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Gsm architecture, gsm network identities, network cases, cell planning, and compound charging

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Gsm architecture, gsm network identities, network cases, cell planning, and compound charging

  1. 1. GSM ARCHITECTURE, GSM NETWORK IDENTITIES, NETWORK CASES, CELL PLANNING, AND COMPOUND CHARGING Prepared by: Zorays Khalid (Internee)
  2. 2. ERICSSON’S GSM SYSTEM ARCHITECTURE • Cellular Matara Ericsson 20 (GSM 900 and GSM 1800) • Cellular Mobile System 40 (GSM 1900) • Table System P-GSM E-GSM GSM 1800 GSM 1900 BW 25 MHz 35 MHz 75 MHz 60 MHZ Radio 125 175 375 300 Channels Wave length ~33 cm ~33cm ~17cm ~16 cm
  3. 3. CAPACITY AND FREQUENCY RE-USE • Limited frequencies • Capacity: Number of frequencies in the cell • Interference is avoided by allocating different frequencies in adjacent cells and reallocating these frequencies in a honeycomb pattern • The lower frequency re-use distance, the more capacity is available.
  4. 4. GSM TRANSMISSION PROCESS 1.ADC 2.Segmentation 3.Speech Coding 4.Channel Coding 5. Interleaving 6.Ciphering/Encryption 7.Burst Formatting
  5. 5. LOGICAL CHANNELS • Each time slot on the TDMA frame is a physical channel. • 8 physical channels per carrier. • Control Channels 1.Broadcast (connects) 2.Common (request access) 3.Dedicated (set-up) • Traffic Channels
  6. 6. AXE STRUCTURE • Non- Application Modularity based AXE 105 e.g. BSC node • Application Modularity based AXE 106 (discussed)
  7. 7. SWITCHING SYSTEM • Mobile services Switching Center/ Visitor Location Register • Gateway Mobile services Switching Center • Home Location Register • Interworking Location Register* • Authentication Center and Equipment Identity Register
  8. 8. MSC • Switching and call routing • Charging and Service provisioning • Communication with HLR • Communication with VLR • Communication with MSC • Control of connected BSC’s • Direct Access to Internet Services
  9. 9. VLR • Temporary storage location for Mobile Subscription within particular MSC service area. • On entering new MSC service area, It 1. Checks data base that MS is listed or not using IMSI 2. If not listed, it requests HLR to send a copy of MS subscription 3. HLR does so and updates itself and instructs old VLR to delete it. 4. VLR stores this information.
  10. 10. GMSC • It enables MSC to interrogate HLR in order to route a mobile terminating call*. • Find and interrogate HLR for roaming number. • Routes the call according to the interrogation.
  11. 11. HLR • It is a permanent store for person’s subscription information e.g. IMSI, MSISDN, subscriber supplementary services, subscriber location information (i.e. MSC service area), subscriber authentication information. • Subscription database management • Communication with the MSC’s • Communication with GMSC’s • Communication with AUC’s • Communication with VLR’s/ILR’s
  12. 12. CALL SETUP • Marking the MS as active in the VLR • The authentication procedure • Start Ciphering • Equipment Identification • Sending the B-subscriber’s number to the network • Checking if the subscriber has the service “Barring of outgoing calls” activated
  13. 13. MOBILE INTELLIGENT NETWORK • Ericsson’s MIN nodes are • SSF: SSP acts as an interface between the call control functions of the mobile network and the service control functions of a Service Control point. • SCF: SCP contains the intelligence of the MIN services. • SDP • Manages data which is used by MIN.
  14. 14. GSM NETWORK IDENTITIES • These are the unique numbers used to locate a mobile subscriber e.g., E.164 numbering plan is used in PSTN/ISDN network • Three main types of GSM Network Identities 1.Subscriber Related Identities 2.Equipment Related Identities 3.Location Related Identities
  15. 15. SUBSCRIBER RELATED IDENTITIES • MSISDN • IMSI • TMSI
