GSM 3G Basic

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GSM 3G Basic

  1. 1. 1 Agenda, GSM & MPA Training course • Agenda: » Definition and History. » GSM Services. » GSM System architecture. » GSM Functional model. » GSM Radio (Um) Interface. » GSM A-bis. » GSM A-Interface. » GSM A-Interface BSSAP. » GSM A-Interface DTAP. » GSM Inter-MSC Signalling MAP. » GSM Signalling procedures » Evaluation.
  2. 2. 2 Global System for Mobile Communication (Groupe Spéciale Mobile) GSM
  3. 3. BTS Definition and History
  4. 4. • Does mobile mean that you have to be driving in a car ? • Does it work in aeroplanes ? • ………onboard ships in the ocean ? • …….inside buildings ?? • ….. everywhere in the nature ? ? ? ? ? ? SONOFON M N SONOFON M N SONOFON M N SONOFON M N SONOFON M N What is Mobile telephony ??
  5. 5. Local Exchange Mobile Switching Centre fixed medium Mobile Station fixed location Variable Location Diffuse Medium Telephone SONOFON M N Basic concept - 1 GSM vs. fixed network Telephony
  6. 6. NMT 450/900 C-Netz RTMS AMPS Nordic Countries, France, Belgium, Netherland, Switzerland, Austria, Turkey, Yugoslavia, Thailand, Malaysia, North Africa West Germany, Portugal UK, Ireland, Italy, Spain, Austria, Greece, Hong Kong, China, Malaysia, Thailand, Sri Lanka USA, Canada, Australia, New Zealand, Malaysia, Pakistan Singapore, Hong Kong Analog Mobile Systems RC 2000 Italy France TACS / ETACS
  7. 7. PCS 1900 GSM at 1900 MHz C-NET Analog 450 MHz UMTS / IMT-2000 (FPLMTS) CT2 DCS 1800 GSM at 1800 MHz Cordless Trunked mobile radio (TETRA) Satellite (IRIDIUM) GSM Digital 900 MHz Mobile Other systemsCT0,CT1 DECT GSM Digital 900 MHz NMT Analog 450/900 MHz TACS/ETACS Analog 900 MHz AMPS Analog 800 MHz GSM Digital 900 MHz DAMPS (TDMA) GSM Digital 900 MHz CDMA The evolution
  8. 8. 8 • The GSM Standard is divided into phases (phase 1, phase 2 and phase 2+) all the phases has been finalized by ETSI. • Many of the GSM networks in operation today are currently using the phase 2. However many of the GSM network operators are starting to implement phase 2+. • The ETSI GSM standard specification is around 5500 pages, and are divided into12 series. GSM Standard part 1
  9. 9. • Series 00 Preamble • Series 01 General • Series 02 Service aspects • Series 03 Network Aspects • Series 04 BS-MS interface / protocols • Series 05 Physical layer of radio path • Series 06 Speech Encoding • Series 07 Adaptation techniques • Series 08 BS-MSC interface • Series 09 Interworking procedures (network) • Series 10 Interworking between services • Series 11 Equipment and type approval specifications • Series 12 Operation and maintenance procedures GSM Standard part 2
  10. 10. • GSM 900 » The original system » Widely applied in EUR • DCS 1800 » Typical expansion path when running out of capacity with GSM 900 • PCS 1900 » Widely used in the United States GSM systems today
  11. 11. • Specification start-up: 1980 • First network in operation: Jan. 1992 (Radiolinja, Finland) • Forecast in 1995: » At the ITU's Telecom '95 event, were stated that we will reach 100 million subscribers Worldwide before the year 2000. • September 1997: ~55 million subscribers. ~1 new subscriber each second. ~250 networks in 110 countries. • July 1998: » More than15 months early then year 2000 the magic figure of 100 million subscribers was reached. • Today : Over 200 million subscribers. 369 networks in 137 countries. Status
  12. 12. BTS GSM Services
  13. 13. BTS • Telephony • Data services (up to 9600 b/s) • Fax group 3 (special modem) • Short Message Service (SMS) • Supplementary services, e.g. » Call Forwarding » Call Barring » Call Waiting » Three Party Service » Advice of Charge Services
  14. 14. BTS • Integrated voice/data (ISDN) • Improved performance • Improved security » Digital encryption » Authentication (IMSI) » TMSI assignment • All types of Mobile Stations • Automatic roaming • Sophisticated radio functions » Discontinuous transmission - DTX » Frequency hopping GSM Features
  15. 15. BTS • Half-rate and enhanced full-rate speech • New supplementary services: » Display of called and calling user's number » Multi-party conversations (up to 6 parties) » Closed user groups / virtual private networks » Call completion services (busy, no answer etc.) » Intelligent network services (CAMEL) » Roaming between GSM and DCS 1800 (PCS 1900) • High speed data services: » High Speed Circuit Switched Data (HSCSD) » General Packet Radio Service (GPRS) Services, phase 2 and 2+
  16. 16. BTS System architecture.
  17. 17. Base Station Controller BSC Public Switched Telephone Network Base Mobile Station (MS) Mobile Switching Centre MSC (PSTN) Station Subsystem (BSS) A-Inter A-bis Um 2 Mbit/s PCM Air Interface BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Equip. Id Register EIR Authen. Centre AUC Visitor Location Register VLR Home Location Register HLR Mobile Switching Centre MSC MAP ISUP / TUP MAP MAP MAP ISUP / TUP ISUP / TUP MAP System Overview
  18. 18. Home Location Register Visitor Location Register Mobile Switching Centre Base Station Controller Base Transceiver Station MSC BTS BSC VLR HLR SONOFON M N System Building Blocks
  19. 19. • “Home Base” of information regarding customers subscribing to a particular operators GSM network • Keeps track of subscriber profile, conditions and whereabouts MSC BTS BSC VLR HLR SONOFON M N HLR (Home Location register)
  20. 20. BTS • Subscriber information: » IMSI (International Mobile Subscriber Identity) » MSISDN (International Mobile Station ISDN Number) » MS Category (e.g. payphone) » Authentication vectors (RAND, SRES and Kc: AUC and SIM) » Allowed services (subscription data) • Mobile location information: » VLR number » (MSRN - Mobile Station Roaming Number) HLR contains
  21. 21. • Database with information about mobile users present/active in the network segment served by the MSC • Handles true visitors as well as subscribers of the operator himself MSC BTS BSC VLR HLR SONOFON M N VLR (Visitor Location register)
  22. 22. BTS • Subscriber information: » IMSI » TMSI - Temporary Mobile Subscriber Identity » MS category » Authentication vectors » Allowed services • Mobile location information: » MSRN - Mobile Station Roaming Number » LAI - Location Area Identity VLR contains.
  23. 23. • Contains the radio transmitters and receivers (transceivers) covering a certain geographical area of the GSM network MSC BTS BSC VLR HLR SONOFON M N BTS (Base Transceiver Station)
  24. 24. • Controls a group of BTS’s in relation to power control and handover. • The combination of a BSC and its BTS’s is called a Base Station Subsystem (BSS). • The interface between the BTS and the is called the A-bis interface. MSC BTS BSC VLR HLR SONOFON M N BSC (Base Station Controller)
  25. 25. • Serves a number of BSS’s (Base Station Subsystem) via the A-interface. • Responsible for call control (set-up, routing, control and termination of the calls) • Management of inter-MSC handover and supplementary services, and for collecting charging/accounting information. • Gateway to other to other GSM networks and public-switched networks) BSC (Base Station Controller) MSC BTS BSC VLR HLR SONOFON M N
  26. 26. 26 • Contains the individual subscriber-identification key (also contained in the SIM), and provides the subscriber data to the HLR and VLR used for authentication and encryption of calls. AUC HLR AUC - Authentication Centre BTS
  27. 27. 27 BTS • Stores information about mobile stations in use and may block calls from a MS if the MS is stolen, not type-approved or has faults which may disturb the network. • Each MS is identified by a unique International Mobile Station Equipment Identity (IMEI) MSC EIR EIR - Equipment Identity Registration.
  28. 28. • Power: » - Class 1: 20 W Vehicle/ » - Class 2: 8 W portable » - Class 3: 5 W Hand-held » - Class 4: 2 W Hand-held » - Class 5: 0.8 W Hand-held (MS) Mobile Station
  29. 29. BTS Functional model.
  30. 30. 30 Base Station Controller BSC Public Switched Telephone Network Base Mobile Station (MS) Mobile Switching Centre MSC (PSTN) Station Subsystem (BSS) A-Inter A-bis Um 2 Mbit/s PCM Air Interface BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Equip. Id Register EIR Authen. Centre AUC Visitor Location Register VLR Home Location Register HLR Mobile Switching Centre MSC MAP ISUP / TUP MAP MAP MAP ISUP / TUP ISUP / TUP MAP The overview of the System.
  31. 31. • Call Management (CM) » Call Control (CC) » SMS » Non Call-related SS • Mobility Management (MM) • Radio Resource Management (RR) CM MM RR BTS BSC MSC VLR HLR SONOFON M N A functional model
  32. 32. 32 • DTAP - Direct Transfer Application Part • BSSMAP - BSS Management Application Part • CM - Call Management • MM - Mobile Management • RR - Radio Resource Management • BTSM - BTS Management • SCCP - Signalling Connection Control Part • MAP - Mobile Application Part • TCAP - Transaction Capability Application Part • ISUP - ISDN User Part • MTP - Message Transfer Part DTAPCM MM RR Sig. layer 2 Layer 1 (air) Sig. layer 2 Sig. layer 1 MTP SCCP BSSMAPRR (CM+MM) MS BSC MTP MTP SCCP SCCP CM MM BSSMAP TCAP MAP I S U P MSC Sig. layer 2 Layer 1(air) BTS (CM) (MM) (RR) (CM) (MM) (RR) (CM) (MM) (LAPDm) (LAPDm) (LAPD) Sig. layer 2 Sig. layer 1 (LAPD) BTSM BTSMRR' Um Interface Abis Interface A Interface Inter-MSC Layer 1 Layer 2 Layer 3 GSM Protocol Architecture
  33. 33. 33 • The Network layer contains the signalling procedures and is divided into: » CC - Call Management. » MM - Mobility Management. » RR - Radio Resource Management. Layer 3 Network Layer BTS
  34. 34. 34 BTS • Call Management takes care of the ordinary call-control procedure: » Establishment and release of calls, as well as access to services and facilities. • CM is divided into: » Call Control (CC), short messages services (SMS). » Non-call-related supplementary services (SS). Layer 3 Call Management (CM)
  35. 35. 35 • Mobility Management handles roaming and authentication procedure. Layer 3 Mobility Management (MM) BTS
  36. 36. 36 • Radio Resource Management comprise: » Paging. » Radio-channel access. » Ciphering. » Handover. » Radio-signal control » Radio-signal measurement BTS Layer 3 Radio Resource Management (RR)
  37. 37. 37 BTS • The Data Link Protocol is used at the Um and A-bis interface, the Data Link Protocol is based on LAPD (ISDN D-channel layer 2 protocol). • On the A-Interface MTP and SCCP are used as signaling-transport function. • On the inter-MSC interface, MTP is used for ISUP, TUP and MTP + SCCP + TCAP is used for MAP. Layer 2 Data Link Protocol.
