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CAMEL in GPRS prepaid service

ghlee@alumni.csie.nctu.edu.tw

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Outline Evolution of IN GPRS overview CAMEL in GPRS Discussion

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Plain Old Telephone Service Service logic were hardwired in switching systems. Network operators discuss services customers

required with switch vendors. (no standard) Once services were implemented, they were not

easily modified.

service logichardwired

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Stored Program Control In the mid-1960s, stored program control

(SPC) switching systems were introduced. As a result, it was easier to introduce new

services. Service logic was not modular.

service logicprogrammable

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Common Channel Signaling In the mid-1970s, common channel signaling network

(CCSN) was introduced. Signaling system number 7 (SS7) is the protocol that

runs over the CCSN. SS7 network separates the call setup information and

talk path from the common trunk that runs between switching systems.

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SS7 network components signal switching points (SSPs)—SSPs are telephone switch

es equipped with SS7-capable software and terminating signaling links. They generally originate, terminate, or switch calls.

signal transfer points (STPs)—STPs are the packet switches of the SS7 network. They receive and route incoming signaling messages to destination.

signal control points (SCPs)—SCPs are databases providing information necessary for advanced call-processing capabilities

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SS7 network

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The Introduction of IN During the mid-1980s, Telcordia Technologies resp

onded to RBOCs’s request and developed the concept of Intelligent Network 1 (IN/1).

Service logic splits from switching system, now resides in service control points (SCP).

service logicnow here

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Call Model PICs represent switching system states that a call goes throug

h from origination to termination. SSPs check TDPs to see if there are any active triggers. If an active trigger is detected, normal switching system call pr

ocessing is suspended until the SSP and SCP complete communications.

SSP suspended,and ask SCP what to do in next step

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GPRS logical architecture

Gf

Uu

Um

D

Gi

Gn

Iu Gc

C E

Gp

Gs

Signalling and Data Transfer Interface

Signalling Interface

MSC/VLR

TE MT UTRAN TE PDN

Gr Iu

HLR

Other PLMN

SGSN

GGSN

Gd

SM-SC SMS-GMSC

SMS-IWMSC

GGSN

EIR SGSN

Gn CGF

Ga Ga

Billing System

Gb

TE MT BSS

R

A

R

CAMEL GSM-SCF

Ge

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Transmission plane in 2.5G

Relay

NetworkService

GTP-U

Application

IP

SNDCP

LLC

RLC

MAC

GSM RF

SNDCP

LLC

BSSGP

L1bis

RLC

MAC

GSM RF

BSSGP

L1bis

Relay

L2

L1

IP

L2

L1

IP

GTP-U

IP

Um Gb Gn GiMS BSS SGSN GGSN

NetworkService

UDPUDP

Frame relay

Radio dep

Radio indep

Multiplexing layer

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Signaling plane in 2.5G

BSSGPRelay

GMM/SM

LLC

RLC

MAC

GSM RF

GMM/SM

LLC

BSSGP

L1bis

Um GbMS BSS 2G-SGSN

NetworkService

RLC

MAC

GSM RF L1bis

NetworkService

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Multiplexing of network protocols

Packet DataProtocol

SNDCP

LLC Information

Signalling SMS

LLC

NSAPI

NSAPI + Control

DataControl

SNDC Header

LLC Header

TLLI

RLC or BSSGP

Data

N-PDU

SAPI

IP/X.25

Transmission planeSignaling plane

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User plane in 3G

L1

RLC

PDCP

MAC

E.g., IP,PPP

Application

L1

RLC

PDCP

MAC

ATM

UDP/IP

GTP-U

AAL5

Relay

L1

UDP/IP

L2

GTP-U

E.g., IP,PPP

3G-SGSNUTRANMS

Iu-PSUu Gn Gi

3G-GGSN

ATM

UDP/IP

GTP-U

AAL5

L1

UDP/IP

GTP-U

L2

Relay

ATM

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Control plane in 3G

RLC

RRC

L1

GMM /SM / SMS

RRC

MAC

ATM

RANAP

AAL5

Relay

ATM

AAL5

3G SGSNRNSMS

Iu-PsUu

RLC SCCP

SignallingBearer

MAC

L1

SignallingBearer

RANAP

SCCP

GMM /SM / SMS

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CAMEL architectureHLR gsmSCF

MS

Visiting NetworkInterrogating Network

Home Network

CAP

Home/Interrogating/Visiting Network

SGSN

gprsSSF

MAP

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MAP/CAP protocol stack

MAP

TCAP

SCCP

MTP3

MTP2

L1

MAP

TCAP

SCCP

MTP3

MTP2

L1

SGSN HLRGr

CAP has the same underlying protocol stack as MAP. Ge interface is first defined in 3G, but didn’t appea

r in 2.5G.

