GSM 系統簡介及其發展趨勢 期末專題 Introduction to GPRS Mobility Management

1. GSM系統簡介及其發展趨勢期末專題Introduction to GPRS Mobility Management 第 5 組 8717805 陳元凱 8717801 逄愛君 8817530 張哲航 8517011 鄭旭詠 8517019 鄭雅馨 June 19 2000 1 NCTU/CSIE/PCS Lab. 2000/6/19

2. OUTLINE • GPRS Brief • Mobility management • GPRS attach • Location management functions • Cell update • Routing area update • Combined RA/LA update • Conclusion & Discussion

3. GPRS Brief - Logical Architecture

4. GPRS Signalling Plane • Logical Link Control(LLC) • provides a highly reliable ciphered logical link • GPRS Mobility Management and Session Management(GMM/SM) • This protocol supports mobility management functionality such as GPRS attach, GPRS detach, security, routing area(RA) update, location update, PDP context activation, and PDP context deactivation. • MM contexts are established in the MS and SGSN • MM contexts -The mobility information that held at MS and SGSN

5. GPRS MM Contexts • Partial information of SGSN MM contexts • Partial information of MS MM contexts

6. GPRS MM: Basic Concepts • The definition of Routing Area(RA) • subset of GSM LA, 1 cell  RA  LA • MS updates its location when it changes the “big area” (RA update) • When MS is in STANDBY state (there is no call established) + save battery, less MS originated updates + UL radio resource is not wasted so much for MM messages - Paging load increase • MS updates its location to network in every cell range(Cell update) • MS is in READY state (a call is established) + MS’s location is always known in accuracy of cell - MS’s battery is draining due to frequently cell updates - UL radio resource is wasted with frequently cell updates

7. GPRS MM: Basic Concepts • GPRS Mobility Management(MM) Functionality • GPRS attach function • To know who is the MS and what it can or is allowed to do • GPRS detach function • Leave the system • Purge function • Allow an SGSN to inform HLR that is has deleted the MM and PDP contexts of a detached MS • Security function • Authentication of subscriber • User identity confidentiality • User data and GMM/SM signalling confidentiality (MS – SGSN) • Identity check procedures • Location Management function (Routing Area update & Location update) • to know the location of the MS • Route the MT packets to the MS • MO packet has no routing problem (MS -> SGSN, SGSN -> GGSN) • Subscriber management function

8. GPRS MM – Two Access Cases • Non-anonymous access case • The MM state relates only to GPRS MM activities of a subscriber • The MM state is independent of the number and state of PDP contexts for that subscriber • The movement from one state to the next is dependent on the current state(IDEL, STANDY, or READY) and the event occurred(e.g., GPRS Attach) • Anonymous access case • The MM state relates to GPRS MM activities of an MS represented only by an Auxiliary TLLI • The AA MM state machine is independently handled by the MS and network, and may coexist with an IMSI-based MM state machine. • Several AA MM states machines may coexist in the same MS and SGSN simultaneously

9. GPRS Mobility Management States • IDLE State • GPRS MS is unreachable • MS may receive PTM-M message • MS shall perform GPRS Attach procedure to establish MM contexts in the MS and SGSN • STANDBY State • MS is attached to GPRS MM. MS and SGSN have established MM contexts. • MS can receive PTM-M and PTM-G data(i.e. can receive paging message) • PTP data reception and transmission, and PTM-G data transmission are not possible • MS execute MM procedure to inform SGSN when MS enter a new RA • MS does not inform SGSN when a change of cell in the same RA • READY state • MS can send and receive PDP PDU, and receive PTM-P and PTM-G data

10. Non-Anonymous Access MM States MS request access and logical link to SGSN is initiated MS sends an LLC PDU to the SGSN SGSN receive an LLC PDU from the MS

11. GPRS Attach and Detach Functions • Two types of attach function • GPRS attach • Combined GPRS/IMSI attach • Operations of Attach procedure • Inform the network for the MS’s request to be active • Network should check the MS’s identify • Download MS’s subscription information from HLR to SGSN • Update MSC/VLR, if IMSI Attach is also performed • Two types of detach function • MS-initiated Detach procedure • Network-Initiated Detach procedure • SGSN-initiated detach procedure • HLR-initiated detach procedure

12. Combined GPRS/IMSI Attach Procedure (P-TMSI, old RAI, Attach type, …) (IMSI)

13. Location Management • Location management functions • cell and PLMN selection • for network to know the RA for MSs in STANDBY and READY states • for network to know the cell identity for MSs in READY state • When to do • MS detect it has enter a new cell or a new RA • MS determine to perform periodic RA updates • Procedures • Cell update procedure • RA update procedures • Intra SGSN RA update procedure • Inter SGSN RA update procedure • Combined RA/LA update procedures • Combined intra SGSN RA/LA update procedure • Combined inter SGSN RA/LA update procedure • Periodic RA and LA update procedure

14. Location Management Procedures • Cell update procedure • When MS enters a new cell inside the current RA and MS is in READY state • If the RA has changed, a RA update is executed instead of a cell update • By sending an LLC frame containing P-TMSI to the SGSN • The SGSN records this MS’s change of cell • RA update procedures • When • A GPRS-attached MS detects that it has entered a new RA • When the periodic RA update timer has expired • A suspended MS is not resumed by the BSS • Intra SGSN RA update • Same SGSN, old RAI • E.g., periodic RA update • Inter SGSN RA update • New SGSN

15. Inter SGSN RA Update Procedure 1. Old SGSN store New SGSN address 2. Start Timer and STOP the TX of N_PDU to MS (old RAI, old P-TMSI signature, Update Type) Old SGSN duplicate the buffered N-PDUs and start tunnelling them to the new SGSN

16. Combined Inter SGSN RA/LA Update Procedure

17. Conclusions • User data transmission during attach, auth., RA update procedure may be lost and may therefore have to be retransmitted • GPRS HO - Mobile IP

18. References [1] GSM 02.60:”Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Service description; Stage 1”, Nov. 1999 [2] GSM 03.60:”Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Service description; Stage 2”, Nov. 1999 [3] GSM 03.64:”Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Overall description of the GPRS radio interface; Stage 2”, Nov. 1999 [4] Hannu H. Kari, HUT/ITSE, the presentation of GPRS Mobility Management, Feb. 1999.