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Channel Overview 3 Types Broadcast Control Channel: Point to Multipoint, Downlink (BTS) to MS)

Channel Overview 3 Types Broadcast Control Channel: Point to Multipoint, Downlink (BTS) to MS)

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Channel Overview 3 Types Broadcast Control Channel: Point to Multipoint, Downlink (BTS) to MS)

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  1. Channel Overview • 3 Types • Broadcast Control Channel: Point to Multipoint, Downlink (BTS) to MS) • (A) BCCH (Board cast Control Channel) It inform the Mobile about system confirmation parameter (LAI, Cell -Identity, Neighbouring Cell Identity. MS select best cell to attach BCCH on full power, never Frequency hopped. • (B) FCCH (Frequency Correction Channel) Which is used to allow a MS to accurately tune to a BS; FCCH Transmits a constant frequency burst of the Radio carrier that is used by the MS for frequency correction.

  2. (C) SCH (Synchronization Channel);- SCH is used to synchronize time. SCH carries TDMA Frame number and BSIC (Base Station Identity Code) • CCCH (Common Control channel). They are Point To Multi Point and UP or Down link and carry signaling information necessary for Access Management function (e.g. allocation of dedicated control channels.) This include --- • 1. PCH (Paging Channel)- Down Link, used for paging when Incoming call. • 2. RACH (Random Access Channel)- Used by MS to request allocation of a specific dedicated control channel. (SDCCH) either in response to a paging message or for call Origination/Registration from the MS. This is an uplink Channel and Point to Point. • 3. AGCH- Down Link- To assign a specific dedicated control channel (SDCCH) to MS (When MS request on RACH). It is Down Link Channel.

  3. Dedicated Control Channel • Full Duplex, Point, For Signalling between BTS, & Certain MS. • (A) SACCH- (Slow Associated Control Channel) • (B) FACCH- (Fast Associated Control Channel) • (C) SDCCH- (Stand Alone Dedicated Control Channel) Duplex chl.which is always allocated to TCH or SDCCH. • SACCH- Slow Associated Control Channel. • It is used for: • Radio link supervision measurement • Power Control • Timing Advance Information • In 26 Frame Traffic Multiframe 13th frame (frame no. 12) is used fro SACCH. SACCH – for NON URGENT PROCEDURES.

  4. FACCH – Fast Associated Control • - Used for Urgent Signalling; like handover during a call. • - During call data is transmitted over TCH instead of Traffic data, this is marked by a flag known as stealing Flag. • SDCCH – Stand alone dedicated Control Channel. • - Duplex, P to P used for Signalling in Higher Layer. • - Carry all Signals when no TCH is allocated to MS. • - Used for Service request, location update, Subscribers Authentication, Ciphering , Equipment Validation, Assignment of a TCH

  5. Mobile Location Update-Request for Service Um A B MS BSS MSC New VLR • MS enters a new area under the control of new VLR. MS came from old VLR. MS listen to LAI (on BCCH) and compare this LAI to old LAI (in SIM) • 1. MS detects a new LA and send channel request over RACH. • 2. BSS receives channel request and allocates a SDCCH and forward channel assignment on AGCH. • 3. MS send Location update request on SDCCH. In this message are TMSI & old LAI • 4. BSS send update request to MSC. • 5. MSC inform VLR for Location update request. MS can identify itself by IMSI or TMSI, in this case it is TMSI, and old LAI. Channel Request RACH 1 Dedicated Signaling Channel Assignment AGCH 2 Location Update Request (TMSI,old LAI SDCCH 3 Location Update Request (TMSI,old LAI 4 Location Update Request (TMSI,old LAI 5

  6. Um A B MS BSS MSC New VLR Request IMSI 6 6. VLR analyses that TMSI received is old. For registration the IMSI of MS is required. VLR request to MSC to get IMSI 7. MSC forward, request for IMSI to MS through BSS. 8. MS reads IMSI and send to BSS over SDDCH and BSS sends to MSC. 9. MSC forwards the IMSI to VLR Request IMSI 7 SDCCH IMSI Acknowledge (IMSI) 8 SDCCH 9 IMSI Acknowledge (IMSI)