  16. 16. TMSI MSC/VLR allocate TMSI to IMSI (SIM) at time of registration. It helps protect subscriber identity Significant with MSC/VLR It is changed on location update 8 digits Subscriber Identity confidentiality is enforced when subscriber is using PLMN prevents tracing of the mobile IMSI For identification over radio path and through the network. Network related subscriber info. for all signaling in a PLMN. Ki, A3, A8 VLR,SIM,HLR MCC+MNC+MSIN MSISDN 0313 5171 327 CME 20 CC+NDC (PLMN codes) +SN = 15 dig. Max CMS 40 NDC -> NPA
  17. 17. EQUIPMENT RELATED IDENTITIES • IMEI • IMEISV
  18. 18. IMEISV Software version helps determine services of MS and speech coding capabilities IMEI 356384 00 610648 6 TAC + FAC + SNR + spare bit Uniquely identifies MS equipment to network For security procedures stolen/unauthorize d access to the network EIR functions
  19. 19. LOCATION RELATED IDENTITIES • MSRN • LAI • CGI • BSIC • LN • RSZI
  20. 20. MSRN • It is assigned during establishment of a call to a roaming subscriber • CC + NDC + SN* LAI • Required for routing • Paging: MSC knows current LA of MS • Location updating • MCC + MNC + LAC* CGI • For Identifying individual cells within a Location Area • 65536 X 65536 = 4.3 billion max. no. of cell identities in one operator’s network
  21. 21. BSIC • To distinguish b/w different base stations ending on same frequency • NCC* + BCC* LN • Geographical • For local/regional subscription • CC + NDC + LSP* RSZI • For regional subscription • CC + NDC + ZC
  22. 22. TRAFFIC CASES • MS in Idle mode • MS in Active mode 1.Mobile Originated 2.Mobile Terminated
  23. 23. ATTACHING TO THE NETWORK A. IMSI attach On switching MS 1. It scans all RF channels tuning to the strongest carrier and checks If it is a BCCH and tries otherwise 2nd strongest carrier to lock with. 2. If BCCH belongs to other network only “Emergency calls allowed” 3.List stored in a memory to directly find specific carriers
  24. 24. ATTACHING TO THE NETWORK MS sends IMSI attach message signifying that it turned from detached to idle. VLR determines if subscriber already present If not, it asks for a copy of subscriber info from HLR VLR updates MS to idle MS is informed in an acknowledgement message
  25. 25. ATTACHING TO THE NETWORK (CONT.) B. Location Updating, type IMSI attach In case Location Area has changed while MS was detached VLR is updated of this new location during IMSI attach
  26. 26. ROAMING IN THE NETWORK A. Changing cell within a Location Area No update b/c MS knows that the new cell belongs to the same Location Area by listening to BCCH B. Location Updating, same MSC/VLR area In case MS detects a change in LAI by listening to BCCH* and comparing with the one stored on the SIM. It requests the network for update via Location Updating Message
  27. 27. ROAMING IN THE NETWORK (CONT.) MS connects via SDCCH and authentication is performed MSC/VLR authenticates that MS belongs to the network or not and requests the RBS and MS to release the signaling channel accordingly
  28. 28. ROAMING IN THE NETWORK (CONT.) C. Location Update, New MSC/VLR Now if MSC/VLR do not find the MS registered HLR is requested to provide a copy of MS subscription New VLR is informed of location and status, meanwhile HLR updates itself Old VLR is told to remove MS subscription VLR acknowledges to MS
  29. 29. ROAMING IN THE NETWORK (CONT.) D. Location Updating, type Periodic BCCH let’s know the refreshing rate If MS misses such a registration, network marks it detached preventing needless paging MS tries to register until it gets acknowledgement
  30. 30. DETACHING FROM THE NETWORK A. IMSI detach On Switching off, VLR marks the corresponding IMSI detach HLR not informed, no acknowledgement sent to MS B. Implicit detach In case of periodic registration failure
  31. 31. TRAFFIC CASES: CALL FROM AN MS MS uses RACH to ask for Signaling channel BTS assigns a signaling channel (SDCCH) using AGCH MS sends a call set-up request to MSC/VLR via SDCCH* MSC/VLR forwards B-number to an exchange in the PSTN. If answered, connection is established. The MSC/VLR instructs the BTS to allocate an idle TCH. The RBS and MS tunes to the TCH
