Overview of GSM Architecture

Transcription

1 Overview of GSM Architecture GSM/DCS1800 System Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-2

2 Milestones of the GSM /89~1991/ CEPT decides to establish a Groupe Speciale Discussion & adoption of a list of GSM becomes a technical committee within Mobile (GSM) to develop a set of common recommendations to be generated by the group > ETSI & splits up into GSM group 1-4, later standards for a future pan-european cellular 100 recommendations in series of 12 volumes called Special Mobile Group (SMG) 1-4 mobile network Establishment of 3 work parties to define & Initial Memorandum of Understanding (MoU) The GSM specifications for the 900 describe the services offered in a GSM (radio signed by telecommunication network operator MHz are also applied at 1800 MHz interface, signaling protocol, interfaces,...) organizations band (DCS1800), a PCN applications initiated in the UK July:: Planned GSM commercial launch of GSM The GSM-MoU has 62 members (signatories) in Over 64 million subscribers service in Europe (MoU plan) delayed to countries worldwide; in addtion 32 potential because of non-availability of type-approved member (observers/applicants) in 19 other terminals countries Official commercial launch of GSM service in Europe GSM networks operational or under development in 60 countries worldwide, with over 5.4 million subscribers GSM Global System for Mobile Communication GSM/DCS1800 System (1) Page-3 GSM Services Service Category Service Comments Tele-services Bearer Services Supplementary Services y Telephony (Speech) y Emergency calls (speech) y Short Message services: point-to-point & point-to-multi-point (cell broadcast) y Tele-fax y Asynchronous data y Synchronous data y Asynchronous PAD (packet switched, packet assembler/disassembler) access y Alternate speech & data y Call forwarding y Call barring y Full rate (13Kbps) y Alphanumeric information: user to user & network to all users y Group 3 y bps y bps y bps y bps Phase 1 Services GSM/DCS1800 System (2) Page-4

3 GSM Services Service Category Service Comments Tele-services Bearer Services Supplementary Services y Telephony (Speech) y Short Message services: y Synchronous dedicated packet data access y Calling/connected line identity presentation y Calling/connected line identity restriction y Call waiting y Call hold y Multiparty communication closed user group y Advice of charge y Half rate (6.5 Kbps) y General Improvements y bps Online charge information Phase 2 Services GSM/DCS1800 System (3) Page-5 GSM/DCS1800 System ) Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-6

4 GSM System Architecture BTS HLR VLR AUC BTS BSC PSTN MS BTS MSC ISDN BTS BTS BSC Data Network BTS OMC Operation & Maintenance Subsystem MS Base Station Subsystem Network Switching Subsystem Public Network GSM/DCS1800 System (4) Page-7 GSM System Architecture Functional Entities of GSM AUC HLR PSTN D VLR C EIR B F BTS OMC GMSC E MSC BSC BSC Abis (through ISDN protocol) AUCšAuthentication Center HLRšHome Location Register BTSšBase Transceiver Station MSCšMobile Switching Center BSCšBase Station Controller OMCšOperation and Maintenance Center EIRšEquipment Identity Register VLRšVisited Location Register GMSCšGateway Mobile Switching Center A BTS Um MS GSM/DCS1800 System (5) Page-8

5 Mobile Station Mobile Station Types Vehicle-mounted stations portable stations handheld stations Mobile Station Power Classes Vehicular & portable units can be either class I or class II Handheld units can be class III, IV, & V Class Class Max. Max. RF RF Power Power (W) (W) I I II II 8 8 III III 5 5 IV IV 2 2 V GSM/DCS1800 System (6) Page-9 Identities of Mobile Station Mobile station has three identities International Mobile Subscriber Identity (IMSI) International Mobile Equipment Identity (IMEI) Temporary Mobile Subscriber Identity (TMSI) GSM/DCS1800 System (7) Page-10

6 Identities of Mobile Station International Mobile Subscriber Identity IMSI is assigned to an MS at subscription time It uniquely identifies a given MS It contains 15 digits Mobile Country Code (MCC) 3 digits (home country) Mobile Network Code (MNC) 2 digits (home GSM PLMN) Mobile Subscriber Identification(MSIN) National Mobile Subscriber Identity(NMSI) MCC = Germany NMC = private operator D3 private Mobile Subscriber Identification Number (MSIC) GSM/DCS1800 System (8) Page-11 Identities of Mobile Station International Mobile Equipment Identity (*#06#) IMEI uniquely identifies the MS equipment It is assigned by the equipment manufacturer It contains 15 digits Type Approval Code (ATC) 6 digits Final Assembly Code (FAC) 2 digits Serial Number (SNR) 6 digits Spare (SP) 1 digit GSM/DCS1800 System (9) Page-12

