6 Monitoring and CCBS Call Reporting

03.933GPPStage 2Technical realization of Completion of Calls to Busy Subscriber (CCBS)TS

6.1 Monitoring

6.1.1 Overview

Monitoring is the process where the subscriber state is observed and reported. When monitoring is started, the current subscriber state is reported and any subsequent changes of subscriber state are reported until monitoring is stopped.

Monitoring subscriber state information will be necessary against MS B and may also be necessary against MS A.

For both these cases the monitoring functionality is located in the appropriate serving VMSC/VLR and is controlled from the appropriate HLR. The actions on the A-side and B-side for monitoring are completely independent and the following description is generic to cover either case. The HLR sends an explicit Start Reporting signal to the VLR to initiate monitoring. The VLR acknowledges the request confirming that monitoring has started and indicates the current status of the subscriber state in the VMSC/VLR. The VLR will continue to send an Event Report to the HLR whenever the appropriate subscriber state transition event occurs. The HLR sends an explicit Stop Reporting signal to the VLR when reporting on the subscriber state transitions is no longer required.

6.1.2 Monitoring Subscriber B-state information

The CCBS service requires monitoring of the subscriber state at the called destination network (B-side). This monitoring enables the HLR B to be aware of any transition of subscriber state in VMSC/VLR B while there is an active CCBS Request in the HLR B queue. The basic service operation is that, when the destination B subscriber state becomes Idle, the HLR B is informed and a Remote User Free indication is sent towards the originating A network at the appropriate time. If subsequently to that event the destination B subscriber state becomes not Idle or not reachable, then the HLR B is informed by the VMSC/VLR B in order that it can take an appropriate action towards HLR A, e.g. defer sending of the Remote User Free indication.

6.1.3 Monitoring Subscriber A state information:

Monitoring Subscriber A state information will be necessary if the Remote User Free indication from Destination B network cannot be acted upon because e.g. MS A is not idle or not reachable and leads to the CCBS request being suspended. The service action in this event is that, when the subscriber state subsequently becomes Idle, the HLR A is informed and a Resume indication is sent towards the destination B network at the appropriate time.

6.2 MSC/VLR Monitoring Model

The Monitoring model represents the information related to the status of the subscriber connection in the MSC/VLR. A generic monitoring model is used in the MSC/VLR covering the needs of both subscriber A and subscriber B state information for CCBS. The MSC/VLR monitoring model for CCBS is shown in figure 6.2.1. Note that state transitions reported to the HLR are shown as solid lines.

Figure 6.2.1: MSC/VLR Monitoring Model

6.2.1 Subscriber status

The monitoring model in the MSC/VLR makes use of the three subscriber states described in table 6.2.1.

NOTE: Refer to GSM 03.78 for equivalent subscriber state description.

Table 6.2.1: Subscriber States

Subscriber states

Description (for monitoring purposes)

Notes

IDLE

The state of the MS is neither "NOT IDLE" nor "NOT REACHABLE"

"Assumed Idle"

NOT IDLE

The MS is engaged on a transaction for a MO or MT circuit switched call

"CAMEL busy"

NOT REACHABLE

The MSC/VLR can determine from its internal data that the MS is not reachable e.g. IMSI detached, Restricted Area, No Page Response.

"Network Determined Not Reachable"

For each subscriber state a description can be found on the entry events, functions and exit events.

6.2.1.1 Idle

Entry events:

– Indication of last call released (Mobile Originated or Mobile Terminated);

– Indication of radio link failure;

– Indication of MS activity related to e.g. MO-SMS, MT-SMS and CISS;

– IMSI Attached;

– Location Update.

Functions:

– Events leading to a transition to the Not Idle or Not Reachable subscriber state are awaited.

Exit events:

– A Mobile Originated Set-up message is received from the MS for first (and only) call;

– A Mobile Terminated Set-up message is sent to the MS for first (and only) call.

– IMSI Detached;

– Roaming in LA not allowed;

– No Page Response;

– An exception condition is encountered e.g. Cancel Location indication received.

6.2.1.2 Not Idle

Entry events:

– A Mobile Originated Set-up message is received from the MS for first (and only) call;

– A Mobile Terminated Set-up message is sent to the MS for first (and only) call.

Functions:

– Events leading to a transition to the Idle or Not Reachable subscriber state are awaited.

Exit events:

– Indication of last call released (Mobile Originated or Mobile Terminated);

– Indication of radio link failure;

– An exception condition is encountered e.g. Cancel Location indication received.

6.2.1.3 Not Reachable

Entry events:

– IMSI Detached;

– Roaming in LA not allowed;

– No Page Response.

Functions:

– Events leading to a transition to the Idle or Not Idle subscriber state are awaited.

Exit events:

– Indication of MS activity related to e.g. MO-SMS, MT-SMS and CISS;

– IMSI Attached;

– Location Update;

– A Mobile Originated Set-up message is received from the MS for first (and only) call;

– A Mobile Terminated Set-up message is sent to the MS for first (and only) call;

– An exception condition is encountered e.g. Cancel Location indication received.

6.2.2 Reporting of subscriber state transitions

Transitions between subscriber states are reported from the MSC/VLR, while monitoring in the MSC/VLR is on going. The table 6.2.2 indicates which transitions are monitored in the MSC/VLR and whether these are reported to the HLR for the CCBS service. An appropriate Event Report signal is sent from the VLR to the HLR when a relevant state transition occurs. The Event Report signal includes a status parameter which reflects the subscriber state information.

