4.2 Detection Points (DPs)

23.0783GPPCustomised Applications for Mobile network Enhanced Logic (CAMEL) Phase 4Release 17Stage 2TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.2.1 Definition and description

Certain basic call events may be visible to the GSM Service Control Function (gsmSCF). The DPs are the points in call at which these events are detected. The DPs for Mobile Originated Calls and Mobile Terminated Calls are described in subclauses 4.4.2 and 4.4.3.

A DP can be armed in order to notify the gsmSCF that the DP was encountered, and potentially to allow the gsmSCF to influence subsequent handling of the call. If the DP is not armed, the processing entity continues the processing without gsmSCF involvement.

Three different types of DPs are identified:

– Trigger Detection Point – Request (TDP‑R).

This detection point is statically armed and initiates a CAMEL control relationship when encountered and there is no existing relationship due to the same CSI. Processing is suspended when the DP is encountered.

– Event Detection Point – Request (EDP‑R).

This detection point is dynamically armed within the context of a CAMEL control relationship. Processing is suspended when encountering the DP and the gsmSSF waits for instructions from the gsmSCF.

– Event Detection Point – Notification (EDP‑N).

This detection point is dynamically armed within the context of a CAMEL control relationship. Processing is not suspended when encountering the DP.

The DPs are characterized in the following subclauses.

4.2.1.1 Arming/disarming mechanism

A DP may be statically armed or dynamically armed.

The following arming rules apply:

– A DP for mobile terminating call handling is statically armed in the GMSC as a result of T‑CSI delivery from the HLR. A DP for mobile terminating call handling is statically armed in the VMSC as a result of VT‑CSI delivery from the VLR. A DP for forwarding leg handling is statically armed in the GMSC as result of O‑CSI and/or D‑CSI delivery from the HLR. A DP for mobile originating call or forwarded leg handling is statically armed in the VMSC as a result of O‑CSI and/or D‑CSI delivery from the VLR.

– A DP is dynamically armed by the gsmSCF within the context of a CAMEL control relationship (between the gsmSSF and the gsmSCF).

– A Request Report BCSM Event information flow for a detection point for a leg overwrites any previous Request Report BCSM Event information flow for that detection point for that leg.

The following disarming rules apply:

– A statically armed DP is disarmed when the O‑CSI, D‑CSI, T‑CSI or VT‑CSI that caused the DP to be statically armed is withdrawn in the HLR. Only TDP‑Rs can be disarmed using this mechanism.

– If an armed EDP is met, then it is disarmed.

– If an EDP is met that causes the release of the related leg, then all EDPs related to that leg are disarmed.

– If a call is released, then all EDPs related to that call are disarmed.

– If an EDP is met, then other EDPs are disarmed, in accordance with the implicit disarming rule table (see subclause 4.4.4).

– If an EDP is armed, it can be explicitly disarmed by the gsmSCF by means of the Request Report BCSM Event information flow.

4.2.1.2 Criteria

Criteria are the conditions that must be met in order for the gsmSSF to request instructions from the gsmSCF.

4.2.1.2.1 Criteria at DP Collected_Info

The criteria for a mobile originating call are checked in the originating MSC.

The criteria for a mobile forwarded call are checked in the forwarding MSC.

For early forwarded calls in the GMSC, the HLR may decide not to include the DP Collected_Info trigger criteria in the subscriber data sent to the GMSC if the trigger criteria for the call are not met.

For optimally routed late forwarded calls, the MSC may decide not to include the DP Collected_Info trigger criteria in the Resume Call Handling information flow sent to the GMSC, if the trigger criteria for the call are not met.

The following criteria are applicable for DP Collected_Info:

– Destination number triggering criterion: The HLR may store a list of up to 10 destination numbers and/or up to 3 number lengths. There is no restriction on the nature of address. There is no restriction on the numbering plan indicator. This criterion may be defined to be either "enabling" or "inhibiting".