  32. 32. CALL SET-UP 1. MSC/VLR knows that the MS is in which LA, it sends a paging message to the BSC. 2. The BSC distributes the paging message to different BTS in the desired Location Area using PCH. 3. When MS detects its MSIN it sends a request for signaling channel using RACH 4. The BSC uses AGCH to inform MS about SDCCH and SACCH 5. SDCCH and SACCH are used for call set-up. A TCH is allocated and SDCCH is released. 6. The MS and BTS switches to the TCH frequency and time slot. During call, SACCH is used to keep call status. 7. FACCH checks for handover*.
  33. 33. CALL TO AN MS • The exact location of the MS called is unknown • Paging is done • MSISDN is analyzed in PSTN (a call to MS) • GMSC finds out which HLR does it belong to…. • Checks if C-number call forwarding is activated • HLR requests MSRN from MSC/VLR…..sent to GMSC
  34. 34. CALL TO AN MS • GMSC analyzes MSRN and routes the call to the MSC/VLR • MSC/VLR knows about LA the MS is situated in and a paging message is sent • BSC uses PCH to page IMSI or TMSI* • The rest is the same.
  35. 35. CELLS • Cell planning: Site, equipment and its configuration • A cell may be defined as an area of radio coverage from one BTS*/hexagon (graphically). • Two main Types: 1. Omni directional Cell (360 degrees/coverage) 2. Sector Cell (in a given direction only e.g. 120 or 180 degrees/ capacity)
  36. 36. CELL PLANNING PROCESS Start (go C.W.) Traffic and Coverage Analysis Nominal Cell Plan Surveys System Design Implementation
  37. 37. OVERLAID/UNDERLAID SUBCELLS • A way to increase traffic capacity without building new sites • Overlaid at lower power level (smaller coverage area) • Underlaid at a bit higher power level (larger coverage area comparatively) and thus two different frequency re-use patterns.
  38. 38. CHARGED CALLS CS1+ • Ericsson’s IN protocol supporting all capabilities of Ericsson INAP 2.1 and ETSI Core INAP CS1 • Applies to Originating, Terminating, and Forwarded Calls in the HPLMN and Terminating Calls in the VPLMN
  39. 39. ORIGINATING CHARGED CALL • I am a Charging System Subscriber* • I initiate a call • My Originating IN Category Key in the VLR routes the call to SSF • SSF collects call data and triggers CCN • CCN selects SDP and sends call data (MNP/LBC are performed optionally) • SDP reserves money from the account and sends the calculated time to CCN + announc. • CCN tells SSF to play announcements if requested • CCN directs SSF to setup the call and monitors it based on calculated call time. • Call lasts longer than the time sent to SSF ….. CCN is notified • CCN requests another reservation from SDP
  40. 40. ORIGINATING CALL • SDP makes new charging analysis and deducts the amount previously reserved from the account* • SDP reserves money for next period and forwards a new call time to CCN • CCN passes the new call time on to SSF • If my account balance reaches account empty limit • In case the call lasts longer, a notification is sent to CCN • CCN requests SDP to reserve another amount • SDP makes a new charging analysis and updates the account • Since no enough funds the SDP calculates call time to CCN together with an indication • A call cutoff warning announcement is played after a fixed time • This time between call cutoff warning and call cutoff is excluded from new call time and passed on to SSF
  41. 41. ORIGINATING CALL • SSF notifies CCN that the time sent has expired • CCN send remaining 30 seconds to SSF • SSF tells CCN that these 30 seconds have expired • CCN tells SSF to play call cutoff announcement and to disconnect • SSF notifies CCN about call disconnect • CCN sends a final report to SDP where final charging is done • SDP also rates the total call and sends the report to CCN • CCN tells a call release to SSF.
