gprsivar
TRANSCRIPT
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General Packet Radio Service(GPRS)
Mobile Telematics 2004
Ivar Jørstad
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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 packet
switched 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
Netwo
k
Se
v¡
ce
Iu-ps
Gb
Um
MS
Relay
GERAN SGSN
/ Ack UnackRLC
MACMAC
/ Ack UnackRLC
Common protocols
Iu influenced protocols
Gb influenced protocols
FRIP
L2FR
BSSGP
Netwo¢ k
Se¢ v £ ce
IP
L2
L1L1L1
GTP-U
L2
UDP/IP
L1
GTP-U
L2
UDP/IP
As defined in
Iu Specs.
As defined in
Iu 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/UnackRLC
MACMAC
Ack/UnackRLC
Common p¥ otocols
¦ u in§ luenced p ¥ otocols
Gbin § luenced p ¥ otocols
FRIP
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/UnackRLC
MACMAC
Ack/UnackRLC
Common p© otocols
u in luenced p © otocols
Gbin luenced p © otocols
FRIP
L2FR
BSSGP
Network
Service
IP
L2
L1L1
LAPDm LAPDm
RRRRC
L2
L1
RANAP
SCCP
As Defined
in 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 (P AGCH)
± 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 or multiplexing 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
± OneP
hase Access, or ± Two Phase Access
MS BSS MS BSS
P ACKET CHANNEL REQUESTPRACH
P ACKET UPLINK ASSIGNMENT P AGCH
TBF Est. By MS: One Phase Access
P ACKET CHANNEL REQUESTPRACH
P ACKET RESOURCE REQUESTP ACCH
P ACKET UPLINK ASSIGNMENT P ACCH
TBF Est. By MS: Two Phase Access
P ACKET UPLINK ASSIGNMENT P AGCH
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MAC: TBF Establishment
Network initiated
MS BSS
P ACKET P AGING REQUEST PPCH
P ACKET CHANNEL REQUESTPRACH
P ACKET P AGING RESPONSEP ACCH
P ACKET DOWNLINK ASSIGNMENT P ACCH or P AGCH
TBF Est. By Network
P ACKET IMMEDIATE ASSIGNMENT P AGCH
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MAC: Channel Access & Resource
Allocation
Slotted Aloha
± Used inP
RACH MSs send packets in uplink direction at the beginning of
a 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 Allocation
1. MS finds it¶s USF in RLC/MAC PDU header. On the next uplinkblock:
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 of resources
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 Level Agreements
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 ³Station´ 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 logicalP
DP
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
ActivatePDP Context Request
Create PDP ContextRequest
CreateP
DP
ContextResponse
ActivatePDP Context Accept
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PDP Context Procedures
GGSN initiated
MS BSS SGSN GGSN
ActivatePDP Context RequestCreate PDP ContextRequest
Create PDP Context
Response ActivatePDP 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 PDP context
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The end... (a bit sudden?)
Thanks for listening on our ?SBPSCH? ;)