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  2. 2. GSM: SYSTEM ARCHITECTURE 3.2 Prof. Anir udha Sah oo
  3. 3. AUTHENTICATION: Confirm the true identity of the user(or device). Ensures that the subscriber is authorized access to the network. GOALS: Protection of the network against unauthorized use. Protect the operator against the billing fraud.
  4. 4. AUTHENTICATION: Authenticates the identity of the subscriber through the use of a challenge-response mechanism. MS requests access to the network. Forward the IMSI and authentication request to the request authentication The MSC will forward the IMSI to the HLR and Authentication Center (AuC). Triplets. IMSI HLR MS IMSI Request authentication Triplets request Triplets MSC BS AuC TMSI-Temporary Mobile Subscriber Identity HLR-Home Location Register MSC-Mobile Switching Center IMSI-International Mobile Subscriber Identity V f v d e r i y a l i i t y
  5. 5. AUTHENTICATION: The AuC will use the IMSI to look up the Ki associated with that IMSI. The Auc will also generate a 128-bit random number called the RAND. Ki-Individual subscriber authentication key. It is a 128-bit number that is paired with an IMSI when the SIM IMSI card is created. Authentication Center RAND Ki
  6. 6. AUTHENTICATION: The RAND and the Ki are inputted into the A3 encryption algorithm as well as A8 encryption algorithm. The output is the Signed Response (SRES) and Ciphering key(Kc) correspondingly. The RAND, SRES, and Kc are collectively known as the Triplets. RAND RAND Ki A8 A3 32-bit SRES Ki 64-bit Kc
  7. 7. AUTHENTICATION: Once the AuC has generated the triplets, it forwards them to theThe HLR subsequently sends them to the requesting HLR. MSC. MSC stores the Kc and the SRES but forwards the RAND to the MS The and orders it to authenticate. Triplets MSC SRES HLR Request triplets Kc IMSI Triplets IMSI Request authentication Triplets MS AuC BS
  8. 8. AUTHENTICATION: The MS has the Ki stored on the SIM card. The A3 and A8 algorithms also reside on the SIM card. The RAND and Ki are inputted into the A3 and A8 algorithm. Generate the SRES and the Kc respectively. RAND MS Ki Ki RAND SIM A3 SRES A8 Kc
  9. 9. AUTHENTICATION: The MS stores the Kc on the SIM card and sends the generated SRES back to the network. Triplets RAND MSC SRES Kc IMSI Request authentication Triplets IMSI IF SRES = SRES AUTHENTICATION SUCCESSFUL Triplets Request TMSI or IMSI access Request triplets MS HLR AuC
  10. 10. GSM LOCALIZATION: Kind of cell phone tracking mechanism that's possible in GSM phones. The GSM system always knows where a user is currently located. Same phone number is valid worldwide. GSM system performs periodic location updates, even if the user does not use the MS. -provided that the MS is still logged on to the GSM network and is not completely switched off.
  12. 12. GSM LOCALIZATION: HOW? The HLR contains information about the current location. The VLR that is currently responsible for the MS informs the HLR about the location of the MS when it changes. Localization can be done in following four ways.. -Network based -Handset based -SIM based -Hybrid
  13. 13. GSM LOCALIZATION : HYBRID BASED LOCALIZATION: Uses a combination of Network based, Handset based & SIM based technologies. -makes the location more accurate. Example : Global Positioning System (GPS) space based satellite navigation system. allows small electronic receivers to determine their location
  14. 14. GSM LOCALIZATION: To locate an MS and to address the MS following numbers are required..  Mobile Station International ISDN Number (MSISDN) :  Important for GSM user.  Associated with SIM.  Consists of –    Country Code (CC) National Destination Code(NDC) Subscriber Number (SN)
  15. 15. GSM LOCALIZATION: International Mobile Subscriber Identity(IMSI) :  GSM uses the IMSI for internal unique identification of a subscriber.  Consists of – Mobile Country Code (MCC) Mobile Network Code(MNC) Mobile Subscriber Identification Number(MSIN)
  16. 16. GSM LOCALIZATION: Temporary Mobile Subscriber Identity(TMSI):  Give the exact identity of the user signaling over the air interface.  GSM uses the 4 byte TMSI.  TMSI is selected by the current VLR.  Only valid temporarily and within the location area of VLR.
  17. 17. GSM LOCALIZATION: Mobile Station Roaming Number(MSRN) :  Temporary address.  Hides the location of a subscriber.  Consists of – Visitor Country Code(VCC) Visitor National Destination Code (VNDC)
  18. 18. GSM HANDOVER: Handover is the process of switching a radio connection from one BS to another in order to maintain seamless radio connection during mobile station movement. HANDOVER BTS BTS
  19. 19. 1 Handover request GSM HANDOVER: 1 3 5 6 4 2 2 Forward MSC new BSCa handover request from the old BSC. a handover The receives handoverthe handover by transmitting initiates complete MS sendsthe old radio channels inmessage to the old BSC via new Releasestothe the request to the new BSC. sends handover bursts to the the old MSC forwardsthe MS the connection the MS In order to command establish via old BSC. BSC. BSC. BSC new MSC 3 Handover 2 1 command 4 Handover burst 3 5 Handover BSC BSC 5 complete 6 Release 4 5 3 6 HANDOVER SUCCESSFUL 4 BTS BTS NEW OLD
  20. 20. Questions ?
  21. 21. THANK YOU