General Packet Radio Service GPRS

1
General Packet Radio Service (GPRS)
Sylvain FIORONI Thierry BOUSSAC
3/11/2002

• "This report was prepared for Professor L.
  Orozco-Barbosa in partial
• fulfillment of the requirements for the course
  ELG/CEG 4183"

2
Outline

• Context of GPRS
• Architecture
• Functioning
• Future trends

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Context of GPRS
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Data transmission in wireless networks

• Key point of next generations cellular networks
• GSM uses CSD technology (Circuit Switched Data)
• 9.6 kb/s bandwidth1
• Essentially text application
• web browsing, WAP, SMS

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3G networks

• 3G UMTS
• 384 kb/s 2Mb/s
• Multimedia applications videoconference
• Very expensive(1)
• Technology not yet ready(2)
• Need for a smooth transition ?
• 2.5 G Networks

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2.5G Networks

• HSCSD High Speed Circuit Switched Data
• GPRS General Packet Radio service
• EDGE Enhanced Data rates for Global Evolution

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Architecture of GPRS
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GPRS General Packet Radio service

• Uses packet switching
• Dynamic Timeslot allocation
• Up to 8 timeslots in each direction
• 4 new coding schemes to reduce error control
  coding upon a sufficient link quality
• theoretical throughput
• 8 timeslots, CS4 21.4kb/s gt 821.4171.2 kb/s
• actually, only CS2(1) available gt 813.4107.2
  kb/s

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GPRS architecture
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GPRS Components

• SGSN (Serving GPRS Support Node)
• Equivalent to MSC in GSM
• GGSN (Gateway GPRS Support Node)
• Equivalent to GMSC in GSM
• PCU (Packet Coding Unit)
• Fragmentation of the packets into radio blocks

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GPRS interfaces

• GPRS Core Network IP based network(1)
• Gn interface between xGSNs
• Gp interface to other GPRS PLMN
• Gi interface to other PSDN
• Internet, Wap Gateway, Enterprise LANs
• GPRS Access Network
• Gb interface from SGSN to PCUs
• Based on Frame Relay
• PCU-BSC proprietary interface
• Called A-ter, A-bis GPRS, A-GPRS(2)

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GPRS interfaces

• Signaling Interfaces to GSM network(SS7 based)
• Gr interface from SGSN to HLR
• Gs interface from SGSN to MSC/VLR
• Gd interface from SGSN to GMSC
• Gc from GGSN to HLR
• Gf from SGSN to EIR

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GPRS protocol stack
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GPRS protocol stack

• Gb Interface
• Network Service part of frame relay network
  (defines end to end virtual circuits NSVC(1))
• BSSGP (BSS GPRS Protocol)
• routing to cells (Virtual Channels BVC)
• flow control for each cell and mobile station(2)
• LLC (Logical Link Control)
• Very similar to HDLC
• Ciphering

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GPRS protocol stack

• Gb interface
• SNDCP (Sub Network Dependent Converging Protocol)
• encapsulation of IP/X25 packets over lower layers
• Compression
• Signalling
• GMM (GPRS Mobility Management) Attach, Routing
  Area Update procedures
• SM (Session Management) PDP Context Activation

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GPRS protocol stack

• Gn, Gp Interface
• Based on TCP/UDP/IP
• lower layers not specified(1)
• TCP ? X25, UDP ? IP
• GTP (GPRS Tunnelling Protocol)
• Encapsulation of packets over lower layers
• mainly security function
• Signaling functions

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Functioning
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Mobile Classes

• Class A
• can be attached simultaneously to GSM and GPRS
• can transmit voice and data at the same time
• Class B
• can be attached simultaneously to GSM and GPRS
• can transmit voice or data
• Class C
• cannot be attached simultaneously to GSM and GPRS

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Attach procedure
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PDP Context activation
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PDP Context activation
193.148.25.89
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QoS Management

• Specification of the requested QoS on PDP context
  activation
• Peak throughput
• Mean throughput
• Precedence priority on MAC layer
• Reliability Functioning mode of LLC, RLC and
  GTP
• Delay responsibility of the operator

Parameters of leaky bucket algorithm in BSSGP
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Future trends

• UMTS ?
• experiences a lot of delay
• licence issue
• very expensive, technology not ready
• Real need for high rates on mobile networks?
• Competition with local networks
• GPRS and 2.5G can be a good compromise
• may last longer than it was supposed to(2)

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Conclusion

• Is there a real need for data on cellular
  networks now ?
• currently too expensive Mobile terminals,
  Utilization fees
• relative failure of WAP
• High competition with wireless LANs
• still waiting for a killer application

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References

• 1 ETSI 3GPP TS 03.60, Digital cellular
  telecommunications system (Phase 2) General
  Packet Radio Service (GPRS) Service description
  Stage 2, version 7.7.0 Release 1998
• 2 ETSI 3GPP TS 08.18, Digital cellular
  telecommunications system (Phase 2) General
  Packet Radio Service (GPRS) Base Station System
  (BSS) - Serving GPRS Support Node (SGSN) BSS GPRS
  Protocol (BSSGP), version 8.9.0, Release 1999
• 3 ETSI(3GPP 03.6, Digital cellular
  telecommunications system (Phase 2)General
  Packet Radio Service (GPRS)Overall description
  of the GPRS radio interfaceStage 2, version
  8.9.0 Release 1999
• 4 Georgios Karagiannis, QoS in GPRS, Ericsson
  open report 5/0362-FCP NB 102 88 Uen, 2000-12-21
• 5 Xavier LAGRANGE, Philippe GODLEWSKI, Sami
  TABANNE, Réseaux GSM - DCS des principes à la
  norme,Paris, HERMES, 1995

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Questions

• What are the three 2.5G networks ?
• Why is the theoretical maximum throughput of GPRS
  unreachable ?
• What are the 5 parameters of QoS defined in GPRS
  ?
• What are the nodes that have been introduced with
  GPRS ?
• What is GTP ?