  38. 38. 38 • Physical Link of the signaling is time slots in the radio carriers and digital PCM lines. BTS Layer 1 Physical Link
  39. 39. Um BTS Radio (Um) Interface
  40. 40. The System Base Station Controller BSC Public Switched Telephone Network Base Mobile Station (MS) Mobile Switching Centre MSC (PSTN) Station Subsystem (BSS) A-Inter A-bis Um 2 Mbit/s PCM Air Interface BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Equip. Id Register EIR Authen. Centre AUC Visitor Location Register VLR Home Location Register HLR Mobile Switching Centre MSC MAP ISUP / TUP MAP MAP MAP ISUP / TUP ISUP / TUP MAP
  41. 41. 41 • DTAP - Direct Transfer Application Part • BSSMAP - BSS Management Application Part • CM - Call Management • MM - Mobile Management • RR - Radio Resource Management • BTSM - BTS Management • SCCP - Signalling Connection Control Part • MAP - Mobile Application Part • TCAP - Transaction Capability Application Part • ISUP - ISDN User Part • MTP - Message Transfer Part DTAPCM MM RR Sig. layer 2 Layer 1 (air) Sig. layer 2 Sig. layer 1 MTP SCCP BSSMAPRR (CM+MM) MS BSC MTP MTP SCCP SCCP CM MM BSSMAP TCAP MAP I S U P MSC Sig. layer 2 Layer 1(air) BTS (CM) (MM) (RR) (CM) (MM) (RR) (CM) (MM) (LAPDm) (LAPDm) (LAPD) Sig. layer 2 Sig. layer 1 (LAPD) BTSM BTSMRR Um Interface Abis Interface A Interface Inter-MSC Protocol Architecture
  42. 42. • GSM has been assigned 1000 radio channels in the 900 MHz band. More precisely: » 890 - 915 MHz “Uplink” » 935 - 960 MHz “Downlink” • A combination of frequency and time division is used. » 124 carriers » Carrier spacing is 200 kHz » 8 timeslots per carrier BTS SONOFON M N GSM 900 Radio (Um) Interface Physical Channels
  43. 43. • GSM has been assigned 2992 radio channels in the 1800 MHz band. More precisely: » 1710 - 1785 MHz “Uplink” » 1805 - 1880 MHz “Downlink” • A combination of frequency and time division is used. » 374 carriers » Carrier spacing is 200 kHz » 8 timeslots per carrier BTS SONOFON M N DCS-1800 Radio (Um) Interface Physical Channels
  44. 44. • Except for the difference in power level range and frequency, PCS-1900 are identical to DCS-1800. • The frequency shift is required in US because of presence of some point to point radio links on the 1800 MHz band. • A combination of frequency and time division is used. » 299 carriers » Carrier spacing is 200 kHz » 8 timeslots per carrier PCS-1900 Radio (Um) Interface Physical Channels BTS SONOFON M N
  45. 45. BTS TDMA Frame Time Slot 4.615 msec 3 57 1 26 1 57 3 TB Coded Data C TS C Coded Data TB 8.25 GP 0.577 msec Duration of 1 bit: 3.692 usec 0 1 2 3 4 5 6 7 TS : Tail bit TS : Training Sequence (setting up the receiver equaliser) GP : Guard Period C : Control bit 13 kbit/s user data TDMA Frame Structure
  46. 46. 46 BTS Physical Channels TS 5 TS 4 TS 3 TS2 TS 1 TS0 TS 4 TS 3 TS2 TS 0 TS7 TS6 TS 5 TS7 TS6 Control Channels Control Channels Traffic Channels Traffic channels showing three timeslot delays between the down and up links. Eight TS, or eight physical channels compromise a FRAME TS 2 TS1 TS 0 TS7 TS 6 TS5 TS 0 TS 7 TS6 TS 5 TS4 TS3 TS 1 TS3 TS2 Downlink Uplink
  47. 47. 47 FCCH burst 3 142 3 8.25 GuardTail TailInformation Tail Information Training 3 57+1 (TCH/FACCH) 26 57+ 1 (TCH/FACCH) 3 Normal burst 8.25 GuardTailInformation Access burst 7 41 36 3 GuardTail Tail 68,25 InformationTraining SCH burst 3 39 64 39 2 8.25 GuardTail TailInformation InformationTraining » Not illustrated is the “dummy” burst which has the same structure as the “Normal” burst. The dummy burst is sent when no information is transmitted on a TCH Radio (Um) Interface burst modulation structure
  48. 48. 48 • For the “Normal” burst, one of the 58 information bits on each side of the training sequence is a flag bit indicating whether the burst is a TCH - traffic channel (0) or for a FACCH - fast associated control channel (1). • The burst is converted to FACCH when signalling is required after a TCH has been allocated. » Note: Each “Normal” burst (TDMA) time slot period consist of 156.25 bits (equal to 33.9 kbit/s per time slot or 270.8 kbit/s per frame carrier), of which 144 (2*57) bits are coded data including forward error correction. All information is transferred in blocks of 456bits divided into four time slot periods (456 = 4*2*57). The maximum net bit rate is 13 kbit/s (Excluding the error correction) Tail Information Training 3 57+1 (TCH/FACCH) 26 57+ 1 (TCH/FACCH) 3 Normal burst 8.25 GuardTailInformation Radio (Um) Interface Normal burst
  49. 49. 49 • The “access” burst is a shortened burst used by the mobile station when it first access a cell. • Its short length guarantees it will arrive within the correct time slot at the BTS receiver if the mobile station is no greater than 35km from the BTS. » 68,25 bits * 3,7gs (1 bit) = 251gs ~ (75Km / 2) = 37,5Km Access burst 7 41 36 3 GuardTail Tail 68,25 InformationTraining Radio (Um) Interface Access burst
  50. 50. • Downstream: » A series of bits intended for different users, who must select only the one intended for him and filter out the rest • Upstream: » Individual bits from each of the users arrive at the BTS » Strict timing of when the MS should transmit is required to avoid collisions at the BTS Time Division Multiple Access burst Wrong Uplink Timing BTS SONOFON M N SONOFON M N SONOFON M N SONOFON M N
  51. 51. 51 15 Km 30 Km1 Km BTS SONOFON M N SONOFON M N SONOFON M N TS TS TS TS TS TS TS Timing advance Access burst • The transmitted radio burst from BTS must travel whatever the distance is to the mobile station , and then transmitted burst from the mobile station (three burst later) must travel back the same distance. By measuring the time between the last bit in the access burst and the last bit in the TS the mobile then know the distance to the BTS and will adjust its Timing advance to compensate for the distance. Timing advance (Access burst)
  52. 52. 52 Mobile Station Timing advance Measurement Report Message Type : 3Fh = Immediate assignment --- Channel description --- Time slot number : .....001 Channel type and TDMA offset : 01011... = SDCCH/8 + SACCH/C8 or CBCH (SACCH/8) Training Sequence Code : 011..... Hopping channel : ...0.... = Single RF channel spare : ....00.. Absolute RF Channel Number : 720 --- Request reference --- Random access information : 4 T1 : 7 T3 : 19 T2 : 7 --- Timing advance --- Timing advance value : ..000010 Spare : 00...... Timing advance = 2 The mobile station is 1km from the BTS.
  53. 53. 53 • The SCH burst is the synchronization channel burst which carries the the BSIC - Base Station Identity Code and the FN - Frame Number. • As this is the first burst decoded by the mobile station it has an extended training sequence. SCH burst 3 39 64 39 2 8.25 GuardTail TailInformation InformationTraining SCH burst
  54. 54. 54 • The FCCH burst is the frequency correction channel burst which is modulated with zero FCCH burst 3 142 3 8.25 GuardTail TailInformation FCCH burst
  55. 55. BTS • Traffic channels (TCH): » Carrying Voice/data » Bm: 13 kbit/s user data » Lm: Half rate (6,5 kbit/s) • Common control channels (CCCH): » Channels that all Mobile Stations can share • Dedicated control channels (DCCH): » Control channels for individual Mobile Stations Radio(Um)Interface Logical Channels
  56. 56. BTS • Broadcast: BCCH » Carry system info intended for everybody, e.g. Location Area Identity • Paging: PCH » To request a specific Mobile User to react/reply, e.g. when there is a call for him • Random Access: RACH » Used by the Mobile Station to initiate contact with the network, e.g. when trying to start a call • Access Granted: AGCH » Used to respond to the RACH to inform that the Mobile is now being allowed to access the network Radio (Um) Interface Common Control Channels
  57. 57. BTS • Stand-alone Dedicated : SDCCH » Used for settling practicalities such as roaming, authentication, encryption and call control before allocating the traffic channel • Slow Associated: SACCH » Associated to a TCH » Used together with the Traffic Channel to deal with control and measurement of radio signals • Fast Associated: FACCH » Large bandwidth version of the SACCH » Used for sudden control action such as handovers » Implemented a robbed bits in a TCH Radio (Um) Interface Dedicated Control Channels
  58. 58. 1 hyperframe = 2048 superframes (3h 28min 53s 760ms) 0 1 2 3 4 5 6 7 1 TDMA frame = 8 timeslots (4.615 ms) 0 1 2 3 4 5 6 2042 2043 2044 2045 2046 2047 0 1 2 3 4 5 6 7 18 19 20 21 22 23 24 25 1 superframe = 26 (51-frames) or 51 (26-frames) multiframes (6.12s) 0 1 2 3 4 5 45 464748 49506 0 1 2 3 4 5 6 7 18 19 20 21 22 23 24 25 1 (26-frame) multiframe = 26 TDMA frames (120ms) 1 (51-frame) multiframe = 51 TDMA frames (235.38 ms) 0 1 2 3 4 5 45 46 4748 49506 0 1 2 3 4 5 6 7 1 TDMA frame = 8 timeslots (4.615 ms) Hyper-, Super- and Multiframes
  59. 59. Downlink and Uplink Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm SA Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm - 0 1 2 3 4 5 6 7TDMA Frame (8 timeslots) F S BCCH PCH/AGCH F S F S SDCCH/1 SDCCH/2 F S SDCCH/3 SDCCH/4 F S SACCH/1 SACCH/2 -PCH/AGCH PCH/AGCH F S BCCH PCH/AGCH F S F S SDCCH/1 SDCCH/2 F S SDCCH/3 SDCCH/4 F S SACCH/3 SACCH/4 -PCH/AGCH PCH/AGCH R R SACCH/1 SACCH/2 R R R R R R SDCCH/1 SDCCH/2R R SDCCH/3 SDCCH/4 R R SACCH/3 SACCH/4 R R R R R R SDCCH/1 SDCCH/2R R SDCCH/3 SDCCH/4 R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R Cyklus: 1 TCH multiframe = 26 TDMA frames = 120 ms 4.615 ms Downlink: Cyklus: 1 CCH multiframe = 51 TDMA frames = 235.38 ms F = Frequency correction burst S = Synchronisation burst R = RACH R R Uplink: TDMA Frame with 1 combined CCH and 7 TCH
  60. 60. R 5xR F 1 F 2 F3 F4 F 5 F6 F4 Omni-directional BTS 3-directional BTS Safety distance BTS BTS BTS BTS • To avoid interference between two cells using the same frequency, a safety distance of about 5 times the cell radius is required. • A BTS may cover one cell (Omni-directional) or several cells (typical three directional cells). • Each cell may be served by on or more TRXs depending on the required capacity. • Note: each TRX controls one carrier with eight TS. Cell Structure
  61. 61. 61 BTS • Mobile station in IDLE mode » Besides listening to the BCCH and the PCH the mobile station is measuring for neighbour cells. • Mobile station in active mode » In active mode the mobile station is using the time between the down and uplink TS (three TS 2ms) to do neighbour cell measuring. • The mobile station can measure up to 31 neighbour cells. » In practice the mobile station measures up to 12 neighbour cells. » Very often only three or four cells are measured. Radio (Um) Interface Neighbour Cells
  62. 62. 62 Mobile Station Neighbour Cells Measurement Report --- MEAS REP --- --- MEAS RES --- NO NCELL M : 100b = 4 neighbour cell measurement result RXL NCEL 1 : 36 = minimum received signal level = -75 dBm to -74 dBm BCCH NCEL1 : 1 BSIC NCEL1 : 57 RXL NCEL 2 : 24 = minimum received signal level = -87 dBm to -86 dBm BCCH NCEL2 : 12 BSIC NCEL2 : 63 RXL NCEL 3 : 23 = minimum received signal level = -88 dBm to -87 dBm BCCH NCEL3 : 7 BSIC NCEL3 : 59 RXL NCEL 4 : 16 = minimum received signal level = -95 dBm to -94 dBm BCCH NCEL4 : 2 BSIC NCEL4 : 56 RXL NCEL 5 : 0 = minimum received signal level less than -110 dBm BCCH NCEL5 : 0 BSIC NCEL5 : 0 RXL NCEL 6 : 0 = minimum received signal level less than -110 dBm BCCH NCEL6 : 0 BSIC NCEL6 : 0
  63. 63. 63 • IMSI » - International Mobile subscriber Number • MSISDN » - Mobile Station ISDN Number • Latest BCCH List » The latest BCCH used last time the mobile station was connected to the network. • Preferred Network List. • Forbidden Network List. • KI » The Key identifier refers to an authentication key for the mobile subscriber. (MS) Mobile Station SIM Card
  64. 64. BTS A-bis