  7. B D New VLR MS MSC HLR AUC • AUTHENTICATION:- Key Ki is • required it resides is 1-AUC, 2-SIM, Ki • never transmitted on AIR. • 10. New VLR sends request to HLR for authentication parameters for this IMSI. • 11. HLR send request to AUC. • 12. AUC using IMSI extracts subs Ki, AUC then generate a RAND Applies the Ki, RAND to Authentication algorithm (A3) and cipher Key generation algorithm (A8) to produce SRES, and cipher Key (Kc) AUC then returns to HLR an authentication triplets RAND, SRES, Kc. • 13. HLR forward authentication triplets to VLR. Get Authentication Parameters (IMSI) 10 Get Authentication Parameters (IMSI) 11 Authentication Parameters (SRES,Kc RAND) 12 Authentication Parameters (SERES,Kc RAND) 13

  8. B D New VLR MS MSC HLR AUC Authenticate Mobile Station (RAND) 14 • 14. VLR keeps 2 parameter Kc, SRES for later use and send message (including RAND) to MSC for MS authentication. • 15. MSC send authentication request to MS, MS reads Ki from SIM, Applies RAND, Ki to algorithm (A3) and Cipher Key generation algorithm (A8) to produce SRES and Kc, MS saves Kc and will use Kc for ciphering. • 16. MS returns the generated SRES to MSC. • 17 MSC send SRES to VLR, VLR compares 2 SRES. It equal, MS passes authentication if unequal then SIM disabled. Now MS is under the control of new VLR and MS can be deregistered from old VLR. Authenticate Mobile Station (RAND) SDCCH 15 Authentication Response (SRES) SDCCH 16 Authentication Response (SRES) 17

  9. D D New VLR Old VLR HLR Mobile location update 18 Update Location (MSRN) • 18. VLR allots MSRN. New VLR sends message to HLR informing it that a given IMSI has changed location and send I/c call on MSRN. • 19. HLR insert the MSRN into the record of IMSI, Now HLR returns to the VLR a copy of Subs profile. • 20. HLR will send a message to old VLR for deleting the old entry of IMSI. • 21. Old VLR frees up the old MSRN and deallocates the VLR entry for the specified IMSI, and sends an acknowledgement to HLR Location Update 19 De-register Mobile Station 20 Mobile Station De-registered 21

  10. Um A B CIPHERING MS MSC New VLR BSS • The HLR&Old VLR have been informed that MS has been registered with an MSC, under control of New VLR, New VLR will allocate a TMSI, before this radio channel is encrypted. • 22. VLR request MSC to Cipher Radio Channel. Cipher Key is included in this message • 23. MSC forward this message to BSS. • 24. BSS retrieves the Kc and ask MS to Cipher in uplink. • 25. MS uses Kc already generated (during authentication) to cipher the Uplink and sends Confirmation over the ciphered channel to BSS. • 26 BSS sends Ciphered complete message to MSC. Cipher_Radio_Channel (Kc) 22 Cipher_Radio_Channel (Kc) 23 Cipher_uplink_Channel SDCCH 24 Uplink_Channel_Ciphered SDCCH 25 The BSS Ciphers The down_link_channel Ciphering Completed 26

  11. Um A B MS MSC New VLR BSS TMSI-REALLOCATION Location Update Accept 27 • 27. VLR Informs MSC for MS Location update. In this message New TMSI included. • 28. MSC forward LA updation message (TMSI) to MS • 29. MS stores New TMSI in SIM. MS now sends update complete message to MSC. • 30. MSC request BSS to release signalling connection. • 31. BSS sends “Radio resource” channel release to MS and releases SDCCH. • 32. BSS then inform MSC that radio channel released. Location Update Accept (TMSI) 28 SDCCH Location Update Complete SDCCH 29 Clear Signaling Connection 30 Release Radio Signaling Channel 31 SDCCH Clear Complete 32

  12. MOBILE TO LAND CALL SCENARIO • FOLLOWING PHASES ARE PERFORMED:- • REQUEST FOR SERVICE • AUTHENTICATION • CIPHERING • EQUIPMENT VALIDATION • CALL SETUP • RELEASE

  13. MOBILE TO LAND CONNECTION Um A B MS MSC VLR BSS • Assume that MS is registered with system and • has been allocated TMSI • User enter the MSISDN and them presses the • “send” Key • 1. MS send a channel request on RACH. • 2. BSS allocates a SDCCH on AGCH. MS Now Communicate on SDCCH with BSS & MSC till TCH is allocated • 3. MS send Service request to BSS on SDCCH. In this message are TMSI & LAI. • 4. BSS send Service request to MSC • 5. MSC forward service request to VLR. Now Authentication & Ciphering phases take place. Channel Request RACH 1 Dedicated Signaling Channel Assignment AGCH 2 Service Request SDCCH 3 Service Request 4 Service Request 5 The Authentication Phase The Ciphering Phase