7 Identities of Mobile Station Temporary Mobile Subscriber Identity TMSI is assigned to MS by the Visitor Location Register (VLR) TMSI uniquely identifies an MS within the area controlled by a given VLR A maximum of 32 bits can be used for TMSI GSM/DCS1800 System (10) Page-13 Identities of Mobile Station Subscriber Identity Module Card (SIM card) IMSI Authentication Key Subscriber information Access control class Cipher key Additional GSM services Location Area Identity Forbidden PLMN GSM/DCS1800 System (11) Page-14

8 Base Station Subsystem Base Station Subsystem (BSS) contains 2 Parts Base Station Controller (BSC) Base Transceiver System (BTS) It contains the Transcoder Rate Adopter Unit (TRAU) GSM-specific speed encoding & decoding is carried out, as well as the rate adaptation function for data Power class are also classified in a similar way to MS with 8 classes in 3 db steps from 2.5 W to 320 W GSM/DCS1800 System (12) Page-15 Network and Switching Subsystem Network and Switching Subsystem contains Switching functions of the GSM MSC & GMSC Database required for the subscriber Mobility management GSM/DCS1800 System (13) Page-16

9 Operational & Maintenance Subsystem Operational and Maintenance Subsystem Responsibility The OMS is responsible for handling system security based on validation of identities of various telecommunication entities. Performed by Authentication Center (AUC): The AUC is accessed by HLR to determine whether an MS will be granted services Equipment Identity Register (EIR): The EIR provides MS information used by the MSC. The EIR maintain a list of legitimate, fraudulent or faulty MSs. In charge of remote operation and maintenance of PLMN. Operational and Maintenance Center (OMC) The functional entity through which the service provider monitors and controls the system. GSM/DCS1800 System (14) Page-17 GSM QoS Requirements GSM Service Quality Requirements QoS QoS Required Time Time Time Time from from switching switching to to service service ready ready 4 4 sec sec in in the the home home system system and and sec sec in in the the visiting visiting system system Connect Connect time time to to called called network network 4 4 sec sec Release Release time time to to called called network network 2 2 sec sec Time Time to to alert alert mobile mobile of of inbound inbound call call 4 4 sec sec in in first first attempt attempt and and sec sec in in final final attempt attempt Maximum Maximum gap gap due due to to handoff handoff ms ms if if intercell intercell and and ms ms if if itracell itracell Maximum Maximum one-way one-way speech speech delay delay 90ms 90ms Intelligibility Intelligibility of of speech speech 90% 90% GSM/DCS1800 System (15) Page-18

10 GSM/DCS1800 System ) Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-19 High-Level View of Some Scenarios GSM Registration Scenarios MS BTS BSC MSC VLR HLR Channel Request Channel activation command Channel activation acknowledge Channel Assignment Location Update Request Authentication Request Authentication Response Comparison of the Authentication parameters Assignment of the new area & TMSI Acknowledgement of new area & TMSI Entry of the new area & identity into VLR & HLR Channel Release GSM/DCS1800 System (16) Page-20

11 GSM Call Flow Scenarios Call Setup with a Mobile to Land Call Part I U m A B MS BSS MSC VLR SETUP_REQ Assign Radio Channel Radio Assignment Complete Call Proceeding Assign Truck & Radio Channel Truck & Radio Assignment complete Access Subscriber Data SUB_DATA_RESP GSM/DCS1800 System (17) Page-21 GSM Call Flow Scenarios Call Setup with a Mobile to Land Call Part II MS MSC PSTN Alerting Connect Connect Acknowledgement NET_SETUP NET_ALERT Connect (Answer) GSM/DCS1800 System (18) Page-22

12 GSM Call Flow Scenarios Call Release With Mobile to Land Call Mobile Initiated U m A MS BSS MSC PSTN CALL_DISC CALL_REL CHH_REL REL_COMP CLR_COMM CLR_COMP NET_REL GSM/DCS1800 System (19) Page-23 GSM Call Flow Scenarios Land to Mobile Call Part I Assumption MS is registered with the system & has been assigned a TMSI MS is in its home system C PSTN MSC HLR VLR INC_CALL 1 GET_ROUT 2 ROUT_INF 3 INCO_CALL 4 PERM_PAGE 5 GSM/DCS1800 System (20) Page-24

13 GSM Call Flow Scenarios Land to Mobile Call (Paging) Part II U m A MS BSS MSC VLR PAGE_MESS CH_REQ DSCH_ASS PAGE_RESP PERM_PAGE PAGE_RESP B PAGE_RESP GSM/DCS1800 System (21) Page-25 GSM Call Flow Scenarios Handoff MS scans transmission from surrounding BSs in the spare timeslots It then reports the measured results back to the fixed network via BS, where the handoff decision is made Classifications Internal Handoff Inter-BSS Handoff External Intra-MSC Handoff Inter-MSC Handoff GSM/DCS1800 System (22) Page-26

14 GSM Call Flow Scenarios Handoff Intra-MSC Handoff GSM/DCS1800 System (22) Page-27 GSM/DCS1800 System ) Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-28

