GSM GPRS. Course requirements: Understanding Telecommunications book by Ericsson (Part D PLMN) + supporting material (= these slides)

Transcription

1 GSM Example of a PLMN (Public Land Mobile Network) At present most successful cellular mobile system (over 200 million subscribers worldwide) Digital (2 nd Generation) cellular mobile system operating in several frequency bands (GSM 900, GSM 1800 = DCS 1800, GSM 1900 = PCS 900) ETSI Specifications ( ) Future evolution?

2 GSM Course requirements: Understanding Telecommunications book by Ericsson (Part D PLMN) + supporting material (= these slides) GPRS Course requirements: GPRS: Architecture, Protocols, and Air Interface article available at If you have problems obtaining this article, please contact the course assistant (Mika Nupponen)

3 Digital PLMN systems (status 2000) 2 nd Generation 3 rd Generation 4 th Generation GSM IS-136 IS-95 GPRS USA EDGE IMT-2000 UMTS W- CDMA TDD CDMA 2000

4 Digital PLMN systems GSM Global System for Mobile communications: (FDMA/)TDMA-based system specified by ETSI Several evolution steps towards 3 rd generation systems: HSCSD High Speed Circuit Switched Data (possibility of combining up to 4 time slots for a data connection) GPRS General Packet Radio Service (packet switching overlay on TDMA radio access network) EDGE Enhanced Data rates for GSM Evolution (change at the air interface: 8 PSK modulation as in UMTS) IS-95 American CDMA system IS-136 American TDMA system

5 UMTS Universal Mobile Telecommunications System UTRA FDD mode (UMTS Terrestrial Radio Access, Frequency Division Duplex mode) W-CDMA UTRA TDD mode CDMA2000 American 3 rd Generation CDMA system IMT-2000 International Mobile Telecommunications (ITU) Other wireless systems & networks: DECT (no roaming), TETRA (not public), HIPERLAN et al., UPT concept, GPS, mobile satellite systems

6 GSM system architecture BSS NSS SIM BTS BSC C VLR N GC HLR BTS OMC database AC EIR

7 GSM: circuit switched connections BSS NSS BSC C VLR GC HLR BTS AC EIR

8 GPRS: packet switched connections BSS NSS BSC PCU C VLR GC HLR BTS SGSN GGSN AC EIR

9 UMTS network architecture Uu Radio access network UTRAN RNC BS Iur Core network (GSM/GPRS-based) Iu CS GC C VLR BS Iub RNC Iu PS SGSN HLR AC Gn GGSN EIR

10 IMT-2000 / UMTS: RNS (access network) Core network (GSM-based) BS RNC C VLR GC BS RNC SGSN GGSN HLR AC EIR

11 Radio interface aspects Radio access techniques (FDMA / TDMA / CDMA) Physical / logical channel structure / GSM burst Modulation method (GK, 8-PSK) Source coding / channel coding / interleaving Radio channel estimation & equalization techniques (constructive use of the multipath channel) Diversity techniques Circuit vs. packet switched access Protocols: random access, power control, handover (with associated measurement procedures)

12 Radio interface access techniques frequency Time division time code nr. Frequency division Code division

13 Radio interface - physical channels Carrier 0 Carrier 1 Carrier 2 Carrier 3 TS0 Typically used for signaling TS1 T S S T T T T T T S S T T T T T T T T T T T T T TS2 TS2 T T T T T T T T T T T T T T T T T T T T T T T T Frame of length 8 time slots

14 Radio interface logical channels Traffic channels Control channels (for signaling) TCH/F Broadcast Common control Dedicated TCH/H SCH PCH SDCCH bidirectional downlink uplink FCCH BCCH AGCH RACH SACCH FACCH

15 GPRS channel structure Carrier 0 TS0 Used for GSM signaling TS1 T S S T T T T T T S S T Carrier 1 Carrier 2 T T T T T T T PDCH:s for GPRS use (for example) T T T T T T T PBCCH Packet Broadcast Control Channel (optional) PCCCH Packet Common Control Channel (optional) PDTCH Packet Data Traffic Channel Also, PACCH and PTCCH possible

16 GSM/GPRS channel allocation example TS7 Only for GPRS TS0 Dynamical allocation (circuit switched GSM channels are given higher priority) time (observation intervals) Allocation schemes are network operator dependent

17 GSM radio interface GSM normal burst: bits (0.577 ms) 3 57 encrypted bits 1 26 training bits 1 57 encrypted bits TDMA frame (4.615 ms): TS7 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 TS1 TDMA multiframe: SACCH = 26 TDMA frames / 51 TDMA frames Idle

18 GSM speech encoding Voice coding: 260 bits in 20 ms blocks (13 kbit/s) - BSC 260 bits 260 bits Channel coding: 456 coded bits (22.8 kbit/s) - BTS 456 bits Interleaving: 8 x 57 bits (22.8 kbit/s) bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame 57 bits 57 bits 57 bits