  14. F MS MSC EIR EQUIPMENT VALIDATION 6 • 6. MSC request MS to send IMIE. • 7. MS send IMEI. • 8. MSC request EIR to Check IMEI. EIR check that IMEI is within valid range and valid equipment. • 9. EIR returns the results to MSC if results are – ve then MSC drop the call. If call continue, then MSC inform the N/W of the event. IMEI Request SDCCH IMEI Response (IMEI) SDCCH 7 Check IMEI 8 IMEI Check Results 9

  15. Um A B MS MSC New VLR BSS • There are 2 steps in setting a call • Setting of a voice path between MS & MSC by allocating a radio traffic channel & a voice Trunk • Setting a voice path between MSC & PSTN. • 10. MS send a call setup request to MSC. It included dialled digit • 11. MSC request VLR to supply subs parameters. Requested message contain digit dialled (DD) and service indication (SI). • 12. VLR will check for call barring etc. VLR will supply subs data for call processing. • 13 MSC will inform MS that call is proceeding . Call Setup Request) 10 SDCCH Access Subscriber Data (DD,SI) 11 Subscriber Data 12 Call Proceeding) 13 SDCCH

  16. Um A B MS MSC New VLR BSS Assign Trunk & Radio (TN) • 14 MSC allocates a trunk to BSS for serving MS and request the BSS (TN) to allocate a radio channel (TCH) for MS. • 15 BSS allocate Radio channel on SDCCH. • 16. MS tunes TCH and send acknowledgement to BSS • 17. BSS connects the radio channel to assigned trunk of MSC, BSS deallocate the SDCCH, BSS send trunk & radio assignment message to MSC. 14 Assign Radio Channel (TCH) 15 SDCCH Radio Assignment Complete 16 SDCCH Trunk & Radio Assignment Complete 17

  17. MS MSC PSTN • CALL SETUP – WITH LAND N/W - A path has been • established between MS & MSC now a path will be established • from MSC to PSTN • 18. MSC send a N/W setup message to PSTN. In message are dialled digit and details of Trunk to be used for call. • 19. PSTN inform MSC with networking alerting message. MS will hear ringing tone from PSTN. • 20. MSC inform MS that the destination number is being alerted. • 21. When B. party go off-hook, PSTN will inform the MSC of this event. Billing start, MS is connected to the destination party. • 22. MSC informs the MS that the Connection has been established. • 23. MS acknowledges the receipt of the connect message. Networking Setup (DD.) 18 Networking Alerting 19 Alerting TCH 20 Connect (Answer) 21 Connect TCH 22 Connect Acknowledgment TCH 23

  18. Um A B MS BSS MSC PSTN RELEASE OF CALL Disconnect TCH • 24. MS initiate the release of call by pressing end button. MS will send the Disconnect message to MSC. • 25. MSC send Release message to PSTN End to END connection is terminated. • 26. MSC send Release message to MS. • 27. MS send Release Complete message. • 28. Voice Trunk between MSC & BSS is released. • 29. The Traffic channel is cleared. • 30. The Release of the Resources is completed. 24 Networking Release 25 Release 26 TCH Release Complete 27 TCH Clear Command 28 Channel Release 29 TCH Clear Command 30

  19. LAND TO MOBILE CALL • PHASES OF A LAND TO MOBILE CALL. • ROUTING ANALYSIS • PAGING • AUTHENTICATION • CIPHERING • EQUIPMENT VALIDATION • CALL SETUP • RELEASE

  20. C PSTN Home MSC HLR VLR ROUTING ANALYSIS • Assume that MS is already registered and • allocated TMSI and MS in his home system • 1. PSTN subscriber dials MS ISDN. • 2. GMSC request HLR to provide routing information about this MS. • 3. HLR provide MSRN to GMSC, if MS is roaming is its home MSC area then MSRN = MS ISDN, if roaming in different MSC area then MS ISDN & MSRN are different. Assume that MS roaming in Home MSC area. • 4. MSC inform VLR for a call to MS, In the message is MSRN. • 5. VLR respond to MSC by LAI & TMSI. Incoming Call (MSISDN) 1 Get Route (MSISDN) 2 Routing Information (MSRN) 3 Incoming call (MSRN) 4 Perform Page (LAI, TMSI) 5

  21. C D PSTN Home MSC Visited MSC VLR • If MS is barred for I/c calls, then VLR inform • MSC accordingly, them MSC will connect • announcement. • IF MS ROAMING IN ANOTHER MSC • AREA. • 4. The call is routed from home MSC to the visited MSC and MSRN is transmitted then to the VLR • 5. The VLR sends a message to the visited MSC asking it to performs paging by passing to it the new LAI & TMSI of the MS. Route the Call (MSRN) 4 Incoming call (MSRN0 Perform Page (LAI, TMSI) 5