15 GSM Time Slot Structure Frequency Bands and Bandwidth Down-link (BS to MS) 935 MHz ~ 960 MHz (25 MHz Bandwidth) Up-link (MS to BS) 890 MHz ~ 915 MHz (25 MHz Bandwidth) GSM 900 Carriers or Channels Each up-link or down-link has 124 Carriers with a bandwidth of 200 KHz, excluding KHz edges of the band The use of carrier 1 and 124 are optional for operators khz 200 khz F 100 khz u = ( N 1) MHz F = ( N 1) MHz N = 1,2,,124 d GSM/DCS1800 System (23) Page-29 Frequency Bands and Bandwidth Down-link (BS to MS) 1805 MHz ~ 1880 MHz (75 MHz Bandwidth) DCS-1800 Up-link (MS to BS) 1710 MHz ~ 1785 MHz (75 MHz Bandwidth) Carriers or Channels Each up-link or down-link has 374 Carriers with a bandwidth of 200 KHz, excluding F F u d = 1710 = ( N 1) MHz ( N 1) MHz 512 N 885 GSM/DCS1800 System (24) Page-30

16 Frequency Bands and Bandwidth FDMA/TDMA Structure The total bandwidth is divided into khz bands (FDMA) Each 200 khz band can support maximum 8 users (TDMA) The GSM can support up to 992 (124 8) simultaneous users with the fullrate speech coder. Freq. #1 TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 Channel #1 Channel #2 Channel #3 Channel #4 Channel #5 Channel #6 Channel #7 Channel #8 Freq. #2 Channel #1 Channel #2 Channel #3 Channel #4 Channel #5 Channel #6 Channel #7 Channel #8 Freq. #124 Channel #1 Channel #2 Channel #3 Channel #4 Channel #5 Channel #6 Channel #7 Channel #8 GSM/DCS1800 System (24) Page-31 Frequency Bands and Bandwidth Time-Division Duplex (TDD) No need for a dedicated duplex stage (duplexer); the only requirements are to have a fast switching synthesizer, RF filter paths & fast antenna switches available Increased battery life or reduced battery weight BS Transmits MS Transmits GSM/DCS1800 System (25) Page-32

17 Frequency Bands and Bandwidth Pulsed Transmission The tendency for a pulsed radio to disturb neighboring frequency channels is called AM splash. 4 db -1 db -6 db -30 db -70 db 10µ s 8µ s10µ s 542.8µ s (147 bits) 10µ s 8µ s10µ s GSM/DCS1800 System (26) Page-33 GSM Time Slot Structure Time Slot Structure or Burst types in GSM Normal Bursts Random Access Burst Frequency Correction Bursts Synchronization Bursts GSM/DCS1800 System (27) Page-34

18 GSM Time Slot Structure Tail Bits (TB) Used as a guard time.& this time covers the periods of uncertainty during the ramping up & down of the power bursts form the MS in accordance with the power-versus-time template Stealing Flag Used as an indication to the decoder of whether the incoming burst is carrying signaling data or user data TB (3 bits) Coded Data (57 bits) Stealing Flag (1 bits) Training Sequence (26 bits) Stealing Flag (1 bits) Coded Data (57 bits) TB (3 bits) Guard Time (8.25 bits) Normal Burst 148 bits = µ s Training Sequence Used to compensate for the effects of multi-path fading. There are 8 different sequences defined in GSM. GSM/DCS1800 System (28) Page-35 GSM Time Slot Structure TB (8 bits) Synchronization Sequence (41 bits) Coded Data (36 bits) TB (3 bits) Guard Time (68.25 bits) 88 bits = µ s Random Access Burst GSM/DCS1800 System (29) Page-36

19 GSM Time Slot Structure TB (8 bits) Fixed bit Sequence (142 bits) TB (3 bits) Guard Time (8.25 bits) 148 bits = µ s Frequency- Correction Burst GSM/DCS1800 System (30) Page-37 GSM Time Slot Structure TB (3 bits) Coded Data (39 bits) Synchronization Sequence (264bits) Coded Data (39 bits) TB (3 bits) Guard Time (8.25 bits) 148 bits = µ s Synchronization Burst GSM/DCS1800 System (31) Page-38

20 GSM/DCS1800 System ) Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-39 GSM Logical Channels Classifications Traffic Channel (TCH) Logic Channel Control Channel (CCH) Cell Broadcast Channel (CBCH) TCH/Full (TCH/F) TCH/Half (TCH/H) Broadcast Channel (BCH) Common Control Channel (CCCH) Dedicated Control Channel (DCCH) Freq. Correction Channel (FCCH) Paging Channel (PCH) Associated Control Channel (ACCH) Stand-Alone Dedicated Control Channel (SDCCH) Synchronization Channel (SCH) Broadcast Control Channel (BCCH) Access Grant Channel (AGCH) Random Access Channel (RACH) Slow Associated Control Channel (SACCH) FACCH/F Fast Associated Control Channel (FACCH) FACCH/H SDCCH/4 SDCCH/8 SACCH/TF SACCH/TH SACCH/C4 SACCH/C8 GSM/DCS1800 System (32) Page-40

