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General Packet Radio Service (GPRS) "This report was prepared for Professor L. Orozco-Barbosa in partial fulfillment ...
Outline <ul><li>Context of GPRS </li></ul><ul><li>Architecture </li></ul><ul><li>Functioning </li></ul><ul><li>Future tren...
Context of GPRS
Data transmission in wireless networks <ul><li>Key point of next generations cellular networks </li></ul><ul><li>GSM : use...
3G networks <ul><li>3G : UMTS </li></ul><ul><ul><li>384 kb/s – 2Mb/s </li></ul></ul><ul><ul><li>Multimedia applications : ...
2.5G Networks <ul><li>HSCSD : High Speed Circuit Switched Data </li></ul><ul><li>GPRS : General Packet Radio service </li>...
Architecture of GPRS
GPRS : General Packet Radio service <ul><li>Uses packet switching </li></ul><ul><li>Dynamic Timeslot allocation </li></ul>...
GPRS architecture
GPRS Components <ul><li>SGSN : (Serving GPRS Support Node) </li></ul><ul><ul><li>Equivalent to MSC in GSM </li></ul></ul><...
GPRS interfaces <ul><li>GPRS Core Network : IP based network (1) </li></ul><ul><ul><li>Gn interface between xGSNs </li></u...
GPRS interfaces <ul><li>Signaling Interfaces to GSM network (SS7 based) : </li></ul><ul><ul><li>Gr interface from SGSN to ...
GPRS protocol stack
GPRS protocol stack <ul><li>Gb Interface : </li></ul><ul><ul><li>Network Service : part of frame relay network (defines en...
GPRS protocol stack <ul><li>Gb interface </li></ul><ul><ul><li>SNDCP (Sub Network Dependent Converging Protocol) </li></ul...
GPRS protocol stack <ul><li>Gn, Gp Interface : </li></ul><ul><ul><li>Based on TCP/UDP/IP </li></ul></ul><ul><ul><li>lower ...
Functioning
Mobile Classes <ul><li>Class A : </li></ul><ul><ul><li>can be attached simultaneously to GSM and GPRS </li></ul></ul><ul><...
Attach procedure MS BSS SGSN GGSN Internet HLR Radius Gb Gr Gn Gi Gi GMM_Attach_Request (IMSI) MAP_update_location MAP_ins...
PDP Context activation MS BSS SGSN GGSN Internet HLR Radius Gb Gr Gn Gi Gi SM_Act_PDP_Context_req(APN) GTP Create_PDP_cont...
PDP Context activation 193.148.25.89 MS BSS SGSN GGSN Internet HLR Radius Gb Gr Gn Gi Gi IP source:193.148.25.89 Dest : 13...
<ul><li>Specification of the requested QoS on PDP context activation : </li></ul><ul><ul><li>Peak throughput  </li></ul></...
Future trends <ul><li>UMTS ? </li></ul><ul><ul><li>experiences a lot of delay </li></ul></ul><ul><ul><ul><li>licence issue...
Conclusion <ul><li>Is there a real need for data on cellular networks now ? </li></ul><ul><ul><li>currently too expensive ...
References <ul><li>[1] ETSI 3GPP TS 03.60, Digital cellular telecommunications system (Phase 2+) General Packet Radio Serv...
Questions <ul><li>What are the three 2.5G networks ? </li></ul><ul><li>Why is the theoretical maximum throughput of GPRS u...
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GPRS

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  • 1 The actual bandwidth of a GSM channel is 21.4kb/s. However, because of error control coding, the bandwidth available for a user is only 9.6 kb/s. This bandwidth is not large enough to enable multimedia applications. Therefore, its usage is essentially restricted to the applications cited below.
  • 1 To install an UMTS network, operators need to almost completely replace the existing GSM network. Some European operators still have not shown a profit from their initial investment. 2 UMTS makes a wide use of ATM with adaptation layer AAL2 on the voice part of the network, which was almost never implemented before.
  • With HSCSD, a user can be statically allocated several timeslots instead of only one, as in CSD; this allows to reach much higher rates though it needs a lot of radio resources. The 57.6kb/s bit rate was calculated with 6 timeslots allocated for one user. With GPRS, one user can also be allocated several timeslots but the allocation is dynamic, which allows to save a lot of resources. EDGE is similar to GPRS, however it uses 8PSK modulation on the radio interface instead of GMSK which allows to multiply the bit rate by 3 (8=2 3 )
  • (1) The use of CS3 and CS4 requires signal/noise ratios that are not currently reached in commercial GSM networks.