– Basic service triggering criterion: The HLR may store a list of up to 5 basic service codes, each of which may represent an individual basic service or a basic service group. Compound basic service group codes, as defined in 3GPP TS 29.002 [34], are not allowed for conditional triggering. This list is a triggering list.

– Forwarding triggering criterion: The HLR may store an indicator that triggering shall occur only for a call which has been subject to the Call Forwarding supplementary service, Call Deflection supplementary service or CAMEL call forwarding. This criterion may be defined to be either "enabling" or "inhibiting".

For MO calls, triggering at DP Collected_Info shall be strictly based on the number received over the access network.
No service selection information, such as  and # digits, or carrier selection information, dialled by the subscriber, shall be removed from the number before conditional triggering check takes place.

For MF calls at the VMSC, triggering at DP Collected_Info shall be strictly based on the number received over the access network (the Deflected-to-Number in the case of Call Deflection), the Forwarded-to-Number retained in the VLR or the Destination Routing Address received in the Connect information flow from the gsmSCF during a Terminating CAMEL Service at the VMSC.
No service selection information or carrier selection information shall be removed from the number before conditional triggering check takes place.

For MF calls at the GMSC, triggering at DP Collected_Info shall be strictly based on the Forwarded-to-Number received from HLR, on the Destination Routing Address received in the Connect information flow from the gsmSCF during a Terminating CAMEL Service or on the Forwarded-to-Number received in the Resume Call Handling information flow.
No service selection information or carrier selection information shall be removed from the number before conditional triggering check takes place.

One or more DP criteria may be applicable. All applicable triggering criteria must be satisfied before the dialogue is established with the gsmSCF.

If the destination number triggering criterion is enabling, then the gsmSSF may establish a dialogue with the gsmSCF if:

– the destination number matches one of the destination number strings defined in the list, or

– the length of the destination number matches one of the destination number lengths defined in the list.

In this test the destination number matches one of the destination number strings in the list if:

– the nature of address of destination number is the same as the nature of address of the destination number string (The numbering plan indicator is not compared);

– the destination number is at least as long as the destination number string in the list, and

– all the digits in the destination number string in the list match the leading digits of the destination number.

If the destination number triggering criterion is inhibiting, then the gsmSSF may establish a dialogue with the gsmSCF if:

– the destination number does not match any of the destination number strings defined in the list, and

– the length of the destination number does not match any of the destination number lengths defined in the list.

In this test the destination number matches one of the destination number strings in the list if:

– the nature of address of the destination number is the same as the nature of address of the destination number string (The numbering plan indicator is not compared);

– the destination number is at least as long as the destination number string in the list, and

– all the digits in the destination number string in the list match the leading digits of the destination number.

The basic service triggering criterion is met if the basic service for the call matches a stored individual basic service code or is a member of the group defined by a stored basic service group code. For a SCUDIF call (see 3GPP TS 23.172 [27]), the basic service triggering criterion is met if one or both the preferred basic service and the less preferred basic service for the call match a stored individual basic service code or is a member of the group defined by a stored basic service group code. For the purpose of this paragraph a general bearer service is a member of the corresponding bearer service group.

If the forwarding triggering criterion is enabling, then the gsmSSF may establish a dialogue with the gsmSCF only if the call has been subject to CAMEL call forwarding or the Call Forwarding supplementary service. If the forwarding triggering criterion is inhibiting, then the gsmSSF may establish a dialogue with the gsmSCF only if the call has not been subject to CAMEL call forwarding or the Call Forwarding supplementary service.

4.2.1.2.2 Criteria at DP Analysed_Information

4.2.1.2.2.1 General

The criteria for a mobile originating call are checked in the originating MSC. The criteria for a mobile forwarded call are checked in the forwarding MSC.

For early forwarded calls in the GMSC, the HLR shall always include the trigger criteria in the subscriber data sent to the GMSC because that the HLR can not check the criteria applicable at DP Analysed_Info, since the number that the criteria check shall be based on, may be modified by a Mobile Terminating or Mobile Forwarding Service Logic for this call.