  65. 65. The System. Base Station Controller BSC Public Switched Telephone Network Base Mobile Station (MS) Mobile Switching Centre MSC (PSTN) Station Subsystem (BSS) A-Inter A-bis Um 2 Mbit/s PCM Air Interface BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Equip. Id Register EIR Authen. Centre AUC Visitor Location Register VLR Home Location Register HLR Mobile Switching Centre MSC MAP ISUP / TUP MAP MAP MAP ISUP / TUP ISUP / TUP MAP
  66. 66. 66 • DTAP - Direct Transfer Application Part • BSSMAP - BSS Management Application Part • CM - Call Management • MM - Mobile Management • RR - Radio Resource Management • BTSM - BTS Management • SCCP - Signalling Connection Control Part • MAP - Mobile Application Part • TCAP - Transaction Capability Application Part • ISUP - ISDN User Part • MTP - Message Transfer Part DTAPCM MM RR Sig. layer 2 Layer 1 (air) Sig. layer 2 Sig. layer 1 MTP SCCP BSSMAPRR (CM+MM) MS BSC MTP MTP SCCP SCCP CM MM BSSMAP TCAP MAP I S U P MSC Sig. layer 2 Layer 1(air) BTS (CM) (MM) (RR) (CM) (MM) (RR) (CM) (MM) (LAPDm) (LAPDm) (LAPD) Sig. layer 2 Sig. layer 1 (LAPD) BTSM BTSMRR' Um Interface Abis Interface A Interface Inter-MSC Protocol Architecture
  67. 67. TS 1 TS 31TS 5 - - - - 16 kbit/s traffic channels 64 kbit/s signalling channels TS = 64 kbit/s timeslot TS 2TS 0 TS 3 TS 4 • One 2Mbit/s line may cover several BTSs. This means that normally several time slots in the same PCM frame are used as signalling channels. » Three time slots divided into one 64Kbit/s signalling channel and eight 16Kbit/s traffic channels are sufficient to cover one TRX, giving up to 10 TRXs and 10 signaling channels per 2 Mbit/s. » In practice , the configuration of the transmission lines depends on the actual network structure and the GSM equipment used. A-bis (A) Layer 1 Structures
  68. 68. 68 Flag 01111110 Flag 0111111016 Bits CRCInformation N - Bits ControlAddress 16 Bits 8 or 16 Bits SAPI TEI C/R EA 0 EA 1 SAPI value 0 1 16 62 63 Related entity Radio signalling Reserved for packet mode /Q.931 Reserved for packet mode /X.25 Operation and maintenance Layer 2 management TEI value 0-63 64-126 For fixed TRX addresses For additional TRX addresses User type All others Reserved for future standardisation Not used in GSM Vendor-specific • SAPI -Service Access Point Identifier • TEI - Terminal End Point Identifier • C/R -Command / Response bit • EA -Address Extension bit » 0 = Extend 1 = Final A-bis Layer 2 Structure
  69. 69. Flag 01111110 Flag 0111111016 Bits CRCInformation N - Bits ControlAddress 16 Bits 8 or 16 Bits 8 7 6 5 4 3 2 1 0 1 1 0 1 S S M M OCTET 1 OCTET 2 + 3 OCTET 4 ( + 5 ) OCTET N OCTET 4 OCTET 4 OCTET 4M M M P P/F P/F N ( R ) N ( R ) N ( S ) Control field bits ( modulo 8 ) I format S format U format 8 7 6 5 4 3 2 1 0 1 1 0 1 S S M M OCTET 4 OCTET 4 OCTET 4M M M P/F N ( R ) N ( R ) N ( S ) Control field bits ( modulo 128 ) I format S format U format P 5 X X X X P/F 5 • N(S) - Transmitter send sequence number • N(R) - Transmitter receive sequence number • S -Supervisory function bit • M -Modifier function bit • P/F - Poll bit when issued as a command Poll bit when issued as a command Final bit when issued as a response • X - Reserved and set to 0 • I forma - Information transfer format » Used for information transfer between layer 3 entities • S format - Supervisory format » Used for control functions • U format - Unnumbered format » Used for additional control functions and information transfer A-bis Layer 2 Control Field
  70. 70. Flag 01111110 Flag 0111111016 Bits CRCInformation N - Bits ControlAddress 16 Bits 8 or 16 Bits Message Discriminator 12345678 Octet 1 Octet 2 Octet n EM Message Type Information Elements 8 7 6 5 4 3 12 Fixed Length Info. Element Format Information Element Identifier Length of Information Elements Content of Information Elements Variable Length Info. Element Format T Information Element Identifier Content of Information Elements T: EM = = 0: Non-transparent message Extension bit (future use) Message Discriminator 0 1 4 6 8 Other Reserved Radio Link Management Dedicated Channel Management Common Channel Management Transceiver Management Reserved for Future Use A-bis Layer 3 Structure I
  71. 71. Radio Link Layer Management messages DATA REQuest (Transfer of transparent messages in layer 2 DATA INDication I-frames on radio interface) ERROR INDication (Indicates protocol error on radio link layer) ESTablish REQuest (Establishment of layer 2 link on radio interface) ESTablish CONFirm ESTablish INDication RELease REQuest (Release of layer 2 link on radio interface) RELease CONFirm RELease INDication UNIT DATA REQuest (Transfer of transparent messages in layer 2 UI- UNIT DATA INDication frames on radio interface) 0000- - - - 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 Message typeCode A-bis Messages, MD=1
  72. 72. Dedicated Channel Management messages: CHANnel ACTIVation (Activation of a radio channel) CHANnel ACTIVation ACKnowledge CHANnel ACTIVation Negative ACKnowledge CONNection FAILure INDication (Failure on radio connection) DEACTIVATE SACCH ENCRyption CoMmanD (Start of ciphering on radio interface) HANDOver DETection (MS handover to new BTS detected) MEASurement RESult (Radio signal measurement data from BTS/MS) MODE MODIFY REQuest(Change of channel mode, e.g. speech to data) MODE MODIFY ACKnowledge MODE MODIFY Negative ACKnowledge A-bis Messages, MD=4, part 1 Message typeCode 001- - - - - 00001 00010 00011 00100 00101 00110 00111 01000 01001 01010 01011
  73. 73. Dedicated Channel Management messages: PHYsical CONTEXT REQuest(Physical context is not specified by ETSI) PHYsical CONTEXT CONFirm RF CHANnel RELease (Release of radio channel) MS POWER CONTROL (Change of MS power level or control limits) BS POWER CONTROL (Change of TRX power level or control limits) PREPROCess CONFIGure(Conveys pre-processing parameters to BTS) PREPROCessed MEASurement RESult (From BTS) RF CHANnel RELease ACKnowledge 001- - - - - 01100 01101 01110 01111 10000 10001 10010 10011 A-bis Messages, MD=4, part 2 Message typeCode
  74. 74. Common Channel Management messages: BCCH INFOrmation (Indicates new information to be sent on BCCH) CCCH LOAD INDication (Indicates load on RACH and PCH) CHANnel REQuired (Reception of RR Channel Request message) DELETE INDication (Deletion of RR Immediate Assign message due to overload on AGCH) PAGING CoMmanD (Requests paging of MS) IMMediate ASSign CoMmanD (Setup of DCCH, answer to CHAN REQ) SMS BroadCast REQuest (Broadcast of SMS-message in cell) A-bis Messages, MD = 6 Message typeCode 00010 - - - 001 010 011 100 101 110 111
  75. 75. TRX Management messages: RF RESource INDication (Interference level on idle radio channels) SACCH FILLing (New filling information to be used on SACCH) OVERLOAD (Control channel or TRX processor overload) ERROR REPORT (Detection of errored message) 00011 - - - 001 010 011 100 A-bis Messages, MD=8 Message typeCode
  76. 76. - Channel number (Indicates channel on radio interface) - Link identifier (Signalling link and SAPI used on radio interface) - Activation type (Intra-cell, inter-cell or additional assignment CHAN ACTIV) - BS power (BTS/TRX power level) - Channel identification (Description of channels allocated to MS) - Channel mode (Indicates discontinuous transmission and channel type, e.g. speech) - Encryption information (Encryption algorithm and key) - Frame number (On radio interface, modulo 42432) - Handover reference (Identical to handover reference in RR information elements) - L1 information (MS power level and timing advance) - L3 information (Contains transparent RR, MM or CM message) - MS identity (IMSI or TMSI) - MS power (MS power level) - Paging group (Identifies MS paging group) - Paging load (Load on paging channel, PCH) - Physical context (Not specified) - Access delay (Delay of MS access burst at random access or handover) - RACH load (Load of random access channel, RACH) - Request reference (Random ref. in RR Channel Request message) A-bis Information Elements, part 1
  77. 77. - Release mode (Normal release or local end release) - Resource information (Interference level for idle TRX channels) - RLM cause (Indicates protocol error on radio link layer) - Starting time (Expressed as Frame Number modulo 42432) - Timing advance (To be used by MS in subsequent communications) - Uplink measurements (Radio signal measurement results from TRX) - Cause (Reason for event/failure) - Measurement result num (For a radio channel; set to 0 at activation) - Message identifier (In ERROR REPORT message: Message type of errored message) - Message indicator (In ERROR REPORT message: Copy of errored message follows) - System info type (Type of RR System Information message) - MS power parameters (Limits set by BSC for BTS control of MS power) - BS power parameters (Limits set by BSC for BTS control of TRX power) - Preprocessing param. (For preproc. of radio measurement data in BTS) - Preprocessed measurements (Preprocessed radio measurement data) - Immediate assign info (Conveys complete RR Immediate Assign msg.) - SMSCB information (SMS-message to be broadcasted in a radio cell) A-bis Information Elements, part 2
  78. 78. Bm + ACCHs Lm + ACCHs SDCCH/4 + ACCH SDCCH/8 + ACCH BCCH Uplink CCCH (RACH) Downlink CCCH (PCH + AGCH) TDMA timeslot number C5 C4 C3 C2 C1 0 0 0 0 1 0 0 0 1 T 0 0 1 T T 0 1 T T T 1 0 0 0 0 1 0 0 0 1 1 0 0 1 0 TN = 0 - 7 Element identifier C5 C4 C3 C2 C1 TN 8 7 6 5 4 3 2 1• C5 - C1 (Channel Number ) describes the types of radio channel used • TN is the physical TDMA time slot number that the radio channel is using. It is coded 0-7 in binary representation (There are 8 timeslots per TRX) Channel number information element
  79. 79. Flag 01111110 Flag 0111111016 Bits CRCInformation N - Bits ControlAddress 16 Bits 8 or 16 Bits Message Discriminator 12345678 Octet 1 Octet 2 Octet n EM Message Type Channel Number T Message Discriminator := 1 (Radio LinkManagement) L3 Information Protocol Discriminator 0 Message Type Information Elements Protocol Discriminator 3 5 6 9 11 15 Call control, packet, suppl. service Mobility management Radio resources management Short message services Non call related suppl. services Reserved for test procedures Other Reserved for future use T := 1 (transparentmessage) TI Flag TI Value Transaction Identifier TI-flag := 0 Message is sent from the TI-originating side TI-flag := 1 Message is sent to the TI-originating side TI-value := 0-7 Reference Information Elements • All CM and MM messages as well as most of the RR messages are transferred across the A-bis interface inside a L3 information element in A-bis layer 3 Radio Link management messages. A-bis Layer 3 Structure II
  80. 80. 80 BTS BSCBTS ENCRyption CoMmanD (Ciphering Mode Command [RR]) ESTablish INDication {MS establishes layer 2 on TCH} DEACTIVATE SACCH {on BTS} RF CHANnnel RELease {release of TCH} DATA REQuest (Release [CM]) DATA INDication (Release Complete [CM]) RF CHANnel RELease {release of SDCCH} DATA INDication (Assign Complete [RR]) {MS now ready on TCH} DATA REQuest (Assign Command [RR]) {assigns TCH to MS} CHANnel ACTIVation ACKnowledge {TCH activ} DATA INDication (Ciphering Mode Complete [RR]) CHANnel ACTIVation {activation of TCH} CHANnel REQuired {MS requests DCCH} CHANnel ACTIVation {activation of SDCCH} CHANnel ACTIVation ACKnowledge {SDCCH activ} IMMediate ASSign CoMmanD {assigns SDCCH to MS} ESTablish INDication (CM Service Request [MM]) {L2 up onSDCCH} DATA INDication (Setup [CM]) DATA REQuest (Call Proceeding [CM]) DATA REQuest (Alerting [CM]) {call setup continues on TCH} RELease INDication {MS releases layer 2 on SDCCH} RF CHANnel RELease ACKnowledge {SDCCH released} . RELease INDicaton {MS releases layer 2 on TCH} DATA INDication (Disconnect [CM]) {MS disconnects call} DATA REQuest (Channel Release [RR]) {to MS, deactivation of TCH} RF CHANnel RELease ACKnowledge {TCH released} Active Call DATA REQuest (Connect [CM]) DATA INDication (Connect Acknowledge [CM]) DATA REQuest (Authentication Request (RAND) [MM]) DATA INDication (Authentication Response (SRES) [MM]) A-bis signalling example
  81. 81. BTS A-Interface.
