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Chapter 3

Chapter 3. General Packet Radio Service (GPRS). GSM. A Brief Introduction. Architecture. Components/ Elements. Mobile Station (MS) Base Station Subsystem (BSS) Base Transceiver Station (BTS) Base Station Controller (BSC) Mobile Switching Center (MSC) Four databases

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Chapter 3

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  1. Chapter 3 General Packet Radio Service (GPRS) Prof. Huei-Wen Ferng

  2. GSM A Brief Introduction Prof. Huei-Wen Ferng

  3. Architecture Prof. Huei-Wen Ferng

  4. Components/ Elements • Mobile Station (MS) • Base Station Subsystem (BSS) • Base Transceiver Station (BTS) • Base Station Controller (BSC) • Mobile Switching Center (MSC) • Four databases • Home Location Register (HLR) • Visitor Location Register (VLR) • Equipment Identity Register (EIR) • Authentication Center (AUC) Prof. Huei-Wen Ferng

  5. Standard Interfaces • Um:MS-BTS • Abis: BTS-BSC • A-interface: BSC-MSC SIM: Subscriber Identity Module Prof. Huei-Wen Ferng

  6. Physical Channel Prof. Huei-Wen Ferng

  7. Physical Channel (Cont’d) Prof. Huei-Wen Ferng

  8. Logical Channel Prof. Huei-Wen Ferng

  9. Logical Channel (Cont’d) • TCH (Traffic Channel) • TCH/F • TCH/H • Signaling channels • BCH (Broadcast CH)->3 CHs • CCCH (Common Control CH)->3 CHs • DCCH (Dedicated Control CH)->3 CHs Prof. Huei-Wen Ferng

  10. GSM Data Prof. Huei-Wen Ferng

  11. Evolution • CSD:Circuit-Switched Data • SMS: Short Message Service • HSCSD: High-Speed CSD • EDGE: Enhanced Data rate for GSM Evolution Prof. Huei-Wen Ferng

  12. Pre-GPRS Systems Prof. Huei-Wen Ferng

  13. SMS in GSM • Two-way non-blocking packet-mode messaging service • Allowing non-real-time (NRT) dialog between mobile terminals • Transmission on GSM’s signaling channel (e.g., SDCCH) • Up to 160 bytes (PTP/broadcast) • Offered message categories • SMS-mobile-terminated PTP (stored intermediately in the SMS service center (SMS-SC)) • SMS-mobile-originated PTP • Cell broadcast SMS Prof. Huei-Wen Ferng

  14. HSCSD • Aggregation of multiple slots in a GSM frame • Speed ranges from 14.4 kbps to 64 Kbps • Using the existing GSM infrastructure • Affects to GSM • Channel allocation • Connection setup • Handoff procedures • Access to the fixed network Prof. Huei-Wen Ferng

  15. GPRS Prof. Huei-Wen Ferng

  16. About GPRS • Initiated in 1994 by ETSI • Services offered: PTP and PTM • Systems adopted: GSM and IS-136 • Speed • Single slot->14.4 kbps • Multiple slot->115.2 kbps • Web page browsing and Internet surfing • Channel allocation • Fixed/Static or dynamic Prof. Huei-Wen Ferng

  17. GPRS Network Architecture Prof. Huei-Wen Ferng

  18. Elements-SGSN • Serving GPRS Support Node (SGSN) • Functions similar to MSC/VLR • Monitors user location • Handles charging data • Provides security via A5 ciphering algorithm • Manages sessions, mobility, and logical channels • QoS management: policing and scheduling • Network access control Prof. Huei-Wen Ferng

  19. Elements-GGSN • Gateway GSN (GGSN) • Inter-works GPRS network with external packet-switched networks • Data formatting • Address translation • Protocol conversion • Routing of packets • Firewall, billing, and packet filtering Prof. Huei-Wen Ferng

  20. GSN • GSN includes SGSN and GGSN • A GPRS network consists of multiple SGSNs but only one GGSN for internetworking • GTP (GPRS Tunnel Protocol) • Communication protocol between two GSNs • User data is encapsulated and tunneled through the IP backbone network Prof. Huei-Wen Ferng

  21. GPRS Coding Schemes • Four schemes: CS-1~CS-4 • Convolutional Code Prof. Huei-Wen Ferng

  22. GPRS Protocol Stack (Data Trans.) Prof. Huei-Wen Ferng

  23. Protocol Description • Layer 1/ Physical layer • PLL (Physical Link sub-Layer) • Data unit framing • Data coding • Error detection and correction • RFL (Radio Frequency sub-Layer) • Conforms to GSM 05 series recommendations • Performs modulation and demodulation • Specifies carrier freq., radio channel structures, raw channel data rates, transceiver characteristics, performance requirements Prof. Huei-Wen Ferng

  24. Protocol Description (Cont’d) • Layer 2/ Data link layer • LLC (Logical Link Control) • Supports PTM transmission • Provides secure logical pipe between MS and SGSN • RLC (Radio Link Control)/ MAC (Medium Access Control) • Provides access signaling • Resolves access contentions • Provides link level ARQ Prof. Huei-Wen Ferng

