6.4 Description of CAMEL State Models

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

GPRS can support multiple PDP contexts simultaneously for an attached subscriber, requiring the behaviour of a GPRS session to be modelled by two state models, one for the attach/detach procedures (GPRS Attach/Detach State Model) and the other for modelling individual PDP Contexts (GPRS PDP Context State Model).

6.4.1 General Handling

The GPRS State Model is used to describe the actions in an SGSN during processing of a GPRS session or PDP Contexts.

The GPRS State Model identifies the points in basic GPRS processing when Operator Specific Service (OSS) logic instances (accessed through the gsmSCF) are permitted to interact with basic GPRS control capabilities.

Figure 6.2shows the components that have been identified to describe a GPRS State Model.

Figure 6.2: GPRS State Model Components

6.4.2 GPRS Attach/Detach State Model

The GPRS Attach/Detach State Model is used to model the behaviour of the GPRS attach/detach procedures.

When encountering a DP the Attach/Detach State Model processing is suspended at the DP and the SGSN indicates this to the gprsSSF which determines what action, if any, shall be taken in case the DP is armed.

Figure 6.3: GPRS Attach/Detach State Model

Table 6.1: Description of GPRS Attach/Detach DPs in the SGSN

CAMEL Detection Point	DP Type	Description
DP Attach	TDP‑R	A request to attach is received.
DP Change of Position GPRS Session	TDP‑R1), EDP‑N	Routeing Area Update is accepted.
DP Detach	EDP‑N, EDP‑R	A detach request is received either from the MS, the SGSN or a ‘Cancel Location’ received from HLR or Inter SGSN Routeing update occurred in the old SGSN.
Note 1: Change of Position GPRS Session is reported as TDP‑R in the case of Inter‑SGSN Routeing Area Update (provided that this DP is statically armed in GPRS‑CSI). Change of Position GPRS Session is reported as EDP‑N in the case of Intra‑SGSN Routeing Area Update (provided that this DP is dynamically armed by the Service Logic).

6.4.2.1 Description of the Attach/Detach model (PIAs)

This subclause describes the model for the attach and detach a GPRS session in the SGSN. For each PIA a description can be found of the entry events, actions and exit events.

6.4.2.1.1 Detached

Entry events:

– Detach (user or network initiated) and clearing of a previous GPRS session.

– Processing of exceptional conditions.

Actions:

– Interface is idled.

– Attach request is received from MS containing the IMSI/P-TMSI and the type of attach requested and, the identity of the MS is established (IMSI) (DP Attach), or Inter-SGSN Routeing Area Update Request is accepted (DP Change of Position GPRS Session).

– Information being analyzed, e.g. GPRS‑CSI is analyzed.

Exit events:

– GPRS‑CSI is analyzed (DP Attach or DP Change of Position GPRS Session).

6.4.2.1.2 Attached

Entry events:

– GPRS‑CSI is analyzed (DP Attach).

Actions:

– MM contexts are established at the MS and the SGSN.

Exit events:

– A GPRS Detach request is received from the MS or from the network (DP Detach).

– Intra-SGSN Routeing Area Update is accepted (DP Change of Position GPRS Session).

– An exception is encountered.

The GPRS Attach/Detach State Model shall only have one or more GPRS PDP Context State Models associated with it when in the Attached state. A GPRS PDP Context State Model cannot exist without its associated GPRS Attach/Detach State Model being in the Attached state. Closure of the GPRS Attach/Detach State Model via a detach will result in the idling of all associated GPRS PDP Context State Models and the release of the associated GPRS PDP Contexts.

It shall not be necessary to trigger a relationship from the GPRS Attach/Detach State Model to the gsmSCF in order for triggering to occur in an associated GPRS PDP Context State Model. However, in this latter case a GPRS Attach/Detach State Model shall still exist at the SGSN. This is so that CSE-initiated detach events sent within a given GPRS PDP Context relationship shall result in the GPRS Attach/Detach State Model transiting to the Detached state. As noted above, in this state no PDP Contexts can exist and so all associated GPRS PDP Context State Models will transit to state Idle.