For optimally routed late forwarded calls, the MSC shall always include the trigger criteria in the Resume Call Handling information flow sent to the GMSC because the MSC can not check the criteria applicable at DP Analysed_Info, since the number that the criteria check shall be based on, may be modified by a Mobile Terminating or Mobile Forwarding Service Logic for this call.

The following criteria are applicable for DP Analysed_Information:

– Destination number triggering criterion: The HLR may store a list of up to 10 destination numbers. There is no restriction on the nature of address. There is no restriction on the numbering plan indicator.

NOTE: The order in which the destination number criteria are checked in the MSC or GMSC is not determined. Hence, overlapping destination number criteria (e.g. use of "0800" and "0800123" for two different services) should be avoided, because they lead to unpredictable behaviour (i.e. either service might be triggered).

For MO calls, triggering at DP Analysed_Info shall be based on the called party number received over the access network or the Destination Routing Address in the Connect information flow from the gsmSCF during a Mobile Originating CAMEL Service.

For MF calls at the VMSC, triggering at DP Analysed_Info shall be based on the number received over the access network (the Deflected-to-Number in the case of Call Deflection), the Forwarded-to-Number retained in the VLR, or the Destination Routing Address in the Connect information flow from the gsmSCF during a Mobile Terminated or Mobile Forwarded CAMEL Service.

For MF calls at the GMSC, triggering at DP Analysed_Info shall be based on the Forwarded-to-Number received from the HLR, on the Destination Routing Address received in the Connect information flow from gsmSCF during a Mobile Terminated or Mobile Forwarded CAMEL Service, or on the Forwarded-to-Number received in the Resume Call Handling information flow.

For NP calls, triggering at DP Analysed_Info shall be based on the number received from gsmSCF. An NP call that is created in the VMSC or GMSC of the served subscriber may be subject to D‑CSI service and N‑CSI service. An NP call that is created in an MSC other than the VMSC or GMSC of the served subscriber, may be subject to N‑CSI service.

For NC calls, triggering at DP Analysed_Info shall be based on the number received from the gsmSCF. An NC call may be subject to N‑CSI service.

4.2.1.2.2.2 Removal of information significant to the serving entity

In order to decide whether triggering shall take place, the trigger criteria need to be compared with the address information. Before the comparison takes place the following information shall be removed from the destination address information:

– Operator specific service selection information that is recognised and treated locally in the serving entity. This shall not lead to a change of the type of number indicator of the address information.

– Carrier selection information. If the removal of carrier selection information also removes international or national (trunk) prefixes (depending on regulatory requirements), then the type of number indicator of the address information shall be changed to "international number" or "national (significant) number" respectively. Otherwise the type of number indicator shall remain unchanged.

The address information in a subsequent Initial DP information flow at DP Analysed_Info shall not contain the removed information, however in the further call handling the serving entity shall invoke the requested services (e.g. carrier selection).

4.2.1.2.2.3 Number comparison

The following procedure shall be performed for the comparison of the destination number triggering criterion and the address information in the given order.

1. The numbering plan indicators of the destination number triggering criterion and the destination number are ignored.

2. The type of number/nature of address indicators of the destination number triggering criterion and the destination number are compared. If there is a match of the type of number indicator, then the check shall be performed by comparing the digits as defined in step 6. If there is no match of the type of number the comparison procedure shall continue as follows.

3. If either or both of the address information and destination number triggering criterion includes a types of number/nature of address indicator other than "unknown", "national (significant) number" or "international number" then the destination number does not match the destination number triggering criterion. Otherwise the comparison procedure shall continue as follows.

4. If there is a number (address information or destination number triggering criterion) with type of number/nature of address "unknown" this number shall be translated based on the numbering plan of the serving entity in either of the following ways:

– if the leading digits refer to an international prefix then those digits shall be removed and the type of number/nature of address shall be set to "international number".

– if the leading digits refer to a national (trunk) prefix then those digits shall be removed and the type of number/nature of address shall be set to "national (significant) number".