  42. 42. SMS IN TRIGGERED CHARGING • An SMS is sent based on OICK and the destination address routes it to the SSF • The SSF collects data about the call and triggers CCN to check the account • The data collected in step 2, is sent in a first interrogation to where the service data scenario of the account is checked and a a preliminary charging analysis takes place • No reservation of money is performed in this step • SDP sends the result of the interrogation to CCN • CCN sends a successful result to the SSF • The MSC delivers the SMS to the SMS-C • The delivery of the SMS is confirmed by the SMS-C • The MSC/SSF triggers CCN to deduct the fee of the SMS • CCN sends a first interrogation to SDP where the service scenario of the account is checked
  43. 43. SMS IN CS+1 • And a preliminary charging analysis takes place • SDP reserves money from the account and sends a successful result together with other call data to CCN • CCN sends a final report to the SDP • SDP rates the total cost, deducts money from the account and sends a final report result to CCN • CCN sends a release operation with a successful deduct code to the MSC/SSF
  44. 44. VOUCHER REFILL THROUGH IVR • A refill call is initiated by me • The call is routed to Interactive Voice Response. The IVR check if the calling party no. is complete • The IVR requests account information from AIR (Account Information and Refill System) • AIR interrogates Account Finder (AF) to get the SDP IP address • AF returns the SDP IP address • AIR uses the SDP IP address to request account and subscriber data information from SDP • SDP checks if any account updates are necessary and sends the result of account information request back to AIR • AIR sends the requested information to IVR e.g. preferred language
  45. 45. VOUCHER REFILL THROUGH IVR • The IVR plays a standard welcome announcement and a menu announcement/. The subscriber selects the menu option voucher refill and enters the voucher activation number • The entered activation code and the mobile number of the subscriber is sent to AIR for verification • AOR requests account information from SDP • SDP sends the result of account information request back to AIR. AIR verifies that the subscriber exists and is not barred from refill • AIR sends the entered voucher activation code to the Voucher Server (VS) for verification • When the VS has verified the voucher activation code and has reserved the voucher, it returns a response to AIR
  46. 46. VOUCHER REFILL THROUGH IVR • AIR receives a response from the VS indicating if the verification was successful or not. It was successful, so AIR sends a refill request to SDP • The account balance increased in SDP database for account • CDR processing is used and has caused an SMS/GPRS barring. Unbarring of SMS and GPRS in the HLR is supported when a certain account threshold has been reached. In this case through a refill • SDP sends the result of the refill back to AIR • The refill was successful so AIR requests the VS to set the voucher in used state • The VS responds with the result back to AIR • AIR sends a response to the IVR including the account balance and an indication if the refill was successful or not
  47. 47. VOUCHER REFILL THROUGH IVR • A CDR including the refill data is generated • The IVR uses the voice prompt to notify the subscriber of the result • The subscriber releases the call
  48. 48. USSD BALANCE ENQUIRY • I originate a USSD message with the USSD service code corresponding to enquiry • The MSC forwards the message to the HLR • The HLR analyses the USSD service code and forwards the message to AIR • AIR interrogates AF to get the SDP IP address • AF returns the SDP IP address • AIR uses the returned SDP IP address to request account and subscriber data information from SDP • SDP sends the requested account information to AIR • AIR reformats the response into a USSD text string and send to the HLR. The response is successful, so the appropriate successful message is sent, otherwise a failure response with the reason for failure would have been sent • The HLR forwards the response to the MSC and the response is displayed on the subscriber’s handset