Table 6.2.2: Reporting of Subscriber States Transitions

Subscriber state transition event

Event reporting
HLR informed

Event report
Subscriber status

IDLE to NOT IDLE

Yes

CCBS Not Idle

IDLE to NOT REACHABLE

Yes

CCBS Not Reachable

NOT IDLE to IDLE

Yes

CCBS Idle

NOT IDLE to NOT REACHABLE

No

NOT REACHABLE to IDLE

Yes

CCBS Idle

NOT REACHABLE to NOT IDLE

No

6.2.2.1 Start Reporting of Monitoring Events

When a Start Reporting signal is received from the HLR, the VLR shall acknowledge the request confirming that monitoring has started and indicate the current status of the subscriber state in the MSC/VLR. The VLR shall subsequently continue to send the Event Reports indicated in table 6.2.2 whenever the appropriate subscriber state transition event occurs.

Note where a single user has a CCBS request activated against him and has an outstanding CCBS request suspended against someone else, (i.e. is effectively both destination B and CCBS subscriber A) reporting on both A-side and B-side is required. In this case, the VLR shall only send a single Event Report as indicated in table 6.2.2 whenever the appropriate subscriber state transition event occurs. The HLR shall not send another Start Reporting signal to the VLR if monitoring is already ongoing in the MSC/VLR for either A-side or the B-side.

6.2.2.2 Stop Reporting of Monitoring Events

When a Stop Reporting signal is received from the HLR, the VLR shall stop sending the Event Reports.

6.3 CCBS Call Reporting

6.3.1 Overview

As well as monitoring of the subscriber state, it is also necessary to report the result of the CCBS Call. The basic reporting requirements are as follows from both the A-side and the B-side.

CCBS Call Reporting – A-side:

The CCBS service logic in the originating network HLR A requires a report on the outcome of the CCBS Call resulting from the acceptance of the CCBS Recall by Subscriber A. The VLR A sends a CCBS Call Report to the HLR A indicating the outcome of the CCBS call processing in MSC/VLR A when e.g. an address complete message (ACM) is received from the destination B network. CCBS Call Reporting on the A-side is completely independent of any monitoring of subscriber state information. The sending of CCBS Call Report is required even when there is no monitoring ongoing in the MSC/VLR.

CCBS Call Reporting- B-side:

The CCBS service logic in the destination network HLR B requires a report on the outcome of CCBS Call processing in the MSC/VLR B. The HLR B initiates the CCBS call outcome reporting in the VLR when the VLR is normally queried to provide routing information for mobile terminated calls (by including an CCBS indicator in the PRN message). The VLR B sends a CCBS Call Report to the HLR B indicating the outcome of the CCBS call processing and the new status of the subscriber state in the MSC/VLR B when e.g. MS B is alerted to the CCBS Call.

6.3.2 Originating Network (A-side)

When a CCBS RUF signal is received by the VLR, CCBS processing in the MSC/VLR leads to a CCBS Recall signal being sent to the MS. When the response to the CCBS Recall is received, the VLR shall subsequently send a CCBS Call Report when the relevant processing for the outgoing CCBS call to the destination network is completed as shown in the SDLs for MSC/VLR A.

6.3.3 Destination Network (B-side)

When an initiate CCBS Call Reporting Request signal (B-side) is received by the VLR in the Provide Roaming Number message, the VLR shall subsequently send a CCBS Call Report when the relevant processing of the incoming CCBS call is completed as shown in the SDLs for MSC/VLR B.

6.3.3.1 Interaction of Event Reporting and CCBS Call Report

Reporting on subscriber state transitions will be ongoing in the MSC/VLR B when a report on the CCBS call outcome is required.

When a subscriber state transition from IDLE to NOT IDLE occurs due to an incoming CCBS call, an Event Report shall not be sent. Instead, a CCBS Call Report (containing CCBS call outcome information and the status) shall be sent to the HLR B. After the CCBS Call Report has been sent, normal Event Reporting will continue i.e. the VLR shall subsequently send only the Event Reports indicated in table 6.2.2 when the next appropriate subscriber state transition event occurs.

6.4 Location Update

The MS may roam to a new MSC/VLR area while monitoring is ongoing in the previous MSC/VLR. When the VLR receives a Cancel Location signal from the HLR due to normal mobility management procedures, any ongoing CCBS related activities associated with the subscriber shall cease.

If the A-side monitoring is ongoing when the HLR receives a Location Update request from the new VLR, the Location Update signal is considered to indicate that the subscriber state is idle and the appropriate CCBS process in the HLR is informed. The normal mobility management procedures will lead to a Cancel Location signal being sent to the old VLR causing the Event Reporting to stop.

If the B-side monitoring is ongoing when the HLR receives a Location Update request from the new VLR, the normal mobility management procedures are followed. On successful completion of Location Update procedure, the HLR shall send a Start Reporting signal to the new VLR. If during the handling of the normal Location Updating procedure, it is detected that the new MSC/VLR does not support CCBS, the HLR shall not send a Start Reporting signal to the new VLR.

NOTE: There is no impact to the MS due to CCBS monitoring, i.e. normal Location Update procedures apply.