Words: 2015
General Packet Radio Service Mario Baldi (Technical University of Torino) mario. baldi[at]polito. it staff. polito. it/mario. baldi © M. Baldi: see page 2 GPRS Politecnico di Torino 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2
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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 GSM Network Architecture BSC MS BTS PSTN ISDN GMSC MSC BTS MS BTS GPRS – 8 BSC EIR MS AUC HLR VLR © M. Baldi: see page 2 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 GPRS Architecture SMS-GMSC SMS-INMSC Gd SGSN Gp Other GPRS PLMN GGSN Gb Gf BTS BSC Gs Gc BTS MS EIR D
GPRS – 11 Gn GGSN Gr PDN Gi HLR MSC/VLR © M. Baldi: see page 2 GPRS Architecture New components SGSN: Serving GPRS Support Node GGSN: Gateway GPRS Support Node Components needing upgrade HLR MSC/VLR Mobile Station GPRS – 12 © M. Baldi: see page 2 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 GGSN Protocol Architecture Routing function IP IP Layer 2 Layer 1 Gi GPRS bearer GPRS – 15 © M. Baldi: see page 2 Integrated Architecture Overview GPRS – 16 © M. Baldi: see page 2 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 nter-PLMN backbone network GPRS – 17 © M. Baldi: see page 2 GPRS Backbone Overview BSC BSC BTS MS PLMN1 Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone BTS SGSN SGSN Gn Gp Border Gateway Inter-PLMN Inter-PLMN GPRS GPRS Backbone Backbone Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone PLMN2 Gn Border Gateway Gn SGSN GGSN Packet Data Packet Data Network(PDN) Network(PDN) Eg. Internet,Intranet Eg. Internet,Intranet Router GGSN Gi LAN Host GPRS – 18 © M. Baldi: see page 2 GTP GPRS Tunneling Protocol Tunnels user data and signaling on the GPRS backbone Encapsulates PDP (Packet Data Protocol) packets
GPRS – 19 © M. Baldi: see page 2 Protocol Architechture Transmission Plane: GTP Signalling Plane GTP tunnel control management protocol Tunnel creation, modification, and deletion GPRS – 20 © M. Baldi: see page 2 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 PDP Address Assignment Static Assigned by network operator Dynamic Assigned by Corresponding GGSN. GPRS – 23 © M. Baldi: see page 2 Packet Routing BSC BTS MS PLMN1 Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone SGSN SGSN GGSN Packet Data Packet Data Network(PDN) Network(PDN) Eg. Internet,Intranet Eg. Internet,Intranet Router LAN Host GPRS – 24 © M. Baldi: see page 2 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 © M. Baldi: see page 2 Packet Routing BSC BSC BTS MS PLMN1 Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone BTS SGSN SGSN Gn Gp Border Gateway Inter-PLMN Inter-PLMN GPRS GPRS Backbone Backbone Intra-PLMN Intra-PLMN GPRS GPRS Backbone Backbone PLMN2 Gn Border Gateway Gn SGSN GGSN Packet Data Packet Data Network(PDN) Network(PDN) Eg.
Internet,Intranet Eg. Internet,Intranet Router GGSN Gi LAN Host GPRS – 26 © M. Baldi: see page 2 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 SGSN decapsulates packet and delivers to MS GPRS – 27 © M. Baldi: see page 2 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 © M. Baldi: see page 2 Radio Interface Protocols: Layer 2 Data Link Media Access Control (MAC) Radio Link Control (RLC) Packet Data Convergence Protocol (PDCP) GPRS – 29 © M. Baldi: see page 2 Radio Interface Protocols: Layer 3 Radio Resource Control (RRC) Iu mode Radio Resource (RR) A/Gb mode GPRS – 30 © M. Baldi: see page 2 Physical Layer Channel separation: 200 kHz Power output control Find minimum acceptable level Synchronization with base station Handover Quality monitoring GPRS – 31 © M. Baldi: see page 2
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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 Physical Channels Packet Data Channel (PDCH) Dedicated to packet data traffic from logical channels Control User data GPRS – 34 © M.
Baldi: see page 2 TDMA Frame Slots and Bursts 960 MHz 959. 8 MHz 124 123 … 200 KHz … 2 935. 2 MHz 935 MHz 1 Downlink 1 2 3 4 5 6 7 1 8 TDMA Frame Time Slot 915 MHz 914. 8 MHz 124 123 … Data Burst = 156. 25 bit periods 200 KHz … 2 Uplink 1 2 3 4 5 6 7 8 1 890. 2 MHz 890 MHz GPRS – 35 1 TDMA Frame © M. Baldi: see page 2 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 © M.
Baldi: see page 2 GPRS Air Inteface Time Slot Number 0 F1 F2 F3 1 2 3 4 5 6 7 0 1 2 3 4 Uplink Carrier Frequency F4 0 F1 F2 F3 F4 1 2 3 4 5 6 7 0 1 2 3 4 Downlink Voice User1 Voice User2 GPRS – 37 GPRS User1 GPRS User2 GPRS User3 © M. Baldi: see page 2 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 © M. Baldi: see page 2
MS Initiated TBF Establishment One Phase Access, or Two Phase Access MS BSS PRACH PACKET UPLINK ASSIGNMENT MS PACKET CHANNEL REQUEST BSS PRACH PACKET CHANNEL REQUEST PAGCH PACKET UPLINK ASSIGNMENT PAGCH PACKET RESOURCE REQUEST PACCH PACKET UPLINK ASSIGNMENT PACCH TBF Est. By MS: One Phase Access GPRS – 39 TBF Est. By MS: Two Phase Access © M. Baldi: see page 2 Network Initiated TBF Establishm. MS PACKET PAGING REQUEST PACKET CHANNEL REQUEST BSS PPCH PRACH PAGCH PACCH PACCH or PAGCH PACKET IMMEDIATE ASSIGNMENT PACKET PAGING RESPONSE PACKET DOWNLINK ASSIGNMENT TBF Est. By Network GPRS – 40 © M. Baldi: see page 2
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 © M. Baldi: see page 2 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 Etc. GPRS – 42 © M. Baldi: see page 2 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 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 © M. Baldi: see page 2 References J. Cai, D. J. Goodman, “General Packet Radio Service in GSM”, IEEE Communications Magazine, Oct 1997 C. Bettstetter, H. -J. Vogel, J. Eberspacher, “GSM Phase 2+ General Packet Radio Service GPRS: Architecture, Protocols, and Air Interface,” IEEE Communications Survey, Vol. 2, No. 3, 1999 , http://www. omsoc. org/pubs/surveys/3q99is sue/bettstetter. html “Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000. GPRS – 46 © M. Baldi: see page 2 References Wikipedia: General Packet Radio Service, http://en. wikipedia. org/wiki/General_Packet_ Radio_Service B. Ghribi and L. Logrippo, “Understanding GPRS: The GSM Packet Radio Service”, Computer Networks, vol. 34, pp. 763–779, 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, 2001. GPRS – 47 © M. Baldi: see page 2