6.2 IDLE / STANDBY / READY State Functionality

03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS

6.2.1 State Transitions and Functions

The movement from one state to the next is dependent on the current state (IDLE, STANDBY, or READY) and the event occurred (e.g., GPRS attach).

Figure 13: Functional Mobility Management State Model

Figure 13 describes the following state transitions:

Moving from IDLE to READY:

– GPRS Attach: The MS requests access and a logical link to an SGSN is initiated. MM contexts are established at the MS and SGSN.

Moving from STANDBY to IDLE:

– Implicit Detach: The MM and PDP contexts in the SGSN shall return to IDLE and INACTIVE state. The MM and PDP contexts in the SGSN may be deleted. The GGSN PDP contexts shall be deleted.

– Cancel Location: The SGSN receives a MAP Cancel Location message from the HLR, and removes the MM and PDP contexts.

Moving from STANDBY to READY:

– PDU transmission: The MS sends an LLC PDU to the SGSN, possibly in response to a page.

– PDU reception: The SGSN receives an LLC PDU from the MS.

Moving from READY to STANDBY:

– READY timer expiry: The MS and the SGSN MM contexts return to STANDBY state.

– Force to STANDBY: The SGSN indicates an immediate return to STANDBY state before the READY timer expires.

– Abnormal RLC condition: The SGSN MM context returns to STANDBY state in case of delivery problems on the radio interface or in case of irrecoverable disruption of a radio transmission.

Moving from READY to IDLE:

– GPRS Detach: The MS or the network requests that the MM contexts return to IDLE state and that the PDP contexts return to INACTIVE state. The SGSN may delete the MM and PDP contexts. The PDP contexts in the GGSN shall be deleted.

– Cancel Location: The SGSN receives a MAP Cancel Location message from the HLR, and removes the MM and PDP contexts.

For anonymous access, a reduced Mobility Management State Model consisting of IDLE and READY states is used. The AA MM state machine is independently handled by the MS and the network and may coexist with an IMSI-based MM state machine. Several AA MM state machines may coexist in the same MS and SGSN simultaneously.

Figure 14: Functional Anonymous Access Mobility Management State Model

Figure 14 describes the following state transitions for anonymous access:

Moving from IDLE to READY:

– AA PDP Context Activation: The MS requests an anonymous access and a logical link to an SGSN is initiated. MM contexts are established at the MS and SGSN, and PDP contexts are established at the MS, the SGSN, and a GGSN.

Moving from READY to IDLE:

– READY timer expiry: The MM and PDP contexts in the MS, the SGSN, and the GGSN are deleted.

– Abnormal RLC condition: The SGSN MM context shall be deleted in case of delivery problems on the radio interface or in case of irrecoverable disruption of a radio transmission.

– AA PDP Context Deactivation: The network (either the SGSN or the GGSN) initiates the AA PDP Context Deactivation procedure, e.g., due to malicious usage of the anonymous service. The MM and PDP contexts in the MS, the SGSN, and the GGSN shall be deleted.

6.2.2 READY Timer Function

The READY timer function maintains the READY timer in the MS and SGSN. The READY timer controls the time an MS remains in READY state in the MS and the SGSN. The READY timer shall be reset and begin running in the MS when an LLC PDU is transmitted, and in the SGSN when an LLC PDU is correctly received. When the READY timer expires, the MS and SGSN MM contexts shall return to STANDBY state. In case of anonymous access the MM context shall be deleted.

The length of the READY timer shall be the same in the MS and SGSN. The initial length of the READY timer shall be defined by a default value. The SGSN, and only the SGSN, may change the length of the READY timer by transmitting a new value in the Attach Accept, Routeing Area Update Accept, or AA PDP Context Accept messages.

If the READY timer length is set to zero, the MS shall immediately be forced into STANDBY state. If the timer length is set to all 1s (binary), then the READY timer function shall be deactivated, i.e., the timer no longer runs and the MS remains in READY state.

6.2.3 Periodic RA Update Timer Function

The Periodic RA Update Timer function monitors the periodic RA update procedure in the MS. The length of the periodic RA update timer is sent in the Routeing Area Update Accept or Attach Accept message. The periodic RA update timer is unique within an RA. Upon expiry of the periodic RA update timer, the MS shall start a periodic routeing area update procedure.

If the MS is in coverage but out of GPRS coverage when the periodic RA update timer expires, then, if the MS is IMSI-attached to a network in network operation mode I, the periodic location update procedure (or other appropriate location update procedure) shall be started immediately. In addition, and irrespective of whether or not the MS was IMSI-attached, regardless of the network operation mode, the periodic RA update procedure (or other appropriate update procedure) shall be started as soon as the MS returns to GPRS coverage.

If the MS is out of coverage when the periodic RA update timer expires then:

– if the MS is both IMSI and GPRS-attached and returns to coverage in a cell that supports GPRS in network operation mode I, then the combined RA / LA update procedure with IMSI attach requested shall be started as soon as the MS returns to coverage;

– if the MS is both IMSI and GPRS-attached and returns to coverage in a cell that supports GPRS in network operation mode II or III, or if a GPRS only-attached MS returns to coverage in a cell that supports GPRS, then the periodic RA update procedure shall be started as soon as the MS returns to coverage; or

– if the MS returns to coverage in a cell that does not support GPRS, and if the MS is IMSI-attached, then the periodic location update procedure (or other appropriate location update procedure) shall be started as soon as the MS returns to coverage in that cell. In addition, and irrespective of whether or not the MS was IMSI-attached, the periodic RA update procedure (or other appropriate update procedure) shall be started as soon as the MS returns to GPRS coverage.

If the MS lost GPRS coverage but the periodic RA update timer did not expire while out of GPRS coverage, then, the MS shall not perform the periodic RA update procedure because of the MS’s return to GPRS coverage.

If the MS lost coverage but the periodic RA update timer did not expire while out of coverage, then the MS shall not perform the periodic RA update procedure because of the MS’s return to coverage.

6.2.4 Mobile Reachable Timer Function

The Mobile Reachable Timer function monitors the periodic RA update procedure in the SGSN. The mobile reachable timer shall be slightly longer than the periodic RA update timer used by an MS.

The mobile reachable timer is stopped when the READY state is entered. The mobile reachable timer is reset and started when the state returns to STANDBY.

If the mobile reachable timer expires, the SGSN shall clear PPF. Typically, this causes the SGSN to stop sending GPRS paging or CS paging messages to the MS, but other features (e.g., MSC/VLR-based call forwarding) may happen immediately. PPF is set when the next activity from the MS is detected. The MM and PDP contexts shall be kept in the SGSN.

When an MS first registers in an SGSN, then PPF is set.