GPRS. General Packet Radio Service. Mario Baldi. Politecnico di Torino

Transcription

1 GPRS General Packet Radio Service Mario Baldi Politecnico di Torino (Technical University of Torino) mario.baldi[at]polito.it staff.polito.it/mario.baldi

2 Copyright Notice This set of transparencies, hereinafter referred to as slides, is protected by copyright laws and provisions of International Treaties. The title and copyright regarding the slides (including, but not limited to, each and every image, photography, animation, video, audio, music and text) are property of the authors specified on page 1. The slides may be reproduced and used freely by research institutes, schools and Universities for non-profit, institutional purposes. In such cases, no authorization is requested. Any total or partial use or reproduction (including, but not limited to, reproduction on magnetic media, computer networks, and printed reproduction) is forbidden, unless explicitly authorized by the authors by means of written license. Information included in these slides is deemed as accurate at the date of publication. Such information is supplied for merely educational purposes and may not be used in designing systems, products, networks, etc. In any case, these slides are subject to changes without any previous notice. The authors do not assume any responsibility for the contents of these slides (including, but not limited to, accuracy, completeness, enforceability, updated-ness of information hereinafter provided). In any case, accordance with information hereinafter included must not be declared. In any case, this copyright notice must never be removed and must be reported even in partial uses. GPRS - 2

3 Generalities Based on the existing GSM infrastructure Packet switching functionality Better data transfer rates Statistical multiplexing Traffic based billing Migration Path to 3G Networks GPRS - 3

4 Service Types Point-to-Point Internet access by user Point-to-Multipoint Delivery of information (e.g. news) to multiple locations or interactive conference applications GPRS - 4

5 Circuit Switched Data (CSD) Before GPRS A channel is allocated to user for duration of connection Inefficient use of resources Time-based billing Deterministic quality of service Resources allocated to communication Suitable to real-time applications GPRS - 5

6 In GPRS Resources are allocated to user only for the time it takes to send each packet A channel may be shared by many users User pays by the packet Ideal for data traffic GPRS - 6

7 Comparison CSD Lower bit rates 14.4kbit/s Reserved bandwidth Fixed access time Time-based billing GPRS Higher bit rates up to 170kbit/s Shared bandwidth Variable access times Traffic based billing GPRS - 7

8 GSM Network Architecture MS BTS BSC PSTN ISDN GMSC BTS BSC MSC MS EIR AUC HLR GPRS - 8 BTS MS VLR

9 Acronyms MS: Mobile Station BSC: Base Station Controler BTS: Base Transciever Station MSC: Mobile Switching Controler GMSC: Gateway Mobile Switching Controler PSTN: Public Switched Telephone Network GPRS - 9

10 Acronyms VLR: Visited Location Register EIR: Equipment Identity Register AUC: Authentication center HLR: Home Location Register PLMN: Public Land Mobile Network E.g., GSM network PDN: Packet Data Network E.g., IP network, Internet, intranet GPRS - 10

11 GPRS Architecture Other GPRS PLMN SMS-GMSC SMS-INMSC Gd SGSN Gp GGSN BTS Gb BSC Gf Gs Gn Gr GGSN Gc Gi PDN MS BTS EIR D HLR GPRS - 11 MSC/VLR

12 GPRS Architecture New components SGSN: Serving GPRS Support Node GGSN: Gateway GPRS Support Node Components needing upgrade HLR MSC/VLR Mobile Station GPRS - 12

13 SGSN Delivers data packets from and to mobile stations Packet Routing and Transfer from MS to GGSN Mobility Management Logical Link Management Authentication Billing and maintaining user profiles GPRS - 13

14 GGSN Interfaces GPRS backbone network with external packet data networks (PDNs) E.g., IP networks, Internet Translation between PDP (packet data protocol) addresses and GSM addresses Authentication and billing Many-to- many relations among SGSNs and GGSNs GPRS - 14

15 GGSN Protocol Architecture IP Routing function IP GPRS bearer Layer 2 Layer 1 Gi GPRS - 15

16 Integrated Architecture Overview GPRS - 16

17 GPRS Backbone Based on the Internet Protocol (IP) Tunnels of data and signaling messages between GPRS support nodes (GSNs) Intra-PLMN backbone network Inter-PLMN backbone network Intra-PLMN backbone networks are connected by Border Gateways and an inter-plmn backbone network GPRS - 17