If the leading digits refer neither to an international prefix nor to a national (trunk) prefix, then the destination number does not match the destination number triggering criterion.

If there is a match of the type of number/nature of address indicator after this number modification, then the check shall be performed by comparing the digits as defined in step 6, otherwise the comparison procedure shall continue as follows.

5. If the type of number/nature of address of the address information or of the destination number triggering criterion is "national (significant) number" this number shall be translated based on the numbering plan of the serving entity to international format by adding the country code of the serving entity to the number string. After this modification the destination number triggering criterion and the destination number shall be in international format and shall be checked by comparing the digits as defined in step 6.

6 If the number of digits in the address information are compared with the number of digits in the destination number triggering criterion, then there is a match if:

– the destination number is at least as long as the destination number string of the destination number triggering criterion, and

– all the digits in the destination number string of the destination number triggering criterion match the leading digits of the destination number.

The check described in this subclause shall be repeated for every number contained in the destination number triggering criterion of the D‑CSI until there is a match DP Analysed_Info is triggered, or until all the destination numbers have been checked without a match. In the latter case DP Analysed_Info is not triggered.

The procedures for the destination number triggering criterion check for N‑CSI are network specific.

The modifications of the address information described in this subclause shall only be done for comparison purposes, i.e. they shall not affect the format of the destination address information sent in the Initial DP information flow.

4.2.1.2.3 Criteria at DP Route_Select_Failure

The HLR may store a list of up to 5 cause values.

The criteria for a mobile originating call are checked in the originating MSC. The criteria for a mobile forwarded call are checked in the forwarding MSC.

For early forwarded calls in the GMSC, the HLR shall always include the trigger criteria in the subscriber data sent to the GMSC because the cause code received from ISUP is used in the trigger criteria check. The cause code is not known at the time of sending the O‑CSI to the GMSC.

For optimally routed late forwarded calls, the MSC shall always include the trigger criteria in the Resume Call Handling information flow sent to the GMSC because the cause code received from ISUP is used in the trigger criteria check. The cause code is not known at the time of sending the O‑CSI to the GMSC.

The following criteria are applicable for DP Route_Select_Failure:

– Release cause code.

The trigger criteria are met if the cause code received from ISUP is equal to at least one of the cause codes in the trigger criteria list. For the purpose of trigger criteria check, the MSC performing the triggering check shall use the "cause value" field of the ISUP "cause indicators" parameter, as defined in ITU‑T Recommendation Q.763 [43].

If an O‑BCSM was already invoked and there is a relationship with the gsmSCF at that moment, then no additional relationship shall be initiated.

4.2.1.2.4 Criteria at DP Terminating_Attempt_Authorised

The HLR may store a list of up to 5 basic service codes, each of which may represent an individual basic service or a basic service group. Compound basic service group codes, as defined in 3GPP TS 29.002 [34], are not allowed for conditional triggering. This list is a triggering list.

The criteria for DP Terminating_Attempt_Authorised are checked in the HLR for the GMSC or in the VLR for the MSC. The HLR shall only include T‑CSI in the CAMEL subscription information sent to the GMSC if the criteria are met. The VLR shall only include VT‑CSI in the CAMEL subscription information sent to the MSC if the criteria are met.

The basic service criterion is met if the basic service for the call matches a stored individual basic service code or is a member of the group defined by a stored basic service group code. For a SCUDIF call (see 3GPP TS 23.172 [27]), the basic service triggering criterion is met if one or both the preferred basic service and the less preferred basic service for the call match a stored individual basic service code or is a member of the group defined by a stored basic service group code.For the purpose of this paragraph a general bearer service is a member of the corresponding bearer service group.

4.2.1.2.5 Criteria at DP T_Busy and T_No_Answer

The HLR may store a list of up to 5 cause values.

The criteria for a mobile terminating call are checked in the GMSC or in MSC.

