1 GPRS —General Packet Radio Service

2 Outline  Introduction  GPRS Applications  GPRS normal service procedures  GPRS Architecture  GPRS protocol layering  GPRS data link layer and coding schemes  GPRS packet transfer  Limitations of GPRS

3 Introduction  The General Packet Radio System (GPRS) is a new service that provides actual packet radio access for mobile Global System for Mobile Communications (GSM) and time-division multiple access (TDMA) users.  The main benefits of GPRS are that it reserves radio resources only when there is data to send and it reduces reliance on traditional circuit-switched network elements.  Theoretical up to kbps transmission speed are achievable using all eight timeslots at the same time.  No dial-up connection is necessary, GPRS facilitates instant connections whereby information can be sent or received immediately as the need arises.  GPRS facilitates several new applications that have not previously been available over GSM networks due to the limitations in speed and message length.  GPRS fully enables Mobile Internet functionality by allowing interworking between the existing Internet and the new GPRS network.

4 GPRS applications  Communications Use the mobile communications network purely as a pipe to access messages or information. — ; fax; unified messaging; intranet/Internet access  Value-added services (VAS) Refer strictly to content provided by network operators to increase the value of their service to their subscribers. — E-commerce; banking; financial trading; Retail; ticket purchasing;  Location-based applications Provide the ability to link push or pull information services with a user's location. — Navigation; traffic conditions; airline/rail schedules; location finder  Vertical applications Apply to systems utilizing mobile architectures to support the carrying out of specific tasks within the value chain of a company. — Freight delivery; fleet management; sales-force automation  Advertising

5 GPRS normal service procedure (continue)  Provision — GPRS services: Point To Point (PTP) and Point To Multipoint (PTM). — Quality of Service (QoS): 1) priority; 2) reliability; 3) delay; 4) user data throughput; 5) scheduled repeated transmission.  Withdrawal  GPRS-Attach and GPRS-Detach — Attach: MS indicates its presence to the PLMN (public mobile network) for the purpose of using the GPRS services. — Detach: MS indicates to the PLMN that the MS will no longer be using the GPRS services  Registration By registering the service parameters, the subscriber optimizes the the its present, dynamic service profile within the limitations of the static subscription profile.  Erasure The subscriber erases previously registered service parameter values from the service profile.

6 GPRS normal service procedure  Interrogation The subscriber interrogates the status/value of registered service parameters as defined in the current service profile.  Activation The subscriber activates each of the registered interworking profiles independently within the limitations of the subscription profile.  De-activation The subscriber de-activates the previously activated interworking profiles independently within the limitations of the subscription profile.  Invocation and operation The GPRS service is invoked upon transmission or reception of GPRS data by subscribers.  PIN and Password Management — Correct subscriber identification has been confirmed by entry of the current GSM PIN when GPRS-Attach operates. — GPRS services is offered to a subscriber with the subscription option of using a password to control the services.

7 GPRS reference architecture GPRS can be thought of as an overlay network onto a GSM network.

8 GPRS elements  New terminals (mobiles): — Required to handle the enhanced air interface and packetize traffic. — A GPRS terminal can be one of three classes: A, B, or C.  BSC/BTS: — BSC is required to provide a physical and logical data interface out of the base station subsystem (BSS) for packet data traffic.  GPRS Network: — Gateway GPRS Service Node (GGSN) performs mobility management functions such as mobile subscriber attach/detach and location management. — Serving GPRS Service Node (SGSN) are interfaces to external IP networks such as the public Internet, other mobile service providers' GPRS services, or enterprise intranets.  GPRS Mobility Management: Mobility management builds on the mechanisms used in GSM networks. — Home location register (HLR) — Visitor location register (VLR)

9 GPRS protocol layering Transmission plane protocol layering

10 The transmission plane covers the protocols for user information transmission and associated control procedures.  Between SGSN and GGSN — GPRS tunnel protocol (GTP)  Between the SGSN and MS — Sub-network Dependent Convergence Protocol (SNDCP) — BSS GPRS protocol (BSSGP)  Between MS and BSS — Physical Link sublayer (PLL) — Physical RF sublayer (RFL) — Radio Link Control (RLC) — Medium Access Control (RLC/MAC) GPRS protocol layering Transmission plane protocol layering

11 GPRS protocol layering Signaling plane protocol layering GPRS-specific mobility management protocol (GMM) is required within MS and SGSN to support the mobility functionality.