21 GSM Logical Channels Traffic Channel Are used to transmit user information (speech or data) 2 categories TCH/Full (TCH/F) Allows the transmission of 13 Kbps of speech TCH/Half (TCH/H) Allows the speech coded at a half rate Logic Channel Traffic Channel (TCH) Control Channel (CCH) Cell Broadcast Channel (CBCH) TCH/Full (TCH/F) TCH/Half (TCH/H) GSM/DCS1800 System (33) Page-41 GSM Logical Channels Control Channel (CCH) Are used to transmit control and signaling information Broadcast Channel (BCH) Common Control Channel (CCH) Dedicated Control Channel (DCCH) Logic Channel Control Channel (CCH) Traffic Channel (TCH) Cell Broadcast Channel (CBCH) Broadcast Channel (BCH) Common Control Channel (CCCH) Dedicated Control Channel (DCCH) GSM/DCS1800 System (34) Page-42

22 GSM Logical Channels Control Channel (CCH) Broadcast Channel (BCH) Are point-to-multipoint, downlink-only channels Classification Broadcast Control Channel (BCCH) Frequency Correction Channel (FCCH) Synchronization Channel (SCH) Logic Channel Control Channel (CCH) Dedicated Control Channel (DCCH) Broadcast Channel (BCH) Common Control Channel (CCCH) Freq. Correction Channel (FCCH) Synchronization Channel (SCH) Broadcast Control Channel (BCCH) GSM/DCS1800 System (35) Page-43 GSM Logical Channels Control Channel (CCH) Common Control Channel (CCH) Are point-to-multipoint, downlink-only channels that are used for paging & access except for RACH. Classifications Paging Channel (PCH) Access Grant Channel (AGCH) Random Access Channel (RACH) Logic Channel Control Channel (CCH) Common Control Channel (CCCH) Broadcast Channel (BCH) Dedicated Control Channel (DCCH) Paging Channel (PCH) Access Grant Channel (AGCH) Random Access Channel (RACH) GSM/DCS1800 System (36) Page-44

23 GSM Logical Channels Control Channel (CCH) Dedicated Control Channel (DCCH) Are bidirectional, point-to-point channels Classifications Stand-Alone Dedicated Control Channel (SDCH) Associated Control Channel (ACCH) Slow Associated Control Channel (SACCH) Fast Associated Control Channel (FACCH) Logic Channel Control Channel (CCH) Dedicated Control Channel (DCCH) Broadcast Channel (BCH) Common Control Channel (CCCH) Associated Control Channel (ACCH) Stand-Alone Dedicated Control Channel (SDCCH) GSM/DCS1800 System (37) Page-45 GSM/DCS1800 System ) Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-46

24 GSM Frame Structure Channel Combinations (I) I : TCH/FS + FACCH/FS + SACCH/FS II : TCH/HS(0,1) + FACCH/HS(0,1) + SACCH/HS(0,1) III: TCH/HS(0) + FACCH/HS(0) + SACCH/HS(0) + TCH/HS(1) + FACCH/HS(1) + SACCH/HS(1) IV: FCCH + SCH + CCCH + BCCH V : FCCH + SCH + CCCH + BCCH + SDCCH/4 + SACCH/4 VI : CCCH + BCCH VII: SDCCH/8 + SACCH/8 Each channel combination requires one single physical channel GSM/DCS1800 System (38) Page-47 GSM Frame Structure Traffic Channel Frame Structure (26-multi-frame) Channel Combinations (II) I : TCH/FS + FACCH/FS + SACCH/FS T 0 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T=TCH, S=SACCH, I=Idle T 10 T 11 S 12 T 13 T Frames = 120 ms T T T 17 T 18 T 19 T 20 T 21 T 22 T 23 T 24 I 25 GSM/DCS1800 System (39) Page-48

25 GSM Frame Structure Traffic Channel Frame Structure (26-multi-frame) Channel Combinations (III) II : TCH/HS(0,1) + FACCH/HS(0,1) + SACCH/HS(0,1) III: TCH/HS(0) + FACCH/HS(0) + SACCH/HS(0) + TCH/HS(1) + FACCH/HS(1) + SACCH/HS(1) T 0 t 1 T 2 t 3 T 4 t 5 T 6 t 7 T 8 t 9 T 10 t 11 S 12 T 13 t 14 T t T 17 t 18 T 19 t 20 T 21 t 22 T t s Frames = 120 ms T=TCH1, S=SACCH1, t=tch2, s=sacch2 GSM/DCS1800 System (40) Page-49 GSM Frame Structure Signaling Channel Frame Structure (51-multi-frame) Channel Combinations (IV) IV : FCCH + SCH + CCCH + BCCH F 0 S 1 T 2 BCCH 2 ~ 5 CCCH 6 ~ 9 F 10 S 11 CCCH 12~19 F S CCCH 22~29 Down-Link :: F=FCCH, S=SCH, B=BCCH, C=CCCH (PCH,AGCH), I=Idle F 30 S 31 CCCH 32~39 F 40 S 41 CCCH 42~49 I 50 R 0 R 1 Up-Link :: R=RACH R 10 R 11 R 20 R Frames = ms R 30 R 31 R 40 R 41 R 50 GSM/DCS1800 System (41) Page-50