  82. 82. The System. Base Station Controller BSC Public Switched Telephone Network Base Mobile Station (MS) Mobile Switching Centre MSC (PSTN) Station Subsystem (BSS) A-Inter A-bis Um 2 Mbit/s PCM Air Interface BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Equip. Id Register EIR Authen. Centre AUC Visitor Location Register VLR Home Location Register HLR Mobile Switching Centre MSC MAP ISUP / TUP MAP MAP MAP ISUP / TUP ISUP / TUP MAP
  83. 83. 83 • DTAP - Direct Transfer Application Part • BSSMAP - BSS Management Application Part • CM - Call Management • MM - Mobile Management • RR - Radio Resource Management • BTSM - BTS Management • SCCP - Signalling Connection Control Part • MAP - Mobile Application Part • TCAP - Transaction Capability Application Part • ISUP - ISDN User Part • MTP - Message Transfer Part DTAPCM MM RR Sig. layer 2 Layer 1 (air) Sig. layer 2 Sig. layer 1 MTP SCCP BSSMAPRR (CM+MM) MS BSC MTP MTP SCCP SCCP CM MM BSSMAP TCAP MAP I S U P MSC Sig. layer 2 Layer 1(air) BTS (CM) (MM) (RR) (CM) (MM) (RR) (CM) (MM) (LAPDm) (LAPDm) (LAPD) Sig. layer 2 Sig. layer 1 (LAPD) BTSM BTSMRR' Um Interface Abis Interface A Interface Inter-MSC Protocol Architecture
  84. 84. 84 BTS • Based on System 7 MTP and SCCP • Uses Base Station Subsystem Application Part (BSSAP) » BSS Management Application Part (BSSMAP) • Radio Resource (RR) and BSC management • Uses SCCP connectionless service » Direct Transfer Application Part (DTAP) • Transfer of Call Control (CM) messages • Transfer of Mobility Management (MM) messages • Uses SCCP connection-oriented service A-Interface
  85. 85. 85 Signalling System Number 7 MTP Level 3 Physical Data Link Network Transport Session Presentation Application OSI Layer SS7 Levels 7 6 5 4 3 2 1 MTP Level 1 MTP Level 2 Physical MTP Level 1 Data Link2 MTP Level 2 MTP Level 3Network3 I S U P SCCP TCAP T U P IN, MAP I S U P Transport Session Presentation Application SCCP • Level 4/User Parts • SCCP
  86. 86. Basic format of MSU - SCCP message LabelSIFF CK F I B FSN F B I B BSNLI > 2SIO User Data MTC SLS Originating Point Code Destination Point Code N x 8 bits 8 bits 14 bits 14 bits4 bits Mandatory fixed part Mandatory variable part Optional part Service Indicator 0 0 1 1 Sub-service Field === MTP === BSN : 66 BIB : 0....... FSN : 4 FIB : 1....... LI : 28 = MSU SPARE : 00...... SIO : 03h = SCCP
  87. 87. 87 SCCP message format • An SCCP Messages contains the following information. » Routing label. » Messages type. » Mandatory fixed part. » Mandatory variable part. » Optional part. Pointer to parameter P Length Indicator of parameter M Parameter M Length Indicator of parameter P Parameter P Parameter name = X Length Indicator of parameter X Parameter X Routing Label Message Type Code Mandatory parameter A Pointer to start of optional part Mandatory parameter F Pointer to parameter M End of optional parameters Parameter name = Z Length Indicator of parameter Z Parameter Z User Data MTC SLS Originating Point Code Destination Point Code N x 8 bits 8 bits 14 bits 14 bits4 bits Mandatory fixed part Mandatory variable part Optional part
  88. 88. Signalling Connection Control Part (SCCP) • The SCCP itself has users called Subsystems (SS). • The SCCP provides additional functions to the MTP for an OSI network service. » In particular, the non circuit related data transfer between signalling end points is supported by the SCCP. • Special protocol functions are provided by SCCP. » Segmentation. • Allows messages of any great length to be transmitted. » Addressing and Routing.
  89. 89. 89 SCCP four classes of service • Basic connectionless Class (Class 0). » Data are transparent independently of each other and may therefore be delivered out of sequence. This corresponds to a pure connectionless network service. • Sequenced connectionless Class (Class 1). » In protocol class 1 the features of class 0 are complemented by a sequence control. • Basic Connection-oriented Class (Class 2). » Bi-directional transfer of NSDUs is done by setting up a temporary or permanent signalling connection. This corresponds to a simple connection- oriented network service. • Flow control connection-oriented Class (Class 3). » In protocol class 3 the features of class 2 are complemented by the inclusion of flow control.
  90. 90. 90 Connection-oriented Data Transfer Data Transfer Data Transfer = Release Resource= Reserved Resource CR CC CC CR RLC RLSD RLSD RLC
  91. 91. 91 Connectionless Data Transfer UDT UDT UDT UDT
  92. 92. BTS • UDT (Unitdata) Class 0 » Used by a SCCP wanting to send data in a connectionless mode. • DT1 (Data Form 1) Class 2 » A Data Form 1 message is sent by either end of a signalling connection to pass transparently SCCP user data between two SCCP nodes. • Note: Only point to point signalling route is used in at the A- inter phase, meaning that the MTP does not have to contain the functions related to the signalling transfer point (STP) and multiple signalling-route management. SCCP Message Types, for A-Interface Class 0 and 2
  93. 93. CR Connection Request CC Connection Confirm CREF Connection Refused RLSD Released RLC Release Complete DT1 Data Form 1 DT2 Data Form 2 AK Data Acknowledgement UDT Unitdata UDTS Unitdata Service ED Expedited Data EA Expedited Data Acknowledgement RSR Reset Request RSC Reset Confirm ERR Protocol Data Unit Error IT Inactivity Test Protocol class 0 X X X X X X X X X X X X X X X X X X X X X X X Message type Code 0000 0001 0000 0010 0000 0011 0000 0100 0000 0101 0000 0110 0000 0111 0000 1000 0000 1001 0000 1010 0000 1011 0000 1100 0000 1101 0000 1110 0000 1111 0001 0000 1 2 3 X X SCCP Message Types
  94. 94. 94 • Message type code • Destination local reference • Source local reference • Called party address • Calling party address • Protocol class • Segmenting/reassembling • Release cause • Return cause • Error cause • Refusal cause • Data • End of optional parameters BTS SCCP Information elements
  95. 95. 95 Short descriptions SCCP Message Types, Class 2 and 3. Part 1 •Connection Request (CR ). » A connection Request message is sent by a calling SCCP to a called SCCP to request the setting up of a signalling connection between the two entities. The required characteristics of the signalling connection are carried in various parameter fields. On reception of a Connection Request message, the called SCCP initiates the setup of the signalling connection if possible. •Connection Confirm (CC ) » A connection confirm message is sent by the called SCCP to indicate to the calling SCCP that it has performed the setup of the signalling connection. On reception of a Connection confirm message, the calling SCCP completes the setup of the signalling connection if possible. •Connection Refused (CREF) » A Connection Refused message is sent by the called SCCP or an intermediate node to indicate to the calling SCCP that the setup of the signalling connection has been refused.
  96. 96. 96 Short descriptions SCCP Message Types, Class 2 and 3. Part 2 •Released (RLSD). » A released message is sent, in the forward or backward direction, to indicate that the sending SCCP wants to release a signalling connection and the associated resources at the sending SCCP have been brought into the disconnect pending condition. It also indicates that the receiving node should release the connection and any other associated resources as well. •Release Complete (RLC). » A Release Complete message is sent in response to the Released message indicating that the Released message has been received, and the appropriate procedures have been completed. •Data Form1 (DT1). » A Data Form 1 message is sent by either end of a signalling connection to pass transparently SCCP user data between two SCCP nodes.
  97. 97. 97 Short descriptions SCCP Message Types, Class 2 and 3. Part 3 •Data Form 2 (DT2). » A Data Form 2 message is sent by either end of a signalling connection to pass transparently SCCP user data between two SCCP nodes and to acknowledge message flowing in the other direction. •data acknowledgement (AK). » A Data Acknowledgement message is used to control the window flow control mechanism, which has been selected for the data transfer phase. •Expedited Data (ED). » An Expedited Data message functions as a Data Form 2 message but includes the ability to bypass the flow control mechanism which has been selected for the data transfer phase. It may be sent by either end of the signalling connection. •Expedited Data acknowledgement (EA). » An Expedited Data Acknowledgement message is used to acknowledge an Expedited Data message.Every ED message has to be acknowledged by an EA message before another ED message may be sent.
  98. 98. 98 Short descriptions SCCP Message Types, Class 2 and 3. Part 4 •Reset Request (RSR). » A Reset Request message is sent to indicate that the sending SCCP wants to initiate a reset procedure (re-initialization of sequence numbers) with the receiving SCCP. •Reset Confirm (RSC). » A Reset Confirm message is sent in response to a Reset Request message to indicate that Reset Request has been received and the appropriate procedure has been completed. •Protocol Data Unit Error (ERR). » A Protocol Data Unit Error message is sent on detection of any protocol errors. •Inactivity Test (IT). » An Inactivity Test message may be sent periodically by either end of a signalling connection to check if this signalling connection is active at both ends, and to audit the consistency of connection data at both ends. •Extended Unitdata (XUDT). » An Extended Unitdata message is used by the SCCP wanting to send data along with optional parameters in a connectionless mode. It can also be used by a SCCP to send data without optional parameters.
  99. 99. 99 Short descriptions SCCP Message Types, Class 2 and 3. Part 5 •Extended Unitdata Service (XUDTS). » An Extended Unitdata Service message is used to indicate to the originating SCCP that a XUDT with optional parameters cannot be delivered to its destination. A XUDTS message is sent only when the option field in the XUDT message is set to "return on error". •Long Unitdata (LUDT). » A Long Unitdata message is used by the SCCP to send data (along with optional parameters) in a connection mode, when MTP-3b capabilities are present. It allows sending of NSDU sizes up to 3952 octets without segmentation. •Long Unitdata Service (LUDTS). » A long Unitdata Service message is used to indicate to the originating SCCP that a LUDT cannot be delivered to its destination. A LUDTS message is sent only when the return option in the LUDT is set.