19 GSM signaling message encoding Signalling message in (split into) block(s) of 184 bits: 184 bits Each block is coded into 456 bits (22.8 kbit/s) 456 bits Interleaving: 8 x 57 bits (22.8 kbit/s) bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame 57 bits 57 bits 57 bits

20 GPRS packet encoding FH For instance, segment of IP packet FCS LLC frame Segment Segment Segment. Segment BH Info BCS T RLC block Convolutional encoding into 456 bits Interleaving: 8 x 57 bits (22.8 kbit/s) bits 4, 12, 20, 28, 36, 44, etc. from the 456 bit frame 57 bits 57 bits 57 bits

21 GSM protocols ( C) U m A bis A CM CM MM DTAP RR LAPDm RR LAPDm BTSM LAPD RR BTSM LAPD MM BSSMAP BSSAP BSSAP SCCP MTP SCCP MTP Radio Radio 64 kb/s 64 kb/s 64 kb/s 64 kb/s BTS BSC C

22 GPRS protocols (user plane) U m G b G n IP/X.25 IP/X.25 SNDCP SNDCP GTP GTP LLC LLC TCP TCP RLC RLC BSSGP BSSGP IP IP MAC MAC NS NS L2 L2 Radio Radio L1bis L1bis L1 L1 BSS SGSN GGSN

23 GSM signaling at layer 3 RR (Radio Resource management) Access and initial assignment (reserving a SDCCH) Handover management MM (Mobility Management) Registration ( power switch on) Location updating ( moves to another location area) Authentication CM (Call control Management) Signaling for setting up and releasing circuit switched connections (very similar to DSS 1 in N-ISDN)

24 Connectivity modes in GSM and GPRS GSM: Disconnected Idle Connected GPRS: Idle Standby Ready is switched off (circuit mode) location updates are performed handovers in c.s. connection is switched off (packet mode) location updates on a larger basis location updates on cell-by-cell basis

25 Random access in GSM / GPRS No communication between and network can be started without first using the random access procedure in network originated activity (paging, e.g. for MTC) originated activity (MOC, location updating, registration, de-registration at power switch-off) 1) sends a short access burst over the RACH (uplink), (Slotted Aloha, collision possibility retransmission) 2) Network (BSC) returns permission message including: - allocated channel (frequency, time slot) - timing advance for correct time slot alignment

26 Important identifiers in GSM II International Mobile Subscriber Identity (global) TI Temporary Mobile Subscriber Identity (local and temporary) Location Area Identity (global) ISDN Mobile Subscriber ISDN number (address of subscriber HLR database) PIN Personal Identification Number (only within ) IMEI International Mobile Equipment Identity (global) Temporary, local numbers for routing (RN, HON )

27 Case study: location updating (1) SIM TI VLR 1 TI II HLR II => VLR 1 VLR 2 Last and TI stored in SIM. monitors broadcast. matching => everything ok!

28 Case study: location updating (2) SIM TI VLR 1 TI II HLR II => VLR 1 VLR 2 different => location update needed!

29 Case study: location updating (3) SIM TI VLR 1 TI II HLR II => VLR 1 VLR 2 TI SIM sends old and TI to VLR 2 But, VLR 2 does not know II!

30 Case study: location updating (4) SIM TI VLR 2 TI VLR 1 TI II => VLR 2 HLR II => VLR 1 => VLR 2 TI VLR 2 sends new to VLR 1 which in turn updates the HLR

31 Case study: location updating (5) SIM TI VLR 1 HLR II => VLR 2 VLR 2 TI II HLR sends II to VLR 2 and cancels subscriber data in VLR 1

32 Case study: location updating (6) VLR 1 SIM TI HLR II VLR 2 Important information for MTC (see below) VLR 2 TI II VLR 2 sends new TI to (SIM). also updates. Compare with slide (1). Location update successful!

33 Case study: mobile terminated call (1) (mobile terminated call = MTC) SIM TI C VLR 2 TI => II HLR GC ISDN => II => VLR 2 ISDN MTC directed through PSTN to GC using ISDN. GC contacts HLR (ISDN is in fact the address of the register location of the subscriber with given II)

34 Case study: mobile terminated call (2) SIM TI C VLR 2 TI => II HLR GC ISDN => II => VLR 2 ISDN => VLR 2 HLR returns to GC the current of called mobile subscriber. The GC can now route the call to the C serving the subscriber

35 Case study: mobile terminated call (3) SIM TI C VLR 2 TI => II HLR II => VLR 2 GC The C broadcasts a paging message (including TI) within the location area defined by

36 Case study: mobile terminated call (4) SIM TI C VLR 2 TI => II HLR II => VLR 2 GC Only the mobile subscriber with the correct TI reacts to the paging. A connection between and C is established and the call set-up is completed.