For mobile terminating calls in the GMSC, the HLR shall include the trigger criteria in the subscriber data sent to the GMSC because the cause code received from ISUP is used in the trigger criteria check. The cause code is not known at the time of sending the T‑CSI to the GMSC.
If the Send Routeing Info ack information flow includes the Not Reachable FTN, then the HLR may decide not to include the trigger criteria, if the HLR has identified that T‑CSI includes DP T_Busy with cause code Not Reachable.

If the Send Routeing Info ack information flow includes the Not Reachable FTN and also T‑CSI, including DP T_Busy with cause code, then the not reachable condition shall be mapped to an ISUP release code, which shall be used for the triggering check.

For Mobile terminating calls in the VMSC, the trigger criteria are received in the VT‑CSI from the HLR in the Insert Subscriber Data information flow. The triggering is based on the ISUP release cause code (call set up result).

The following criteria are applicable for DP T_Busy and DP T_No_Answer:

– Release cause code.

If the cause code is received from ISUP, then the trigger criteria are met if the cause code is equal to at least one of the cause codes in the trigger criteria list. For this check, the MSC shall use the "cause value" field of the ISUP "cause indicators" parameter, as defined in ITU‑T Recommendation Q.763 [43].

If the cause code is received from MAP, then the trigger criteria are met if the cause code is equal to at least one of the cause codes in the trigger criteria list. For this check, the MSC shall use the cause values as defined in table 4.1.

If the trigger criteria are satisfied, then the corresponding Service Logic shall be invoked.
If a T‑BCSM was already invoked and there is a relationship with the gsmSCF at that moment, then no additional relationship shall be initiated.

When the Resume Call Handling information flow is received in the GMSC and the subscriber has T‑CSI then the forwarding reason in the Resume Call Handling information flow shall be used to perform the trigger criteria check for DP T_Busy or DP T_No_Answer. If a match is found, then the corresponding Service Logic shall be invoked.
If a T‑BCSM was already invoked and there is a relationship with the gsmSCF at that moment, then no additional relationship shall be initiated.

Table 4.1: Mapping of Send Info For Incoming Call (SIFIC) ack, Send Routeing Info ack (SRI ack) or Resume Call Handling (RCH) to ISUP release causes for triggering criteria check

SIFIC ack / SRI ack / RCH "forwarding reason"	ISUP release cause number	ISUP release cause name
MS not reachable	20	Subscriber absent
MS Busy	17	User busy
Call deflection (note)	21	Call rejected
No reply	19	No answer from user (user alerted)
NOTE: Call Deflection is used only in the Resume Call Handling information flow, and in the VMSC. The same code point in the Send Routeing Info ack indicates CFU. However, the CFU invocation in the GMSC triggers the Terminating_Attempt_Authorised DP; thus the reason code mapping is not needed in the CFU case.

4.2.1.3 Relationship

If an armed DP is encountered, the gsmSSF provides an information flow via the already established relationship with the gsmSCF.

A relationship between the gsmSSF and the gsmSCF for the purpose of operator specific service processing is considered to be a CAMEL relationship. There are two types of CAMEL relationships:

– A CAMEL control relationship if the gsmSCF is able to influence the call processing via the relationship.

– A CAMEL monitor relationship if the gsmSCF is not able to influence the call processing via the relationship.

4.2.2 DP processing rules

The gsmSSF shall apply the following set of rules during DP processing to ensure a single point of control:

– EDPs are disarmed by the gsmSSF as they are encountered and reported to the gsmSCF, when the occurrence of another EDP causes the implicit disarming of the EDP or when the leg clears.

– A control relationship persists as long as there is 1 or more EDP‑R armed for this portion of the call or if the Process CS_gsmSSF is in any state except Monitoring or Idle.

– A control relationship changes to a monitor relationship if the control relationship does not persist and:

– 1 or more EDP‑N is armed, or

– 1 or more Call information Report is outstanding, or

– an Apply Charging Report is outstanding.

– If a control relationship does not persist and does not change to a monitor relationship then the relationship terminates. A monitor relationship terminates if there are neither EDP‑Ns armed nor reports outstanding or if the call clears.