26 GSM Frame Structure Signaling Channel Frame Structure (51-multi-frame) Channel Combinations (V) V : FCCH + SCJ + CCCH + BCCH + SDCCH/4 + SACCH/4 GSM/DCS1800 System (42) Page-51 GSM Frame Structure Signaling Channel Frame Structure (51-multi-frame) Channel Combinations (VI) VI : CCCH + BCCH Used as a BS has to manages a huge number of transceiver which means the number of CCCHs provided by combination IV is not enough to handle the network Assign additional control channels in combination IV. While combination IV always occupies time slot 0, combination VI is assigned to time slot 2, 4, or 6. The combination VI multi-frame structure is similar to combination IV. GSM/DCS1800 System (43) Page-52

27 GSM Frame Structure Signaling Channel Frame Structure (51-multi-frame) Channel Combinations (VII) VII : SDCCH/8 + SACCH/8 GSM/DCS1800 System (44) Page-53 GSM Frame Structure Frame Hierarchical Structure Hyper-frame,super-frame,multi-frame,frame,time slot A time slot carries bits Stealing Stealing bits Tail Data Bit Training Bit Data Tail Guard GSM Time-Slot (Normal Burst) GSM Frame (4.615 ms) Multi-frame=26 frame (120 ms) 1 Multi-frame=51 frame (3060/13 ms) GSM Super-frame (26 51=1326 frame =6.12 sec) GSM hyper-frame (3.48 hours) GSM/DCS1800 System (45) Page-54

28 GSM Frame Structure T1, T2 & T3 Counters T1 counter counts the super-frames Whenever a super-frame is completed, T1 is incremented by 1 & 0 T T2 counter counts the speech frames, which only occur in 26 multi-frame structure & 0 T2 25.T3 counter counts the signaling frames, which are 51-multi-frame structure & 0 T3 50 GSM/DCS1800 System (46) Page-55 GSM Frame Structure TDMA Frame B T S Example of How a MS Behaves 26 multi-frame 51 multi-frame T T T T T B S B S B S B S B S GSM/DCS1800 System (47) Page-56

29 GSM Frame Structure When a MS is turned on, it has to orient itself within the network 1. It synchronizes itself in frequency 2. It synchronizes itself in time 3. It reads the system & cell data from base channel or more specifically from BCCH To find the frequency where the FCCH, SCH & BCCH are being transmitted Synchronization With the Network The MS uses the SCH for this purpose. Since it has found the FCCH, so it already knows that SCH will be follow in the next TDMA frame GSM/DCS1800 System (48) Page-57 GSM/DCS1800 System ) Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-58

30 GSM Location Updating Scenarios Logical Channel MS BS RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH Channel Request Channel Assignment Request for location updating. This is already transmitted on the assigned channel Authentication Request from the network Authentication Response from the MS Request to transmit in the ciphered mode Acknowledgement of the ciphered mode Confirmation of the location updating including the optional assignment TMSI Acknowledgement of the new location & the temporary identity Channel Release from the network GSM/DCS1800 System (49) Page-59 GSM Call Establishment Scenarios Logical Channel MS BS Mobile Terminated Call PCH RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH FACCH FACCH FACCH TCH Paging of the MS Channel Request Channel Assignment Answer to the paging from the network Authentication Request from the network Authentication Response from the MS Request to transmit in the ciphered mode Acknowledgement of the ciphered mode Set up message for the incoming call Confirmation Assignment of a traffic channel Acknowledgement of the traffic channel Alerting (now the caller gets the ringing sound) Connect message when the MS is off-hook Acceptance of the connect message Exchange of user data (speech) GSM/DCS1800 System (50) Page-60

31 GSM Logical Channels Logic Control Channel Structure Classify by call setup BCH BCCH FCCH CAC (Common Access Channel) (Broadcast Channel) (Before Call Set-up) CCCH SCH PCH CCH (Common Control Channel) (During Call Set-up) SDCCH RACH AGCH USC (User Specific Channel) (After call set-up) SACCH FACCH GSM/DCS1800 System (51) Page-61 GSM/DCS1800 System ) Some Histories & Some Background GSM/DCS1800 System Architecture High-Level View of Some Scenarios GSM Time Slot Structure GSM Logical Channels GSM Frame Structure Low-Level View of Some Scenarios GSM System Diagram& Protocol Stack Different Between GSM and DCS 1800 Page-62

