GSM系统及协议gsmOverview64页英文ppt.ppt

1、Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,1,Overview of the GSM System and Protocol Architecture,Narcisse Mavoha SWISSCOM AG MobileCom August 2000,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,2,Introduction Cellular systems GSM services GSM Architecture GSM special functions G

2、SM protocols Conclusion,Plan,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,3,History 1970: the cellular concept was introduced by Bell Labs 1978: reservation of a frequency band of twice 25Mhz around 900Mhz for mobile communications in Europe 1979: MPS, first operational network, opened in

3、Chicago 1980s: only analog cellular systems (AMPS, ACS, NMT) potential demand larger than expected capacity incompatibility between different systems CEPT creates the Groupe Spcial Mobile to specify a unique radio communication system for Europe at 900Mhz GSM standard elaboration took almost a decad

4、e 1989: GSM becomes an ETSI technical committee 1990: GSM phase 1 specifications (1987 - 1990),Introduction,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,4,History 1991: First GSM spec demonstrated 1992: January - First GSM network operator is Oy Radiolinja Ab in Finland All major European

5、operators begin commercial operations,Introduction,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,5,Cellular systems,Cellular concepts Cellular coverage Radio interface management Consequence of mobility Roaming,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,6,Cellular systems - Conc

6、epts,System providing access to the existing telecommunication networks aimed to users with mobile stations Major differences with wire line telecommunication access: Wide area mobility of subscribers leads them to change their point of access to the network and therefore requires special call routi

7、ng This is the realm of mobility management Link between the subscriber terminal and the fixed infrastructure is not permanent and is subject to fluctuating transmission requirements. This is the realm of radio resource management,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,7,Cellular sys

8、tems - Coverage,Major problems: Propagation attenuation and delay Powerreceived = f(d-) with = 2 (in urban environment = 4) Spectrum scarcity reuse of the radio resource Solution adopted in GSM: Control of the transmitted power reduces interference level caused to the other communications Frequency

9、hopping better transmission quality through frequency diversity improves spectral efficiency through interferer diversity Discontinuous transmission reduces interference level of other communications (VAD) Mobile Assisted HandOver (MAHO) efficient handover decision algorithms aimed at minimizing the

10、 interference generated by the call,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,8,Cellular systems - Radio interface management,Channels characteristics: dynamic allocation release broadcast channels for every mobile dedicated channels for one mobile States of the mobile station: Idle mod

11、e: a mobile station (MS) is listening to the broadcast channels; it has no channels on its own Dedicated mode: a bi-directional channel is allocated to the MS for its communication needs, allowing it to exchange point-to-point information with the infrastructure. Notes: The access procedure is the p

12、articular function which allows the MS to reach the dedicated mode from the idle mode.,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,9,Cellular systems Consequences of mobility,Location management: Location information are maintained and used by the network to locate the MS for call routing

13、 purposes Cells are grouped in Location Area (LA) Each cell belongs to one and only one LA While the MS is changing cell: there is no update when both cells belongs to the same LA Location Update is performed if the new cell is in a different LA,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000

14、,10,Cellular systems Consequences of mobility,Handover: Ability of automatically transferring transaction in progress from one cell to another to avoid the adverse effects of user movements Requires some means of detection measurements, measurements reporting Requires some means of switching from on

15、e cell to another,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,11,Cellular systems Roaming,Ability of originating/receiving calls in other networks Administrative requirements: different operators must agree on charging, subscription, etc different regulatory bodies must agree on the mutua

16、l recognition of type approvals Technical requirements: Transferring call charges, subscription information, location data, etc between networks existence of common access interface single piece of equipment to access the different networks specification of common air interface,Narcisse Mavoha - Swi

17、sscom AG, MobileCom - August 2000,12,GSM services,Speech services Data services Short Message Services (SMS) Supplementary services Local features Subscriber Identity Module Security functions,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,13,GSM services - speech,Classic telephony services

18、between MS users and fixed network users between MS users and MS users Services derived from telephony simple unified procedure for emergency call voice messaging (I.e voice mailbox),Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,14,Other network,GSM services - data,End-to-end communication,

19、TAF: Terminal Adaptation Function IWF: InterWorking Function,MSC/VLR,GSM,IWF,TAF,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,15,GSM services - data,Data through different networks: PSTN, ISDN, PSPDN Characteristics: 300 bits/s up to 9.6 kbits/s synchronous or asynchronous transmission bea

20、rer services data circuit duplex asynchronous (PSTN 300, 1200 bits/s) PAD access (PSPDN 2400, 4800, 9600 its/s) . tele-services telephony, emergency call, SMS, video access, facsimile group 3, .,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,16,GSM services - SMS,Allow subscriber to send/rec

21、eive simple messages (max. 160 characters length) Two services provided: Point-to-point SMS enabling a GSM user to send such a message to another GSM user (ex: paging message) cell broadcast SMS enabling short messages of a general nature to be broadcast at regular intervals to the users in a given