  100. 100. BTS A-Interface BSSAP
  101. 101. 101 • ETSI has specified an SS7 Base Station Subsystem Application Part (BSSAP) as the user of the SCCP/MTP transport service. » SCCP subsystem number for BSSAP is FEh. BTS Base Station Subsystem Application Part (BSSAP)
  102. 102. SCCP Information elements SCCP Header SSN FEh: BSSAP Discriminator 0 0 0 0 0 0 0 0 1 1 DLCI Data Link Connection Identifier Discriminator 0 0 0 0 0 0 0 1 OCTET DLCI2 3 2Length Indicator 1 n n Layer 3 Messages Octet Length Indicator 1 Layer 3 Um Interface Octet Bit no.: 8 7 6 5 4 3 2 1 C2 C1 0 0 0 S3 S2 S1 C2 C1 identifies signaling-radio channel (00: SDCCH/FACCH, 01: SACCH) S3-S1 is the SAPI on the radio interface BSSMAP DTAP LabelSIFF CK F I B FSN F B I B BSNLI > 2 SIO x3h
  103. 103. BTS A-Interface BSSMAP
  104. 104. 104 BTS BSSMAP Format Disc. 0 = BSSMAP Length indicator BSSMAP message type BSSMAP message Information Element Identifier Length of Information Elements Content of Information Elements Information Element Identifier Content of Information Elements Fixed Length Info. Element Format Variable Length Info. Element Format OCTET 1 OCTET 2 OCTET n
  105. 105. BSSMAP Messages, part 1 Assignment messages:(Setup of traffic channels) - Assignment request - Assignment complete - Assignment failure Release messages: - Clear command (Release of traffic channels) - Clear complete - Clear request - SAPI "n" clear command (Control of layer 2 links with SAPI not equal - SAPI "n" clear complete to 0 on the radio interface) - SAPI "n" reject 0000- - - - 0001 0010 0011 0010- - - - 0000 0001 0010 0011 0100 0101 Message typeCode
  106. 106. BSSMAP Messages, part 2 Handover messages: - Handover request (To BSC: Request for handover to that BSC) - Handover required (To MSC: Inter-BSC/MSC handover required) - Handover request ack (To MSC: Acknowledge of Handover request) - Handover command (To BSC: Contains the new radio channel/BTS to which the MS should switch) - Handover complete (To MSC: Commanded handover complete) - Handover failure (To MSC: Commanded handover unsuccessful) - Handover performed (To MSC: BSC has performed intern. handover) - Handover candidate (To BSC: MSC requests list of MS that could enquire be handed over to another cell) - Handover candidate (To MSC: Answer to Handover candidate response enquire) - Handover required reject (To BSC: Required handover unsuccessful) - Handover detect (To MSC: Commanded handover successful) 0001- - - - 0000 0001 0010 0011 0100 0110 0111 1000 1001 1010 1011 Message typeCode
  107. 107. BSSMAP Messages, part 3 General messages: - Reset (Initialisation of BSS or MSC due to failure) - Reset Acknowledge - Overload (Processor or CCCH overload) - Trace invocation (Start production of trace record) - Reset Circuit (Initialisation of single circuit due to failure) - Reset Circuit acknowledge Terrestrial resource messages: - Block (Management of circuits/time slots - Blocking acknowledge between MSC and BTS) - Unblock - Unblocking acknowledge 0011- - - - 0000 0001 0010 0011 0100 0101 0100- - - - 0000 0001 0010 0011 Message typeCode
  108. 108. BSSMAP Messages, part 4 Radio resource messages: - Resource request (Available radio channels in the BSS cells) - Resource indication - Paging (Paging of MS) - Cipher mode command (Commands start of cyphering) - Classmark update (Change of MS power class) - Cipher mode complete (Ciphering is successfully initiated) - Queuing indication (Indicates delay in assignment of traffic channel) - Complete layer 3 (Contains first message received from MS; information sets up SCCP-connection at A-interface) 0101- - - - 0000 0001 0010 0011 0100 0101 0110 0111 Message typeCode
  109. 109. - Circuit identity code (Traffic channel on A-interface) - Radio channel identity (Description of channels allocated to MS) - Resource available (Available radio channels in a cell) - Cause (Reason for event/failure) - Cell identifier (Identity of radio cell) - Priority (Indicates the priority of a request) - Layer 3 header (Protocol discriminator and transaction identifier information to be used on the radio interface) - IMSI - TMSI - Encryption information (Encryption algorithm and key) - Channel type (Speech, data incl. speed or signalling; full or half rate) - Periodicity (Defines periodicity of a particularly procedure) - Number of MSs (No. of handover candidates to be sent to MSC) - Current radio environment (Measurement data on radio cells for handover) - Environment of BS “n” (Data in order of priority on the n preferred new cells for handover) BSSMAP Information Elements, part 1
  110. 110. BSSMAP Information Elements, part 2 - Classmark information type 2 (MS power class + SMS capability) - Interference band to be used (Indicates acceptable interference level) - RR Cause (Reason for RR release) - Trace number (Reference number for a trace record) - Layer 3 information (Contains transparent RR, MM or CM message) - DLCI (Indicates the layer 2 link to be used on the radio interface) - Downlink DTX flag (Disabling of discontinuous transmission) - Cell identifier list (Identifies the cells within a BSS) - Response request (Requests a response on a Handover required messages) - Resource indication method (How the BSS shall transfer resource info) - Classmark information type 1 (MS power class)
  111. 111. BTS A-Interface DTAP
  112. 112. 112 • The Direct Transfer Application sub-Part (DTAP) is used to transfer call control and mobility management messages to and from the MS; » The layer-3 information in these messages is not interpreted by the BSS. BTS Direct Transfer Application sub-Part (DTAP)
  113. 113. 113 BTS Disc. 1 = DTAP Length indicator BSSMAP message type BSSMAP message Information Element Identifier Length of Information Elements Content of Information Elements Information Element Identifier Content of Information Elements Fixed Length Info. Element Format Variable Length Info. Element Format OCTET 1 OCTET 2 OCTET n DTAP Format
  114. 114. 114 BTS • Layer 3 of the DTAP messages has the same format as BSSMAP messages. • The DTAP messages and information elements are identical to the the transparent MM and CM listed in the A-bis section. DTAP messages and elements
  115. 115. 115 BTS MSCBSC SCCP CR (BSSMAP Comp layer 3 info (CM Service Request SCCP CC (BSSMAP Cipher mode command) SCCP DT1 (BSSMAP Cipher mode complete) SCCP DT1 (DTAP (Setup [CM])) SCCP DT1 (DTAP (Call Proceeding [CM])) SCCP DT1 (BSSMAP Assignment request) SCCP DT1 (BSSMAP Assignment complete) SCCP DT1 (DTAP (Alerting [CM])) SCCP DT1 (DTAP (Connect [CM])) SCCP RLC SCCP DT1 (DTAP (Disconnect [CM])) SCCP DT1 (DTAP (Release [CM])) SCCP DT1 (DTAP (Release Complete [CM])) SCCP DT1 (BSSMAP Clear command) SCCP DT1 (BSSMAP Clear complete) SCCP RLSD . . . . .. . . .Active call A-Interface signalling example [MM]))
  116. 116. BTS Inter-MSC Signalling MAP
  117. 117. Base Station Controller BSC Public Switched Telephone Network Base Mobile Station (MS) Mobile Switching Centre MSC (PSTN) Station Subsystem (BSS) A-Inter A-bis Um 2 Mbit/s PCM Air Interface BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Base Transceiver Station BTS Equip. Id Register EIR Authen. Centre AUC Visitor Location Register VLR Home Location Register HLR Mobile Switching Centre MSC MAP ISUP / TUP MAP MAP MAP ISUP / TUP ISUP / TUP MAP The System.
  118. 118. 118 • DTAP - Direct Transfer Application Part • BSSMAP - BSS Management Application Part • CM - Call Management • MM - Mobile Management • RR - Radio Resource Management • BTSM - BTS Management • SCCP - Signalling Connection Control Part • MAP - Mobile Application Part • TCAP - Transaction Capability Application Part • ISUP - ISDN User Part • MTP - Message Transfer Part DTAPCM MM RR Sig. layer 2 Layer 1 (air) Sig. layer 2 Sig. layer 1 MTP SCCP BSSMAPRR (CM+MM) MS BSC MTP MTP SCCP SCCP CM MM BSSMAP TCAP MAP I S U P MSC Sig. layer 2 Layer 1(air) BTS (CM) (MM) (RR) (CM) (MM) (RR) (CM) (MM) (LAPDm) (LAPDm) (LAPD) Sig. layer 2 Sig. layer 1 (LAPD) BTSM BTSMRR' Um Interface Abis Interface A Interface Inter-MSC Protocol Architecture
  119. 119. 119 Signalling System Number 7 MTP Level 3 Physical Data Link Network Transport Session Presentation Application OSI Layer SS7 Levels 7 6 5 4 3 2 1 MTP Level 1 MTP Level 2 Physical MTP Level 1 Data Link2 MTP Level 2 MTP Level 3Network3 I S U P SCCP TCAP T U P IN, MAP I S U P Transport Session Presentation Application SCCP • Level 4/User Parts • SCCP
  120. 120. Signalling Connection Control Part (SCCP) • The SCCP itself has users called Subsystems (SS). • The SCCP provides additional functions to the MTP for an OSI network service. » In particular, the non circuit related data transfer between signalling end points is supported by the SCCP. • Special protocol functions are provided by SCCP. » Segmentation. • Allows messages of any great length to be transmitted. » Addressing and Routing. • See next slide.
  121. 121. SCCP Addressing and Routing. • The SCCP provides its own routing function. » As address parameter the SCCP can use. • DPC and SSN › Routing based on MTP DPC and SSN in Global title (GT). • Global title (GT) › Routing based on global title • E.g. Routing based on MTP DPC and SSN in Global title. Link Set Link Set A Link Set B DPC 1 DPC 2 DPC 3 First Route Second Route Link set A Link set B Link set B Link set B Link set A Link set A MTP DPC = 2
  122. 122. SCCP Addressing and Routing. » When global title (GT) is used different information cant be available. • Translation type, numbering plan, encoding scheme, nature of address, Address and Point Code. • If for example , a destination number of the ISDN or IMSI numbering plan is used, then the SCCP defines the DPC on the basis of a “GT Translation Table” that is available within the signalling point. Link Set Link Set A Link Set B DPC 1 DPC 2 DPC 3 First Route Second Route Link set A Link set B Link set B Link set B Link set A Link set A GT = 3 DPC 2 DPC 1 DPC 3 GT 3 GT 2 GT 1
  123. 123. 123 SCCP Subsystem number (SSN) • SSN 01h = SCCP Management message (SCMG). • The MAP layer consist several of Application Service Elements, so more than one SSN are alocated. » The SSN for MAP are: • 05h = MAP • 06h = HLR • 07h = VLR • 08h = MSC • 09h = EIR • 0Ah = AUC • Within a INAP node, it is the choice of the network operator to which SSN(s) he will assigned to INAP. » Any addressing scheme supported and not reserved by the SCCP may be used. • 91h = GMLC • 93h = gsmSCF • 94h = SIWF • 95h = SGSN • 96h = GGSN
  124. 124. 124 SCCP Management message (SCMG) • The SCCP management function (SCGM). » SCMG are taking care of handling of errors and other problems on subsystems level. • Subsystem-Prohibited. • Subsystem-Status-Test. • Subsystem-Out-of-Service. • Subsystem Congested. » The SCMG messages (SSA, SSP, SST, SOR, SOG) contain mandatory fixed parameters. These parameters are defined in the data field of the UDT and XUDT message.
  125. 125. 125 SCCP four classes of service • Basic connectionless Class (Class 0). » Data are transparent independently of each other and may therefore be delivered out of sequence. This corresponds to a pure connectionless network service. • Sequenced connectionless Class (Class 1). » In protocol class 1 the features of class 0 are complemented by a sequence control. • Basic Connection-oriented Class (Class 2). » Bi-directional transfer of NSDUs is done by setting up a temporary or permanent signalling connection. This corresponds to a simple connection- oriented network service. • Flow control connection-oriented Class (Class 3). » In protocol class 3 the features of class 2 are complemented by the inclusion of flow control.
  126. 126. 126 Short descriptions SCCP Message Types, Class 0 and 1. •Unitdata (UDT). » Used by a SCCP wanting to send data in a connectionless mode. •Unitdata Service (UDTS). » A Unitdata Service message is used to indicate to the originating SCCP that a UDT it sent cannot be delivered to its destination. A UDTS message is sent only when the option field in that UDT is set to "return on error". •TCAP uses the connectionless protocol classes of SCCP only. » In connection with INAP the protocol class 1 is used exclusively. » In connection with MAP the protocol class 0 and 1 is used.