18 GPRS Backbone Overview BSC BSC BTS BTS SGSN PLMN1 MS SGSN Gn Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone Gn GGSN Gn SGSN Gi Border Gateway Gp Inter-PLMN Inter-PLMN GPRS GPRS Backbone Backbone Packet Packet Data Data Network(PDN) Network(PDN) Eg.Internet,Intranet Eg.Internet,Intranet Border Gateway Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone Router LAN Host PLMN2 GGSN GPRS - 18

19 GTP GPRS Tunneling Protocol Tunnels user data and signaling on the GPRS backbone Encapsulates PDP (Packet Data Protocol) packets GPRS - 19

20 Protocol Architechture Transmission Plane: GTP Signalling Plane GTP tunnel control management protocol Tunnel creation, modification, and deletion GPRS - 20

21 Registration of a Mobile Node A mobile station must register itself with GPRS network. GPRS attach GPRS detach GPRS detach can be initiated by the MS or the network. GPRS - 21

22 Session Management Successfully attached MS gets one or more Packet Data Protocol (PDP) address. Unique only for a particular session. PDP address consists of PDP type PDP address assigned to MS Requested quality of service Address of the corresponding GGSN GPRS - 22

23 PDP Address Assignment Static Assigned by network operator Dynamic Assigned by Corresponding GGSN. GPRS - 23

24 Packet Routing BSC BTS MS SGSN PLMN1 Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone SGSN GGSN Packet Packet Data Data Network(PDN) Network(PDN) Eg.Internet,Intranet Eg.Internet,Intranet Router LAN Host GPRS - 24

25 Packet Transfer A laptop connects with a GPRS-capable handset The handset communicates with GSM BS BS sends the GPRS packets to SGSN SGSN encapsulates packets Handset location information is updated in GSM components (e.g., HLR) SGSN sends encapsulated packets to GGSN GGSN decapsulates and sends to PDNs GPRS - 25

26 Packet Routing BSC BSC BTS BTS SGSN PLMN1 MS SGSN Gn Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone Gn GGSN SGSN Gn Gp Gi Border Gateway Inter-PLMN Inter-PLMN GPRS GPRS Backbone Backbone Border Gateway Packet Packet Data Data Network(PDN) Network(PDN) Eg.Internet,Intranet Eg.Internet,Intranet Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone Router LAN Host PLMN2 GGSN GPRS - 26

27 Routing MS roaming in PLMN1 sends IP packet to host (e.g. Web server) Host sends reply packet to MS home PLMN2 PLMN2 s GGSN queries HLR and finds that MS is in PLMN1 Packet is encapsulated and sent to SGSN in PLMN1 Packet travels over inter-plmn backbone not through PDN No encapsulation-decapsulation needed on GPRS backbones GPRS - 27 SGSN decapsulates packet and delivers to MS

28 Radio Interface Protocols User plane and Control Plane Layer 1 Physical (PHY) Combination of TDMA and FDMA TDMA: Time Division Multiple Access FDMA: Frequency Division Multiple Access GPRS - 28

29 Radio Interface Protocols: Layer 2 Data Link Media Access Control (MAC) Radio Link Control (RLC) Packet Data Convergence Protocol (PDCP) GPRS - 29

30 Radio Interface Protocols: Layer 3 Radio Resource Control (RRC) Iu mode Radio Resource (RR) A/Gb mode GPRS - 30

31 Physical Layer Channel separation: 200 khz Power output control Find minimum acceptable level Synchronization with base station Handover Quality monitoring GPRS - 31

32 Release 5 Protocol Architecture Physical Channels Logical, Control and Traffic Channels Media Access Control and Radio Link Control Radio Resource Control and Radio Resource GPRS - 32

33 Physical Channels Defined by timeslot (0-7) and radio frequency channel Shared Basic Physical Sub Channel Shared among several users (up to 8) Uplink Stage Flag (USF) controls multiple access Dedicated Basic Physical Sub Channel One user GPRS - 33

34 Physical Channels Packet Data Channel (PDCH) Dedicated to packet data traffic from logical channels Control User data GPRS - 34