  • SGSN manages the access of the GPRS core network by subscribers and is responsible of the mobility management GGSN is the gateway between the GPRS core network and other Packet Switched Networks like internet. The access to these different networks are designed by Access Point Names (APN) and users can access them by establishing a PDP Context which creates a tunnel to this access point. PCU are responsible of fragmentation and reassembly of packets to make them fit into the classic RLC/MAC blocks of GSM, which allows them to be sent over the air interface. When the packets are fragmented, a temporary block flow identifier (TBFI) is associated to each of them in order to allow the correct reassembly of the packets at the other end.
  • (1) As in any other IP based network, the GPRS core network may also include other elements like DNS servers, routers, switches or RADIUS servers… (2) The name depends on the manufacturer of the equipments
  • Gr interface allows the authentication of users and the management of their subscription to enable their access to the GPRS service Gs interface is used for common GPRS/GSM procedures like attach request. Gd interface is essentially used to access the SMS server in order to send SMS through the GPRS network. Gc interface is optional and is used to allow the management of the access rights to APNs by GGSNs instead of SGSNs Gf interface is used for the authentication of Mobile Equipments Specifications also define Ga interface that is used for billing and that is actually similar to Gn interface.
  • (1) NSVC : Network Service Virtual Circuit : defines the set of DLCI to be used on each switch to reach the other end. (2) flow control mechanism uses the leaky bucket algorithm. The bucket size and the bucket leak rate for each cell are dynamically adjusted in function of the load of BSS (Base Station Subsystem : BSC + BTS).
  • (1) Operators are free to use any architecture. The most commonly used are Fast Ethernet, Frame Relay and ATM.
  • Different multislot classes are also specified for mobile equipments, they define how many timeslots can be used in each direction (uplink and downlink).
  • 1 – The Mobile Station sends an attach request message to the SGSN with its IMSI parameter or a P-TMSI if it already had one. 2 – SGSN initiates an update location procedure with the HLR which allows to check the access right of the user for GPRS services and to indicate which SGSN he uses. 3 – HLR checks the subscription of the user and sends information about it to the SGSN such as the subscribed QoS or the authentication triplets that allows authentication of the subscriber and ciphering 4 – SGSN acknowledges these information 5 – HLR terminates the update location procedure 6 – SGSN sends an Attach_Accept message with the P-TMSI that has been allocated. This P-TMSI is used for the following procedures instead of IMSI to guarantee the confidentiality of the subscriber identity.
  • 1 – The mobile Station initiates an activate_PDP_Context procedure to ask the access to a specified Access Point Name(APN) with a specified QoS 2 – SGSN initiates a Create_PDP_Context procedure with GGSN to create a GTP tunnel for the specified user to the specified APN. 3 – 4 – GGSN can eventually ask for the authentication of the user by a Radius server, using a classic user name and password 5 – GGSN allocates an IP address to the MS. It can be public or private. In the latter case, GGSN will have to do NAT (Network Address Translation) to allow the user to communicate with external networks. 6 – SGSN sends a Activate_PDP_context_response message and transmits the IP address that has been allocated to the MS
  • The MS can then exchange IP packets on Internet, as any other Internet user, since it has its own IP address. The packets are tunneled over the GPRS network, as it would be when using VPN technologies. Instead of accessing internet, it could access an enterprise intranet since GPRS offers a high security level.
  • (1) One of the main reasons to the fact that UMTS is already available in Japan whereas it will certainly not be available in Europe before 2003 is that licenses have been given for free in Japan whereas in Europe, governments have sold them for an huge amount of money. (2) 2.5G networks were supposed to be only a transition to 3G networks and should have been existing for only a couple of years. But some operators are thinking about keeping GPRS or EDGE networks instead of installing UMTS.