12  Logical link control (LLC) — Provides a logical link between the MS and SGSN. — LLC layer protocol functionality is based on link access procedure-D (LAPD).  Radio link control/medium access control (RLC/MAC) — Provides services for information transfer over the physical layer of the GPRS radio interface. — RLC layer is responsible for the transmission of data block across the air interface and the backward error correction (BEC) procedures. — MAC layer is derived from a slotted ALOHA protocol, which performs contention resolution between channel access attempts. GPRS data link layer

13 GPRS packet transformation data flow PHUser data Network layer SNDCP layer Packet (N-PDU) Segment … FHInfoFSC Segment … BHInfoBCSTail Convolutional encoding Burst LLC frame RLC/MAC block Normal burst SNDCP layer LLC layer RLC/MAC layer Physical layer PH: Packet headerFCS: Frame check sequence FH: Frame headerBCS: Block check sequence BH: Block header Payload456 bits Add BCS Add precoded USF Add tail bit CodingPuncture

14 GPRS RLC/MAC block structure

15 GPRS coding schemes Maximal data rate = 8*21.4 = 171.2Kbps per user Scheme Code rate PayloadBCS Pre-coded USF Tail bits Coded bits Punct. bits Data rate (kb/s) SC-11/ SC-2  2/ SC-3  3/ SC

16 GPRS logical channels-PDCH  Packet Broadcast Control Channel (PBCCH)  Packet Broadcast Control Channel (PBCCH) — Broadcast  Packet Common Control Channel (PCCCH)  Packet Random Access Channel (PRACH) — Random access  Packet Paging Channel (PPCH) — Paging  Packet Access Grant Channel (PAGCH) — Access grant  Packet Notification Channel (PNCH) — Multicast  Packet Traffic Channel (PTCH)  Packet Data Transfer Channel (PDTCH) — Data  Packet Associated Control Channel (PACCH) — Associated control

17 Mobile-Originated packet transfer Network MS Packet channel request Random access Time Packet immediate assignment Packet resource assignment Packet resource request Transmission RLC/MAC data Acknowledgement Retransmission of data in error PRACH/RACH PAGCH/AGCH PACCH PDTCH PACCH PDTCH RLC/MAC block USF PATCH

18 Mobile-Terminated packet transfer Network MS Packet paging request Random access Time Packet channel request Packet resource assignment Packet paging response Transmission Frame transmission Acknowledgement Retransmission of blocks in error PPCH/PCH PAGCH/AGCH PACCH PDTCH PACCH PDTCH Packet immediate assignment PRACH/RACH PAGCH/AGCH RLC/MAC block USF PDTCH

19 Throughput VS. Input load in GPRS The throughput of the GPRS system performs as a slotted ALOHA system when the system is stable. When the system is overloaded, the throughput saturates at a maximum value.

20 Limitation of GPRS  Limited cell capacity for all users There are only limited radio resources that can be deployed for both voice and GPRS calls.  Speeds much lower in reality It is unlikely that a network operator will allow all timeslots to be used by a single GPRS user.  Support of GPRS mobile terminate by terminals is no ensured There has been no confirmation from any handset vendors that mobile terminated GPRS calls.  Transit delays GPRS packets are sent in all different directions to reach the same destination. the result is that potential transit delays can occur.  No store and forward There is no storage mechanism incorporated into the GPRS standard, apart from the incorporation of interconnection links between SMS and GPRS.