Full GSM architecture valuable in Telecom companies

1. GSM Global System for Mobiles

6. GS M History

7. Development of the GSM Standard 1982: Groupe Spécial Mobile (GSM) created 1984: Description of GSM features 1985: List of recommendations settled 1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries: 1988: Validation and trials, of the radio interface. 1991: First system trials are demonstrated at the Telecom 91 exhibition. 1992: Official commercial launch of GSM service in Europe. First Launch in Finland 1993: The GSM-MoU has 62 signatories in 39 countries worldwide. 1995: Specifications of GSM phase 2 are frozen. 1999: GSM MoU joins 3GPP (UMTS) GPRS Trials begins 2000: 480M GSM Network operators Worldwide First GPRS Networks roll out End 2002: 792M GSM Net work Operators Worldwide

8. GSM Specifications 12 SERIES OPERATION AND MAINTENANCE 01 SERIES GENERAL 02 SERIES SERVICE ASPECTS 03 SERIES NETWORK ASPECTS 04 SERIES MS-BSS INTERFACE AND PROTOCOLS 05 SERIES PHYSICAL LAYER ON THE RADIO PATH. 06 SERIES SPEECH CODING SPECIFICATIONS 07 SERIES TERMINAL ADAPTERS FOR MOBILE STATIONS 11 SERIES EQUIPMENT AND TYPE APPROVAL SPECIFICATIONS 10 SERIES SERVICE INTERWORKING 09 SERIES NETWORK INTERWORKING 08 SERIES BSS TO MSC INTERFACES

10. Wireless Data Technology Options throughput kbps 10 k 100 k 64 k 1 M 2 M 1 k 1998 1999 2000 2001 2002 Time frame UMTS GPRS HSCSD 9.6 14.4 packet GPRS = G eneral P acket R adio S ervice HSCSD = H igh S peed C ircuit S witched D ata EDGE = E nhanced D ata rate for G SM E volution UMTS = U niversal M obile T elecommunication S ystem EDGE circuit

11. Circuit-Switched or Packet-Switched Circuit mode Packet mode A -> F D -> H C -> G C -> G C -> G C -> G C -> G D -> H D -> H A -> F D -> H D -> H A -> F A -> F A -> F A B C D E F G H

16. GSM System specifications Frequency band Uplink 890 - 915 MHz Downlink 935 - 960MHz Duplex Frequency Spacing 45MHz Carrier separation 200KHz Frequency Channels 124 Time Slots /Frame(Full Rate) 8 Voice Coder Bit Rate 13Kbps Modulation GMSK Air transmission rate 270.833333 Kbps Access method FDMA/TDMA Speech Coder RPE-LTP-LPC

17. Access Techniques Uplink 890 MHz to 915 MHz Down Link 935 MHz to 960 MHz 25 MHz divided into 125 channels of 200 KHz bandwidth 890.0 890.2 890.4 914.8 915.0 935.0 935.2 935.4 959.8 960.0 UP DOWN

22. GSM - Network Structure AuC MS MS BTS BTS BTS BSC BSC MSC MSC VLR VLR GMSC HLR PSTN EIR Um Abis Abis A A OMC Server Um B E E X.25 C F H X.25

23. GSM Network OMC AUC HLR MSC EIR VLR BSC BTS MS External PSTN & PDN N/W SS BSS Switching System Base Station System MS Mobile Station BTS Base transceiver System BSC Base Station Controller MSC Mobile Switching Center HLR Home Location Register VLR Visitor Location Register EIR Equipment Identity Register AUC Authentication Center OMC Operation And Maintenance Center

24. GSM Architecture HLR VLR EIR AUC MSC B S C B S C SMSC PSTN VMSC Mobile Station GSM Air interface OMCR TRAU Base Station System Network and switching subsystem A interface SS7 / speech SS7 X.25 BTS BTS BTS BTS BTS BTS Abis interface A interface OMCS

