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GSM Architecture

GSM Architecture. GSM Architecture. GSM consists of three subsystems: RSS- Radio Subsystem. NSS- Network and Switching Subsystem. OSS- Operation Support Subsystem. GSM Various subsystems.

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GSM Architecture

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  1. GSM Architecture

  2. GSM Architecture • GSM consists of three subsystems: • RSS- Radio Subsystem. • NSS- Network and Switching Subsystem. • OSS- Operation Support Subsystem.

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

  4. GSMFunctions of Mobile Station • Voice and data transmission • Radio Transmission termination • Frequency and time synchronization • Monitoring of power and signal quality of the surrounding cells • Radio channel management

  5. Speech encoding/ decoding • Provision of location updates even during inactive state • Mobility management • Equalization of multi path distortions

  6. GSMMobile Station • 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

  7. GSMSIM Card • 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

  8. Functions of SIM • vAuthentication of the validity of the MS when accessing the network • vUser authentication • vStorage of subscriber-related information, which can be: data fixed during administrative phase (e.g., subscriber identification), and temporary network data (e.g., cell location identity).

  9. GSMMobile Identification Numbers • IMEI • MSISDN Mobile Station International Subscriber Directory Number • IMSI • TMSI • MSRN

  10. MSISDN Mobile Station International Subscriber Directory Number • 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 Variable 1 to 3 digits Variable NDC CC SN N(S)N MSISDN : not more than 15 digits

  11. GSMIMSI • 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.

  12. Contents of IMSI 404571200012345 MCC + MNC + Mobile Subs. Identity no.(MSIN) MCC- Mobile Country Code.(240-sweden) (208-france) MNC- Mobile N/w code. - It varies with PLMN Area. - MP-58, MH-66, GJ-57 , HR-34 - it identifies the home GSM PLMN of Subs. MSIN- It identifies the subs within a GSM PLMN Area. It is assigned by an operator.

  13. 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.

  14. GSM, TMSI • 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

  15. GSMMSRN 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. CC SN NDS CC--Country Code, NDC--National Destination Code, SN-- Subs. No.

  16. GSMIMEI • 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

  17. Radio Subsystem • RSS comprises of all Radio Specific entities. • It consists of • Mobile Station (MS) • Base Station Subsystem (BSS) BTS + BSC

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

  19. Base Tranceiver Station (BTS) • BTS is connected to MS via Um interface or Air interface. • BTS is connected to BSC via Abis interface. • A BTS is a network component that serves one cell and is controlled by a BSC. • The prime responsibility of BTS is to transmit and receive radio signals from a mobile unit over an air interface.

  20. BTS transmits freq. & time Synch. Signals. • For this the signals are encoded, encrypted, multiplexed, modulated and then fed to the Antenna System at the cell site.

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

  22. GSMFUNCTIONS OF BSC-II • 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.

  23. GSMFUNCTIONS OF BSC-III • BSC performs call processing • BSC- BTS configurations as per requirement. • Data from OMC and can be down loaded to BSC

  24. 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

  25. TRAU (Transcoder Rate Adapter Unit) • An important component of the BSS that is considered in the GSM architecture as a part of the BTS is the Transcoder/Rate Adapter Unit (TRAU). • The TRAU is the equipment in which coding and decoding is carried out as well as rate adoption in case of data

  26. TRAU • Although the specifications consider the TRAU as a subpart of the BTS, it can be sited away from the BTS (atMSC), and even between the BSC and the MSC.

  27. TRAU • The transcoder is the device that takes 13-Kbps speech or 3.6/6/12-Kbps data multiplexes and four of them to convert into standard 64-Kbps data.

  28. TRAU • First, the 13 Kbps or the data at 3.6/6/12 Kbps are brought up to the level of 16 Kpbs by inserting additional synchronizing data to make up the difference between a 13-Kbps speech or lower rate data, and then four of them are combined in the transcoder to provide 64 Kpbs channel within the BSS.

  29. Four traffic channel can then be multiplexed on one 64-Kpbs circuit. Thus, the TRAU output data rate is 64 Kpbs. Then, up to 30 such 64-Kpbs channels are multiplexed onto a 2.048 Mpbs

  30. BSS • The BSS can be an integrated (Intg) BSS or a distributed (Dist) BSS. • An integrated BSS is a BSS, which has the BSC, and BTS functionality located in the same physical unit. In a distributed BSS, the BTS and BSC are physically separated. • The BSS can have internally (Int) or externally (Ext) located speech transcoding.

  31. BTS TRAU BSC MSC BTS BSC TRAU MSC BTS BSC TRAU MSC GSMTranscoder Configurations 64Kbps To MS To fixed networks 64Kbps 16 Kbps To MS To fixed networks A-bis Interface To MS To fixed networks RF Air Interface A Interface Transcoder (XC) configurations

  32. GSM ARCHITECTURE Voice/Data-Circuit BTS BSC BTS GMSC MSC PSTN VLR HLR EIR BSC BTS BTS Netowrk Management AUC BTS

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

  34. MSC OVERVIEW • It is high performance digital ISDN switch. • It performs switching function for all MS located in the geographic area covered by its assigned BSSs. • It handles all signaling needed for connection setup, connection release & handover of connections to other MSCs.

  35. MSC-I • Mgmt. of required logical radio link channel during call. • Exchanges of signaling information with other system entities. • Standard function of local exchange switch in the fixed network. (e.g. charging

  36. GSMMSC Functions - II • Echo canceller operation control • Gateway to SMS between SMS centers and subscribers • Handle interworking function while working as GMSC

  37. GSMVISITOR LOCATION REGISTER (VLR)-I • 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

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

  39. GSM Home Location Register(HLR)-I • 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.

  40. GSM Home Location Register(HLR)-II • 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

  41. GSM Home Location Register(HLR)-III • 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

  42. GSMAUTHENTICATION CENTRE (AUC )-I • 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.

  43. GSMEQUIPMENT IDENTITY REGISTER ( EIR ) • 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.

  44. Operation and Maintenance Center (OMC) • The Operations and Maintenance Center (OMC) is the centralized maintenance and diagnostic heart of the Base Station System (BSS). • It allows the network provider to operate, administer, and monitor the functioning of the BSS.

  45. Other Network Elements • Other optional network elements that the MSC can interface include: • Billing Center: • Each MSC writes call accounting records to local disk memory. The Billing Center periodically polls the disk records of each MSC to collect the billing data for the PLMN.

  46. Service Center: • The Service Center interfaces with the MSCs to provide special services, such as the Short Message Service (SMS), to mobile subscribers in the PLMN. • The Billing Center and Service Center are not a basic part of the GSM system.

  47. Mapping model to network Example of a GSM network is shown.

  48. Thank you

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