  22. PAGING Home or Visited VLR Home or Visited MSC Um A B MS BSS Perform Page (TMSI) 6 • 6. MSC used LAI given by VLR to determine which BSS should page, included in the message is the TMSI. • 7. BSS broadcast TMSI, of MS in paging channel (PCH). • 8. MS detects TMSI, or IMSI on paging channel MS asks channel request on RACH. • 9. BSS allocates SDCCH on AGCH. Now onwards MS communicate as SDCCH till MS gets a TCH. • 10. MS responds paging on SDCCH, in the message MS sends TMSI, LAI. • 11. BSS send this message to MSC. • 12. MSC informs its VLR that MS has responded. Page PCH 7 Channel Request RACH 8 Dedicated Signaling Channel Assignment AGCH 9 Page Response (TMSI,LAI) SDCCH 10 Page Response 11 Page Response 12

  23. Home or Visited VLR Home or Visited MSC Um A B MS BSS • Authentication Ciphering, Equipment validation • are done in same manner as in Mobile to Land call. • In the case, the MS is visiting a new MSC area, • the authentication and Equipment Validation are • performed as follows. • The Visited VLR request the authentication parameters from the Home AUC through the Network connecting the two MSCs and then through the “HOME” HLR. • The Equipment Validation phase involves the visited MSC & the “HOME EIR”. • There are again two steps in setting up a voice • path for a call from a mobile to a PSTN subscriber. • The call setup with the mobile :- A voice path is created between MS & MSC by allocating a TCH and a voice trunk. • The call setup with the land N/W:- Where a voice path is established between the MSC & a PSTN N/W The Authentication The Cipher phase The Equipment Validation N/W

  24. Home or Visited MSC MS BSS Call Setup • 13. MSC inform MS that a call can be setup. • 14. MS perform compatibility check it acknowledges the call setup message by setup confirm. • 15. MSC selects a trunk to BSS and request BSS to allot a radio channel (TCH). • 16. BSS allot TCH and transmits an Assignment command over SDCCH to MS. • 17. MS tunes to TCH and transmits an assignment complete message back to BSS. MS user phone rings. MS do not use SDCCH after it gets TCH. • 18. BSS on receiving assignment complete message connects the TCH to Trunk. SDCCH is free now and send Assignment Complete Message to MSC. 13 SDCCH Call Setup Confirm SDCCH 14 Assign Trunk & Radio Channel 15 Assign Radio Channel SDCCH 16 Radio Assignment Complete SDCCH 17 Trunk & Radio Assignment Complete 18

  25. Home or Visited MSC MS PSTN Mobile Alerting TCH • 19. MS got TCH, MS begin alerting the user after if receives a TCH. A alerting message is sent to MSC. • 20. MSC on getting alerting indication from MS will generate ringing to calling party and send a N/W alerting to PSTN. • 21. Mobile subscribers answers, MS stops alerting and send connect message to MSC. • 22. MSC removes audible tone to PSTN, and connects PSTN trunk to BSS trunk and send connect message to PSTN, Billing start. • 23. MSC send a connect acknowledge to MS. 19 Network Alerting 20 Connect (off-hook) TCH 21 Connect 22 Start Billing Connect Acknowledge TCH 23

  26. Um A MS BSS Home or Visited MSC PSTN RELEASE Network Release 24 • 24. MSC receives a Release message from the N/W to terminate the end to end connection. • 25. MSC send disconnect message to MS. • 26. MS send Release to MSC • 27. MSC send Release complete to MS. • 28. Voice trunk between MSC & BSS in cleared. • 29. The Traffic channel is released. • 30. The recourses are completely released. Disconnect) 25 TCH Release TCH 26 27 TCH Clear Command 28 Clear Command 29 Clear Command 30

  27. Phase of a Mobile to Mobile call • Request for Service • Authentication* • Ciphering* • Equipment Validation* • Call Setup • Release • Routing Analysis • Paging • Authentication* • Ciphering* • Equipment Validation* • Call Setup • Release • Phase might not occur Originating Mobile Terminating Mobile

  28. Mobile to Mobile call phase divided in 2 parts • Originating Mobile Point • MS to MSC is same as part of MS to Land call. • Terminating Mobile part same as land to Mobile call, i.e. PSTN to MSC Part.

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