Telecommunication Basics(GPRS Network)

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IS-95 A IS-95 B

GSM GPRS

CDMA-1X

EV-DV

CDMA-1XEV-DO r0

W-CDMA R3

W-CDMA R5

(HSCPA)

CDMA-1XEV-DO rA

W-CDMA R6

(HSUPA)

CDMA-1XEV-DO rB

W-CDMAR7

(HSPA+)

LTEEDGE

UMB

W-CDMAHSPA+Phase2

AMPS

NMT

LTE Advanced

802.15e Wave1(Mobile WiMAX)

802.15e Wave2(Mobile WiMAX)

802.16eWiMAX R1.5

802.16nWiMAX R2.0

GSM track

CDMA track

WiMAX track

What is GPRS ?

GPRS (General Packet Radio Service)

Part of GSM phase 2+

Required many new network elements into NSS

Provides connections to external packet data networks (Internet, X.25)

Benefits

Resources are reserved only when needed and charged accordingly

Connection setup times are reduces

Enables new services opportunities

General = Not restricted to GSM use

Packet Radio = Enable Packet mode communication over air

Service = Not System, Existing BSS (Partially also NSS) infrastructure is used

GPRS Characteristics

GPRS uses packet switched resource allocation

Resource allocated only when data is to be sent/received

Flexible channel allocation

One to eight time slots

Available resources shared by active users

Up and Down link channels reserved separately

GPRS and circuit switched GSM services can use same time slots alternatively

Traffic characteristics suitable for GPRS

Intermittent, busty data transmissions

Frequent transmissions of small volumes of data

Infrequent transmission of larger volumes of data

GPRS Architecture

BTS

BSC

UmPSTN

SS7Network

DataNetwork(Internet)

DataNetwork(X.25)

Local areaNetwork

Local areaNetwork

Coperate1Server

Coperate2Server

SMS-GMSC

Gd

HLR/AuCGr

EIR

MAP-F

Router

Router

MSC

Inter-PLMNBackboneNetwork

Gp

Gi.IP

Gi.X.25

Intra-PLMNBackboneNetwork

(IP Based)

GdGr

Gs

Gb

Gn

Serving GPRSSupport Node(SGSN)

BorderGateway (BG)

Point-To-MultipointService Center

(PTM-SC)

Gn

Gateway GPRSSupport Node

(GGSN)

GSM to GPRS

Interfaces

Radio Interface Protocols

2 Plane

User plane

Control Plane

3 Layers

Layer 1 : Physical (PHY)

Layer 2 :

Data Link

Media Access Control (MAC)

Radio Link Control (RLC)

Packet Data Convergence Protocol (PDCP)

Layer 3 :

Radio Resource Control (RRC) for lu mode

Radio Resource (RR) for A/Gb mode

Protocol Stack

GPRS Control Plane Protocol Stack

GMM/SM (New in GPRS)

