3. GSM PHASE 2+ GENERAL PACKET RADIO
SERVICE GPRS: Architecture,Protocols,and
Air
interface
Christian Bettstetter,Hans-Jorg Vogel,and Jorg Eberspacher
TECHNISCHE UNIVERSITÄT MÜNCHEN (TUM)
May 7, 2010 IEEE Communications Surveys
3
5. About GPRS
• Bearer service for GSM
• Data rate : 14.4 to 115.2 Kbps
• Modulation Technique: GMSK
• Type of Connection: Packet - Switched
Technology
• Replacement of HSCSD
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6. What was lacking in HSCSD?
• Connection setup time too long
• Inefficient resource utilization for bursty traffic.
• Higher call blocking probability
• High cost of service
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7. GPRS: Benefits
• High speed
• Efficient resource utilization.
• Important step on the path to 3G
• Billing : Amount of data transferred
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8. GSM : Review
• GSM-900:
Uplink: 890 MHz – 915 MHz (25 MHz)
Downlink: 935 MHz – 960 MHz (25 MHz)
Data rate: 9.6kbps
• Frequency Division Multiple Access
Channels are 200 kHz wide.
• Time Division Multiple Access
8 timeslots each channel
May 7, 2010 8
10. GSM: System Architecture
• Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
• Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)
• Network Subsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)
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11. GSM System Architecture
PSTN
ISDN
PDN
MS
BTS MSC
BSC GMSC
MS
BTS
BSC
MS VLR
EIR
BTS AUC
HLR
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12. GPRS Network Elements
• GPRS Architecture is same as GSM except few
modifications:
GPRS includes GSNs
1. SGSN
2. GGSN
GPRS Register
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13. GPRS System Architecture
SMS-GMSC Other
GPRS
Gd
PLMN
MS
BTS SGSN
Gp
BSC
GGSN
Gb
MS Gn GGSN
Gf
BTS PDN
BSC Gr Gi
Gs Gc
MS
EIR
BTS
HLR+GPRS
May 7, 2010 13
Register
MSC/VLR
14. SGSN – Serving GPRS Support Node
• Delivers data packets to mobile stations and vice
versa.
• Detect and Register new GPRS MS in its serving
area.
• Packet Routing
• Authentication
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15. GGSN – Gateway GPRS Support Node
• Interfaces GPRS backbone network &
external packet data networks
• Converts the GPRS packets from SGSN to
the PDP format
• Stores profile of the user in its location register
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16. GPRS Register
• GPRS Register is integrated with GSM-HLR.
• Maintains the GPRS subscriber data and Routing
information.
• Stores current SGSN address
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17. GPRS Classes
• Class A
– MS supports simultaneous operation of GPRS
and GSM services
• Class B
– It can only use one of the two services at a given
time.
• Class C
- MS can attach for either GPRS or GSM services
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20. Overview
GPRS Standard
GSM to GPRS
Air Interface Resources
GPRS Multislot Classes
Ericsson’s implementation of GPRS
GPRS Attach
PDP context Activation
GPRS security
Protocol Architecture
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21. GPRS Standard
• Evolution of the GSM standard
• European Telecommunications Standards
Institute.(ETSI)
• 3rd Generation Partnership Project (3GPP)
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22. GSM to GPRS
• SGSN and GGSN
• Hardware Upgrades
– BSS
– PCU is added to BSC
• Software Upgrades
– MSC/VLR
– HLR
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28. Ericsson’s implementation of GPRS
• Fast deployment while keeping entry costs low.
• SGSN and GGSN combined into one physical
node.
• Ericsson’s AXB 250 platform.
• Hardware redundancy and the open telecom
platform (OTP)
• (O&M) activities toward the GSNs are handled via
a Java-based graphical user interface (GUI), called
the Packet eXchange.