  127. 127. 127 Connectionless Data Transfer UDT UDT UDT UDT
  128. 128. 128 Signalling System Number 7 Level 4/User Parts TCAP MTP Level 3 Physical Data Link Network Transport Session Presentation Application OSI Layer SS7 Levels 7 6 5 4 3 2 1 MTP Level 1 MTP Level 2 Physical MTP Level 1 Data Link2 MTP Level 2 MTP Level 3Network3 I S U P SCCP TCAP T U P INAP, MAP I S U P Transport Session Presentation Application SCCP TCAP
  129. 129. Transaction Capabilities Application Part (TCAP) • Definition » The overall objective of TCAP is to provide means for the transfer of information between nodes, and to provide generic services to applications, while being independent of any of these. » Transaction Capabilities in the SS7 protocol are functions that control non-circuit-related information transfer between two or more signalling nodes via a signalling network. • For use between » Exchanges » An exchange and a network service centre » Network service centres
  130. 130. 130 TCAP / SCCP classes • ITU-T has only specified the use of SCCP class 0 and 1 (connectionless transfer) This means that the intermediate service part (ISP) is empty/not needed because no layer 4, 5 and 6 functions are required for control of SCCP.
  131. 131. 131 The ASN.1 notation • TCAP is build on ANS.1 abstract notation. • The ASN.1, abstract syntax notation one, is a formal language for defining high level protocol information by means of user defined data types. It was standardized by CCITT in 1984 but is now also adopted by ISO in conjunction with BER as part of OSI applications. ASN.1`s prime use has been in the definition of application protocols, but is also used in definition of presentation protocols. The grammar of the syntax is the Backus-Naur Form (BNF) as used in other programming languages.
  132. 132. TCAP Applications • Mobile services (MAP) » e.g. • Location updating/roaming • Non-call related supplementary services • Charging information • Supplementary services (INAP/CAMEL) » e.g. • Number conversion (800, VPN). • Credit check. • Prepaid/calling card • Prepaid roaming. • Operation and Maintenance (OMAP)
  133. 133. Messages Structure when TCAP is used. • TCAP is an user of SCCP. MAXIMUM 272 OCTETS SIFF CK F I B FSN F B I B BSNLI > 2SIO Optional part Mandatory variable part Mandatory fixed part MTC SLS OPC DPC Messages Component Messages Component Length Transaction information element Messages Length Messages Type Tag Higher layer (INAP, CAMEL or MAP) The messages type (MTC) is always UDT or UDTS, if the higher layer is MAP CAMEL or INAP MTP SCCP TCAP
  134. 134. TCAP sub-layers • TCAP is divided into two sub-layers • Transaction sub-layer » Is a simple transport service for the component sub-layer (comparable to an “envelope” containing a group of components to be processed at the remote end) • Component sub-layer » Deals with individual actions or data, called components (e.g. one mobile phone)
  135. 135. TCAP Message types • Transaction Sub-layer » Unidirectional (used when no need to establish a transaction) » Begin (initiate transaction) » End (terminate transaction) » Continue (continue transaction) » Abort (terminate transaction in abnormal situation) • Component Sub-layer » Invoke (request operation to be performed at remote end) » Return Result(last) (successful completion of operation, contains last/only result) » Return Error (reports unsuccessful completion of operation) » Reject (incorrect component received at remote end) » Return Result (contains part of result of operation)
  136. 136. 136 TCAP Structure Message type tag Total message length Transaction portion information element Component portion tag Component type tag Component length Component portion information element Component Abort Cause Dialogue Portion Component Portion Destination Transaction Identifier Originating Transaction Identifier Tag Length Contents Tag Length Contents Invoke ID Linked ID Operation Code Sequence Error Code Problem Code - Unidirectional - Begin - End - Continue - Abort - Invoke - Return Result (Last) - Return Result (Not Last) - Return Error - Reject
  137. 137. • The table shows where ORIG and DEST TID is used. Transaction portion information element • The application on higher layer (MAP and INAP) are using the ORIG and DEST TID within the “Transaction portion info element” to differ between the transactions send to and from the application. » ORIG TID (Originating Transaction Identifier). • The originating transaction ID is assigned by the node sending a message, and is used to identify the transaction at that end. » DEST TID (Destination Transaction Identifier). • The destination transaction ID identifies the transaction at the receiving end. Unidirectional Begin Continue End Transaction Abort ORIG ID DEST ID YES NO YES YES YESNO NONO YESNO
  138. 138. Component portion information element • The application on higher layer (MAP, CAMEL and INAP) are using the Invoke ID and Linked ID within the “Component portion info element” to correlate the question and answer within transactions send to and from the application. » Invoke ID • An Invoke ID is used as a reference number to identify uniquely an operation. It is present in the Invoke component and in any reply to the Invoke (Return Result, Return Error or Reject), enabling the reply to be correlated with the invoke. » Linked ID • A Linked ID is included in an invoke component by a node when it responds to an operation invocation with a linked operation invocation. The node receiving the Linked ID uses it for correlation purposes, in the same way that it uses the invoke ID in Return Result, Return Error and Reject components.
  139. 139. 139 TCAP Signaling Example. BEGIN ORIG TID: 75 INVOKE INVOKE ID: 0 CONTINUE ORIG TID: 18 DEST TID: 75 INVOKE INVOKE ID: 0 CONTINUE ORIG TID: 75 DEST TID: 18 RET RES L INVOKE ID: 0 CONTINUE ORIG TID: 18 DEST TID: 75 INVOKE INVOKE ID: 1 CONTINUE ORIG TID: 18 DEST TID: 75 INVOKE INVOKE ID: 2 CONTINUE ORIG TID: 75 DEST TID: 18 RET RES L INVOKE ID: 2 CONTINUE ORIG TID: 75 DEST TID: 18 RET RES L INVOKE ID: 1 END DEST TID: 75 INVOKE INVOKE ID: 0 Application Begin Data send Data received Data send Data send Data received Data received Application End
  140. 140. 140 BTS Signalling System Number 7 Level 4/User Parts MAP MTP Level 3 Physical Data Link Network Transport Session Presentation Application OSI Layer SS7 Levels 7 6 5 4 3 2 1 MTP Level 1 MTP Level 2 Physical MTP Level 1 Data Link2 MTP Level 2 MTP Level 3Network3 I S U P SCCP TCAP T U P INAP, MAP I S U P Transport Session Presentation Application SCCP TCAP MAP
  141. 141. BTS • MAP = Mobile Application Part • Users: MSC, HLR, VLR, EIR • Applications: » Location updating/roaming » Incoming call routing information (MSRN) » Subscriber service information » Non-call related supplementary services » Short message service delivery » MS equipment identity (IMEI) » Charging information MAP
  142. 142. Called party address Message type Calling party address Protocol class 0, 1 Pointers MAP Info. TCAP part Sub-system Number (part of the address field) SCCP User Data Format of SCCP message for MAP information LabelSIFF CK F I B FSN F B I B BSNLI > 2 SIO x3h
  143. 143. 143 MAP information in TCAP Message type tag Total message length Transaction portion information element Component portion tag Component type tag Component length Component portion information element Component Tag Length Contents Tag Length Code Parameter
  144. 144. • The inter-MSC interface are: » The MSC-VLR interface. » The MSC-HLR interface. » The HLR-VLR interface. » The MSC-MSC interface. » The MSC-EIR interface. » The VLR-VLR interface. » The MSC-ISDN/telephone network interface. BTS Inter-MSC Signalling
  145. 145. 145 BTS OperationValue 1 Update location area 2 Update location 3 Cancel location 4 Provide roaming number 5 Detach IMSI 6 Attach IMSI 7 Insert subscriber data 8 Delete subscriber data 9 Send parameters 10 Register SS 11 Erase SS 12 Activate SS 13 Deactivate SS 14 Interrogate SS 15 Invoke SS 16 Forward SS notification 17 Register password 18 Get password 19 Process unstructured data MAP Operations Part 1
  146. 146. 146 BTS 20 Send info for incoming call 21 Send info for outgoing call 22 Send routing information 23 Complete call 24 Connect to following address 25 Process call waiting 26 Page 27 Search for mobile subscriber 28 Perform handover 29 Send end signal 30 Perform subsequent handover 31 Allocate handover number 32 Send handover report 33 Process access signalling 34 Forward access signalling 35 Note internal handover 36 Register charging information 37 Reset 38 Forward check SS indication MAP Operations Part 2 OperationValue
  147. 147. 147 BTS 39 Authenticate 40 Provide IMSI 41 Forward new TMSI 42 Set ciphering mode 43 Check IMEI 45 Send routing info for SM 46 Forward short message 47 Set message-waiting data 48 Note MS present 49 Alert service centre 50 Activate trace mode 51 Deactivate trace mode 52 Trace subscriber activity 53 Process access request 54 Begin subscriber activity MAP Operations Part 3 OperationValue
  148. 148. 148 BTS Home side Visited side INVOKE (Update Location) BEGIN INVOKE (Insert Subscriber Data) CONTINUE RETURN RESULT CONTINUE (Update Location) END (Insert Subscriber Data) RETURN RESULT MAP - signalling Location Updating example
  149. 149. BTS GSM Signalling procedures
  150. 150. BTS • Call Management » Ordinary Call Control (as usual) • Mobility Management » Location Updating (Roaming) » Authentication • Radio Resource Management » Paging » Network Access » Encryption » Radio Signal Control » Radio Signal Measurements » Handover Special signalling procedures for GSM
  151. 151. Area 1 Area 2 BTS BTS BTS BTS •An MM procedure •Reasons for roaming: » MS has detected that it has entered into a new location area (by listening to Broadcast system info) •Types of roaming: » Inside same VLR area • The HLR does not need to know » Another VLR area • In this case the HLR is informed MSC VLR MSC VLR SONOFON M N Location Updating (Roaming)
  152. 152. MS BT S BS C MS C VLR 1 VLR 2 HLR Location Update Request (old LAI, TMSI) [MM] Update Location Area (old LAI, new LAI, TMSI) Send Parameters (old LAI, TMSI) Send Parameters Result (IMSI) Update Location (IMSI, MSRN, VLR no) Cancel Loc (IMSI, VLR' no) Cancel Location Ack Update Location Ack Insert Subscriber Data (IMSI, service inf) Subscriber Data Acknowledge Update Location Area Ack Forward New TMSI (TMSI)Location Update Accept (new LAI, TMSI) [MM] TMSI Reallocation Complete [MM] TMSI Ack Channel Release [RR] Clear Command [RR] Um/A-bis/A signalling MAP signalling Location Updating (Roaming)
  153. 153. • A RR procedure • The Handover process is the situation where a Mobile Station changes from being served by one Antenna to another • Handovers take place during a call • Handover are done automatically • Crossing the boundary of two adjacent cells is the typical example of a Handover Handovers. BTS BTS
  154. 154. • Major types of handovers » Intra BSC » Inter BSC » Inter MSC • Purpose of handover » Poor quality connection • Avoid loosing contact to the mobile station » Fault in the MS or BTS/BSC » Network management Intra BSC Inter BSC Inter MSC BSC MSC - A MSC - B BSC BSC BTS BTS BTS BTS SONOFON M N SONOFON M N SONOFON M N TRAU Signaling
  155. 155. Send handover report Um/A-bis/A signalling MAP signalling ISUP/TUP signalling MS BT S BSC- A MSC- A BSC- B MSC- B VLR- B Handover Required (new BTS) [RR] Perform handover (new BTS, Ch type) Handover Request (new BTS) Handover Req Ack (Radio Ch) Allocate handover number (MSRN) (MSRN) Radio Ch Ack (Radio Ch, MSRN) IAM (MSRN) ACMHandover Command (Radio CH) [RR] Handover Complete [RR] Clear Command[RR] Clear Complete[RR] Send End Signal Answer Measurement Result [RR] Handover, example
  156. 156. BTS • A CM procedure • Distinguish two types » Mobile Terminating Call • i.e. a call from the fixed network to a Mobile Station » Mobile Originating Call • i.e. a call from a Mobile Station to the fixed network Call Setup
  157. 157. BTS • Problems and answers » Where in the world is the Mobile Station • Look it up in the HLR • (The HLR may have to ask the VLR) » How to Make the Mobile Station Aware that a call is waiting • Page it in the cell where it is located » What does the MS do when being paged ? • Asks for a Radio channel • Tells the system that it is ready • Now the usual setup flow follows Mobile Terminating Call
  158. 158. IAM (MSISDN, service) BTS BSC MS C VLR HLR GMS C ISD N Send Routing Info (MSISDN) Roaming Number (MSRN) Routing Info (MSRN) Provide Roaming Number (IMSI) IAM (MSRN, service) Send Info Incoming Call (MSRN, service) Page (IMSI, TMSI, LAI) Paging Request (TMSI) [RR] Paging Response (TMSI) [RR] Page Result Complete Call (service) Channel Request [RR] Immediate Assign [RR] SETUP (service) [CM] Call Confirm [CM] Assign Command [RR] Assign Req [RR] Assign Complete [RR] Alerting [CM] ACM Connect [CM] ANM Connect Ack [CM] Complete Call Result MS Um/A-bis/A signalling MAP signalling ISUP/TUP signalling Incoming Call
  159. 159. BTS • Problems and Answers » How the mobile gets in contact with the network • Switch the MS on • Request a channel • Tell the network what kind of service is wanted » How does the network respond • Verifies the Mobile identity (authentication) • Assigns a traffic channel • And then everything proceed as usual Mobile Originating Call
  160. 160. BTS BSC MSC VLR ISDN Immediate Assign [RR] CM Service Req (IMSI, transact) [MM] Process Access Request Authenticate (RAND) Authentication Request (RAND) [MM] Authentication Response (SRES) [MM] Authentication Response (SRES) Set ciphering mode (key) Ciphering Mode Command (key) [RR] Ciphering Mode Complete [RR] Access Request Ack SETUP (service, called number) [CM] Send info for o/g (service, called number) Complete callCall Proceeding [CM] Assign Request [RR]Assign Command [RR] Assign Complete [RR] IAM ACM ANM Alerting [CM] Connect [CM] Connect Ack [CM] CM copy [MM] MS Channel Request/Required [RR] Um/A-bis/A signalling MAP signalling ISUP/TUP signalling Outgoing Call from MS
  161. 161. 161 Signalling System Number 7 Level 4/User Parts INAP MTP Level 3 Physical Data Link Network Transport Session Presentation Application OSI Layer SS7 Levels 7 6 5 4 3 2 1 MTP Level 1 MTP Level 2 Physical MTP Level 1 Data Link2 MTP Level 2 MTP Level 3Network3 I S U P SCCP TCAP T U P INAP, MAP I S U P Transport Session Presentation Application SCCP TCAP INAP
  162. 162. CS1 / IN / INAP • Abbreviations. » CS1 = Intelligent Network Capability Set 1. » IN = Intelligent Network. » INAP = Core Intelligent Network Application Part • The intelligent Network (IN) is a control architecture for telecommunication network service. » The goal of the IN service control architecture is to provide a framework, which allows the Network Operator to create , to control and to manage services more efficiently, economically and rapidly as the present network architecture allows.
