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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)
3.2 PS Attach Accept (P-TMSI)
3.3 PS Attach Complete
3.1 PS Attach Request (IMSI)
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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)
3.2 PS Attach Accept (P-TMSI)
3.3 PS Attach Complete
3.1 PS Attach Request (IMSI)
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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.