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General Packet Radio Service (GPRS)
"This report was prepared for Professor L. Orozco-Barbosa in partial
fulfillment of the requirements for the course ELG/CEG 4183"
Sylvain FIORONI
Thierry BOUSSAC
3/11/2002
Outline
• Context of GPRS
• Architecture
• Functioning
• Future trends
Context of GPRS
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 …
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
2.5G Networks
• HSCSD : High Speed Circuit Switched Data• GPRS : General Packet Radio service
• EDGE : Enhanced Data rates for Global Evolution
CCSSDD 99..66kkbb//ss
HSCSD 57.6kb/s
GGPPRRSS 171.2kb/s
EDGE 384kb/s
UUMMTTSS 2Mb/s
Architecture of GPRS
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 => 8*21.4=171.2 kb/s
– actually, only CS2(1) available => 8*13.4=107.2 kb/s
GPRS architecture
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
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)
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– …
GPRS protocol stack
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
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
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
Functioning
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
Attach procedure
MS
BSS SGSN GGSN
Internet
HLR Radius
Gb
Gr
Gn
Gi
GiGMM_Attach_Request (IMSI)
MA
P_u
pdat
e_lo
catio
n
MA
P_i
nser
t_su
bscr
_dat
a
MA
P_i
nser
t_su
bscr
_dat
a_ac
k
MA
P_u
pdat
e_lo
catio
n_co
mp
GMM_Attach_Accept(P-TMSI)
PDP Context activation
MS
BSS SGSN GGSN
Internet
HLR Radius
Gb
Gr
Gn
Gi
GiSM_Act_PDP_Context_req(APN)
GTP Create_PDP_cont_req(APN)
Aut
h_re
ques
t
Aut
h_ac
cept
GTP Create_PDP_cont_acc(@IP)
SM_Act_PDP_Context_resp(@IP)
PDP Context activation
MS
BSS SGSN GGSN
Internet
HLR Radius
Gb
Gr
Gn
Gi
Gi
193.148.25.89
IP source:193.148.25.89Dest : 134.214.164.24
• 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
QoS Management
Parameters of leaky bucket algorithm in BSSGP
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)
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
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 interface;Stage 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
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 ?
