipment. They are listed and described in the GSM network elements section of this chapter. GSM subsystems In addition, the network includes subsystems that are not formally recognized as network elements but are necessary for network operation. These are described in the GSM subsystems (non-network elements) section of this chapter. Standardized Interfaces GSM specifies standards for interfaces between network elements, which ensure the connectivity of GSM equipment from different manufacturers. These are listed in the Standardized interfaces section of this chapter. Network Protocols For most of the network communications on these interfaces, internationally recognized communications protocols have been used These are identified in the Network protocols section of this chapter. GSM Frequencies The frequency allocations for GSM 900, Extended GSM and Digital Communications Systems are identified in the GSM frequencies section of this chapter.

Transcript of GSM Introduction

  • 05/31/13Tempus Telcosys 1ADA CELLWORKS PVT LTD
  • INTRODUCTION The global system for mobile communications (GSM)is a set of recommendations and specifications for adigital cellular telephone network (known as a PublicLand Mobile Network, or PLMN). Theserecommendations ensure the compatibility of equipmentfrom different GSM manufacturers, and interconnectivitybetween different administrations, including operationsacross international boundaries.05/31/13Tempus Telcosys 2
  • THE GSM NETWORK The GSM network is comprised of the following components: Network Elements The GSM network incorporates a number of network elements tosupport mobile equipment. They are listed and described in the GSMnetwork elements section of this chapter. GSM subsystems In addition, the network includes subsystems that are not formallyrecognized as network elements but are necessary for networkoperation. These are described in the GSM subsystems (non-networkelements) section of this chapter. Standardized Interfaces GSM specifies standards for interfaces between network elements,which ensure the connectivity of GSM equipment from differentmanufacturers. These are listed in the Standardized interfaces section ofthis chapter.05/31/13Tempus Telcosys 3
  • THE GSM NETWORK - CONTINUED Network Protocols For most of the network communications on these interfaces,internationally recognized communications protocols have been used These are identified in the Network protocols section of this chapter. GSM Frequencies The frequency allocations for GSM 900, Extended GSM and DigitalCommunications Systems are identified in the GSM frequencies sectionof this chapter.05/31/13Tempus Telcosys 4
  • DIGITAL NETWORKS GSM networks are digital and can cater forhigh system capacities. They are consistentwith the world wide digitization of thetelephone network, and are an extension ofthe Integrated Services Digital Network(ISDN), using a digital radio interfacebetween the cellular network and the mobilesubscriber equipment.05/31/13Tempus Telcosys 5
  • INCREASED CAPACITY The GSM system provides a greater subscriber capacity thananalogue systems. GSM allows 25 kHz. Per user, that is, eightconversations per 200kHz. Channel pair (a pair comprising onetransmit channel and one receive channel). Digital channel codingand the modulation used makes the signal resistant to interferencefrom the cells where the same frequencies are re-used (co-channelinterference); a Carrier to Interference Ratio (C/I) level of 9 dB isachieved, as opposed to the 18 dB typical with analogue cellular.This allows increased geographic reuse by permitting a reduction inthe number of cells in the reuse pattern. Since this number is directlycontrolled by the amount of interference, the radio transmissiondesign can deliver acceptable performance.05/31/13Tempus Telcosys 6
  • CGI : CELL GLOBAL IDENTITY05/31/13Tempus Telcosys 7MCC MNC LAC CILAICGIMCC = Mobile Country CodeMNC = Mobile Network CodeLAC = Location Area CodeCI = Cell Identity
  • MSISDN05/31/13Tempus Telcosys 8CC NDC SN98 XXX 12345CC = Country CodeNDC = National Destination CodeSN = Subscriber Number
  • MSISDN The Mobile Subscriber ISDN (MSISDN)number is the telephone number of the MS.This is the number a calling party dials toreach the subscriber. It is used by the landnetwork to route calls towards the MSC.05/31/13Tempus Telcosys 9
  • IMSI IMSI (International Mobile SubscriberIdentity) Network Identity Unique To A Sim.05/31/13Tempus Telcosys 10MCC MNC MSIN404 XX 12345..10SIM = Subscriber Identity ModuleMCC = Mobile Country CodeMNC = Mobile Network CodeMSIN = Mobile Subscriber Identity Number
  • IMEI IMEI : Serial number unique to each mobile05/31/13Tempus Telcosys 11TAC FAC SNR SP6 2 6 1IMEI = International Mobile Equipment IdentityTAC = Type Approval CodeFAC = Final Assembly CodeSNR = Serial NumberSP = Spare
