gprs channel information

7/29/2019 GPRS channel information

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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



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



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 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 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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