6.4.3 GPRS PDP Context State Model

The GPRS PDP Context State Model is used to model the behaviour for the GPRS PDP Context procedures. There is one PDP Context State Model per GPRS PDP context.

When encountering a DP the PDP Context State Model processing is suspended at the DP and the SGSN indicates this to the gprsSSF which determines what action, if any, shall be taken in case the DP is armed.

Figure 6.4: GPRS PDP Context State Model

Table 6.2: Description of GPRS PDP Context DPs in the SGSN

CAMEL Detection Point	DP Type	Description
DP PDP Context Establishment	TDP‑R1), EDP‑R, EDP‑N	Activate PDP Context request is received from the MS.
DP PDP Context Establishment Acknowledgement	TDP‑R2), EDP‑R, EDP‑N	Create PDP Context response is received from the GGSN.
DP PDP Context Disconnection	EDP‑N, EDP‑R	Deactivate PDP Context Request is received from the MS, Delete PDP Context request is received from the GGSN. Inter SGSN Routeing update occurred in old SGSN.
DP Change of Position Context	TDP‑R3), EDP‑N, EDP‑R	Routeing Area Update is accepted.
NOTE 1: The PDP Context Establishment shall be reported as TDP‑R (provided that this DP is statically armed in GPRS‑CSI) if there is no relationship with the gsmSCF. If there is a relationship with the gsmSCF it shall be reported as EDP‑R or EDP‑N if armed so. NOTE 2: The PDP Context Establishment Acknowledgement shall be reported as TDP‑R (provided that this DP is statically armed in GPRS‑CSI) if there is no relationship with gsmSCF. If there is a relationship with the gsmSCF, it shall be reported as EDP‑R or EDP‑N if armed so. NOTE 3: Change of Position Context is reported as TDP-R in the case of Inter-SGSN Routeing Area Update (provided that this DP is statically armed in GPRS‑CSI) if there is no relationship with the gsmSCF. Change of Position Context is reported as EDP‑N or EDP‑R in the case of Inter-SGSN Routeing Area Update (provided that this DP is armed as generic EDP) if there is a relationship with the gsmSCF. Change of Position Context is reported as EDP‑N in the case of Intra-SGSN Routeing Area Update (provided that this DP is dynamically armed by the Service Logic).

6.4.3.1 Description of the PDP Context model (PIAs)

This subclause describes the model for PDP Context State Model in the SGSN. For each PIA a description can be found of the entry events, actions and exit events.

6.4.3.1.1 Idle

Entry events:

– Deactivation (user or network initiated) and clearing of a previous PDP Context.

– Processing of exceptional conditions.

Actions:

– Interface is idled.

– Activate PDP Context request is received from MS (containing NSAPI, PDP Type, PDP Address, Access Point Name, QoS Requested, PDP Configuration Options), or Inter-SGSN Routeing Area Update is accepted (DP Change of Position Context).

– Information being analyzed, e.g. GPRS‑CSI is analyzed.

Exit events:

– GPRS‑CSI is analyzed (DP PDP Context Establishment or DP Change of Position Context, new SGSN).

6.4.3.1.2 PDP Context Setup

Entry events:

– GPRS‑CSI is analyzed (DP PDP Context Establishment).

Actions:

– APN and GGSN selection procedure is performed for a primary PDP context as specified in Annex A of 3GPP TS 23.060 [15]. APN and GGSN selection procedure is not performed for a secondary PDP context.

– Access Point Name is verified against the subscription. If the gsmSCF has provided an Access Point Name then the Access Point Name provided by the gsmSCF is checked against the subscription. For details refer to 3GPP TS 23.060 [15] Annex A.

– The operator determined barring category "Barring of all Packet Oriented Services " is checked and invoked if necessary.

– The operator determined barring category "Barring of Packet Oriented Services from access points that are within the HPLMN whilst the subscriber is roaming in a VPLMN" is checked and invoked if necessary.

– The operator determined barring category "Barring of Packet Oriented Services from access points that are within the roamed to VPLMN" is checked and invoked if necessary.

– The SGSN ensures that an already active PDP context is not reactivated.

– GGSN address is derived from the Access Point Name by interrogation of a DNS. The Access Point Name consists of a Network Identifier and an Operator Identifier.