22、geographical area (e.g road traffic information),Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,17,GSM services - SS,Modify and enrich the basic services, mainly by allowing the user to choose how calls towards or from himself are treated by the network Ex: call forwarding advice of charge C

23、losed User Group .,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,18,GSM services - Local features,Dialing of abbreviated number storage/edition of SMS automatic repeat of failed outgoing calls Automatic answering of incoming calls .,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,19,

24、GSM services - SIM,Plug-in card containing subscriber specific data (e.g password, PIN, SMS, ) A MS cannot be used without a SIM card except for emergency calls Roaming between different MS (SIM roaming),Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,20,GSM services - Security functions,Subs

25、criber authentication (to prevent access of unregistered users) Radio path ciphering (to prevent third party tapping) Subscriber identity protection (to prevent subscriber location disclosure),Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,21,GSM architecture,Three description axes Static fu

26、nctional view Static equipment view Dynamic view Frontiers of the system Internal GSM organization Interfaces Subsystems Components Databases,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,22,GSM architecture,Two dimensional view of the network - Abstraction dimension - Spatial dimension Thr

27、ee description axes - Static functional view - Static equipment view - Dynamic view,Frontiers of the system,Operator,Users,External networks,Increasing level of abstraction,Spatial distribution,Physical grouping (machine),Distributed functional plane (field of cooperation),Narcisse Mavoha - Swisscom

28、 AG, MobileCom - August 2000,23,GSM architecture - overview,MSC,HLR,BSC,BTS,BTS,BSC,BTS,MSC,EIR,VLR,BTS,GMSC,AuC,Base Station Subsystem,Air interface,Abis interface,A interface,Network and Switching Subsystem,Network management,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,24,GSM architectu

29、re - interface,Air interface define the radio interface handles communication between MS and BTS for the transmission of analog signals use LAPDm protocol Abis interface handles communication between BTS ans BSC for: the radio traffic management the BTS exploitation and maintenance Use LAPD protocol

30、,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,25,GSM architecture - interface,A interface handles communication between BSC and MSC for the traffic management use SS#7 signaling use BSSAP application protocol dedicated to GSM,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,26,GSM ar

31、chitecture - Subsystems,BSS (Base Station Subsystem) radio channel configuration messages on the broadcast channels frequency hopping power control channel coding and decoding speech coding and decoding adaptation of the data rte transmission speed,Narcisse Mavoha - Swisscom AG, MobileCom - August 2

32、000,27,GSM architecture - Subsystems,NSS (Network and Switch Subsystem) routing and switching Home Location Register (HLR) Visitor Location Register (VLR) Equipment Identity Register (EIR) Authentication Center (AuC) Security functions and access control management System operation and maintenance,N

33、arcisse Mavoha - Swisscom AG, MobileCom - August 2000,28,GSM architecture - Subsystems,OSS (Operation SubSystem) Subscriber management add/delete subscription, charging tickets, . Network management Observe and drive the network system load, system tuning, . Maintenance detecting, locating and corre

34、cting faults and breakdowns,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,29,GSM architecture - Components,Mobile Service and Switching Centre (MSC) manages communications and dialog with the user asks for connections establishment and release asks for transmission mode executes the necessa

35、ry actions for inter-BSCs transfer (Handover),Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,30,GSM architecture - Components,Base Station Controller (BSC) executes radio connection establishment and release manages radio resources manage transmission mode maintains radio connections supervi

36、ses the BSs transfer (handover) analyses measurements to decide whether a handover is needed or not.a,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,31,GSM architecture - Components,Base Transceiver Station (BTS) provides the means for transmission on the air interface (transmission, recepti

37、on, modulation, coding, ciphering, etc) does and report measurements manages the level 2 of the air interface Mobile Station (MS) mobile terminal for the GSM subscriber communicate with the system via the air interface,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,32,GSM architecture - Data

38、bases,HLR maintains and updates the mobile subscribers location and service profiles information VLR maintains the same information as the HLR locally (e.g where the subscriber is roaming) defined as a stand-alone function but is usually view by vendors as part of the MSC,Narcisse Mavoha - Swisscom

39、AG, MobileCom - August 2000,33,GSM architecture - Databases,EIR used to list the subscribers equipment identities, which are used for unauthorized subscriber equipment and hence denial of service by the network AuC provides the keys and algorithm for maintaining the security of subscriber identities

40、, and for encrypting information passed over the Air interface,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,34,GSM special functions,Mobile identity management Call routing Radio channel structure Handover Power control and time advance,Narcisse Mavoha - Swisscom AG, MobileCom - August 200

41、0,35,GSM special functions - Mobile identity management,In the fixed network: MSISDN, MSRN the Mobile Subscriber Integrated Service Digital Network number (MSISDN) allows the routing towards a gateway MSC, a special MSC, which query the Mobile Subscriber Roaming Number (MSRN) from the HLR (see call

42、routing example later) The MSRN given by the VLR to the GMSC via the HLR, allows to route the call to the final MSC (see call routing example later),MSISDN or MSRN structure,Country Code,National Destination Code,Subscriber Number,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,36,GSM special

