4.5 Description of CAMEL State Models

23.2783GPPCustomised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4IM CN InterworkingRelease 17Stage 2TS

In the IM Subsystem, calls are controlled by the Serving CSCF (S‑CSCF) where a subscriber is registered. A state model describes the call control behaviour of an IM‑SSF.

4.5.1 General Handling

The Basic Call State Model (BCSM) is used to describe the handling of originating and terminating calls. It identifies the points in a call where gsmSCF based service applications is permitted to interact with the call control capabilities of an IM‑SSF. Figure 4.3 illustrates how transitions between states, Detection Points and Points In Call components are shown in the BCSM diagrams.

Figure 4.3: BCSM Components

4.5.2 Originating CAMEL Basic Call State Model (O‑IM‑BCSM)

4.5.2.1 Description of the O‑IM‑BCSM

The O‑IM‑BCSM is used to model the behaviour of an IM‑SSF for an originating call. When an armed DP is encountered, O‑IM‑BCSM processing is suspended at the DP and the IM‑SSF indicates this to the gsmSCF if appropriate.

Figure 4.4: Originating CAMEL Basic Call State Model (O‑IM‑BCSM)

The following table 4.1defines the DPs that apply to originating calls.

Table 4.1: Description of the O‑IM‑BCSM DPs in an IM‑SSF

CAMEL Detection Point:	DP Type	Description:
DP Collected_Info	TDP‑R	Indication that the O‑IM‑CSI is analysed
DP Analysed_Information	TDP‑R	Availability of routeing address and nature of address.
DP Route_Select_Failure	TDP‑R, EDP‑N, EDP‑R	Indication that the session establishment failed.
DP O_Busy	EDP‑N, EDP‑R	Indication that: – a busy indication is received from the terminating party, – a not reachable event is determined upon a SIP error response.
DP O_No_Answer	EDP‑N, EDP‑R	Indication that: – an application timer associated with the O_No_Answer DP expires, – a no answer event is determined upon SIP a error response
DP O_Answer	EDP‑N, EDP‑R	Indication that the session is accepted and answered by the terminating party.
DP O_Disconnect	EDP‑N, EDP‑R	A disconnect indication is received from the originating party or from the terminating party.
DP O_Abandon	EDP‑N, EDP‑R	Indication that a disconnect indication is received from the originating party during the session establishment procedure.

4.5.2.2 Description of Points In Call

This clause describes the Points In Call for originating calls. The entry events, actions and exit events are described for each Point in Call.

4.5.2.2.1 O_Null & Authorise_Origination_Attempt_Collect_Info

Entry events:

– Disconnection and clearing of a previous call (DP O_Disconnect) or default handling of exceptions by IM‑SSF completed.

– Abandon event is reported from Analyse_Information or Routing and Alerting PIC.

– Exception event is reported.

Actions:

– Interface is idled.

– Originating call: SIP INVITE request message containing the dialled number is received from MS.

– Information being analysed e.g., O‑IM‑CSI is analysed.

Exit events:

– Originating CSI is analysed.

– An exception condition is encountered. For this PIC, if the call encounters one of these exceptions during the PIC processing, the exception event is not visible because there is no corresponding DP. Example exception condition: Calling party abandons call.

4.5.2.2.2 Analyse_Information

Entry events:

– Originating CSI is analysed. (DP Collected Info).

– New routeing information is received when Busy event (DP O_Busy), Route Select Failure event (DP Route_Select_Failure), Not Reachable event (DP O_Busy) or No Answer event (DP O_No_Answer) is reported from Routing and Alerting PIC.

– New routeing information is received when Disconnect event is reported from O_Active PIC.

Actions:

– Compare the called party number with the dialled services information.

Exit events:

– Availability of routeing address and nature of address. (DP Analysed_Information).

– An exception condition is encountered (e.g. wrong number)- this leads to the O_Exception PIC.

– Calling party abandons the call- this leads to the O_Abandon DP.

4.5.2.2.3 Routing and Alerting

Entry events:

– Availability of routeing address and nature of address. (DP Analysed_Information).

