Broadcast Approach for UMTS Mobility Database Recovery (蘇淑茵)

8/14/2019 Broadcast Approach for UMTS Mobility Database Recovery ( )

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Broadcast Approach for UMTS MobilityBroadcast Approach for UMTS Mobility

Database RecoveryDatabase Recovery

Sok-Ian Sou (),EE, NCKU


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Outlines

Background GPRS MM/SM

Broadcast Approach

Analytic Model

Numerical Results

Conclusions


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BackgroundBackground


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94 97 98 1999 2000 2002

CT-2

(,,,)

Fixed Line

96 2005

3G MNP

Source:

2007:WiMAX


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Introduction (1/ 2)

Based on the existing GSM infrastructure

Provide end-to-end packet-switched services

GPRS standard

Initialized by ETSI/SMG in 1994

The main set of GPRS specifications wasapproved by SMG#25 in 1997.

Completed in 1999

GPRS core network is designed for GSM, IS-136, and 3G.


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Introduction (2/ 2)

New radio channels are defined.

The allocation of these channels is flexible.

One ~ eighttime slots

Several active users can share a single time slot.

Theuplinks and the downlinks are allocatedseparately.

4 radiochannel coding schemes

9 Kbps ~ 150 Kbps

GPRS fast reservation


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GPRS System

GPRS

PSTN

HLR

SGSN GGSN

Gb

Gn Gi

GSM

PCU

BSS

GatewayMSC/VLR

VisitedMSC/VLR


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GPRS MM/ SMGPRS MM/ SM


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GPRS Service Domain

The core network consists of two servicedomains:

Circuit-switched service (CS) domain

Packet-switched service (PS) domain

Note that a GPRS MS can be

IMSI-attached and GPRS-attachedGPRS-attached only

IMSI-attached only

The IMSI attach is the same as that for a GSM MS.


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GPRS MM/ SM To transfer a packet in PS domain, two

important issues:

Mobility Management

Mobility Management context, MM context

Attach, Detach, Routing Area Update,

Security

Session Management

Packet Data Protocol context, PDP Context

PDP Context Activation, Deactivation, PDPContext Modification

Quality-of-service (QoS) profile


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MM Context v.s. PDP Context

MM Context

PDP Context

QoS Profile

PDP Context

QoS Profile

PDP Context

QoS Profile


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GPRS Attach Procedure

Step 1: Both the MM states in MS and theSGSN are moved to the READY state.

Step 2: An MM context (Mobility Managementcontext) is created in each of MS and SGSN.

Step 3: Authentication/Ciphering may beperformed.

Step 4: A logical link is established between MSand SGSN.


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Mobility Management (MM) Context The MM context consists

MM state

OtherMM-related information:Routing area, cellidentity, VLR number, P-TMSI, MSISDN, IMSI.

Both inMSandSGSN


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Mobility Management State

Three states in the state

machine IDLE: MS is not known

to GPRS.

STANDBY: MS isattached to GPRS. MS istracked by the SGSN atthe RA level.

READY: MS is trackedat the cell level. Packetdata units can only bedelivered in this state.

Idle

Standby

Ready


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Mobility Management Finite

State Machine (1/ 2) T1 (IdleReady): MS perform

GPRS attach.

T2 (ReadyIdle): MS isdetached from the GPRS.

T3 (StandbyReady): MSsends a packet to SGSN.

T4 (ReadyStandby): a Readytimer is timeout.

T5 (StandbyIdle): when

tracking of MS is lost.

Idle

Standby

Ready

T1

T3T4

T5

T2


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SGSNSGSN

Location updateLocation update

Cell changedCell changed

READY StateREADY State

RARA

SGSNSGSN

Location updateLocation update

STANDBY StateSTANDBY State

RA changedRA changed

Low paging costLow paging cost

High location update costHigh location update cost

High paging costHigh paging cost

Low location update costLow location update cost

The transitions from cell tracking to RA tracking affectthe location update and paging signaling cost.

Location Update vs. Paging


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Mobility Management Finite

State State (2/ 2) Exercised in both the SGSN and the MS.

In Mobility Management Context

MM

context

MM

context

MS SGSN

dataHTTP session

ReadyStandbyReady ReadyStandby

PDP content

activation

PDP content

Deactivation


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PDP (Packet Data Protocol)

To create a data transmission path,MS initiate PDP Context Activation

procedure. Two PDP states:ACTIVEorINACTIVE.

PDP context in ACTIVE state contains

mapping and routing informationforpacket transmission between MS andGGSN.

The PDP contexts stored in MS, HLR,

SGSN, and GGSN.