32 GSM System Diagram GSM System Block Diagram Information Processing RF Baseband Processing Speech Digitizing & source coding Channel coding Interleaving Source deconding & D/A Channel decoding De-interleaving Speech Encryption Decryption Burst formatting Burst deformatting MS Modulation Demodulation MSC GSM/DCS1800 System (52) Page-63 GSM System Diagram Source (Speech) Coding Mobile Station (Analog Signal) Low-pass filter, then A/D converter, then RPE-LTP speech encoder MSC (Base Station) (Digital Signal) 8-bit A-law to 13-bit Uniform converter, then RPE-LTP speech encoder Mobile Station =104 kbps 13 kbps Analog Signal MSC Digital Signal Low-Pass Filter A/D Converter RPE-LTP Encoder To Channel Encoder 13 kbps 8bit A-law to 13bit Uniform Converter =104 kbps RPE-LTP Encoder To Channel Encoder GSM/DCS1800 System (53) Page-64

33 GSM System Diagram Source (Speech) Coding Regular Pulse Excited Long-Term Prediction (RPE-LTP) Encoder Input has bit rate of 104 kbps Has net bit rate of 13 kbps Output from RPE-LTP 260 bits every 20 ms bits bits per per 55 ms ms Bits Bits per per ms ms Linear Linear Prediction Prediction Coding Coding (LPC) (LPC) filter filter Long Long Term Term Prediction Prediction (LTP) (LTP) filter filter Excitation Excitation Signal Signal Total Total Class Class II (class (class Ia=50, Ia=50, class class Ib=132) Ib=132) Class Class II II GSM/DCS1800 System (54) Page-65 GSM System Diagram RPE-LTP Speech Encoder 260 bits 20 ms Class I: 182 bits 50 bits 132 bits Cyclic Redundancy Encoder 53 bits 4 tail bits all equal to zero 185 bits 189 bits Speech & Channel Coding Class II: 78 bits 1/2 Convolutional Encoder 378 bits 20 ms 456 bits GSM/DCS1800 System (55) Page-66

34 GSM System Diagram Structure of Interleaver interleaving speech frames onto TDMA frame GSM/DCS1800 System (56) Page-67 GSM System Diagram TCH/F Kbps refers to the user s transmission rate, the actual rate is brought up to 12 Kbps through channel coding in the terminal equipment; that is, 12 Kbps is the rate delivered to the MS. User Information 240 bits 20 ms Add 4 0 bits 1/2 Convolutional Encoder Data & Channel Coding (I) 488 coded bits Puncturing of 32 coded bits 20 ms 456 bits GSM/DCS1800 System (57) Page-68

35 GSM System Diagram Data & Channel Coding (II) Structure of Interleaver The blocks are spread over 22 bursts. Even though the interleaving covers 22 bursts, it is referred to as a 19-bursts interleaving plan. 456 bits = 16 parts of 24 bits each (16 24= 384) + 2 parts of 18 bits each (2 18=36) + 2 parts of 12 bits each (2 12=24) + 2 parts of 6 bits each (2 6=12) A burst (time slots) contains information from either 5 or 6 consecutive data blocks; that is,c 4 parts of 24 bits each and 1 part of 18 bits ( = 114) or d 4 parts of 24 bits each and 1 part of 12 bits each and 1 part of6 bits each ( =114) 1st & 22nd burst contains 6 bits each (12 bits); 2nd & 21st burst contain 12 bits each (24 bits); 3rd & 20th carry 18 bits each (36 bits) & we have 6 bursts. We need another 16-burst. We then put 24 bits in each of the 4th~19the bursts (384 bits). GSM/DCS1800 System (58) Page-69 GSM System Diagram Channel Coding of Signaling Channels Signaling information contains a maximum of 184 bits. It does NOT make a difference whether the type of signaling information to be transmitted is mapped onto a BCCH, PCH, SDCCH or SACCH. The format always stays the same. Special format are reserved for the SCH & RACH FCCH requires no coding at all Signaling Information Signaling & Channel Coding (I) 184 bits Block Encoder (Fire Code) 1/2 Convoluational Encoder Fire coded adds 40 parity bits to the 184 bit = 224 fire-coded bits, then adds 4 0 bits 456 bits GSM/DCS1800 System (59) Page-70

