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General Packet Radio Service(GPRS)
Mobile Telematics 2004
Ivar Jrstad
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References
Ganz et. al. (Release 5)
3GPP TS 23.060 (Service Description,Stage 2, Release 6)
3GPP TS 43.051 (Radio Access Network,
Overall Description, Stage 2, Release 6)
GPRS Protocol Stack White Paper
(Vocal Technologies Ltd. http://www.vocal.com)
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Introduction
Packet switched data on top of GSM network
Goals of GPRS: Efficient bandwidth usage for bursty data traffic
(e.g. Internet)
Higher data rates
New charging models
Initially specified by ETSI
Specifications handed over to 3GPP
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Architecture Overview
A lot of releases (R97, R98, R99, R4 etc.)
A *lot* of specifications... Considered in this overview:
Release 5 (Ganz) / 6 (most recent TS at 3GPP)
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GPRS Release 5/6
Two modes determined by generation of
core network: 2G core => A/Gb
3G core => Iu
Iu interface added in rel. 5 to align with
UMTS
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GERAN Reference Architecture
GSM/UMTSCore Network
GERAN
Gb
A
Iu
MSUm
Iur-g
BSC
BTS
BTS
BSS
BSS
MS
Iur-g
UTRAN
RNC3GPP TS 43.051 (Release 6)
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A/Gb mode
Class A: MS can operate simultaneous
packet switched and circuit switched services Class B: MS can operate either one at one
time
Most common for handsets today
Class C: MS can operate only packetswitched services
E.g. expansion cards for laptops
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Iu mode
CS/PS mode: Same as Class A in A/Gb
mode PS mode: MS can only operate packet
switched services
CS mode: MS can only operate circuit
switched services
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User Plane Protocol Architecture
PHY
RLC
PDCP
LLC
SNDCP
PHY
RLC
PDCP
SNDCP
LLC
BSSGP
Network
Service
Iu-ps
Gb
Um
MS
Relay
GERAN SGSN
/Ack UnackRLC
MACMAC
/Ack UnackRLC
Common protocols
Iu influenced protocols
Gb influenced protocols
FRIP
L2FR
BSSGP
Network
Service
IP
L2
L1L1L1
GTP-U
L2
UDP/IP
L1
GTP-U
L2
UDP/IP
As defined inIu Specs.
As defined inIu Specs.
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Control Plane Protocol Architecture
RR
PHY
RLC
LLC
GMM/SM
PHY
RLC
RRC
GMM/SM
LLC
BSSGP
Network
Service
Iu-ps
Gb
Um
MS
Relay
GERAN SGSN
Ack/Unack
RLC
MACMAC
Ack/Unack
RLC
Common protocols
Iu influenced protocols
Gb influenced protocols
FR
IP
L2FR
BSSGP
Network
Service
IP
L2
L1L1
LAPDm LAPDm
RRRRC
RR
PHY
RLC
LLC
GMM/SM
PHY
RLC
RRC
GMM/SM
LLC
BSSGP
Network
Service
Iu-ps
Gb
Um
MS
Relay
GERAN SGSN
Ack/Unack
RLC
MACMAC
Ack/Unack
RLC
Common protocols
Iu influenced protocols
Gb influenced protocols
FR
IP
L2FR
BSSGP
Network
Service
IP
L2
L1L1
LAPDm LAPDm
RRRRC
L2
L1
RANAP
SCCP
As Definedin Iu Specs.
L3
L2
L1
RANAP
SCCP
As Definedin Iu Specs.
L3
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Service Types
Point-to-Point
Internet access by user Point-to-Multipoint
Delivery of information (e.g. news) to multiple
locations or interactive conference applications
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Internet (IP) Multimedia Subsystem
New in Release 5
Simultaneous access to multiple differenttypes of real-time and non-real-time traffic
IMS provides synchronization between such
components
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Radio Interface Protocols
User plane and Control Plane
Three layers Layer 1; Physical (PHY)
Layer 2; Data Link, Media Access Control (MAC),
Radio Link Control (RLC) and Packet Data
Convergence Protocol (PDCP) Layer 3; Radio Resource Control (RRC) for Iu
mode and Radio Resource (RR) for A/Gb mode
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Physical Layer
Combined Frequency Division Multiple Access
(FDMA) and Time Division Multiple Access (TDMA)
(GSM)
Channel separation: 200 kHz
Power output control; find minimum acceptable level
Synchronization with base station
Handover
Quality monitoring
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Release 5 Protocol Arch.