  163. 163. CS1 / IN / INAP • INAP supports interactions between the following three Functions » - Service Switching Function (SSF). » - Service Control Function (SCF). » - Specialized Resource Function (SRF). • INAP provides a set of predefined Messages and parameters that can be used in the intelligent Network predefined functions, however Extension Fields is allowed. » Those parameter are operator specific, and therefore not known by the MPA. • INAP is not like the MAP where all transactions shall be ended by TC_END. In INAP a TC_END shall no longer be maintained if both part involved in the transaction knows that no more data is required. » Those cases are called pre-arranged end. The MPA doesn't know those cases, and therefore not able to to make a correct sequence recording.
  164. 164. 164 Short descriptions INAP Operations Part 1 •Initial DP. Direction: SSF -> SCF » This operation is used after a TDP to indicate request for service. •Assist Request Instructions. Direction: SSF -> SCF or SRF -> SCF » This operation is used when there is an assist or a hand-off procedure and may be sent by the SSF or SRF to the SCF. This operation is sent by the SSF or SRF to the SCF, when the initiating SSF has set up a connection to the SRF or to the assisting SSF as a result of receiving an Establish Temporary Connection or Connect (in case of hand-off) operation from the SCF. •Establish Temporary Connection. Direction: SCF -> SSF » This operation is used to create a connection to a resource for a limited period of time (e.g. to play an announcement, to collect user information); it implies the use of the assist procedure. •Disconnect Forward Connection. Direction: SCF -> SSF » This operation is used to disconnect a forward temporary connection or a connection to a resource.
  165. 165. 165 Short descriptions INAP Operations Part 2 •Connect To Resource. Direction: SCF -> SSF » This operation is used to connect a call from the SSP to the PE containing the SRF. •Connect. Direction: SCF -> SSF » This operation is used to request the SSF to perform the call processing actions to route or forward a call to a specified destination. To do so, the SSF may or may not use destination information from the calling party (e.g., dialed digits) and existing call setup information (e.g., route index to a list of trunk groups), depending on the information provided by the SCF. •Release Call. Direction: SCF -> SSF » This operation is used to tear down an existing call at any phase of the call for all parties involved in the call. •Request Report BCSM Event. Direction: SCF -> SSF » This operation is used to request the SSF to monitor for a call-related event (e.g., BCSM events such as busy or no answer), then send a notification back to the SCF when the event is detected.
  166. 166. 166 Short descriptions INAP Operations Part 3 •Event Report BCSM. Direction: SSF -> SCF » This operation is used to notify the SCF of a call-related event (e.g., BCSM events such as busy or no answer) previously requested by the SCF in a Request Report BCSM Event operation. •Request Notification Charging Event. Direction: SCF -> SSF » This operation is used by the SCF to instruct the SSF on how to manage the charging events which are received from other FEs and not under control of the service logic instance. The operation supports the capabilities to cope with the interactions concerning charging. •Event Notification Charging. Direction: SSF -> SCF » This operation is used by the SSF to report to the SCF the occurrence of a specific charging event type as previously requested by the SCF in a Request Notification Charging Event operation. The operation supports the capabilities to cope with the interactions concerning charging.
  167. 167. 167 Short descriptions INAP Operations Part 4 •Collect Information. Direction: SCF -> SSF » This operation is used to request the SSF to perform the originating basic call processing actions to prompt a calling party for destination information, then collect destination information according to a specified numbering plan (e.g., for virtual private networks). •Continue. Direction: SCF -> SSF » This operation is used to request the SSF to proceed with call processing at the DP at which it previously suspended call processing to await SCF instructions (i.e., proceed to the next point in call in the BCSM). The SSF continues call processing without substituting new data from SCF. •Initiate Call Attempt. Direction: SCF -> SSF » This operation is used to request the SSF to create a new call to one call party using address information provided by the SCF. •Reset Timer. Direction: SCF -> SSF » This operation is used to request the SSF to refresh an application timer in the SSF.
  168. 168. 168 Short descriptions INAP Operations Part 6 •Furnish Charging Information. Direction: SCF -> SSF » This operation is used to request the SSF to generate, register a call record or to include some information in the default call record. The registered call record is intended for off-line charging of the call. •Apply Charging. Direction: SCF -> SSF » This operation is used for interacting from the SCF with the SSF charging mechanisms. The Apply Charging Report operation provides the feedback from the SSF to the SCF. •Apply Charging Report. Direction: SSF -> SCF » This operation is used by the SSF to report to the SCF the occurrence of a specific charging event as requested by the SCF using the Apply Charging operation. •Call Gap. Direction: SCF -> SSF » This operation is used to request the SSF to reduce the rate at which specific service requests.
  169. 169. 169 Short descriptions INAP Operations Part 7 •Activate Service Filtering. Direction: SCF -> SSF » When receiving this operation, the SSF handles calls to destination in a specified manner without sending queries for every detected call. It is used for example for providing Tele-voting or mass calling services. Simple registration functionality (counters) and announcement control may be located at the SSF. The operation initializes the specified counters in the SSF. •Service Filtering Response. Direction: SSF -> SCF » This operation is used to send back to the SCF the values of counters specified in a previous Activate Service Filtering operation. •Call Information Report. Direction: SSF -> SCF » This operation is used to send specific call information for a single call to the SCF as requested by the SCF in a previous call Information Request. •Call Information Request. Direction: SCF -> SSF » This operation is used to request the SSF to record specific information about a single call and report it to the SCF (with a call Information Report operation).
  170. 170. 170 Short descriptions INAP Operations Part 8 •Send Charging Information. Direction: SCF -> SSF » This operation is used to instruct the SSF on the charging information to be sent by the SSF. The charging information can either be sent back by means of signalling or internal if the SSF is located in the local exchange. In the local exchange this information may be used to update the charge meter or to create a standard call record. The charging scenario supported by this operation is scenario 3.2 (refer to Annex B where these are defined). •Play Announcement. Direction: SCF -> SRF » This operation is to be used after Establish Temporary Connection (assist procedure with a second SSP) or a Connect to Resource (no assist) operation. It may be used for in-band interaction with an analogue user, or for interaction with an ISDN user. In the former case, the SRF is usually collocated with the SSF for standard tones (congestion tone etc.) or standard announcements. In the latter case, the SRF is always collocated with the SSF in the switch. Any error is returned to the SCF. The timer associated with this operation must be of a sufficient duration to allow its linked operation to be correctly correlated.
  171. 171. 171 Short descriptions INAP Operations Part 9 •Prompt And Collect User Information. Direction: SCF -> SRF » This operation is used to interact with a user to collect information. •Specialized Resource Report. Direction: SRF -> SCF » This operation is used as the response to a Play Announcement operation when the announcement completed report indication is set. •Cancel. Direction: SCF -> SRF or SCF -> SSF » This generic operation cancels the correlated previous operation or all previous requests. The following operations can be cancelled ”Play Announcement and Prompt And Collect User Information”. •Activity Test. Direction: SCF -> SSF » This operation is used to check for the continued existence of a relationship between the SCF and SSF. If the relationship is still in existence, then the SSF will respond. If no reply is received, then the SCF will assume that the SSF has failed in some way and will take the appropriate action.
  172. 172. IN Signalling procedures
  173. 173. The System. • SSF = Service Switching Function • SCF = Service Control Function • SRF = Specialized Resource Function • SSP = Service Switching Point • SMP = Service management Point. • SCP = Signalling Control Point Local exchange Local exchange LAN / WANIP IP SSF SSF SCF SRF IP Mobile switching Center
  174. 174. The System • Service Management Point (SMP). » Management of • data. • statistic. » Introduction of new services. » Administration of the SCP. • Service Switching Point (SSP) » Access point for the service user. * » Execution of service functions. * service user: A user of an IN Service, the so-called customer. • Service Control Point (SCP). » Call control and routing. • Selection code dependent, origin dependent, state dependent. • Intelligent Periphery (IP). » Announcement. » Speech recognition. • E.g. voice dialling. » Speech synthesis.
