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GSM Architecture

GSM Architecture. Network Subsystem includes the equipments and functions related to end-to-end call. Radio Subsystem includes the equipments and functions related to the management of the connections on the radio path.

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GSM Architecture

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  1. GSM Architecture

  2. Network Subsystem includes the equipments and functions related to end-to-end call. Radio Subsystem includes the equipments and functions related to the management of the connections on the radio path. 3. Operations and Maintenance subsystem includes the operation and maintenance of GSM equipment for the radio and network interface. GSMVarious subsystems

  3. B T S B T S MSC VLR B T S MSC VLR Network Architecture 1 MSC=16 BSC 1 BSC=1024 TRU OSS ( HLR PSTN ISDN Data Networks BSC A Interface A-bis interface Air interface BSC:BASE STATION CONTROLLER, BTS: BASE TRANSRECEIVER STATION, OSS: OPERATION AND SUPPORT SUBSYSTEM.ss

  4. GSM Service Area: Total area served by the combination of all member countries where a mobile can be served. PLMN Service Area:It is one N/W area. MSC Service Area:There can many MSC/VLR in one PLMN area.It is one Mobile Exch. Area. GMSC: All I/C calls for PLMN N/W will be routed through GMSC. In a GSM/PLMN N/W all mobile terminated calls will be routed to a Gateway MSC. Call connections between PLMNs , or to fixed N/Ws must be routed to a GMSC.The GMSC contains the Inter working functions to make these connections. Location Area Cells GSMNetwork Structure

  5. LOCATION AREA:There are several LA in a MSC/VLR combination A LA is a part of the MSC/VLR service area in which a MS may move freely without updating location information to the MSC/VLR exchange that control the LA. Within a LA a paging message is broadcast in order to find the called mobile subs. LA can be identified by system using the LAI. CELL.A cell is an identity served by one BTS. The MS distinguishes between cells using the BASE STATION IDENTIFICATION CODE(BSIC) that the cell site broadcast over the air.

  6. V GSMPLMN Service Area I I II MSC MSC VLR VLR MSC MSC VLR IV III

  7. GSMMSC Service Area LA2 LA3 LA1 VLR MSC LA4 LA6 LA5

  8. GSMCells LA2 LA3 LA1 VLR LA6 C3 LA4 C2 C1 MSC C4 C5 LA5 C6 C=CELL

  9. GSMRelation between areas in GSM Location Area Cell Area served by a BTS Location Area MSC Service Area PLMN Service Area GSM Service Area

  10. GSMLA Coding MCC LAC MNC 3 digit 3 digit 2 Octets LAI MCC:Mobile country code, MNC: Mobile N/W Code, LAC: Location Area code

  11. Voice and data transmission Frequency and time synchronization Monitoring of power and signal quality of the surrounding cells Provision of location updates even during inactive state Equalization of multi path distortions GSMFunctions of Mobile Station

  12. Portable, vehicle mounted, hand held MS identified by unique IMEI(International Mobile Equipment Identity) Shall display at least last ten received, dialled and missed calls Minimum talk time of 1hr 30 min. and standby time of 80 hrs 160 characters long SMS GSMMobile Station

  13. GSMMobile Station - Power Levels Vehicle mounted

  14. Mobile station Power adjustable in 2 db steps.down to 13 db(20mw) , under remote control from BTS . BTS measure received power from MS (minimum) . This is to minimize Co-channel Interference. Adjustment with 13 TDMA frame(60 ms). The required power level is determined by BSC.