  • Transcript of "GPRS"

    1. 1. General Packet Radio Service (GPRS) &quot;This report was prepared for Professor L. Orozco-Barbosa in partial fulfillment of the requirements for the course ELG/CEG 4183&quot; Sylvain FIORONI Thierry BOUSSAC 3/11/2002
    2. 2. Outline <ul><li>Context of GPRS </li></ul><ul><li>Architecture </li></ul><ul><li>Functioning </li></ul><ul><li>Future trends </li></ul>
    3. 3. Context of GPRS
    4. 4. Data transmission in wireless networks <ul><li>Key point of next generations cellular networks </li></ul><ul><li>GSM : uses CSD technology (Circuit Switched Data) </li></ul><ul><ul><li>9.6 kb/s bandwidth 1 </li></ul></ul><ul><ul><li>Essentially text application </li></ul></ul><ul><ul><ul><li>web browsing, WAP, SMS … </li></ul></ul></ul>
    5. 5. 3G networks <ul><li>3G : UMTS </li></ul><ul><ul><li>384 kb/s – 2Mb/s </li></ul></ul><ul><ul><li>Multimedia applications : videoconference… </li></ul></ul><ul><ul><li>Very expensive (1) </li></ul></ul><ul><ul><li>Technology not yet ready (2) </li></ul></ul><ul><li>Need for a smooth transition  </li></ul><ul><ul><li>2.5 G Networks </li></ul></ul>
    6. 6. 2.5G Networks <ul><li>HSCSD : High Speed Circuit Switched Data </li></ul><ul><li>GPRS : General Packet Radio service </li></ul><ul><li>EDGE : Enhanced Data rates for Global Evolution </li></ul>
    7. 7. Architecture of GPRS
    8. 8. GPRS : General Packet Radio service <ul><li>Uses packet switching </li></ul><ul><li>Dynamic Timeslot allocation </li></ul><ul><li>Up to 8 timeslots in each direction </li></ul><ul><li>4 new coding schemes to reduce error control coding upon a sufficient link quality </li></ul><ul><li>theoretical throughput : </li></ul><ul><ul><li>8 timeslots, CS4 : 21.4kb/s => 8*21.4=171.2 kb/s </li></ul></ul><ul><ul><li>actually, only CS2 (1) available => 8*13.4=107.2 kb/s </li></ul></ul>
    9. 9. GPRS architecture
    10. 10. GPRS Components <ul><li>SGSN : (Serving GPRS Support Node) </li></ul><ul><ul><li>Equivalent to MSC in GSM </li></ul></ul><ul><li>GGSN : (Gateway GPRS Support Node) </li></ul><ul><ul><li>Equivalent to GMSC in GSM </li></ul></ul><ul><li>PCU : (Packet Coding Unit) </li></ul><ul><ul><li>Fragmentation of the packets into radio blocks </li></ul></ul>
    11. 11. GPRS interfaces <ul><li>GPRS Core Network : IP based network (1) </li></ul><ul><ul><li>Gn interface between xGSNs </li></ul></ul><ul><ul><li>Gp interface to other GPRS PLMN </li></ul></ul><ul><ul><li>Gi interface to other PSDN : </li></ul></ul><ul><ul><ul><li>Internet, Wap Gateway, Enterprise LANs… </li></ul></ul></ul><ul><li>GPRS Access Network </li></ul><ul><ul><li>Gb interface : from SGSN to PCUs </li></ul></ul><ul><ul><ul><li>Based on Frame Relay </li></ul></ul></ul><ul><ul><li>PCU-BSC : proprietary interface </li></ul></ul><ul><ul><ul><li>Called A-ter, A-bis GPRS, A-GPRS… (2) </li></ul></ul></ul>
    12. 12. GPRS interfaces <ul><li>Signaling Interfaces to GSM network (SS7 based) : </li></ul><ul><ul><li>Gr interface from SGSN to HLR </li></ul></ul><ul><ul><li>Gs interface from SGSN to MSC/VLR </li></ul></ul><ul><ul><li>Gd interface from SGSN to GMSC </li></ul></ul><ul><ul><li>Gc from GGSN to HLR </li></ul></ul><ul><ul><li>Gf from SGSN to EIR </li></ul></ul><ul><ul><li>… </li></ul></ul>
    13. 13. GPRS protocol stack
    14. 14. GPRS protocol stack <ul><li>Gb Interface : </li></ul><ul><ul><li>Network Service : part of frame relay network (defines end to end virtual circuits : NSVC (1) ) </li></ul></ul><ul><ul><li>BSSGP (BSS GPRS Protocol) </li></ul></ul><ul><ul><ul><li>routing to cells (Virtual Channels : BVC) </li></ul></ul></ul><ul><ul><ul><li>flow control for each cell and mobile station (2) </li></ul></ul></ul><ul><ul><li>LLC (Logical Link Control) </li></ul></ul><ul><ul><ul><li>Very similar to HDLC </li></ul></ul></ul><ul><ul><ul><li>Ciphering </li></ul></ul></ul>
    15. 15. GPRS protocol stack <ul><li>Gb interface </li></ul><ul><ul><li>SNDCP (Sub Network Dependent Converging Protocol) </li></ul></ul><ul><ul><ul><li>encapsulation of IP/X25 packets over lower layers </li></ul></ul></ul><ul><ul><ul><li>Compression </li></ul></ul></ul><ul><ul><li>Signalling : </li></ul></ul><ul><ul><ul><li>GMM (GPRS Mobility Management) : Attach, Routing Area Update procedures… </li></ul></ul></ul><ul><ul><ul><li>SM (Session Management) : PDP Context Activation </li></ul></ul></ul>