25. Fundamentals GSM utilizes two bands of 25 MHz. 890-915 MHz band is used for uplink while the 935-960 MHz is used for downlink. The frequency bands are divided into 200 KHz wide channels called ARFCNs (Absolute Radio Frequency Channel Numbers) i.e. there are 125 ARFCNs out of which only 124 are used. Each ARFCN supports 8 users with each user transmitting / receiving on a particular time slot (TS). 960 MHz 959.8MHz 200KHz 935 MHz 935.2 Mhz 915 MHz 200KHz 45 MHz Downlink (TDMA frame) = 8 TS Uplink (TDMA frame) Delay TS: Time slot 914.8 MHz 890.2 MHz 890 MHz DOWNLINK UPLINK Therefore 1 TDMA frame = 156.25 x 8 = 1250 bits and has a duration of 576.92  s x 8 = 4.615 ms The technology 1 2 …… …… . 123 124 1 2 …… …… . 123 124 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 Data burst = 156.25 bit periods = 576.9  s

36. Interfaces and Protocols Um Abis A C B E D F Digital Networks POTS TUP ISUP MAP MAP MAP BSSAP LAPD LAPDm G

37. GSM Entities and Signaling Architecture

39. Functional Plane of GSM MS BTS BSC MSC/ HLR GMSC VLR MS BTS BSC MSC/VLR HLR GMSC CC MM RR Trans

48. Channels : differentiating between Physical and Logical channels Physical channels : The combination of an ARFCN and a time slot defines a physical channel. Logical channels : These are channels specified by GSM which are mapped on physical channels.

49. Channel concept Physical channel : One timeslot of a TDMA-frame on one carrier is referred to as a physical channel. There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7) Logical channel: A great variety of information must be transmitted between BTS and the MS,for e.g. user data and control signaling.Depending on the kind of information transmitted we refer to different logical channels.These logical channels are mapped on physical channel.

50. Logical Channels on Air interface LOGICAL CHANNELS COMMON CHANNELS DEDICATED CHANNELS BROADCAST CHANNELS COMMON CONTROL CHANNELS DEDICATED CONTROL CHANNELS TRAFFIC CHANNELS FCCH BCCH SCH SDCCH SACCH FACCH PCH AGCH RACH TCH/F TCH/EFR TCH/H

64. Speech Coding BP A/D SPEECH ENCODER CHANNEL CODING LP D/A SPEECH DECODER CHANNEL DECODING BAND PASS 300 Hz - 3.4 kHZ Every 125  s value is sampled from analog signal and quantised by 13 bit word Data rate = 13/125*10 -6 = 104 kbps Every 20ms 160 samples taken Data rate = 160 * 13/20ms = 104 kbps Linear Predictive Coding & Regular Pulse Excitation Analysis 1. Generates 160 filter coeff 2. These blocks sorted in 4 sequence 1,5,9,…37 / 2,6,10----38/ 3,7,11…39/8,12,16…40 3. Selects the sequence with most energy So data rate = 104/4 = 26 kbps Long term prediction analysis 1. Previous sequences stored in memory 2. Find out the correlation between the present seq. And previous sequences 3. Select the highest correlation sequence 4. Find a value representing the difference between the two sequences. Reduces data rate = 26 kbps/2 = 13 kbps ie 260 bits in 20ms 50 132 78 1A 1B 2 1A = Filter Coeff block ampl, LTP params 1B = RPE pointers & pulses 2 = RPE pulse & filter params 50 3 132 4 3 crc bits Four 0 bits for codec 378 coded bits Conv coding rate = 1/2 delay = 4 78 456 bits in 20 ms = 22.8 kbps 57 x 8 = 456 To modulator

65. Interleaving 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 Encoded speech blocks - Diagonal Interleaving Even bits Odd bits Tb 3 Coded Data 57 F 1 Training Sequence 26 F 1 Coded Data 57 Tb 3 Gp 8.25 Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 Encoded control channel blocks - Rectangular Interleaving Even bits Odd bits Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3

