Microsoft PowerPoint - Broadcast Approach for UMTS Mobility Database Recovery.pptBroadcast Approach for UMTS Mobility Broadcast Approach for UMTS Mobility Database RecoveryDatabase Recovery
Sok-Ian Sou (),
CT-2
(,,,)
• Provide end-to-end packet-switched services
• GPRS standard Initialized by ETSI/SMG in 1994 The main set of GPRS specifications was approved by SMG#25 in 1997. Completed in 1999
• GPRS core network is designed for GSM, IS- 136, and 3G.
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• New radio channels are defined.
• The allocation of these channels is flexible. One ~ eight time slots Several active users can share a single time slot. The uplinks and the downlinks are allocated separately. 4 radio channel coding schemes
• 9 Kbps ~ 150 Kbps GPRS fast reservation
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• The core network consists of two service domains:
Circuit-switched service (CS) domain Packet-switched service (PS) domain
• Note that a GPRS MS can be IMSI-attached and GPRS-attached GPRS-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:
• Session Management Packet Data Protocol context, PDP Context PDP Context Activation, Deactivation, PDP Context Modification Quality-of-service (QoS) profile
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MM Context PDP Context
GPRS Attach Procedure
• Step 1: Both the MM states in MS and the SGSN are moved to the READY state.
• Step 2: An MM context (Mobility Management context) is created in each of MS and SGSN.
• Step 3: Authentication/Ciphering may be performed.
• Step 4: A logical link is established between MS and SGSN.
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Mobility Management (MM) Context
• The MM context consists MM state Other MM-related information:Routing area, cell identity, VLR number, P-TMSI, MSISDN, IMSI. Both in MS and SGSN
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• Three states in the state machine
IDLE: MS is not known to GPRS. STANDBY: MS is attached to GPRS. MS is tracked by the SGSN at the RA level. READY: MS is tracked at the cell level. Packet data units can only be delivered in this state.
Idle
Standby
Ready
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Mobility Management Finite State Machine (1/2) • T1 (Idle→Ready): MS perform
GPRS attach.
• T4 (Ready→Standby): a Ready timer is timeout.
• T5 (Standby→Idle): when tracking of MS is lost.
Idle
Standby
Ready
T1
T3T4
T5
T2
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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 affect the 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
PDP (Packet Data Protocol)
• To create a data transmission path, MS initiate PDP Context Activation procedure.
Two PDP states: ACTIVE or INACTIVE. PDP context in ACTIVE state contains mapping and routing information for packet transmission between MS and GGSN.
• The PDP contexts stored in MS, HLR, SGSN, and GGSN.
Active
Inactive
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GGSN
RNC
4 5
SGSN: Serving GPRS Support Node MS: Mobile Station RNC: Radio Network Controller Node B: Base Station CBC: 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, an MS performs the RA update procedure.
MS SGSN
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 MM context 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 a recovered SGSN, a specific broadcast message “MM Reset” issued from the OMC.
• The MSs in the serving area of the SGSN listen to 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 L3 message where the MM Reset information is carried in the reserved field.
• The delivery path is (1) (2) (3)
MS UTRAN SGSN
1. Restart Indication
OMC
3.2 PS Attach Accept (P-TMSI)
3.3 PS Attach Complete
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Broadcast Approach through CBCH
• The second method utilizes the CBC to deliver a SIM-specific broadcast 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
3.2 PS Attach Accept (P-TMSI)
3.3 PS Attach Complete
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Analytic Model
• Input Parameters Tr : the fixed retransmitted period Nr : the maximal number of retransmissions µB : the rate that a wireless link is in Bad state µG : the rate that a wireless link is in Good state λu : the normal SGSN registration rate λp : 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 the MM context of the MS is re-established
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µ µ µ µ
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where
u r
L fT u B G BB BB
P P e e PE N P P e P
λ λ
− −
−
− − − = − + + − −
P e µ µµ µ µ µ
− + = + +
µG = 10µB, VB = 1/µB 2 and VG = 1/µG
2
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• Tr = 5/µB, VB = 1/µB 2 and VG = 1/µG
2
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• Nr=2, µG = 10µB, VB = 1/µB 2, VG = 1/µG
2 and 1/λp = 5/µB
• Tr=5/µB, µG = 10µB, VB = 1/µB 2, VG = 1/µG
2 and 1/λp = 5/µB
Conclusions • We studied the UMTS mobility database recovery.
• We described a broadcast approach that allows the MS to detect lost MM context in SGSN, and speeds up the process for SGSN recovery.
• A broadcast message is periodically retransmitted Nr times with period Tr.
• Pf decreases as Tr increases, Pf decreases as the rate µB increases.
• When Nr=0, Pf is not affected by the variance VB and VG. For Nr>0, Pf is significant increases when VB (or VG) increases.