Actions:

– Information is being analysed and/or translated according to dialling plan to determine routeing address.

– Routeing address being interpreted.

– Call is being processed by the terminating half BCSM. Continued processing of SIP call session setup (e.g., ringing) is taking place. Waiting for indication from terminating half BCSM that the call has been answered by terminating party.

Exit events:

– Indication from the terminating half BCSM that the call is accepted and answered by terminating party (DP O_Answer).

– An exception condition is encountered – this leads to the O_Exception PIC.

– Calling party abandons the call- this leads to the O_Abandon DP.

– A busy indication is received from the terminating party – this leads to the O_Busy DP.

– A not reachable indication is received from the terminating party – this leads to the O_Busy DP.

– Attempt to select the route for the call fails – this leads to the Route_Select_Failure DP.

If the no reply timer expires and DP O_No_Answer is armed – this leads to the O_No_Answer DP.

4.5.2.2.4 O_Active

Entry events:

– Indication from the terminating half BCSM that the call is accepted and answered by the terminating party (DP O_Answer).

Actions:

– SIP session established between originating party and terminating party. – Call release is awaited.

Exit events:

– A disconnection indication is received from the originating party, or received from the terminating party via the terminating half BCSM. (DP – O_Disconnect).

– An exception condition is encountered.

4.5.2.2.5 O_Exception

Entry events:

– An exception condition is encountered. In addition to specific examples listed above, exception events include any type of failure, which means that the normal exit events for a PIC can not be met.

Actions:

– Default handling of the exception condition is being provided. This includes general actions necessary to ensure that no resources remain inappropriately allocated such as:

– If any relationship exists between the IM‑SSF and the gsmSCF, the IM‑SSF shall send an error information flow closing the relationships and indicating that any outstanding call handling instructions will not run to completion.

– Resources made available for setting up the SIP call session are released.

Exit events:

– Default handling of the exception condition by IM‑SSF completed.

4.5.3 Mapping of SIP Method/Response to O‑IM-BCSM Detection Points

This clause describes mapping of SIP methods and responses to CAMEL Detection Points.

Table 4.2: Mapping of SIP Method/Response to CAMEL O‑IM-BCSM DPs

CAMEL O‑IM‑BCSM DP:	SIP Method/Response
DP Collected_Info	INVITE
DP Analysed_Information	N/A
DP Route_Select_Failure	4XX (except 401, 407, 408, 480, 486), 5xx, and 6xx (except 600, 603)
DP O_Busy	486 Busy Here 600 Busy Everywhere
DP O_No_Answer	603 Decline 408 Request Timeout 480 Temp Unavailable
DP O_Answer	200 OK
DP O_Disconnect	BYE
DP O_Abandon	CANCEL

4.5.4 Terminating CAMEL Basic Call State Model (T‑IM‑BCSM)

4.5.4.1 Description of the T‑IM‑BCSM

The T‑IM-BCSM is used to model the behaviour of an IM‑SSF for a terminating call. When a DP is encountered, T‑IM-BCSM processing is suspended at the DP and IM‑SSF indicates this to the gsmSCF if appropriate.

Figure 4.5: Terminating CAMEL Basic Call State Model (T‑IM‑BCSM)

The following table 4.3defines the DPs that apply to terminating calls.

Table 4.3: Description of T‑IM‑BCSM DPs in the S‑CSCF

CAMEL DP:	DP Type	Description:
DP Terminating_Attempt_ _Authorised	TDP‑R	Indication that the VT‑IM‑CSI is analysed.
DP T_Busy	TDP‑R, EDP‑N, EDP‑R	Indication that: – a busy indication is received from the terminating party, – a not reachable event is determined (e.g. terminating party is not currently registered).
DP T_No_Answer	TDP‑R, EDP‑N, EDP‑R	Indication that an application timer associated with the T_No_Answer DP expires.
DP T_Answer	EDP‑N, EDP‑R	Session is accepted and answered by terminating party.
DP T_Disconnect	EDP‑N, EDP‑R	A disconnect indication is received from the terminating party or from the originating party.
DP T_Abandon	EDP‑N, EDP‑R	A disconnect indication is received from the originating party during the session establishment procedure.