67. Normal Burst T 3 Coded Data 57 S 1 T. Seq. 26 S 1 Coded Data 57 T 3 GP 8.25 Tail Bit(T) :Used as Guard Time Coded Data :It is the Data part associated with the burst Stealing Flag :This indicates whether the burst is carrying Signaling data (FACCH) or user info (TCH). Training Seq. :This is a fixed bit sequence known both to the BTS & the MS.This takes care of the signal deterioration. 156.25 bits 0.577 ms

68. T 3 Training Sequence 41 Coded Data 36 T 3 GP 68.25 Random Access Burst T 3 Fixed Bit Sequence 142 T 3 GP 8.25 T 3 Coded Data 39 Training Sequence 64 Coded Data 39 T 3 GP 8.25 Synchronization Burst 156.25 bits 0.577 ms 156.25 bits 0.577 ms 156.25 bits 0.577 ms Freq. Correc. Burst

70. Timing Advance 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 MS1 near MS2 far 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 At BTS 0 1 2 3 4 5 6 7 MS1 near 0 1 2 3 4 5 6 7 MS2 far 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 At BTS

77. MS Location Update (registration) MS BTS BSC (G)MSC VLR HLR Action Channel Request (RACH) Channel Assignment (AGCH) Authentication Request (SDCCH) Authentication Response (SDCCH) Comparison of Authentication params Accept LUP and allocTMSI (SDCCH) Ack of LUP and TMSI (SDCCH) Entry of new area and identity into VLR and HLR Channel Release (SDCCH) Location Update Request (SDCCH) TMSI + old LAI

83. MS MS BTS BTS BTS BSC BSC MSC VLR GMSC HLR PSTN EIR AuC  Mobile Originated Call Req for dedicated channel for signaling (RACH) Give SDCCH Allocates SDCCH using the AGCH Sends call set-up request including dialled digits on SDCCH Call set-up forwarded to BSC Call set-up forwarded to MSC Authentication request (SDCCH) Authentication response (SDCCH) Authentication response (SDCCH) Assigns TCH Req Activate TCH TCH assigned Assn complete Release SDCCH SDCCH released ACM Ring tone over FACCH Ring alert Called Sub answers Connect message Ring tone ceases over FACCH Speech path enabled

85. Mobile Terminated Call Authentication and Ciphering procedure done as seen in Location Updation MS MS BTS BTS BTS BSC BSC MSC VLR GMSC HLR PSTN EIR AuC Land to Mobile call (MSISDN) Query for VLR info Reply (MSRN) Route to MSC Query VLR for LAC and TMSI Paging the area (+TMSI) TMSI Paged on PCH Paging Ch. REQ over RACH Allocate SDCCH over AGCH Page RESP on SDCCH ( TMSI + LAI) Page RES Page RES Assign. REQ Assignment CMD (= TCH) on SDCCH * MS tunes * Assgn CMP * Phone rings Connect traffic Ch.to trunk frees SDCCH Assgn CMP Network Alerting

89. Power Control BTS commands MS at different distances to use different power levels so that the power arriving at the BTS’s Rx is approximately the same for each TS - Reduce interference - Longer battery life

92. Handover Types BSC BSC BSC BSC MSC MSC GMSC C-1 C-2 C-3 C-4

93. Periodic Measurement Reports (SACCH) Cell 1 Cell 2 BSC BTS 1 BTS 2 Intra BSC handover Periodic Measurement Reports (SACCH) Periodic Measurement Reports HO required Activate TCH(facch) with HoRef# if 1. Check for HO passed 2. Channel avail in new BTS Acknowledges and alloctes TCH (facch) HO cmd with HoRef# Receives new BTS data(FACCH) MS tunes into new frequency and TS and sends HO message to new BTS (facch) HO performed Release TCH

98. Thank you

99. Location Updates Location Updates can be classified into two: Periodic Location Updates: This occurs as per the timer set by the network operator. If the MS does not perform this update the MSC marks the MS as ‘Detached’ on the VLR. Location Update on a handover: This occurs if during a handover the MS is moved into a new Location Area Code (LAC).