    16. 16. GPRS protocol stack <ul><li>Gn, Gp Interface : </li></ul><ul><ul><li>Based on TCP/UDP/IP </li></ul></ul><ul><ul><li>lower layers not specified (1) </li></ul></ul><ul><ul><li>TCP  X25, UDP  IP </li></ul></ul><ul><ul><li>GTP (GPRS Tunnelling Protocol) </li></ul></ul><ul><ul><ul><li>Encapsulation of packets over lower layers </li></ul></ul></ul><ul><ul><ul><li>mainly security function </li></ul></ul></ul><ul><ul><ul><li>Signaling functions </li></ul></ul></ul>
    17. 17. Functioning
    18. 18. Mobile Classes <ul><li>Class A : </li></ul><ul><ul><li>can be attached simultaneously to GSM and GPRS </li></ul></ul><ul><ul><li>can transmit voice and data at the same time </li></ul></ul><ul><li>Class B : </li></ul><ul><ul><li>can be attached simultaneously to GSM and GPRS </li></ul></ul><ul><ul><li>can transmit voice or data </li></ul></ul><ul><li>Class C : </li></ul><ul><ul><li>cannot be attached simultaneously to GSM and GPRS </li></ul></ul>
    19. 19. Attach procedure MS BSS SGSN GGSN Internet HLR Radius Gb Gr Gn Gi Gi GMM_Attach_Request (IMSI) MAP_update_location MAP_insert_subscr_data MAP_insert_subscr_data_ack MAP_update_location_comp GMM_Attach_Accept(P-TMSI)
    20. 20. PDP Context activation MS BSS SGSN GGSN Internet HLR Radius Gb Gr Gn Gi Gi SM_Act_PDP_Context_req(APN) GTP Create_PDP_cont_req(APN) Auth_request Auth_accept GTP Create_PDP_cont_acc(@IP) SM_Act_PDP_Context_resp(@IP)
    21. 21. PDP Context activation 193.148.25.89 MS BSS SGSN GGSN Internet HLR Radius Gb Gr Gn Gi Gi IP source:193.148.25.89 Dest : 134.214.164.24
    22. 22. <ul><li>Specification of the requested QoS on PDP context activation : </li></ul><ul><ul><li>Peak throughput </li></ul></ul><ul><ul><li>Mean throughput </li></ul></ul><ul><ul><li>Precedence : priority on MAC layer </li></ul></ul><ul><ul><li>Reliability : Functioning mode of LLC, RLC and GTP </li></ul></ul><ul><ul><li>Delay : responsibility of the operator </li></ul></ul>QoS Management Parameters of leaky bucket algorithm in BSSGP
    23. 23. Future trends <ul><li>UMTS ? </li></ul><ul><ul><li>experiences a lot of delay </li></ul></ul><ul><ul><ul><li>licence issue </li></ul></ul></ul><ul><ul><ul><li>very expensive, technology not ready </li></ul></ul></ul><ul><ul><li>Real need for high rates on mobile networks? </li></ul></ul><ul><ul><ul><li>Competition with local networks </li></ul></ul></ul><ul><li>GPRS and 2.5G can be a good compromise </li></ul><ul><ul><li>may last longer than it was supposed to (2) </li></ul></ul>
    24. 24. Conclusion <ul><li>Is there a real need for data on cellular networks now ? </li></ul><ul><ul><li>currently too expensive : Mobile terminals, Utilization fees… </li></ul></ul><ul><ul><li>relative failure of WAP… </li></ul></ul><ul><ul><li>High competition with wireless LANs </li></ul></ul><ul><li>still waiting for a killer application </li></ul>
    25. 25. References <ul><li>[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 </li></ul><ul><li>[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 </li></ul><ul><li>[3] ETSI(3GPP 03.6, Digital cellular telecommunications system (Phase 2+);General Packet Radio Service (GPRS);Overall description of the GPRS radio interface;Stage 2, version 8.9.0 Release 1999 </li></ul><ul><li>[4] Georgios Karagiannis, QoS in GPRS, Ericsson open report 5/0362-FCP NB 102 88 Uen, 2000-12-21 </li></ul><ul><li>[5] Xavier LAGRANGE, Philippe GODLEWSKI, Sami TABANNE, Réseaux GSM - DCS: des principes à la norme,Paris, HERMES, 1995 </li></ul>
    26. 26. Questions <ul><li>What are the three 2.5G networks ? </li></ul><ul><li>Why is the theoretical maximum throughput of GPRS unreachable ? </li></ul><ul><li>What are the 5 parameters of QoS defined in GPRS ? </li></ul><ul><li>What are the nodes that have been introduced with GPRS ? </li></ul><ul><li>What is GTP ? </li></ul>
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