• A router function has been integrated into the GSN
May 7, 2010 28
29. GPRS ATTACH
HLR
MSC/VLR
3
MS 3
BSC 2
1
3
2
1 SGSN GGSN
4 2
BTS IP
4 networ
1 .MS Request k
2. Authentication insertion
3. Subscriber Data
Backbone
4. Attach Confirmation Network
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30. PDP context activation.
HLR
MS
BSC
1
1 SGSN[DNS]
GGSN 5
BTS 4
IP
2,3 networ
1 .MS Request k
4 4
2. Request Validates
3. APN is sent to DNS
Backbone
4. GTP tunnel. Network
5. IP address allocation to MS
May 7, 2010 30
31. GPRS SECURITY
• User authentication (GSM style)
• The GPRS tunneling protocol (GTP) encapsulates
user packets.
• IPSec functionality provides secure connections
between the SGSN and GGSN
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32. Protocol Stack
MS BSS (PCU) SGSN GGSN
Application
IP / X.25 IP / X.25
SNDCP SNDCP GTP GTP
LLC UDP/ UDP/
LLC LLC TCP
TCP
RLC RLC BSSGP BSSGP IP IP
Frame Frame
MAC MAC L2 L2
Relay Relay
GSM RF GSM RF GSM RF L1 L1 L1
Um Gb Gn Gi
May 7, 2010 32
33. Real time Video Communications over GPRS
N.Fabri,Stewart Worall,Abdul Sadka,Ahmet Kandoz
University of Surrey ,United Kingdom
May 7, 2010 33
34. GPRS - Applications
• Chat
• Textual and visual information
• Web browsing
• Document sharing, Email
• Vehicle Positioning
• Home Automation
May 7, 2010 34
35. Need of the technology
• Enhanced Multimedia services on go
• Integration of video, audio and data i.e rich web
contents
– Implication on design
• Quality of service
• Access to some bearer channels
• Use of standardised protocols
• Presents the model using ETSI`s GPRS as an
access channel for the services
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36. GPRS support for video com..
Two main reasons
• Multislotting
– increases the throughput capabilities of a single
terminal
• IP Support
– To work with internet multimedia applications
May 7, 2010 36
37. • SNDCP: formats network packets for
transmission over GPRS and multiplexing of
data
• LLC: links MS to SGSN
• RLC/MAC layer : fixed length segmented
data
– Access to physical channel
– Access method
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39. Video communication
• Video over IP is used
• Real time service
– Streaming of stored video
– Conversational video
• PDTCH: Packet Data traffic Channel is used
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41. Video Compression
• Two main standardized codecs
– ITU-T`s H.26
– ISO MPEG-4
• Bothe are based on the same technology
– MPDCT
• However MPEG-4 is more efficient
– It manipulate objects in realtime by use of BIFS
To vary volume, position, colour etc
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42. MPEG-4 Encoder
• It produces three streams
– Audio
– Video
– BIFS
• Flex Mux tool is used to combine the
streams before transmission
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43. Error Resilience Tools
• Places the coded data in regular sized packets
with a synchronization sequence
• Any packet can be decoded independently
• Data Partitioning: separates motion and header
data from textured data in each video packet.
– Less distortion in original data
– Not all are very sensitive to error
– Use of Reversible Variable Length Codes (RVLCs)
May 7, 2010 43
44. MPEG-4 Frames
– Intra frames
• Independent of any frames
• Used to prevent error propagation by regularly
refreshing the display
• Much larger comparatively
• Dropping the bit rate
• Data loss can occur even when there is no channel
errors.
– Inter frames
• Predicted from previous frames
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45. Adaptive Inter Refresh (AIR)
• Codes fixed number of intra block in each
frame
• SAD is used to mark each block as intra
coded by comparing it to a threshold value.
May 7, 2010 45
47. Channel Allocation
• PRMA (Packet Resource Multiple Access)is
used
• The MS sends access burst and is assigned
Temporary Block Flow (TBF) untill LLC
PDUs are to transmit.
• Normal delay is from 200 to 300ms
• Not suitable for critical data
May 7, 2010 47