Physical Channels
Logical, Control and Traffic Channels Media Access Control and Radio Link
Control
Radio Resource Control and Radio Resource
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Physical Channels
Defined by timeslot (0-7) and radio frequency
channel Shared Basic Physical Sub Channel
Shared among several users (up to 8)
Uplink Stage Flag (USF) controls multiple access
Dedicated Basic Physical Sub Channel
One user
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Physical Channels
Packet Data Channel (PDCH)
Dedicated to packet data traffic from logicalchannels (next slide)
Control
User data
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Logical Channels
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Logical Channels
Mapped by the MAC to physical channels
Control channels for control, synchronizationand signaling Common
Dedicated
Broadcast
Packet Traffic channels Encoded speech
Encoded data
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Control Channels
Packet Common Control Channel (PCCCH)
Paging (PPCH) Random Access (PRACH)
Grant (PAGCH)
Packet Notification (PNCH)
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Control Channels
Packet Dedicated Control Channel (PDCCH)
Operations on DBPSCH Slow Associated Control Channel (SACCH)
Radio measurements and data
SMS transfer during calls
Fast Associated Control Channel (FACCH)
For one Traffic Channel (TCH)
Stand-alone Dedicated Control Channel (SDCCH)
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Control Channels
Packet Broadcast Control Channel (PBCCH)
Frequency correction channels Synchronization channel (MS freq. vs. BS)
Broadcast control channel for general information
on the base station
Packet broadcast channels Broadcast parameters that MS needs to access network
for packet transmission
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Packet Traffic Channels
Traffic Channels (TCH)
Encoding of speech or user data
Channels are either predetermined multiplexed ormultiplexing determined by MAC
Full rate/half rate
On both SBPSCH and DBPSCH
Modulation techniques GMSK
8-PSK
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Media Access Control (MAC)
Connection oriented
Connections are called Temporary Block Flows
(TBF)
Logical unidirectional connection between two MAC entities
Allocated resources on PDCH(s)
One PDCH can accomodate multiple TBFs
Temporary Flow Identity (TFI) is unique among concurrentTBFs in the same direction
Global_TFI to each station
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MAC: TBF Establishment
MS initiated One Phase Access, or
Two Phase Access
MS BSS MS BSS
PACKET CHANNEL REQUESTPRACH
PACKET UPLINK ASSIGNMENT PAGCH
TBF Est. By MS: One Phase Access
PACKET CHANNEL REQUESTPRACH
PACKET RESOURCE REQUESTPACCH
PACKET UPLINK ASSIGNMENT PACCH
TBF Est. By MS: Two Phase Access
PACKET UPLINK ASSIGNMENT PAGCH
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MAC: TBF Establishment
Network initiated
MS BSSPACKET PAGING REQUEST PPCH
PACKET CHANNEL REQUESTPRACH
PACKET PAGING RESPONSEPACCH
PACKET DOWNLINK ASSIGNMENT PACCH or PAGCH
TBF Est. By Network
PACKET IMMEDIATE ASSIGNMENT PAGCH
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MAC: Channel Access & Resource
Allocation
Slotted Aloha Used in PRACH
MSs send packets in uplink direction at the beginning ofa slot
Collision: Back off -> timer (arbitrary) -> re-transmit
Time Division Multiple Access (TDMA)
Predefined slots allocated by BSS Contention-free channel access
All logical channels except PRACH
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MAC: Resource Allocation
Mechanisms
Uplink State Flag (USF, 3bits) associated with an assignedPDCH (USF on each downlink Radio Block)
USF_GRANULARITY assigned during TBF est.
