Broadcast Approach for UMTS Mobility Database Recovery. Sok-Ian Sou ( 蘇淑茵 ), EE, NCKU

Transcription

1 Broadcast Approach for UMTS Mobility Database Recovery Sok-Ian Sou ( 蘇淑茵 ), EE, NCKU 1

2 Outlines Background GPRS MM/SM Broadcast Approach Analytic Model Numerical Results Conclusions 2

3 Background 3

4 台灣電信業務開放近程 開放 CT-2 開放四項行動通信業務 ( 行動電話, 呼叫器, 行動數據, 特哥大 ) 3G MNP 2007: WiMAX Fixed Line Source: 中華電信研究所 4

5 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 was approved by SMG#25 in Completed in 1999 GPRS core network is designed for GSM, IS- 136, and 3G. 5

6 Introduction (2/2) 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 6

7 GPRS System GSM Visited MSC/VLR Gateway MSC/VLR PSTN BSS HLR PCU Gb SGSN Gn GGSN Gi 外部數據網路 GPRS 7

8 GPRS MM/SM 8

9 GPRS Service Domain 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. 9

10 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, PDP Context Modification Quality-of-service (QoS) profile 10

11 MM Context v.s. PDP Context MM Context PDP Context PDP Context QoS Profile PDP Context QoS Profile QoS Profile 11

12 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. 12

13 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 13

14 Mobility Management State 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 14

15 Mobility Management Finite State Machine (1/2) T1 (Idle Ready): MS perform GPRS attach. T2 (Ready Idle): MS is detached from the GPRS. T3 (Standby Ready): MS sends a packet to SGSN. T4 (Ready Standby): a Ready timer is timeout. T5 (Standby Idle): when tracking of MS is lost. T1 Idle T5 Standby T4 T3 Ready T2 15

16 Location Update vs. Paging The transitions from cell tracking to RA tracking affect the location update and paging signaling cost. READY State SGSN STANDBY State SGSN Location update Cell changed Low paging cost High location update cost High paging cost Location update Low location update cost RA changed RA 16

17 Mobility Management Finite State State (2/2) Exercised in both the SGSN and the MS. In Mobility Management Context MS MM context MM context SGSN PDP content activation HTTP session PDP content Deactivation data Ready Standby Ready Standby Ready 17

18 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. Active Inactive The PDP contexts stored in MS, HLR, SGSN, and GGSN. 18

19 3G and B3G Architecture (1/2) 19

20 3G and B3G Architecture (2/2) 3GPP R7 3GPP R6 HSPA GGSN SGSN GGSN SGSN Direct tunnel RNC RNC NodeB NodeB GGSN SGSN Direct tunnel BTS with RNC funct. = control plane = user plane 20

21 Broadcast Approach 21

22 UMTS Broadcasting Architecture signaling signaling and data UTRAN e CBC RA2 MS RA2 MS b 3 3 Node B Node B 2 2 d RNC 5 1 f 4 OMC a SGSN 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 22

23 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) 2.1 PS Attach Request (IMSI) 2.2 PS Attach Accept (P-TMSI) 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. 23

24 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. 24

25 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 OMC SGSN 2.2 MM Reset (through BCCH/PBCCH) 2.1 MM Reset 1. Restart Indication 3.1 PS Attach Request (IMSI) 3.2 PS Attach Accept (P-TMSI) 3.3 PS Attach Complete (a) MM Reset message sent through BCCH/PBCCH 25

26 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) MS CBC OMC SGSN 2.2 MM Reset (through CBCH) 2.1 MM Reset 1. Restart Indication 3.1 PS Attach Request (IMSI) 3.2 PS Attach Accept (P-TMSI) 3.3 PS Attach Complete (b) MM Reset message sent through CBCH 26

27 Analytic Model Input Parameters T r : the fixed retransmitted period N r : the maximal number of retransmissions µ B : the rate that a wireless link is in Bad state µ G : the rate that a wireless link is in Good state λ u : the normal SGSN registration rate λ p : the incoming packets arrival rate Output Measures P f : the probability that the MS fails to receive the MM Reset message with N r +1 transmissions E[N L ] : the expected number of lost packets between when the SGSN restarts and when the MM context of the MS is re-established 27

28 Derivation for P f The output measure P f is derived as P f ( µ ) Nr B+ µ G Tr µ G µ G + µ Be = µ B + µ G µ B + µ G 28

29 Derivation for E[N L ] The output measure E[N L ] is derived as Nr λutr λutr Nr λ p µ G(1 PBB) 1 PBB e [1 ( e PBB ) ] EN [ L ] = P λ f ut + r λ u µ B + µ G 1 PBB 1 e PBB where 1 ( B G) Tr PBB µ B µ Be µ + = + µ µ B µ + G 29

30 Effects of T r and N r on P f µ G = 10µ B, V B = 1/µ B2 and V G = 1/µ G 2 30

31 Effects of µ B on P f T r = 5/µ B, V B = 1/µ B2 and V G = 1/µ G 2 31

32 Effects of V B on P f T r = 5/µ B and µ G = 10µ B 32

33 Effects of T r on E[N L ] N r =2, µ G = 10µ B, V B = 1/µ B2, V G = 1/µ G 2 and 1/λ p = 5/µ B 33

34 Effects of N r on E[N L ] T r =5/µ B, µ G = 10µ B, V B = 1/µ B2, V G = 1/µ G 2 and 1/λ p = 5/µ B 34

35 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 N r times with period T r. P f decreases as T r increases, P f decreases as the rate µ B increases. When N r =0, P f is not affected by the variance V B and V G. For N r >0, P f is significant increases when V B (or V G ) increases. E[N L ] is a decreasing function of the normal SGSN registration rate λ u, E[N L ] decreases as N r increases. 35