GPRS Mobility Management and Session Management

GPRS Attach/Detach

PDP Context 구성 및 해제

GPRS 단말 위치 갱신 – Routing Area Update/Location Update

인증

Radio Resource Assign

LLC

GMM/SM

GSM RF

Um Gb

MAC

RLC

LLCRelay

GSM RF

NetworkService

MAC

RLC BSSGP

L1bis

BSSGP

NetworkService

LLC

GMM/SM

L1bis

MS BSS (PCU) SGSN

Protocol Stack

GPRS Traffic Protocol Stack

IP/X.25

LLC

SNDCP

GSM RF

Application

Um GnGb

MAC

RLC

IP/X.25

GTP

L1

L2

LLC

GSM RF

Frame RelayMAC

RLC BSSGP

L1bis

BSSGP

Frame Relay

LLC

SNDCP GTP

L1bis L1

L2

IP

MS BSS (PCU) SGSN GGSN Gi

IP

UDP/TCP UDP/TCP

END

NODE

X.25IP

Assignment of functions

Function MS BSS SGSN GGSN HLR

Network Access Control

Registration √

Authentication and Authorization √ √ √

Admission Control √ √ √

Message Screening √

Charging Data Collection √ √

Packet Routing & Transfer

Relay √ √ √ √

Routing √ √ √ √

Addressing Translation and Mapping √ √ √

Encapsulation √ √ √

Tunneling √ √

Compression √

Ciphering √ √ √

Mobility Management √ √ √ √

Logical Link Management

Logical Link Establishment √ √

Logical Link Maintenance √ √

Logical Link Release √ √

Radio Resource Management

Um Management √ √

Cell Selection √ √

Um-T ranx √ √

Path Management √ √

Gateway GPRS Support Node

Typically located at one of the MSC sites

One (or few) per operator

Main functions

Interface to external data networks

Resembles to a data network router

Forwards end user data to right SGSN

Converts the GPRS packets from SGSN to the PDP format

Routes mobile originated packets to right destination

Converts PDP addresses change to GSM addresses of the destination user

Filters end user traffic

Collects charging information for data network usage

Data packets are not sent to MS unless the user has activated the PDP address

Performs authentication

Many-to-many relations among SGSNs & GGSNs

Serving GPRS Support Node

Functionally connected with BSC, physically can be at MSC or BSC

site

One for few BSCs or one (or few) per every BSC

One SGSN can support BSCs of several MSC sites

Main functions

Delivers data packets to mobile stations & vice-versa

Authenticates GPRS mobiles / Maintain user profile

Handles mobile’s registration in GPRS network

Handles mobile’s mobility management / Packet Routing, Transfer

Relays MO and MT data traffic

TCP/IP header compression, V.42bis data compression, error control MS- SGSN (ARQ)

Collect charging information of air interface usage

Other Elements

Entity Functionality

BG(Border Gateway)

Not defined within GPRS

Routes packets from SGSN/GGSN of one operator to a SGSN/GGSN of an other

operator

Provides protection against intruders from external networks

DNS(Domain Name Server)

Translates addresses from ggsn1.oper1.fi-format to 123.45.67.98 format

Charging Gateway Collects charging information from SGSNs and GGSNs

PTM-SC(Point to Multipoint-Service Center)

PTM Multicast (PTM-M)

- Downlink broadcast, No subscription, No Ciphered

PTM Group call (PTM-G)

- Closed or open groups, Down/Up link, Ciphered

Geographical area limitation

GPRS Backbones

GPRS Backbones

Enables communication between GPRS Support Nodes based on private IP

Network

IPv6 is the ultimate protocol

IPv4 can be used as an intermediate solution

Intra-PLMN backbone

Connect GPRS Support Nodes of one operator

Operator decides the network architecture

LAN, Point-to-Point links, ATM, ISDN, …

Inter-PLMN backbone

Connects GPRS operators via BGs

Provides international GPRS roaming

Operators decide the backbone in the roaming agreement

Physical Channels

FDMA + TDMA

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 support

Packet Data Channel (PDCH)

Dedicated to packet data traffic from logical channels (Refer Next Slide)

Control

User data

Logical Channels

Mapped by the MAC to physical channels

Control channels for control, synchronization and signalingCommon/Dedicated/Broadcast

Packet Traffic ChannelsEncoded speech/Encoded data

Packet Data Logical Channels

PDTCHPDCCHPCCCH PBCCH

Traffic Channels

[Up]

PDTCH/DPDTCH/HPACCHPTCCH/DPTCCH/UPBCCHPACCHPTCCH/DPTCCH/UPTCCH/U

Control Channels

[Down] [Down] [Down][Down] [Down] [Down][Up] [Up][Up/Down]

PPCH = Packet Paging ChannelPAGCH = Packet Access Grant ChannelPNCH = Packet Notification ChannelPACCH = Packet Associated Control ChannelPTCCH = Packet Timing Advance Control Channel

PCCCH = Packet Common Control ChannelPBCCH = Packet Broadcast Control ChannelPDCCH = Packet Dedicated Control ChannelPDTCH = Packet Traffic ChannelPRACH = Packet Random Access Channel

Up = Uplink DirectionDown = Downlink Direction

Control Channels

Packet Common Control Channel (PCCCH)

Paging (PPCH)

Random Access (PRACH)

Grant (PAGCH)

Packet Notification (PNCH)

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

Packet Traffic Channels

TCH

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 (Gaussian Minimum Shift Keying) = MSK + Gaussian filter

8-PSK

GPRS Mobile Types

A/Gb mode

lu mode

Class Description

Class A Simultaneous GPRS and conventional GSM operation

Supports simultaneous circuit switched and GPRS data transfer

Class B

Can be attached to both GPRS and conventional GSM services simultaneously

Can listen circuit switched and GPRS pages (via GPRS)

Supports either circuit switched calls or GPRS data transfer but not simultaneous communication

Most common for handsets today

Class C

Alternatively attached in GPRS or conventional GSM

No simultaneous operation

‘GPRS only’ mobiles also possible (e.g. for telemetric applications)

E.g. expansion cards for laptops

Mode Description

CS/PS Same as Class A in A/Gb mode

PS MS can only operate packet switched services

CS MS can only operate circuit switched services

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

IP Multimedia Subsystem

Simultaneous access to multiple different types of real-time and non-real-time

traffic

IMS provides synchronization between such components

Mobility Management (1/2)