  15. SIM Module Unique Subscriber’s ID IMSI and ISDN PIN( Personal Identification Number) Key Ki( Identification Key) , Kc and A3,A5 and A8 algorithms SIM has CPU, ROM, RAM and EPROM GSMSIM Card

  16. IMEI MSISDN IMSI TMSI MSRN GSMMobile Identification Numbers

  17. Mobile Subscriber’s ISDN Number The MSISDN is registered in the telephone directory and used by the calling party for dialing. MSISDN shall not exceed 15 digits. NDS--National Significant Number---Give Routing Information to reach HLR N(S)N--National Significant Number GSMMSISDN 1 to 3 digits Variable Variable CC NDC SN N(S)N MSISDN : not more than 15 digits

  18. International mobile subscriber’s Identity The IMSI is an unique identity which is used internationally and used within the network to identify the mobile subscribers. The IMSI is stored on the subscriber identity module (SIM), the HLR, VLR and AC database. GSMIMSI

  19. 3 digits Not more than 9 digits MCC MNC MSIN NMSI IMSI : Not more than 15 digits GSMIMSI 3 digits MCC--Mobile Country Code, MNC--Mobile N/W Code, MSIN--Mobile Station Identification Number NMSI--National Mobile Station Identity,assigned by Individual Administration. Mobile station Identification Number. It identifies the subs. In a PLMN. First 3 digit identifies the Logical HLR-id of Mobile subs.

  20. Temporary Mobile subscriber’s Identity The TMSI is an identity which guarantees the integrity of the mobile subscribers on the radio interface and protect the Subs. from being identified by those attempting to monitor the Radio CHL. The VLR assigns a TMSI to each mobile subscribers entering the VLR area. Assigned only after successful authentication. TMSI has only local significance i.e. within VLR & area controlled by the VLR TMSI changes on location updation TMSI is less than 8 digit GSM, TMSI

  21. Mobile Station Roaming Number The MSRN is used in the GMSC to set up a connection to the visited MSC/VLR. MSRN--is a temporary identity which is assigned during the establishment of a call to a roaming subs. GSMMSRN CC SN NDS CC--Country Code, NDC--National Destination Code, SN-- Subs. No.

  22. International Mobile Equipment Identity The IMEI is an unique code allocated to each mobile equipment. It is checked in the EIR. IMEI check White List Grey List Black List GSMIMEI

  23. MSC/VLR BSC BSC BSC n BTS n BTS RADIO SUB SYSTEM (RSS) RSS

  24. Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna Transcoding and rate adaption Functionality Time and frequency synchronisation signals transmission. 11 power classes from .01 watts to 320 watts GSMFUNCTION OF BTS -I

  25. Frequency hopping Random access detection Uplink radio channel measurements BTS mainly consists of a set of transceivers (TRX). GSMFUNCTION OF BTS -II

  26. FREQUENCY HOPPING The Mobile Radio Channel is a Frequency selective Fading channel, slow hopping freq. Of a CHL.changes with every TDMA Frame. RATE--216.7 Hops/sec. It reduces the S/N ratio. Base Band Hoping: It involves hopping between freq. On different transreceivers in a cell. Synthesizer Hoping: Hopping from freq. To freq. On the same transreceiver in a cell.

  27. TIMING ADVANCE It It is a solution to time alignment. It works by instructing the mis aligned MS to transmit its burst earlier or later than it normally would. Transmission would occur earlier or later related to previous position ,to reach its timeslot at the BTS in right time . Max. bit times= 63. For 35 KM. With extended range distances up 70 Km or even 121 Km can be handled, using 2 T/S. It Ii

  28. It is connected to BTS and offloads MSC Radio resource management Inter-cell handover Reallocation of frequencies Power control GSMFUNCTIONS OF BSC-I

  29. Time delay measurement of the received signals from MS with respect to BTS clock. Performs traffic concentration to reduce the number of lines from BSC to MSC. GSMFUNCTIONS OF BSC-II

  30. BTS BSS BTS BTS MSC BTS BSC BTS BTS BTS GSMMSC-BSS Configurations Multi - cell site (sector Cells Configuration -5 A A Single - cell site Configuration -1 A Many single cell sites BSS A-bis A-bis Multi - cell site = multi--BTS site Configuration -6 MCC: Mobile Switching Centre BSS: Base Station System BSC: Base Station Controller BTS: Base Transceiver Station

  31. (PSTN) (BSS) Network and Switching Subsystem (NSS) SS7 Signalling D Traffic Path VLR HLR AUC C F E Other MSC A EIR MSC