Dynamic Allocation1. MS finds its USF in RLC/MAC PDU header. On the next uplink
block:
2. If USF_GRANULARITY=0, transmit one radio block
3. If USF_GRANULARITY=1, transmit four cons. radio blocks
Extended Dynamic Allocation Same as Dynamic, except the four radio blocks are transmitted
on different PDCHs
Exclusive Allocation
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Radio Link Control
Can provide reliability for MAC transmissions
Transparent mode
No functionality Acknowledged mode
Selective Repeat ARQ
Sender: Window
Receiver: Uplink ACK/NACK or Downlink ACK/NACK
Unacknowledged mode Controlled by numbering within TBF
No retransmissions
Replaces missing packets with dummy information bits
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Radio Resource Control/Radio
Resource
Radio resource management
RRC in Iu mode Broadcasts system information
Considers QoS requirements and ensures allocation ofresources
RR in A/Gb mode Maintains at least one PDCH for user data and control
signaling
Allocates new DBPSCHs
Intracell handover of DBPSCHs
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QoS Support
End-to-end QoS may be specified by Service LevelAgreements
Assumes that IP multimedia applications are able to Define their requirements
Negotiate their capabilities
Identify and select available media components
GPRS specifies signaling that enable support for
various traffic streams Constant/variable bit rate Connection oriented/connection less
Etc.
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QoS Profile for GPRS Bearers
Describes applications characteristics and QoSrequirements
4 parameters: Service precedence
3 classes
Reliability parameter
3 classes
Delay parameters 4 classes
Throughput parameter
Maximum and mean bit rates
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QoS Profile for GPRS Bearers
QoS profile is included in Packet Data
Protocol (PDP) context
Negotiation managed through PDP
procedures (activation, modification and
deactivation)
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Packet Classification and Scheduling
TBF tagged with TFI
TFI different for each TBF
Packet scheduling algorithms are not defined by the
standard; defined and implemented by GPRS
network designers and carriers
GPRS *can* enable per-flow quantitative QoS
services with proper packet classification and
scheduling algorithms...Hmmm.
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Mobility Management
Two procedures:
GPRS Attach/Detach (towards SGSN/HLR)
Makes MS available for SMS over GPRS
Paging via SGSN
Notification of incoming packet
PDP Context Activation/Deactivation
Associate with a GGSN
Obtain PDP address (e.g. IP)
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GPRS Mobile Station States
GPRS protocol stack (MS) can take on 3different states
IDLE
STANDBY
ACTIVE/READY
Data can only be transmitted in the ACTIVEstate
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Routing to MS
IDLE state
No logical PDP context activated
No network address (IP) registered for the terminal
No routing of external data possible
Only multicast messages to all GPRS handsets
available
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Routing to MS
STANDBY state
Only routing area is known
RA is defined by operator => allows individual
optimizations
When downlink data is available, packet paging
message is sent to routing area
Upon reception, MS sends it's cell location to theSGSN and enters the ACTIVE state
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Routing to MS
ACTIVE state
SGSN knows the cell of the MS
PDP contexts can be activated/deactivated
Can remain in this state even if not data istransmitted (controlled by timer)
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PDP Contexts
Packet Data Protocol (PDP)
Session
Logical tunnel between MS and GGSN
Anchored GGSN for session
PDP activities
Activation Modification
Deactivation
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PDP Context Procedures
MS initiated
MS BSS SGSN GGSN
Activate PDP Context Request
Create PDP Context
Request
Create PDP Context
Response
Activate PDP Context Accept
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PDP Context Procedures
GGSN initiated
MS BSS SGSN GGSN
Activate PDP Context RequestCreate PDP Context
Request
Create PDP Context
ResponseActivate PDP Context Accept
Packets from ext. nw.
PDU notification req.
PDU notification resp.
Request PDP Context activation
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Secondary PDP Contexts
Used when the QoS requirements differ from
Primary PDP Context
Same IP address
Same APN
E.g., for IMS; signaling on primary PDP
context and user data on secondary PDPcontext
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The end... (a bit sudden?)
Thanks for listening on our ?SBPSCH? ;)
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