4.5.4.2 Description of Points In Call

This clause describes the Points In Call for terminating calls. The entry events, actions and exit events are described for each Point in Call.

4.5.4.2.1 T_Null

Entry events:

– Disconnection and clearing of a previous call (DP T_Disconnect) or default handling of exceptions by IM-SSF completed.

– Abandon event is reported from Terminating Call Handling PIC.

– Exception event is reported.

Actions:

– Interface is idled.

– SIP INVITE message for terminating call request is received, the appropriate information is analysed.

– VT‑IM‑CSI is analysed.

Exit events:

– Terminating CSI is analysed.

– An exception condition is encountered. For this PIC, if the call encounters one of these exceptions during the PIC processing, the exception event is not visible because there is no corresponding DP.

Example exception condition is:

– Calling party abandons call.

4.5.4.2.2 Terminating Call Handling

Entry events:

– Terminating CSI (if available) is analysed. (DP Terminating_Attempt_Authorised).

– New routeing information is received when Busy event (DP T_Busy) or No Answer event (DP T_No_Answer) is reported from Terminating Call Handling PIC.

– New routeing information is received when Disconnect event is reported from T_Active PIC.

– New routeing information is received when the terminating party not reachable is reported from Terminating Call Handling PIC.

Actions:

– Routeing address and call type being interpreted. The next route or terminating access is being selected.

– The terminating party is being alerted. Waiting for the call to be answered by terminating party.

Exit events:

– Call is accepted and answered by terminating party.

– An exception condition is encountered – this leads to the T_Exception PIC. Example exception conditions: the SIP call session request was not successful.

– Calling party abandons the call – this leads to the T_Abandon DP.

– A busy indication is received from the terminating party’s P‑CSCF – this leads to the T_Busy DP.

– Not reachable event detected from the terminating party’s P‑CSCF – this leads to the T_Busy DP.

– If no reply timer expires and DP T_No_Answer is armed – this leads to the T_No_Answer DP.

4.5.4.2.3 T_Active

Entry events:

– Indication that the call is accepted and answered by the terminating party. (DP T_Answer).

Actions:

– SIP session established between originating party and terminating party.

– Call release is awaited.

Exit events:

– A disconnection indication is received from the terminating party, or received from the originating party via the originating half BCSM. (DP T_Disconnect).

– An exception condition is encountered. In addition to specific examples listed above, exception events include any type of failure that means that the normal exit events for a PIC can not be met.

4.5.4.2.4 T_Exception

Entry events:

– An exception condition is encountered. In addition to specific examples listed above, exception events include any type of failure, which means that the normal exit events for PIC cannot be met.

Actions:

– Default handling of the exception condition is being provided. This includes general actions necessary to ensure that no resources remain inappropriately allocated such as:

– If any relationship exists between the IM‑SSF and the gsmSCF, the IM‑SSF shall send an error information flow closing the relationships and indicating that any outstanding call handling instructions will not run to completion.

– Resources made available for setting up the SIP call session are released.

Exit events:

– Default handling of the exception condition by IM‑SSF completed.

4.5.5 Mapping of SIP Method/Response to T‑IM‑BCSM Detection Points

This clause describes mapping of SIP methods and responses to CAMEL Detection Points.

Table 4.4: Mapping of SIP Method/Response to CAMEL T‑IM‑BCSM DPs

CAMEL T‑IM‑BCSM DP:	SIP Method/Response
DP Terminating_Attempt_ _Authorised	INVITE
DP T_Busy	4XX (except 401, 407, 408, 480), 5xx, and 6xx (except 603)
DP T_No_Answer	603 Decline 408 Request Timeout 480 Temp Unavailable
DP T_Answer	200 OK
DP T_Disconnect	BYE
DP T_Abandon	CANCEL