– Create PDP Context Request is sent to the GGSN.

Exit events:

– Create PDP Context Response is received from the GGSN (DP PDP Context Establishment Acknowledgement).

– An exception is encountered.

6.4.3.1.3 PDP Context Established

Entry events:

– GPRS‑CSI is analyzed (DP PDP Context Establishment Acknowledgement or DP Change of Position Context).

Actions:

– PDP context is established at the MS and the SGSN.

Exit events:

– Deactivation of the PDP Context is received from the MS or the GGSN, or is due to an inter SGSN routing area update (DP PDP Context Disconnection, old SGSN).

– Intra-SGSN Routeing Area Update Request is received from the MS (DP Change of Position Context).

– Inter-SGSN Routeing Area Update (DP Change of Position Context, new SGSN).

– An exception is encountered.

6.4.3.1.4 Change of Position Context

Entry events:

– Inter SGSN Routing Area update accepted (new SGSN).

– Intra SGSN Routeing Area update request received from the MS.

Actions:

– PDP Context (containing NSAPI, PDP Type, PDP Address, Access Point Name, QoS Requested, PDP Configuration Options) is reestablished in case of Inter-SGSN Routeing Area update accepted (new SGSN).

– Intra SGSN Routeing Area updated.

Exit events:

– reestablishement of the PDP context at the new SGSN and return to PDP context established in case of inter SGSN Routeing Area update accepted in new SGSN (PIA PDP context established).

– Routeing Area update completed in case of intra SGSN Routeing Area update (PIA PDP context established).

6.4.4 GPRS CAMEL Scenarios

Two different scenarios are applicable for CAMEL control of GPRS.

Scenario 1:
Scenario 1 allows CAMEL control of the GPRS session and of multiple PDP contexts related to this session within a single GPRS dialogue.

Scenario 2:
Scenario 2 allows CAMEL control of single PDP contexts. Multiple PDP contexts are controlled in this scenario via multiple GPRS dialogues.

Scenario 1 and scenario 2 are mutually exclusive, i.e. it is not possible to use both for one GPRS session at the same time in one SGSN. A GPRS session is involved in GPRS CAMEL at one moment in time either by using scenario 1 or by using possible multiple instances of scenario 2. GPRS sessions in different SGSNs are independent from a CAMEL perspective.

6.4.4.1 GPRS CAMEL Scenario 1

Scenario 1 allows CAMEL control of the GPRS session and of multiple PDP contexts related to this session within a single GPRS dialogue (Session dialogue).

Figure 6.5: GPRS CAMEL Scenario 1

A GPRS dialogue in scenario 1 always consists of one GPRS Attach/Detach State Model and optionally of additional multiple GPRS PDP Context State Models related to the Attach/Detach State Model for the GPRS session. There is at most one GPRS Attach/Detach State Model per non idle GPRS session in one SGSN and at most one PDP Context State Model per active GPRS PDP context in one SGSN. The various PDP Context State Models are treated independently of each other.

The GPRS dialogue and the relationship between the GPRS Attach/Detach State Model and the gsmSCF are always initiated using the TDPs of the GPRS Attach/Detach State Model.

The gsmSCf requests further control or monitoring of individual GPRS PDP contexts using the Request Report GPRS Event information flow. To be informed about new individual PDP contexts the gsmSCF arms the DP ‘PDP Context Establishment’ or the DP ‘PDP Context Establishment Acknowledgement’ generically, i.e. without a PDP ID, as an EDP. To be informed about the handed over PDP contexts the gsmSCF arms the DP ‘Change of Position Context’ generically as an EDP‑N or EDP‑R.

Each GPRS PDP context is identified by a PDP ID. The PDP ID is assigned by the SGSN during PDP context establishment. The PDP ID is unique within one GPRS dialogue. The Request Report GPRS Event information flows to control new or handed over PDP contexts do not include a PDP ID. There is no ‘PDP ID’ related to the GPRS Attach/Detach State Model.

The PDP Id is reported to the gsmSCF in the first event notification for that PDP context.