36 GSM System Diagram Structure of Interleaver Signaling & Channel Coding (II) Bit Bit Number of of the the Coded Coded Bits Bits Position within within the the frame frame structure Even Even bits bits of of burst burst N Even Even bit bit of of burst burst N+1 N Even Even bit bit of of burst burst N+2 N Even Even bit bit of of burst burst N+3 N Odd Odd bits bits of of burst burst N+4 N Odd Odd bits bits of of burst burst N+5 N Odd Odd bits bits of of burst burst N+6 N Odd Odd bits bits of of burst burst N+7 N+7 GSM/DCS1800 System (60) Page-71 GSM System Diagram GMSK is a constant-envelop variety of modulation & it lacks of AM in the carrier with a consequent limiting of the occupied bandwidth. The constant amplitude of the GMSK signal makes it suitable for use with high-efficiency amplifiers. Modulation (I) GSM/DCS1800 System (61) Page-72

37 GSM Protocol Stack MS BTS BSC MSC Signaling Architecture CM CM Layer 3 MM RR RR BTSM RR BTSM BSSMAP DTAP MM BSSMAP/ DTAP LAPDm Layer 1 LAPDm LAPD LAPD Layer 1 Layer 1 Layer 1 SCCP MTP SCCP MTP General View of GSM protocol Um Abis A GSM/DCS1800 System (62) Page-73 GSM Protocol Stack Responsibilities of LAPD/LAPDm Organization of Layer 3 information into frames Peer-to-peer transmission of signaling data in defined frame formats Recognition of frame formats Establishment, maintenance & termination of one or more data links on signaling channels (Un)Acknowledgement of transmission & reception of numbered information frames (Iframes) Unacknowledge transmission & reception of unnumbered information frames (UI-frames) GSM protocol (I) Layer 2 (Data Link Layer) GSM/DCS1800 System (63) Page-74

38 GSM Protocol Stack Layer 2 (Data Link Layer) Format A Address Field (variable length) Control Field (8 bits) Length Indication (variable length) Fill Field (variable length) Format B Address Field (variable length) Control Field (8 bits) Length Indication (variable length) Information Field (variable length) Fill Field (variable length) GSM protocol (II) Frames Format 4 types of formats: A, B, Abis, Bbis The bis designation is sometimes written as a prime mark (Abis = A ) GSM/DCS1800 System (64) Page-75 GSM Protocol Stack Layer 2 (Data Link Layer) Format Abis Length Indication (variable length) Fill Field (variable length) Format Bbis Length Indication (variable length) Information Field (variable length) Fill Field (variable length) GSM protocol (III) Frames Format 4 types of formats: A, B, Abis, Bbis The bis designation is sometimes written as a prime mark (Abis = A ) GSM/DCS1800 System (65) Page-76

39 GSM Protocol Stack Network Layer Also referred to as the signaling layer Use a protocol that contains all the functions & details necessary to establish, maintain & then terminate mobile connections for all the services offered within a GSM.. The network layer also provides control functions to support additional services such as supplementary services & short message services 3 sub-layers Radio Resource Management (RR) Mobility Management (MM) Connection Management (CM) GSM protocol (IV) Layer 3 (Network Layer) GSM/DCS1800 System (66) Page-77 GSM Protocol Stack Radio Resource Management sub-layer (RR sub-layer) is responsible for The management of the frequency spectrum The GSM s reactions to the changing radio environment Everything related to maintaining a clear channel between the system and the MS Handoff from one cell to another Procedures for the RR sub-layer used to cover these tasks Channel assignment Channel release Channel change & handoff procedure Change of channel frequencies, hopping sequences (hopping algorithms) and frequency tables Measurement reports from the MS Power control and timing advance Cipher mode setting GSM protocol (V) Layer 3 (Network Layer) GSM/DCS1800 System (67) Page-78

40 GSM Protocol Stack Mobility Management sub-layer (MM sub-layer) is responsible for cope with all the effects of handling a mobile user that are not directly related to the radio function such as Support of user mobility, registration, and management of mobility data Checking the user and equipment identity Checking if the user is allowed to use the services and what kind of extra services are allowed Support of user confidentiality (registering the user under a TMSI) Provision of user security Provision of an MM connection to the CM sublayer Procedures for the MM sub-layer used to cover these tasks Location Update procedure Periodic updating authentication procedure IMSI attach & detach procedure. TMSI reallocation procedure Layer 3 (Network Layer) Identification procedure GSM protocol (VI) GSM/DCS1800 System (68) Page-79 GSM Protocol Stack Connection Management sub-layer (CM sub-layer) is responsible for It manages all the functions necessary for circuit-switched call control & there are other entities within the CM sub-layer to cope with providing supplementary services & SMS Procedures for the CM sub-layer used to cover these tasks Call establishment procedures for mobile-originated calls Call establishment procedure for mobile-terminated call Changes of transmission mode during an ongoing call (incall modification) Call reestablishment after interruption of an MM connection Dual-tone Multi-frequency (DTMF) control procedure for DTMF transmission. GSM protocol (VII) Layer 3 (Network Layer) GSM/DCS1800 System (69) Page-80