43、 functions - Mobile identity management,In the mobile network: IMSI, TMSI the International Mobile Station Identity is used through the SS#7 network. Several MSISDN can be assiciated with one IMSI the Temporary Mobile Station Identity is computed by the VLR when the MS arrives in a new LA. It replac

44、es the IMSI for confidentiality reason on the radio interface,IMSI structure,Mobile Country Code,Mobile Network Code,Mobile Subscriber Number,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,37,GSM special functions - Call routing examples,MSC/VLR,HLR,BSC,BTS,PSTN,MTC,1,2,3,6,8,9,10,GMSC,7,5,4

45、,1 & 2 & 3 MSISDN 4. IMSI 5. MSRN 6. MSRN 7. MSRN 8. TMSI (computed in theVLR) 9. TMSI 10. TMSI,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,38,GSM special functions - Radio channels structure,Common channels Broadcast Channels (BCH) only downlink channels, to broadcast configuration infor

46、mation FCCH: Frequency Correction Channel SCH: Synchronization Channel BCCH: Broadcast Control Channel,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,39,GSM special functions - Radio channels structure,Common channels Common Control Channels (CCCH) bi-directional channels (uplink & downlink)

47、 to send signaling information when accessing the system. RACH: Random Access Channel (MS asks for an access procedure - slotted Aloha) AGCH: Access Grant Channel, resource allocation PCH: Paging Channel, looking for an MS CBCH: Cell Broadcast Channel, broadcast of short messages,Narcisse Mavoha - S

48、wisscom AG, MobileCom - August 2000,40,GSM special functions - Radio channels structure,Dedicated channels (allocated to only one MS) Dedicated Control Channels (DCCH) bi-directional channels (uplink & downlink) to send specific signaling information for a communication. SACCH: Slow Access Control C

49、hannel, for reporting radio measurements and cells configuration FACCH: Fast Access Control Channel, to transmit handover information(slot stealing from TCH) SDCCH: Stand-alone Dedicated Control Channel, for identity exchange, encryption, location updating, signaling for traffic channel allocation,N

50、arcisse Mavoha - Swisscom AG, MobileCom - August 2000,41,GSM special functions - Radio channels structure,Dedicated channels (allocated to only one MS) Traffic Channels (TCH) bi-directional channels (uplink & downlink) to transmit communication information (speech & data). Can be used in full or hal

51、f rate,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,42,GSM special functions - Radio channels structure,Channel description Multiple access technique: FDMA + TDMA Available frequencies: 50Mhz allocated in 2 bands 25Mhz bandwidth for uplink: 890-915Mhz 25Mhz bandwidth for downlink: 935-960M

52、hz 45Mhz separation between down and uplink carrier spacing 200khz,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,43,GSM special functions - Radio channels structure,Channel description Other characteristics: 124 channels available starting at 890.2Mhz TDMA factor of 16 in combination with a

53、 carrier spacing of 200khz (spectrum efficiency 12.5khz per channel) 6.5kbits/s for speech TDMA scheme uses a gross bit rate of about 270kbits/s Gaussian Minimum Shift Keying (GMSK) modulation,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,44,GSM special functions - Radio channel structure:

54、Hierarchy of frame,24,25,0,1,2,3,4,5,6,7,TDMA frame 4.615 ms,0,1,2,49,50,0,1,2,26 multiframe 120 ms,51 multiframe 235 ms,hyperframe = 2048 superframe 3h 28mn 53s 760ms,Superframe = 26 x 51 multiframe 6.12 s,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,45,GSM special functions - Handover,Pu

55、poses: when channel quality is too low: rescue handover to optimize the interference level: confinement handover visiting cell is congested whereas neighbour cells are not: traffic handover,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,46,GSM special functions - Handover,When MS moves aroun

56、d, handover can occur: between channels in the same cell between channels in different cell under the same BSS coverage between cells under the coverage of different BSSs between cells under the coverage of different MSCs,Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,47,GSM special function

57、s - Handover,Handover used in coordination with location updating if needed: Type of Handover: Network Controlled HandOver (NCHO), measurement and decision made by the network (e.g NMT, TAC, AMPS). Mobile Assisted HandOver (MAHO), measurements done both the network and the MS, decision made by the n

58、etwork (e.g GSM, ADC, JDC) Mobile Controlled HandOver (MCHO), measurements done both the network and the MS, decision made by the mobile (e.g DECT),Narcisse Mavoha - Swisscom AG, MobileCom - August 2000,48,GSM special functions - Handover,Decisioon criteria: Static data, such as the maximum transmis

59、sion power of: the MS the serving cell the BTS of neighbour cells Real time measurements performed by the mobile the downlink transmission quality the downlink reception level on the current channel the downlink reception levels from neighbour cells Real time measurements performed by the BTS the uplink transmission quality (raw bit error rate) the uplink reception level on the current channel the time advance (see power control section) Traffic considerations, cell capacity and lo