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Gsm basics

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  • 1. GSM & MNPPeshwa Acharya 1
  • 2. GSM  -­‐  Some  facts  •  GSM stands for Global System for Mobile Communications•  It is estimated that 80% of the global mobile market uses this standard.•  GSM evolved because of the need for a standard mobile telephone system that could be deployed across Europe•  It uses the Gaussian Minimum Shift Keying [ GMSK ] technique for modulation•  GSM networks operate in the 900 MHz or 1800 MHz bands
  • 3. Why  GSM?  •  Dominant global market share•  Large number of infrastructure and handset vendor’s giving advantage in terms of price and other commercial terms•  Wide choice of handsets•  Seamless interoperability between networks and handsets•  Global footprint for international roaming including SMS, data and other value added services
  • 4. GSM  Architecture  PSTN    GMSC        VLR        HLR    MSC        AUC   Network Switching      EIR     System    BSC    BTS   Mobile Station  BTS    BTS   BSS
  • 5. Mobile  Station  (MS)   Mobile   Sta+on   Subscriber  IdenAty   Mobile  Equipment   Module  [  SIM  ]      Mobile  staAon    provides  user  access  to  GSM  network  for    Voice  &  Data    Subscriber  data  is  read  from  a  SIM  card  that  plugs  into  MS    Each  MS  has  a  unique  number  called  as    IMEI  number,      Mobile  Transmit  and  Receive  voice  at  13  KB/s    over  air  interface  
  • 6. Base  Transceiver  Station  (BTS)     Air  interface  signalling        Ciphering     Speech  processing  (channel  coding,  interleaving,  and  burst   formaTng)      GeneraAon  of  alarms  and  staAsAcs      Baseband/Radio  frequency  transformaAon  
  • 7. BSC  -­‐  Base  Station  Controller   • ConnecAon  establishment  between   the  MS  and  the  NSS   •   Mobility  management   •   StaAsAcal  raw  data  collecAon   •   Several  BTSs  are  connected  to  the   BSC   •   BSC  Manages  channel  allocaAon,   handovers  and  release  of  channels   at    connected  BTSs  
  • 8. MSC – Mobile Switching Centre •   Exchange  where  calls  are   established,  maintained  and   released     •   Database  for  all  subscribers   and  their  associated  features.     •   Communicates  with  the  BSCs     •   MSC  is  weighted  on  the   number  of  subscribers  it  can   support.  
  • 9. HLR  -­‐  Home  Location  Register   •  MSC  has  all  subscriber  database  stored  in  HLR   •  HLR  has  all  permanent  subscriber  database   •  MSC  communicates  with  HLR  to  get  data  for  subscribers  on  call   MSC   HLR          •  HLR will have the series of all subscriber numbers, which may not be activated or issued .  
  • 10. VLR – Visiting Location Register•  A  subscripAon  when  acAvated  is  registered  in  VLR  •  VLR  has  all  the  subscriber  numbers  which  are  acAve.  •  VLR  has  a  temporary  database  of  all  acAve  subscribers  (on/ off,  locaAon  informaAon)   HLR   MSC   VLR  
  • 11. VLR – Visiting Location Register HLR   MSC   VLR   VLR   MSC  •  MSC  communicates  with  HLR  for  subscribers  coming  from   different  MSCs.  If  the  subscriber  is  found  valid,  then  it   registers  the  subscriber  in  the  VLR  
  • 12. AUC – Authentication Centre•  AuthenAcaAon  is  a  process  by  which  a  SIM  is  verified  •  Secret  data  and  the  verificaAon  process  algorithm  are  stored  in   AUC  •  AUC  is  the  element  which  carries  out  the  verificaAon  of  the  SIM  •  AUC  is  associated  with  the  HLR     MS   MSC   HLR   AUC  
  • 13. EIR  (Equipment  Identity  Register)  •  EIR  is  the  Mobile  Equipment  Database  which  has  a  series  of   IMEIs  •  MSC  asks  the  Mobile  to  send  its  IMEI  •  MSC  then  checks  the  validity  of  IMEI  with  the  EIR  •  All  IMEIs  are  stored  in  EIR  with  relevant  classificaAons   EIR   MSC