41 GSM Protocol Stack Layer 3 (Network Layer) Message Structure Double Check the frame format??? TI flag (1 bit) TI (3 bits) Protocol Discriminator (4 bits) 0 (1 bit) Message Type (7 bits) Information Elements Mandatory (variable bytes) Information Elements Optional (variable bytes) TI:: Transaction Identifier GSM protocol (VIII) GSM/DCS1800 System (70) Page-81 GSM Protocol Stack Layer 3 (Network Layer) Message Structure TI flag (1 bit) TI (3 bits) Protocol Discriminator (4 bits) 0 (1 bit) Message Type (7 bits) Information Elements Mandatory (variable bytes) Information Elements Optional (variable bytes) It is used to distinguish between (possible) multiple parallel CM connections and between the various transactions taking place over these simultaneous CM connections GSM protocol (IX) GSM/DCS1800 System (71) Page-82

42 GSM Protocol Stack Layer 3 (Network Layer) Message Structure TI flag (1 bit) TI (3 bits) Protocol Discriminator (4 bits) 0 (1 bit) Message Type (7 bits) Information Elements Mandatory (variable bytes) Information Elements Optional (variable bytes) Protocol Protocol Protocol Protocol Discriminator Discriminator Radio Radio Resource Resource Mgmt Mgmt M obility obility M gm gm t t Call Call Control Control Short Short Message Message Service Service Supplementary Supplementary Service Service Test Test Procedure Procedure All All other other value value are are reserved reserved GSM protocol (X) GSM/DCS1800 System (72) Page-83 GSM Protocol Stack Layer 3 (Network Layer) Message Structure TI flag (1 bit) TI (3 bits) Protocol Discriminator (4 bits) 0 (1 bit) Message Type (7 bits) Information Elements Mandatory (variable bytes) Information Elements Optional (variable bytes) It indicates the function of the Layer 3 message Uses only low 6 bits for addressing 64 different message in a protocol, another bit is used a send sequence variable & may be used for MM and CM messages GSM protocol (XI) GSM/DCS1800 System (73) Page-84

43 GSM Protocol Stack Layer 3 (Network Layer) Message Structure TI flag (1 bit) TI (3 bits) Protocol Discriminator (4 bits) 0 (1 bit) Message Type (7 bits) Information Elements Mandatory (variable bytes) Information Elements Optional (variable bytes) There are 4 possible combination of Information Element Mandatory fixed length Mandatory variable length Optional fixed length Optional variable length GSM protocol (XII) GSM/DCS1800 System (74) Page-85 GSM Protocol Stack Layer 3 (Network Layer) Example of a Call Establishment Sequence MS Transmits Network Transmits Channel Request Ö Õ Immediate Assignment Ö Õ Authentication Request Connection Management Service Request Authentication Response Ö Õ Ciphering Mode Command Setup Ö Call proceeding Õ Assignment command Ciphering Mode Complete GSM protocol (XIII) Assignment Complete Ö Alerting Õ Connect Connect Acknowledge Ö GSM/DCS1800 System (75) Page-86

44 Digital Cellular System (DCS)-1800 General Description As a European ETSI standard for PCN Based on GSM technology but configured around a hand-portable Based on GSM technology to overcomes the development problems Lower power mobile station & smaller cell size cell radius 1 km in a dense urban environment cell radius 5 km in the rural environment GSM/DCS1800 System (76) Page-87 Digital Cellular System (DCS)-1800 Technical Description The allocated bandwidth 1710~1880 MHz providing 75 MHz duplex bands with a 20 MHz spacing The BTS links to the BSC may use 38 GHz radio to avoid laying costly underground cable links Mobile and Base Station Power Class Class Class Max. Max. RF RF Power Power (W) (W) I I 1 1 II II Mobile Station Class Class M ax. ax. RF RF Pow Pow er er (W (W ) ) I I 20~ 20~ ( 40) ( 40) II II 10~ 10~ ( ( 20) 20) III III 5~ 5~ ( ( 10) 10) IV IV 2.5~ 2.5~ ( 5) ( 5) Base Station GSM/DCS1800 System (77) Page-88

45 Digital Cellular System (DCS)-1800 DCS1800 vs. GSM DCS-1800 provides a maximum of 375 radio channels compared to 124 for GSM-900 DCS-1800 is designed to support hand-portable terminal with a transmit power not exceeding 1 W GSM/DCS1800 System (78) Page-89 GSM/DCS í3kh Ý * Çï Äe Õ»K AMPS AMPS 090, 090, »K GSM GSM , 0932, »K DCS DCS ój æ ò»k DCS DCS òñ Õ»K DCS DCS Õ ò >K DCS DCS ~ ! Õ ÄK DCS DCS ~ ! Õ ûk DCS DCS ~ òñ Õ >K GSM GSM ~ Õ ò ÄK GSM GSM ~ h\ Õ ûk GSM GSM ~ GSM/DCS1800 System (79) Page-90