  175. 175. 175 Simple IN call service • The dialled number will be translated into anther number. » Process: • The service user are dialling e.g. 800 or free number. • At the the IN the number is converted into an E.164 number. • The call is then forwarded to the destination. SSP (SSF) SCP (SCF)Local Exchange IAM (CLD CLG) TC_BEGIN InitialDP (CLD CLG) TC_END Connect(CLD CLG) IAM (CLD CLG) ISUP signalling INAP signalling
  176. 176. 176 Simple IN call service with Busy/No answer Monitoring • The dialled number will be translated into anther number. » Process: • Same as last slide, but in case of busy or No answer. The call will be forwarded to an alternative number (e.g another phone or voice mail) SSP (SSF) SCP (SCF)Local Exchange IAM (CLD CLG) TC_BEGIN InitialDP (CLD CLG) TC_CONTINUE RequestReportBCSMEvent, connect IAM (CLD CLG) REL(Busy) TC_CONTINUE EventReportBCSMEvent(Busy) TC_CONTINUE Connect (New CLD) IAM (New CLD CLG) CON ISUP signalling INAP signalling
  177. 177. 177 Simple IN call service with announcement. » Process: • Same as last slide, but in this case the call are forwarded to an (e.g. Waiting announcement or voice mail) SSP (SSF)Local Exchange IAM (CLD CLG) TC_BEGIN InitialDP (CLD CLG) TC_CONTINUE ConnectToResource PlayAnnouncement Internal IPCON TC_CONTINUE SpecializedRescourceReport Setup & PA AnnCompleted TC_CONTINUE DisconnectForwardConnection, ReleaseCall ReleaseRel ISUP signalling INAP signalling
  178. 178. 178 Virtual Private Network Call (VPN) MSC/SSP (SSF) SCP (SCF)MS ISUP signalling INAP signalling IAM (CLD:6198 CLG: 26126134) TC_BEGIN InitialDP (CLD:26126198 CLG: 26126134 ORIG CLD 6198 TermAttemptAuthorized 26126198) TC_END Connect (CLD:26126198 ORIG: CLD 6198 CLG: 6138 ORIG CLG: 26126134) IAM (CLD:26126198, CLG: 6138, ORIG: CLD 6198, ORIG CLG: 26126134) ACM ANM Now the usual Call flow follows
  179. 179. 179 Outgoing Prepaid Call from MS MSC VLR ISDN CM Service Req (IMSI, transact) [MM] Process Access Request Authenticate (RAND) Authentication Request (RAND) [MM] Authentication Response (SRES) [MM] Authentication Response (SRES) Set ciphering mode (key) Ciphering Mode Command (key) [RR]Ciphering Mode Complete [RR] Access Request Ack SETUP (service, called number) [CM] Send info for o/g (service, called number) Complete call Call Proceeding [CM]Assign Command [RR] Assign Complete [RR] IAM ACM ANM Alerting [CM]Connect [CM]Connect Ack [CM] CM copy [MM] MS Um/A-bis/A signalling MAP signalling ISUP/TUP signalling SC P INAP signalling InitialDP (CollectInfo) ApplyCharging (Continue)
  180. 180. BTS TRAU Transcoder Rate Adaptation Unit
  181. 181. BTS • TRAU - Transcoder / Rate Adaptation Unit Functions: » Conversion of speech from 64 kbit/s on PCM (A-law) to 13/6.5 kbit/s on the GSM radio interface » Intermediate rate adoption of data from V.110 frames to the special TRAU frames on the A-bis interface TRAU
  182. 182. 182 13Kbit/s speech channel T R A U BTS BSC MSC BTS BSC MSC BTS BSC MSC T R A U T R A U Um A-bis A-Interface Possible Locations of the TRAU.
  183. 183. BTS • Bandwidth: 13 kbit/s • Encoding algorithm: Regular Pulse Excitation with Long Term Prediction (RPE LTP): » Speech is sampled 8000 times per second » Each sample is converted into a 13 bit digital value » Every 20 ms a 260 bit segment is generated (13 kbit/s) » The segment is divided by importance into 182 class 1 bits and 78 class 2 bits » For protection, the 182 class 1 bits are mapped into 378 bits » The resulting 456 bits (378 + 78) are divided into 8x57 bits » The data are transmitted in 4 consecutive TDMA blocks • Resulting overall delay is 57.5 msec. GSM Speech Encoding
  184. 184. BTS • TRAU is controlled by BTS • In-band signalling used, if TRAU not at BTS • Control functions: » Shift between speech and data » Shift between full rate and half rate channels » Timing of speech frames (BSS - MS) » Comfort noise (Discontinuous Transmission) Control of TRAU
  185. 185. Synchronization 0000000000000000 D/C/T - Bits user data/control bitsUser data bits D - Bits Control bits 1 C1 - - - - - - - - - - C15 TS 0 TS 31 C1 - C4 C5 C6 - C11 C12 - C15 Frame type: Speech/Idle speech/Data/O&M Channel type: Full rate/half rate Speech: Time alignment (250/500 us) Data: Intermediate RA (8 or 16 kbit/s) Speech: Frame indicators (BFI, SID, TAF) C16 C17 - C21 T1 - T4 Speech: Spare Speech: Time alignment bits Speech: Frame indicator (SP) 0 16 32 304 320Bit TRAU frame 16 kbit/s PCM frame 2 Mbit/s TS 1 TS 2 TRAU Signalling
  186. 186. BTS GSM 3G
  187. 187. 187 • As early as 1994, a Special Mobile Group started to think about a High Speed Data upgrade for GSM. • The first step was HSCSD (High Speed Circuit Switched Data). » HSCSD is a circuit-switched extension to GSM. • The next step was GPRS. » GPRS is a packet-switched extension to GSM. History
  188. 188. 188 • HSCSD (High Speed Circuit Switched Data). » HSCSD invented the principle of timeslot bundling to achieve higher throughput rates. » HSCSD is the simplest high speed data upgrade for GSM. » HSCSD provides GSM users with a bandwidth of up to 57.6 Kbps. » HSCSD does not require a hardware upgrade within BSS or core network (NSS), but different mobile stations. • Even though HSCSD is easy to implement into the GSM network hardly any operator have decided to implement it. » The commercial implementations of HSCSD barely exceed a speed of 38.4 Kbps. » The most common implementation is 14,4 Kbps which only requires one full rate TCH. What is HSCSD?
  189. 189. 189 • GPRS (General Packet Radio Service) is a packet oriented data service for IP and X.25 over GSM networks. • GPRS provides data speeds up to 170 Kbps. » Normally GSM only provides 9.6 Kbps, however, HSCSD provides GSM users with a bandwidth up to 57.6 Kbps. • GPRS provides an “always on” functionality, without continuous consumption of resources. • GPRS is a step stone to 3rd generation networks. » EDGE. Almost similar to GRPS, but three times faster. » UMTS. What is GPRS?
  190. 190. 190 • EDGE is mainly concerned with the modulation scheme on the Air-Interface. » Originally, EDGE was the abbreviation for Enhanced Data rates for GSM Evolution. Nowadays, EDGE is the acronym for Enhanced Data rates for Global Evolution. • EDGE is using frequency modulation scheme 8-PSK in order to increase the Data speed. » Applying 8-PSK-modulation to such a network implies shrinking of the cell size. » GSM and GPRS are using the same modulation scheme GPSK. • Not only is a new core network required, but also additional BTSs and a new cell structure. » EDGE requires a major hardware upgrade and this is extremely costly to the operator. Why not choose EDGE if it is almost similar to GRPS?
  191. 191. 191 • Introduction of a new modulation technique – 8PSK, 8 Phase Shift Keying. 8PSK enables air interface bitrates roughly 3 times higher than traditional GMSK (Gaussian Minimum Shift Keying) • However, the major disadvantage of 8-PSK modulation is that it includes amplitude modulation. Q I Start +90 (same bit) -90 (diff bit) Q I (1,1,1) (0,1,1) (1,0,0) (1,0,1) (0,0,1) (0,0,0) (0,1,0) (1,1,0) 8PSK: 1 Symbol = 3 bits GMSK: 1 Symbol = 1 bit EGPRS (Enhanced GPRS)
  192. 192. BTS The GPRS network and it’s new elements.
  193. 193. 193 From GSM to GPRS Network Um MAP ISUP MAP MAP ISUP GSM A A-bis BSS PSTN/ISDN R Gi Gp Gb Gs Gf Gr PDN Private Backbone Gn Gn GPRS Gc PDN
  194. 194. 194 • Handles: » PDP contexts for Mobile Stations. » Determines Quality of Service assigned to the user. » Routes packets to Mobile Stations. » “Pages” Mobile Stations when data is to be sent. • Stores: » Subscriber data for all Mobile Stations in the location area. • Security: » Authentication by means of identity or equipment check. » P-TMSI is allocated by SGSN. » Ciphering. (Not only in ”Um as in GSM” but all the way down to SGSN). SGSN (Service GPRS Support Node)
  195. 195. 195 • Handles: » Gateway to the Internet. » Routes IP packets to the appropriate SGSN. • If the Mobile Station changes the SGSN during ready mode, the GGSN is used as data packet buffer. • Stores: » Subscriber data for active Mobile Stations. • Security: » Firewall. » Screening. GGSN (Gateway GPRS Support Node)
  196. 196. 196 • New fields have been added to HLR in order to serve the GPRS Network. » IMSI is still the reference key. • SGSN Number. › The SS7 address of SGSN currently serving the MS. • SGSN Address. › The IP address of SGSN currently serving the MS. • MS purged for GPRS. › Indicates that MM and PDP context of the MS are deleted from SGNS. • GGSN List. › The GGSN number and optional IP address are related to the GGSN which will be contacted when activity from the MS is detected. • Each IMSI “subscriber” record contains zero or more of the following PDP context. › PDP Type. (e.g.. X25 or IP). › PDP Address. (Note: This field will be empty if dynamic IP add is used.). › QoS Profile. (Qos profile for this PDP context). › VPLMN Address allowed. › Access Point name. (A label according DNC naming list). HLR (Home Location Register)
  197. 197. 197 • In GPRS, LA is divided into RA. Each RA contains one or more cells. LA = Location Area. LAI = MCC+MNC+LAC RA = Routing Area (Subset of LA) RAI = LAI+RA PCU = Packet Control Unit. CCU = Channel Codec Unit. LA 1 LA 2 RA 1 RA 3 RA 5 RA 2 RA 4 BTS + CCU • In a RA, the RAI is broadcasted as System Information. • When an MS is crossing an RA border the MS will initiate an RA update procedure. • New elements (CCU , PCU) are added to the BSS in order to support new coding schemes introduced by GPRS. BSS
  198. 198. BTS The GPRS GPRS Air and A-bis Interface
  199. 199. 199 BTS CS-4 CS-3 CS-2 CS-1 Coding Schemes in GPRS • To achieve higher throughput rates per timeslot than plain GSM, GPRS introduces three new coding schemes. » CS-1. Throughput =< 8kbit/s. Also provided by GSM. » CS-2. Throughput =< 12kbit/s. » CS-3. Throughput =< 14.4kbit/s. » CS-4. Throughput =< 20kbit/s. • Due to unpredictable environment of the radio transmission the distance between MS and the cell impacts the QoS. » The different CS are therefore not always available.
  200. 200. 200 • Channel Codec Unit (CCU). » The existing CCU used in GSM is upgraded to handle GPRS. • CH Coding (CS-2 …. CS-4). • Radio Channel Management (Signal, Strength, Quality and TA). • Packet Control Unit (PCU). » The PCU is a very important function for the interfaces in GPRS. • Communication with CCU using in-band signalling. (One can say that the PCU is the TRAU of the GPRS network). • PDCH scheduling. • Segmentation (LLC to RLC blocks). • Error Handling (Retransmission of data packets). TA = Timing Advance. PDCH = Packet Data Channel. TRAU = Transcoder Rate Adaptation Unit (Part of a GSM Network). LLC = Logical Link Control which is part of the GPRS protocol stack.. RLC = Radio Link Control which is part of the GPRS protocol stack.. CCU & PCU
  201. 201. 201 PCU (Packet Control Unit) • Interface the new GPRS core network to the existing GSM BSS. » Converting packet data coming from the SGSN in so called PCU-frames that have the same format as TRAU-frames. These PCU-frames are transparently routed through the BSC and towards the BTS. The BTS needs to determine the respective coding scheme and other options before processing a PCU- frame. • Takes over all GPRS radio related control functions from the BSC.
  202. 202. 202 • Three different classes of mobile stations have been defined. • Class A. » The Mobile Station class A supports simultaneous monitoring and operation of packet-switched and circuit-switched services. • Class B. » The Mobile Station class B supports simultaneous monitoring but not simultaneous operation of circuit-switched and packet-switched services. • Class C. » The Mobile Station class C supports either circuit-switched or packet-switched monitoring and operation at a given time. The Mobile Station
  203. 203. 203 GPRS Protocols
  204. 204. 204 • Like MM in GSM, GMM are used to keep track of the current location of an MS and to initiate security procedures. • GMM is a function that is mainly handled between the mobile station and the SGSN. However, the HLR is also involved. • There are various scenarios defined in GPRS to update a subscriber's location within the network. The most important ones are: » Routing Area Update (Intra-SGSN and Inter-SGSN) » GPRS Attach and Detach » Cell Update (only while in GMM-Ready State) • The GMM cell update procedure replaces in GPRS what is known as handover procedure in circuit-switched GSM. • Due to the fact that a GPRS MS is not constantly “connected” to the network, the GMM has introduced a new state, called “Ready State”. GMM (GPRS Mobility Management)

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