June 19 2000

1
GSM??????????????Introduction to GPRS
Mobility Management

• ? 5 ?
• 8717805 ??? 8717801 ??? 8817530 ???
• 8517011 ??? 8517019 ???
• 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)
• MSs location is always known in accuracy of
  cell
• - MSs 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 -gt SGSN,
  SGSN -gt 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 MSs request to be
  active
• Network should check the MSs identify
• Download MSs 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 MSs 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 02.60Digital cellular
  telecommunications system (Phase 2) General
  Packet Radio Service (GPRS) Service description
  Stage 1, Nov. 1999
• 2 GSM 03.60Digital cellular
  telecommunications system (Phase 2) General
  Packet Radio Service (GPRS) Service description
  Stage 2, Nov. 1999
• 3 GSM 03.64Digital 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.