Editor's Notes

  • Talk about guard band, explain how wavelength is related to power required …….lately draw connect with GMSK
    Note in GSM network the bit rate (Transmission Rate) over the air interface is 270kbits/s
  • 2 and 3 are performed together

  • Note: The method of placing logical channels over physical channels is called mapping.
    Full rate
    Half rate
    EFR
  • Subscription details include
    Identity numbers for the subscriber
    Supplementary service information (e.g. call forwarding enabled?)
    Activity of MS (idle)
    Current Location Area of MS
  • MS as Receiver
  • HLR redundancy
  • Authentication procedure:
    MSC/VLR transmits RAND to the MS
    MS computes SRES using RAND and the Ki using A3
    MS computes Kc using RAND and Ki using A8
    SRES is sent back to MSC/VLR : SRES from AUC and MS are compared and hence network access is granted.

    Ciphering:
    M (ciphering mode command) and Kc are sent from MSC/VLR to the BTS
    M is forwarded to the MS
    M is encrypted using Kc and the TDMA frame no. (A5) is fed
    Encrypted message is sent to BTS
    BTS decrypts it and if successful cyphering mode completion message is sent to MSC

    Equipment Identification:
    MSC/VLR requests IMEI from MS
    MS sends IMEI to MSC
    MSC/VLR send IMEI to EIR
    EIR examines three lists (white all GSM countries, black barred, gray operator level )
    Result is sent to MSC which decides whether to allow access or not

  • Servicing node MSC/VLR no.
    LAC = 2^16 = areas to be defined in one PLMN
  • Network colour code : across border: distinguishes PLMN but not operator
    Base Sation colour code : b/w RBS using same freq.
    ZC = 16 digits
  • BCCH also informs of maximum output power allowed in a cell and identity of BCCH carriers for neighboring cells so MS has a list of BCCH carriers on which it will perform measurements to assist an efficient handover.
  • MS purging : VLR about to remove subscriber record
    HLR sets MS purged flag making it unreachable to prevent unnecessary load
  • In active mode network decides which cell to move in.

    B-number:
    Goes to Register Function which stores the incoming digits and co-ordinates call setup procedures.
    Call supervision and Co-ordination of function takes on as the call is established
  • One of the key elements of a mobile phone or cellular telecommunications system, is that the system is split into many small cells to provide good frequency re-use and coverage. However as the mobile moves out of one cell to another it must be possible to retain the connection. The process by which this occurs is known as handover or handoff

    Types of GSM handover
    Within the GSM system there are four types of handover that can be performed for GSM only systems:
    Intra-BTS handover: This form of GSM handover occurs if it is required to change the frequency or slot being used by a mobile because of interference, or other reasons. In this form of GSM handover, the mobile remains attached to the same base station transceiver, but changes the channel or slot.
    Inter-BTS Intra BSC handover: This for of GSM handover or GSM handoff occurs when the mobile moves out of the coverage area of one BTS but into another controlled by the same BSC. In this instance the BSC is able to perform the handover and it assigns a new channel and slot to the mobile, before releasing the old BTS from communicating with the mobile.
    Inter-BSC handover: When the mobile moves out of the range of cells controlled by one BSC, a more involved form of handover has to be performed, handing over not only from one BTS to another but one BSC to another. For this the handover is controlled by the MSC.
    Inter-MSC handover: This form of handover occurs when changing between networks. The two MSCs involved negotiate to control the handover.
     
  • In pico, cells it may not be true.
    Capacity is determined by no. of frequencies in a cell.
  • IN application protocol (INAP) CS1+ is based on ETSI core INAP CS1, enhanced with ITU-T CS1 and CS2 functions. Ericsson has added specific functions to create the Ericsson INAP CS1+ protocol. (SSF/CCN) (Table 3 : Charging System Overview)
  • * Assumption : I still have some funds in my account
  • r

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