35 TDMA Frame Slots and Bursts 960 MHz MHz Time Slot KHz... Downlink MHz 2 1 TDMA Frame 935 MHz 915 MHz MHz 124 Data Burst = bit periods KHz... Uplink MHz 1 TDMA Frame GPRS MHz

36 Multi Slot Operation GPRS allows a mobile to transmit data in up to 8 PDCHs Eight-slot operation 3-bit USF at beginning of each radio block in downlink points to next uplink radio block Comparison with single-slot GSM Higher delay at higher load Low blocking rate Improved Throughput GPRS - 36

37 GPRS Air Inteface Time Slot Number F1 F2 Uplink Carrier Frequency F3 F F1 F2 F3 Downlink F4 Voice User1 Voice User2 GPRS User1 GPRS User2 GPRS User3 GPRS - 37

38 Media Access Control (MAC) Connection oriented Connections are called Temporary Block Flows (TBF) Logical unidirectional connection between two MAC entities Allocated resources on PDCH(s) One PDCH can accomodate multiple TBFs Temporary Flow Identity (TFI) is unique among concurrent TBFs in the same direction Global_TFI to each station GPRS - 38

39 MS Initiated TBF Establishment One Phase Access, or Two Phase Access MS BSS MS BSS PACKET CHANNEL REQUEST PRACH PACKET CHANNEL REQUEST PRACH PACKET UPLINK ASSIGNMENT PAGCH PACKET UPLINK ASSIGNMENT PAGCH PACKET RESOURCE REQUEST PACCH PACKET UPLINK ASSIGNMENT PACCH TBF Est. By MS: One Phase Access TBF Est. By MS: Two Phase Access GPRS - 39

40 Network Initiated TBF Establishm. MS PACKET PAGING REQUEST BSS PPCH PACKET CHANNEL REQUEST PRACH PACKET IMMEDIATE ASSIGNMENT PAGCH PACKET PAGING RESPONSE PACKET DOWNLINK ASSIGNMENT PACCH PACCH or PAGCH TBF Est. By Network GPRS - 40

41 Channel Access & Resource Allocation Slotted Aloha Used in PRACH (packet random access) MSs send packets in uplink direction at the beginning of a slot Collision: Back off -> timer (arbitrary) -> retransmit Time Division Multiple Access (TDMA) Predefined slots allocated by BSS Contention-free channel access All logical channels except PRACH GPRS - 41

42 Quality of Service (QoS) Support Service Level Agreements to specify End-toend QoS IP multimedia applications must be able to Define their requirements Negotiate their capabilities Identify and select available media components GPRS signaling supports various traffic types Constant/variable bit rate Connection oriented/connection less GPRS - 42 Etc.

43 QoS Profile for GPRS Bearers Describes QoS requirements 4 parameters: Service precedence 3 classes Reliability 3 classes Delay 4 classes Throughput Maximum and mean bit rates GPRS - 43

44 QoS Profile for GPRS Bearers QoS profile is included in Packet Data Protocol (PDP) context Negotiation managed through PDP procedures Activation Modification Deactivation GPRS - 44

45 Packet Classification and Scheduling TBF tagged with TFI TFI different for each TBF Packet scheduling algorithms are not defined by the standard Defined and implemented by GPRS network designers and carriers GPRS supports per-flow quantitative QoS with proper packet classification and scheduling algorithms (?) GPRS - 45

46 References J. Cai, D. J. Goodman, General Packet Radio Service in GSM, IEEE Communications Magazine, Oct 1997 C. Bettstetter, H.-J. Vögel, J. Eberspächer, "GSM Phase 2+ General Packet Radio Service GPRS: Architecture, Protocols, and Air Interface," IEEE Communications Survey, Vol. 2, No. 3, 1999, sue/bettstetter.html Wireless Internet Access based on GPRS, IEEE Personal Comm. April GPRS - 46

47 References Wikipedia: General Packet Radio Service, Radio_Service B. Ghribi and L. Logrippo, Understanding GPRS: The GSM Packet Radio Service, Computer Networks, vol. 34, pp , 2000 Herman Rao Yi-Bing Lin, I. Chlamtac, General Packet Radio Service (GPRS): Architecture, Interfaces, and Deployment, Journal of Wireless Communiations and Mobile Computing, vol. 1, n. 1, GPRS - 47