CAP

TCAP

SCCP

MTP3

MTP2

L1

CAP

TCAP

SCCP

MTP3

MTP2

L1

gprsSSF gsmSCFGe

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Overall CAMEL Architecture

gsmSCF

GPRSDialogueHandler

gprsSSF

SGSN GGSNMobileStation

CAP Interface

Internal CAP Interface

Internal Interface

GTP

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Detection Points (DPs) GPRS events maybe made visible to gsmSC

F. DPs are points at which these events are detected.

DPs can be armed to notify gsmSCF GPRS event was encountered, and to allow gsmSCF to influence subsequent handling of GPRS session/PDP Context.

If DP isn’t armed, processing entity continues processing without gsmSCF involvement at the DP.

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Detection Points (DPs) 3 different types of DP:

Trigger Detection Point-Request (TDP-R)

Event Detection Point-Request (EDP-R) Event Detection Point-Notification

(EDP-N)

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Detection Points (DPs) TDP-R

Statically armed, initiate a CAMEL control relationship When GPRS event is encountered, processing is suspende

d EDP-R

Dynamically armed within CAMEL control relationship When GPRS event is encountered, processing is suspende

d and gprsSSF waits for inst from gsmSCF EDP-N

Dynamically armed within CAMEL control relationship When GPRS event is encountered, processing is not suspe

nded.

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GPRS Attach/Detach State Model

3 DPs are defined: DP Attach DP Change of Position

GPRS session DP Detach

Inter SGSNRouteing areaupdate

Attached

Attach request

Detached

User- or network initiateddetach

AD_Exception

Attach

Detach

Change of Position GPRS Session

Intra SGSN Routeingarea update

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GPRS PDP Context State Model

4 DPs are defined: DP PDP Context Es

tablishment DP PDP Context Es

tablishment Ack DP PDP Context Di

sconnection DP Change of Posi

tion Context

PDP ContextSetup Req

PDP_Context_Setup

PDP_Context_Established

Idle

C_Exception

PDP Context Est.

PDP ContextSetup Ack.

PDP Context Est. Ack.

Routeing area update

User or networkinitiated disc.

PDP ContextDisconnection

Routeing area update

Change ofPosition context

Change of Position Context

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GPRS CAMEL Scenarios 2 scenarios for CAMEL control of GPRS

Scenario 1 Allows CAMEL control of GPRS session and of multiple

PDP contexts within 1 GPRS dialogue Scenario 2

Allows CAMEL control of a single PDP contexts Multiple PDP contexts are controlled via multiple GPR

S dialogues. Scenario 1 and scenario 2 are mutually excl

usive.

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GPRS CAMEL Scenario 1 Involves Attach/Detach state model Uses less resource (tcap dialogue) More complicated when implementation

SGSN / SSP SCP

A/DSM

PDP#2SM

PDP#1SM

GPRS Dialogue

Information flow related toPDP Context #1

Information flow related tothe Session

Information flow related toPDP Context #2

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GPRS CAMEL Scenario 2 Doesn’t involves Attach/Detach state model Uses more resource (tcap dialogue) Simpler when implementation

SGSN / SSP SCP

PDP#2SM

PDP#1SM

GPRS Dialogue #2

Information flow related toPDP context #1

Information flow related toPDP context #2

GPRS Dialogue #1

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GPRS Attach The message sequence chart is too large to fit

in this slide. Please see the supplementary document from 3GPP 23060 spec.

Notice the “Insert subscriber data” procedure, GPRS-CSI (CAMEL Subscription Information) is sent from HLR to SGSN.

2.5G HLR does not keep GPRS-CSI, nor does it send GPRS-CSI to SGSN.

3G HLR could keep GPRS-CSI, also it sends GPRS-CSI when doing “Insert subscriber data” procedure.

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GPRS-CSI GPRS-CSI contains following information

gsmSCF Address Service Key Default GPRS Handling TDP List CAMEL Capability Handling CSI state Notification flag gsmSCF address list for CSI

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PDP Context Activation in 2.5G

C1 :DP for CAMEL_GPRS_PDP_Context_Establishment C2 :DP for CAMEL_GPRS_PDP_Context_Establishment_Acknowledgement

2G-GGSN

9. Activate PDP Context Accept

4. Create PDP Context Response

4. Create PDP Context Request

1. Activate PDP Context Request

2G-SGSNBSS

2. Security Functions

MS

7. BSS Packet Flow Context Procedures

C1

C2

3. Invoke Trace

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PDP Context Activation in 3G

C1 :DP for CAMEL_GPRS_PDP_Context_Establishment. C2 :DP for CAMEL_GPRS_PDP_Context_Establishment_Acknowledgement

3G-GGSN

9. Activate PDP Context Accept

4. Create PDP Context Response

4. Create PDP Context Request

1. Activate PDP Context Request

3G-SGSNUTRANMS

5. Radio Access Bearer Setup

C1

C2

6. Invoke Trace

8. Update PDP Context Response

8. Update PDP Context Request

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CAMEL procedures for charging activities

Procedure ssf -> scf scf ->ssfApplyChargingGPRS -

ApplyChargingReportGPRS

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InitialDPGPRS -

ContinueGPRS -

EventReportGPRS -

RequestReportGPRSEvent

-

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Discussion