3 different state

Data can only be transmitted in the ACTIVE state

State Description

IDLE

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

STANDBY

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 locations to the SGSN and enters the ACTIVE state

ACTIVE

SGSN knows the cell of the MS

PDP contexts can be activated/deactivated

Can remain in this state even if not data is transmitted (controlled by timer)

Mobility Management (2/2)

Mobility Management Message

Cell update

When MS changes the cell within a Routing Area in READY state

Routing Area update

When MS changes the cell between Routing Area in READY or STANDBY state

Two types of Routing Area Updates

from MS’s point of view only one type

Intra-SGSN Routing Area Update

Inter-SGSN Routing Area Update

Periodic Routing Area updates are applicable

PDP Contexts

Packet Data Protocol (PDP)

Session

Logical tunnel between MS and GGSN

Anchored GGSN for Session

PDP activities

Activation

GGSN에게 단말의 존재를 알림

GPRS Data 수신/전송을 위해 (Session 이용을 위해), 반드시 IP 할당이 필요하며,

IP 주소 등을 할당하는 과장

Modification

Deactivation

PDP Context Procedures

MS initiated

GGSN initiated

Activate PDP Context Request

Create PDP Context Request

Create PDP Context Response

Activate PDP Context Accept

MS BSS GGSNSGSN

MS BSS GGSNSGSN

Packet from ext. nw.PDU Notification Request

PDU Notification Response

Activate PDP Context Activation

Activate PDP Context RequestCreate PDP Context Request

Create PDP Context Response

Activate PDP Context Accept

GPRS Call Scenario 1

GPRS Attach

MS BSS HLR/AuCSGSN

PreviousSGSN

Packet Channel Request

Packet Uplink Assignment

RLC Block (attach request)Attach Request

Send Authentication Info.

Send Authentication Info RRPacket Control

Acknowledgment Authentication andCiphering Request

Packet Downlink Assignment

RLC blocks (Authentication and Ciphering Request)

Packet Downlink Ack

Packet Channel Request

Packet Uplink Assignment

RLC blocks (Authentication and Ciphering Response)

Packet Uplink Ack

Packet ControlAcknowledgement

Authentication andCiphering Response Update GPRS Location Cancel Location

Cancel Location RRInsert Subscriber Data

Insert Subscriber Data RR

Update GPRS Location RRAttach Accept

RLC blocks (Attach accept)

Packet Downlink Ack

Packet Downlink Reponses

Packet Uplink Assignment

RLC blocks (Attach complete)

Packet Uplink Ack Attach Complete

Packet Control Acknowledgement

GPRS Call Scenario 2

GPRS/GSM Attach

MS BSS

HLR/AuCSGSN

MSC/VLR

PreviousMSC/VLR

PreviousHLR/AuC

Attach RequestSend Authentication Info

Send Authentication Info RR

Authentication and Ciphering Request

Authentication and Ciphering Response

Update GPRS LocationCancel Location

Cancel Location RR

Insert Subscriber Data

Insert Subscriber Data RR

Update GPRS Location RR

Update Location Request

Update Location

Cancel Location

Cancel Location RR

Insert Subscriber Data

Insert Subscriber Data RR

Update Location RR

Update Location Accept

Attach Accept

Attach Complete

GPRS Call Scenario 3

RA update

MS BSSHLRNew

SGSNOld

SGSN GGSN

Routing Area Update Request

SGSN Context Request

SGSN Context Response

Authentication and Ciphering Authentication and Ciphering

SGSN Context Acknowledge

Forward Buffered PDUs

Update PDP Context Request

Update PDP Context Response

Update GPRS Location

Cancel Location

Insert Subscriber Data

Insert Subscriber Data RR

Update Subscriber Data RR

Routing Area Update Accept

Routing Area Update Complete

[별첨] GSM vs. GPRS

Initial Call Process Time (s)

GSM Call 4

Train Model 30

Login and Authenticate 11

Download mail 180

Total 3min 45s

Subsequent Call

Repeat Above 3min 45s

Initial Call Process Time (s)

GPRS Call 4

Login and Authenticate 11

Download mail 180

Total 3min 45s

Subsequent Call

Not applicable – Permanent Virtual Circuit

0

Email via GSM Email via GPRS

User Modem ModemEmailServer

EmailServer

GSM PSTN Internet GPRS Internet

Auth.Server

Auth.Server

VirtualGPRS

Data Tunnel

AuthenticatedPath to Email

Server