  25. Protocol Description (Cont’d) • Relay function • In the BSS, relays LLC PDUs between the Um and Gb interfaces • In the SGSN, it relays packet data protocol (PDP) PDUs between the Gb and Gn interfaces Prof. Huei-Wen Ferng

  26. Protocol Description (Cont’d) • SNDCP (Sub-Network-Dependent Convergence Protocol) • Handles TCP/IP headers and data compression • Deals with multiplexing, encryption, and segmentation • BSSGP (BSS GPRS Protocol) • QoS • Routing between BSS and SGSN Prof. Huei-Wen Ferng

  27. GPRS QoS Issues • Access delay: 4 classes (Um~Gi) • Priority: 3 classes • Reliability: 5 classes • Mean throughput: 31 classes • Peak throughput: 9 classes (Gi~R) Prof. Huei-Wen Ferng

  28. Access Delay Prof. Huei-Wen Ferng

  29. The Others • Priority classes: high, medium, and low • Reliability classes: relates to prob. Of corruption, loss, mis-sequencing, duplication of packets • Mean throughput classes: class 1 (0.22bps)~class 30 (111kbps), class 31 (best effort) • Peak throughput classes: 8 kbps~2048 kbps • <Remark>: delay class and mean throughput are used by the SGSN for scheduling and admission control Prof. Huei-Wen Ferng

  30. MSDRA MAC Protocol • MSDRA: Master-Slave Dynamic Rate Access • Channel concept • PDCH (Packet Data CHannels) • Channels are dedicated to packet mode transfer • Uplinks and downlinks are basically used as independent channel resources • Further divided into MPDCH (Master PDCH) and SPDCH (Slave PDCH) Prof. Huei-Wen Ferng

  31. Channel Concept (Cont’d) • SPDCHs: the channels on which user data and signaling is transferred • Packet Traffic Channels (PTCHs) • Dedicated to one MS or a group of MSs used for user data transfer • Packet-Associated Control Channels (PACCHs) • Transport signaling info related one MS • Packet Data Broadcast Channels (PDBCHs) • Downlink to broadcast user data Prof. Huei-Wen Ferng

  32. Channel Concept (Cont’d) • MPDCHs: accommodate Common Control Channels (CCHs) that carry the signaling information required to initiate packet transfer • PRACH (Packet Random Access CH) • Uplink to initiate data transfer of the MS • PPCH (Packet Paging CH) • Downlink to inform MSs about incoming packets • PPRCH (Packet Paging Response CH) • Uplink to respond to paging • PAGCH (Packet Access Grant CH) • Downlink to send CH reservation info to an MS • PBCCH (Packet Broadcast Control CH) • Downlink to broadcast all GPRS-specific info. Prof. Huei-Wen Ferng

  33. Phases of MAC • MAC is based on a slotted ALOHA reservation protocol which has three phases on the uplink • Contention phase • Notification • Transmission • Two phases on the downlink • Notification • Transfer Prof. Huei-Wen Ferng

  34. PRACH Performance Analysis • RACH and PRACH: slotted ALOHA with retransmission (# of max. retrx.=7) • Assumption • Equal new call arrival rates • System is memoryless • Capture effect is considered Prof. Huei-Wen Ferng

  35. Performance Analysis (Cont’d) • For infinite number of users, PDF of interfering packets is Poisson where G is total access attempts • Pc(Su|n): the prob of success of a test packet given n interfering packets • PC(Su|n)=Pr(Pt>zPn), z is the capture ratio Prof. Huei-Wen Ferng

  36. Performance Analysis (Cont’d) • Pc(Su|n) is given by • Pc(Su) is given by • The access throughput is Prof. Huei-Wen Ferng

  37. Performance Analysis (Cont’d) • The prob that a packet will be successfully exactly k transmissions • Average number of transmissions needed for a successful reception Prof. Huei-Wen Ferng

  38. Performance Analysis (Cont’d) Prof. Huei-Wen Ferng

  39. Channel Allocation for GPRS • Packet Data Traffic CH (PDTCH) • Packet Common Control CH (PCCCH) • Packet Dedicated Control CH (PDCCH) Prof. Huei-Wen Ferng

  40. Allocation Algorithms • Fixed resource allocation (FRA) • Fixed resource allocation with queue capacity (FRAQ) • Dynamic resource allocation (DRA) • Dynamic resource allocation with queue capacity (DRAQ) Prof. Huei-Wen Ferng

  41. EGPRS (EDGE) • Initiated in 1997 • Using the GPRS core network but a new air interface with 8 coding schemes • 8-PSK modulation • Max data rate: 384 kbps Prof. Huei-Wen Ferng

  42. Prof. Huei-Wen Ferng

  43. References • Book: Wireless Personal Communications Systems by D. J. Goodman • Paper: GPRS-features and packet random access channel performance analysis by A. Gyasi-Agyei et al. • Paper: Concepts, services, and protocols of new GSM phase 2+ General Packet Radio Service by G. Brasche et al. • Paper: Channel allocation for GPRS by Phone Lin et al. Prof. Huei-Wen Ferng

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