  • SUBSCRIBER IDENTIFICATION International Mobile Subscriber Identity (IMSI) Just the IMEI identifies the mobile equipment, other numbers areused to identify the mobile subscriber. Different subscriber identitiesare used in different phases of call setup. The International MobileSubscriber Identity (IMSI) is the primary identity of the subscriberwithin the mobile network and is permanently assigned to thatsubscriber. Temporary Mobile Subscriber Identity (TMSI) The GSM system can also assign a Temporary Mobile SubscriberIdentity (TMSI). After the subscribers IMSI has been initialized on thesystem, the TMSI can be used for sending backward and forward acrossthe network to identify the subscriber. The system automaticallychanges the TMSI at regular intervals, thus protecting the subscriberfrom being identified by someone attempting to monitor the radiochannels. The TMSI is a local number and is always transmitted withthe Local numbers and is always transmitted with the Location AreaIdentification (LAI) to avoid ambiguities.05/31/13Tempus Telcosys 12
  • SUBSCRIBER IDENTIFICATION MODULE(SIM) By making a distinction between the subscriber identity and themobile equipment identity, a GSM PLMN can route calls andperform billing based on the identity of the subscriber rather thanthe mobile equipment being used. This can be done using aremovable Subscriber Information Module (SIM). A smart card isone possible implementation of a SIM module. IMSI. This is transmitted at initialization of the mobile equipment. TMSI This is updated periodically by the PLMN MSISDN This is made up of a country code, a national code and asubscriber number. Location Area Identity (LAI) This identified the current location ofthe subscriber. Subscriber Authentication Key (KI) This is used to authenticatethe SIM.05/31/13Tempus Telcosys 13
  • EQUIPMENT IDENTITY NUMBER International Mobile station Equipment Identity (IMEI) Each MS is identified by an International Mobile station EquipmentIdentity (IMEI) number which is permanently stored in the mobileequipment. On request, the MS sends this number over thesignalling channel to the MSC. The IMEI can be used to identify MS,sthat are reported stolen or operating incorrectly. Equipment Identity Register ( EIR ) A listing of the allowed IMEI is maintained by the PLMNs in theEquipment Identity Register (EIR) to validate the mobile equipment.05/31/13Tempus Telcosys 14
  • Frequency BandsUplink 890 915 MHz 25 MHz05/31/13Tempus Telcosys 15Downlink 935 960 MHz 25 MHz100 KHz 200 KHz 100 KHz1 43 1242 .A 200 KHz carrier spacing has been chosen. Excluding 2x100 KHz edges ofthe band, this gives 124 possible carriers for the uplink and downlink. Theuse of carrier 1 and 124 are optional for operators.
  • GSM Network Architecture05/31/13Tempus Telcosys 16BTSBTSBTSBTSBTSBSCBSCTRAUMSCHLRAUCVLREIRPSTNSMSC
  • MS Mobile Station Mobile station provides user access to GSM networkfor voice and data All GSM mobiles comply to GSM standards Subscriber data is read from a SIM card that plugsinto ME05/31/13Tempus Telcosys 17SIM MEMS
  • MS (cont..) Each MS has a unique number called as IMEInumber, which is stored in EIR forauthentication purposes Mobile camps on to the GSM networkthrough the BTS serving the cell Mobile also scans neighboring cells andreports signal strengths Mobile transmits and receives voice at 13 kb/sover the air interface05/31/13Tempus Telcosys 18
  • Mobile Station Output Power CLASS 1 20 watts Vehicle and Portable CLASS 2 8 watts Portable and Vehicle CLASS 3 5 watts Hand-Held CLASS 4 2 watts Hand-Held (GSM) CLASS 5 0.8 watts Hand-Held (DCS1800) Output power determines: Accessibility in areas of coverage Talk Time and Standby time05/31/13Tempus Telcosys 19
  • Mobile Station Identities CC Country Code NDC National Destination Code SN Serial Number05/31/13Tempus Telcosys 20MSISDN : Mobile Station ISDN NumberIt is the human identity used to call a MobileStationCC SNNDC MSISDN98 250 00134
  • IMSI (International MobileSubscriber Identity) MCC Mobile Country Code MNC Mobile Network Code MSIN Mobile Subscriber Identity Number05/31/13Tempus Telcosys 21MCC MSINMNC IMSI3 2 or 3Not more than 15NMSI
  • IMEI (International MobileEquipment Identity) TAC Type Approval Code FAC Factory Assembly Code SNR Serial Number SP Spare digit (usually used to specifysoftware version)05/31/13Tempus Telcosys 22TAC SPFAC IMEISNR6 162 15
  • SIM ( Subscriber IdentityModule) Removable module inserted when thesubscriber wants to use the ME Two sizes: credit card size and stamp size SIM features and contents are personalized bythe Service Activator ROM 6kb to 16 kb RAM 128 bytes to 256 bytes EEPROM 3kb to 8 kb05/31/13Tempus T