Active

Inactive


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3G and B3G Architecture (1/ 2)


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3G and B3G Architecture (2/ 2)

GGSN

RNC

3GPP R6

= user plane

SGSN

NodeB

GGSN

3GPP R7

NodeB

RNC

Directtunnel

GGSN

HSPA

BTS with

RNCfunct.

Directtunnel

SGSN

= control plane

SGSN


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Broadcast ApproachBroadcast Approach


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UMTS Broadcasting Architecture

signalingsignaling and data

f

a

MS

RA2

MS

RA2

Node B

Node B

RNC

UTRAN

d

e

SGSN

1OMC

CBC

2

2

3

3

4

5

SGSN: Serving GPRS Support Node MS: Mobile Station

RNC: Radio Network Controller Node B: Base StationCBC: Cell Broadcast Center RA: Routing Area

UTRAN: UMTS Terrestrial Radio Access Network

OMC: Operations and Maintenance Center

b


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Message Flow for the Registration of MS

Suppose that after the SGSN has restarted, anMS performs the RA update procedure.

MS SGSN

2.1 PS Attach Request (IMSI)

2.2 PS Attach Accept (P-TMSI)

1.1 Routing Area Update Request (P-TMSI)

1.2 Routing Area Update Reject (Network Failure)

2.3 PS Attach Complete

If the MS is smart enough to detect that the MMcontext does not exist in the SGSN, it can directly

perform PS attach without executing RA update.


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The Broadcast Approach

When the OMC is alerted by the restart of arecovered SGSN, a specific broadcast

message MM Reset issued from the OMC.

The MSs in the serving area of the SGSN listento this message via the broadcast channel.


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Broadcast Approach through

BCCH/PBCCH The first method utilizes the L3 message (RRC SYSTEM

INFORMATION TYPE 3) on the broadcast channel.

Through BCCH/PBCCH, the UTRAN broadcasts this L3message where the MM Reset information is carried in thereserved field.

The delivery path is (1)(2)(3)

MS UTRAN SGSN

1. Restart Indication

(a) MM Reset message sent through BCCH/PBCCH

OMC

2.1 MM Reset2.2 MM Reset(through BCCH/PBCCH)





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Broadcast Approach through CBCH

The second method utilizes the CBC to deliver a SIM-specificbroadcast short message.

Through CBCH, the MM Reset information which in a SIM-based

message is broadcast.

The delivery path is (4)(5)(2)(3)

(b) MM Reset message sent through CBCH

MS CBC SGSN

1. Restart Indication

OMC

2.1 MM Reset2.2 MM Reset

(through CBCH)





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Analytic Model

Input Parameters

Tr: the fixed retransmitted period

Nr

: the maximal number of retransmissions

B: the rate that a wireless link is in Bad state

G: the rate that a wireless link is in Good state

u: the normal SGSN registration rate

p: the incoming packets arrival rate

Output Measures

Pf: the probability that the MS fails to receive the

MM Reset message with Nr+1 transmissions E[NL] : the expected number of lost packets

between when the SGSN restarts and when theMM context of the MS is re-established


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Derivation for Pf

( ) r B G r N

T

G G Bf

B G B G

eP

+ +=

+ +

The output measure Pf is derived as


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Derivation for E[NL]

The output measure E[NL] is derived as

where

(1 ) 1 [1 ( ) ][ ]

1 1

u r u r r r

u r

T TN Np G BB BB BB

L fT

u B G BB BB

P P e e P E N P

P e P

= +

+

( )1 B G r T

BB B BB G

P e

+ = + +


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Effects ofTrand Nron Pf

G= 10B, VB= 1/B2 and VG= 1/G

2


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Effects ofB on Pf Tr= 5/B, VB= 1/B

2 and VG= 1/G2


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Effects ofVB on Pf

Tr= 5/Band G= 10B


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Effects ofTron E[NL]

Nr=2, G= 10B, VB= 1/B2, VG= 1/G

2 and

1/p= 5/B


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Effects ofNron E[NL]

Tr=5/B, G= 10B, VB= 1/B2, VG= 1/G

2 and

1/p= 5/B


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Conclusions

We studied the UMTS mobility database recovery.

We described a broadcast approach that allows the MS todetect lost MM context in SGSN, and speeds up the process

for SGSN recovery.

A broadcast message is periodically retransmitted Nr timeswith period Tr.

Pfdecreases as Tr increases, Pfdecreases as the rate Bincreases.

When Nr=0, Pf is not affected by the variance VBand VG. ForNr>0, Pf is significant increases when VB(or VG) increases.

E[NL] is a decreasing function of the normal SGSN

registration rate u, E[NL] decreases as Nr increases.

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Broadcast Approach for UMTS Mobility Database Recovery (蘇淑茵)