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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

GSM 系統簡介及其發展趨勢期末專題

Introduction to GPRS Mobility Management

1NCTU/CSIE/PCS Lab. 2000/6/19


OUTLINE

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


GPRS Brief - Logical Architecture

Gf

D

Gi

Gn

Gb

Gc

CE

Gp

Gs

Signalling and Data Transfer Interface

Signalling Interface

MSC/VLR

TE MT BSC TEPDN

R Um

GrA

HLR

Other PLMN

SGSN

GGSN

Gd

SM-SCSMS-GMSCSMS-IWMSC

GGSN

EIR

SGSN

Gn

CGF

GaGa

BillingSystem

BTS

Abis


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

BSSGPRelay

GMM/SM

LLC

RLC

MAC

GSM RF

GMM/SM

LLC

BSSGP

L1bis

Um GbMS BSS SGSN

NetworkService

RLC

MAC

GSM RF L1bis

NetworkService


GPRS MM Contexts Partial information of SGSN MM contexts

Partial information of MS MM contexts

IMSI IMSI is the main reference key. MM State Mobility management state, IDLE, STANDBY, or READY. P-TMSI Packet Temporary Mobile Subscriber Identity. P-TMSI Signature A signature used for identification checking purposes. IMEI International Mobile Equipment Identity MSISDN The basic MSISDN of the MS. Routeing Area Current routeing area. Cell Identity Current cell in READY state, last known cell in STANDBY or IDLE state. Cell Identity Age Time elapsed since the last LLC PDU was received from the MS at the SGSN. VLR Number The VLR number of the MSC/VLR currently serving this MS. New SGSN Address The IP address of the new SGSN where buffered and not sent N-PDUs should be

forwarded to. Authentication Triplets Authentication and ciphering parameters. … … Each MM context contains zero or more of the following PDP contexts:

Field SIM Description

IMSI X International Mobile Subscriber Identity. MM State Mobility management state, IDLE, STANDBY, or READY. P-TMSI X Packet Temporary Mobile Subscriber Identity. P-TMSI Signature X A signature used for identification checking purposes. Routeing Area X Current routeing area. Cell Identity Current cell. Kc X Currently used ciphering key. CKSN X Ciphering key sequence number of Kc. Ciphering algorithm Selected ciphering algorithm. Classmark MS classmark. DRX Parameters Discontinuous reception parameters. … … Each MM context contains zero or more of the following PDP contexts: … …


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


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


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

GPRS MM – Two Access Cases


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


Non-Anonymous Access MM States

PDU transmission

Implicit Detachor

Cancel Location

GPRS Attach GPRS Detach GPRS Attach

PDU reception

GPRS Detachor

Cancel Location

MM State Model of MS MM State Model of SGSN

IDLE

READY

STANDBY

IDLE

READY

STANDBY

READY timer expiryorForce to STANDBYorAbnormal RLC condition

GPRS Detach(by MS or Network)

READY timer expiryorForce to STANDBY

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


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


Combined GPRS/IMSI Attach Procedure

7d. Cancel Location Ack

7c. Cancel Location

7b. Update Location

7g. Update Location Ack

7e. Insert Subscriber Data

7f. Insert Subscriber Data Ack

6d. Insert Subscriber Data

6c. Cancel Location Ack

6b. Cancel Location

3. Identity Response

2. Identification Response

2. Identification Request

1. Attach Request

5. IMEI Check

3. Identity Request

4. Authentication

6a. Update Location

7a. Location Update Request

7h. Location Update Accept

6f. Update Location Ack

6e. Insert Subscriber Data Ack

MS BSS new SGSN old SGSN GGSN HLREIR

oldMSC/VLR

newMSC/VLR

9. Attach Complete

8. Attach Accept

10. TMSI Reallocation Complete

(P-TMSI, old RAI, Attach type, …) (IMSI)


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


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


Inter SGSN RA Update ProcedureMS BSS new SGSN HLRGGSNold SGSN

2. SGSN Context Response

3. Security Functions

1. Routeing Area Update Request

2. SGSN Context Request

6. Update PDP Context Request

6. Update PDP Context Response

7. Update Location

10. Update Location Ack

11. Routeing Area Update Accept

8. Cancel Location

8. Cancel Location Ack

9. Insert Subscriber Data Ack

9. Insert Subscriber Data

12. Routeing Area Update Complete

5. Forward Packets

4. SGSN Context Acknowledge

(old RAI, old P-TMSI signature, Update Type)

1. Old SGSN store New SGSN address

2. Start Timer and STOP the TX of N_PDU to MS

Old SGSN duplicate the buffered N-PDUs and start tunnelling them to the new SGSN


Combined Inter SGSN RA/LA Update Procedure

12b. Cancel Location

12c. Cancel Location Ack

12d. Insert Subscriber Data

16. TMSI Reallocation Complete

12f. Update Location Ack

13. Location Update Accept

15. Routeing Area Update Complete

14. Routeing Area Update Accept

8. Cancel Location

8. Cancel Location Ack

6. Update PDP Context Response

6. Update PDP Context Request

7. Update Location

10. Update Location Ack

12a. Update Location

11. Location Update Request

2. SGSN Context Response

3. Security Functions

2. SGSN Context Request

1. Routeing Area Update Request

9. Insert Subscriber Data

9. Insert Subscriber Data Ack

12e. Insert Subscriber Data Ack

MS BSS GGSNold SGSNnew SGSN HLR

newMSC/VLR

oldMSC/VLR

5. Forward Packets

4. SGSN Context Acknowledge


Conclusions

User data transmission during attach, auth., RA update procedure may be lost and may therefore have to be retransmitted

GPRS HO - Mobile IP


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.

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