  32. Manages communication between GSM & other network Call setup functions, basic switching are done MSC takes into account the RR allocation in addition to normal exchange functions MSC does gateway function while its customers roams to other network by using HLR /VLR GSMMSC ( MOBILE SWITCHING CENTRE)

  33. Paging, specifically call handling Location updation Handover management Billing for all subscribers based in its area Reallocation of frequencies to BTSs in its area to meet heavy demands GSMMSC Functions - I

  34. Echo canceller operation control Signaling interface to databases like HLR, VLR. Gateway to SMS between SMS centers and subscribers Handle interworking function while working as GMSC GSMMSC Functions - II

  35. INTERWORKING FUNCTION -It provide the Interfacing Capability to Data N/Ws. -IMF. A part of MSC, provides the subscriber with access to data rate and protocol conversion facilities so that data can be transmitted between GSM Data Terminal Equipment ( DTE ) and a land line DTE.

  36. It controls those mobiles roaming in its area. VLR reduces the number of queries to HLR One VLR may be incharge of one or more LA. VLR is updated by HLR on entry of MS its area. VLR assigns TMSI which keeps on changing. IMSI detach and attach operation GSMVISITOR LOCATION REGISTER (VLR)-I

  37. IMSI & TMSI MSISDN MSRN. Location Area Supplementary service parameters MS category Authentication Key GSMData in VLR

  38. Reference store for subscriber’s parameters, numbers, authentication & Encryption values. Current subscriber status and associated VLR. Both VLR and HLR can be implemented in the same equipment in an MSC. one PLMN may contain one or several HLR. GSM Home Location Register(HLR)-I

  39. Permanent data in HLR Data stored is changed only by man-machine. IMSI, MS-ISDN number. Category of MS ( whether pay phone or not ) Roaming restriction ( allowed or not ). Supplementary services like call forwarding GSM Home Location Register(HLR)-II

  40. Temporary data in HLR The data changes from call to call & is dynamic MSRN RAND /SRES and Kc VLR address , MSC address. Messages waiting data used for SMS GSM Home Location Register(HLR)-III

  41. AUC is a separate entity and physically included in HLR Protect against intruders in air interface Authentication (Ki) and ciphering (Kc) key are stored in this data base. Keys change randomly with each call Keys are never transmitted to MS on air Only calculated response are sent. GSMAUTHENTICATION CENTRE (AUC )-I

  42. AUC AUTHENTICATION & ENCRIPTION Database Kc SRES RAND HLR IMSI1 ki1 Algorithm for Ciphering A8 ki2 IMSI2 Kc ki3 IMSI3 64 bits Algorithm for Authentication A3 Generation of Random Number RAND SRES 32 bits RAND

  43. This data base stores IMEI for all registered mobile equipments and is unique to every ME. Only one EIR per PLMN. White list : IMEI, assigned to valid ME. Black list : IMEI reported stolen Gray list : IMEI having problems like faulty software, wrong make of equipment etc. GSMEQUIPMENT IDENTITY REGISTER ( EIR )

  44. Operations and Maintenance Centre OMC The centralized operation of the various units in the system and functions needed to maintain the subsystems. Dynamic monitoring and controlling of the network

  45. Functions Of OMC • functions • -O&M data function • -Configuration management • --Fault report and alarm handling • -Performance supervision/management • -Storage of system software and data

  46. Four basic security services provided by GSM Anonymity : TMSI Assignment Authentication Encryption: PIN GSMSecurity Management

  47. ENCRIPTION/CIPHERING To encode the burst so that it can not be interpreted by any other device than the receiver. The ciphering algorithm in GSM is called A5 algorithm. It does not bits to burst, meaning that the I/P and O/P to the ciphering process is the same as the I/P: 456 bits per sec.

  48. GSMEncryption Process Plain Text Encryption Process KEY Cipher-text

  49. GSMGeneric Authentication Process RAND Ki RAND Ki Radio Path IMSI A3 A3 IMSI SRES Compare Response SRES Yes/No

  50. Authentication • Authentication is used to check the validity of a mobile subscriber. At N/W At MS Ki Ki RAND( 128 bits ) A3 A3 SRES SRES ( 32 bits ) =? AUTHENTICATION

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