6.4.4.2 GPRS CAMEL Scenario 2

Scenario 2 allows CAMEL control of single PDP contexts. Multiple PDP contexts are controlled in this scenario via multiple GPRS dialogues (PDP Context dialogues).

Figure 6.6: GPRS CAMEL Scenario 2

A GPRS dialogue in scenario 2 consists of a single GPRS PDP Context State Model. There is no GPRS Attach/Detach State Model involved in this scenario. There is at most one PDP Context State Model per active GPRS PDP context in one SGSN.

There might be multiple GPRS dialogues in scenarios 2 for one GPRS session, each of the dialogues controlling a single GPRS PDP context. The various GPRS dialogues are independent of each other.

The GPRS dialogue and the relationship between the GPRS PDP Context State Model and the gsmSCF are always initiated using the TDPs for the GPRS PDP Context State Model.

Control of further individual GPRS PDP contexts in the same GPRS dialogue as in scenario 1 is not possible. There are no PDP IDs in this scenario.

6.4.5 SGSN Routeing Area Update

6.4.5.1 Intra-SGSN Routeing Area Update

Intra-SGSN Routeing Area Update will be detected via the DP ‘Change of Position GPRS Session’ for the session using the GPRS Attach/Detach State Model and via the DPs ‘Change of Position Context’ for the individual PDP contexts using the GPRS PDP Context State Models.

It will be reported via an EDP‑N if the necessary EDP‑N is armed.

6.4.5.2 Inter-SGSN Routeing Area Update

Inter-SGSN Routeing Area Update from the old SGSN to the new SGSN will be detected via the DP ‘Change of Position GPRS Session’ for the session using the GPRS Attach/Detach State Model and via the DPs ‘Change of Position Context’ using the GPRS PDP Context State Models for the individual PDP contexts which have been handed over.

Scenario 1:

Inter-SGSN Routeing Area Update from the old SGSN to the new SGSN will be detected in the new SGSN via the DP ‘Change of Position GPRS Session’ for the session using the GPRS Attach/Detach State Model and in the new SGSN via the DPs ‘Change of Position Context’ using the GPRS PDP Context State Models for the individual PDP contexts which have been handed over.

In this scenario the DP ‘Change of Position GPRS Session’ is armed as a TDP‑R. If the Routeing Area Update is accepted the gprsSSF reports this TDP‑R to the gsmSCF using the Initial DP GPRS information flow. To be informed about new PDP contexts the gsmSCF arms the DP ‘PDP Context Establishment’ or the DP ‘PDP Context Establishment Acknowledgement’ generically as EDP‑R or EDP‑N. The DPs ‘Change of Position Context’ for the PDP contexts which have been handed over will be reported with all necessary information to the gsmSCF when the gprsSSF is continued, i.e. it is not longer waiting for instructions. Contexts which are not continued in the new SGSN are not reported. The EDPs for new PDP contexts are reported as usual.

The Detach in the old SGSN is reported to the gsmSCF, provided this event is armed. All outstanding reports in the old SGSN are sent to the gsmSCF and all open CDRs are closed.

Scenario 2:

Inter-SGSN Routeing Area Update from the old SGSN to the new SGSN will be detected in the new SGSN via the DPs ‘Change of Position Context’ using the GPRS PDP Context State Models for the individual PDP contexts which have been handed over.

In this scenario the DP ‘Change of Position Context’ is armed as TDP‑R. If the Routeing Area Update is accepted the gprsSSF reports these TDP‑Rs PDP contexts which have been handed over to the gsmSCF using the Initial DP GPRS information flows in multiple GPRS dialogues.

The PDP Context Disconnection in the old SGSN is reported to the gsmSCF, provided this event is armed. All outstanding reports in the old SGSN are sent to the gsmSCF and the open CDR is closed.

6.4.6 Rules for Implicit Disarming of Detection Points

The two tables below give the rules for implicit disarming of event detection points.

Implicit EDP disarming rules are specified for the Attach/Detach State Model and PDP Context State Model. The tables specify which EDP’s shall be disarmed (i.e. MonitorMode set to Transparent) if/when each EDP is encountered, irrespective of the EDP’s MonitorMode (Transparent, NotifyAndContinue, or Request).

EDPs which are armed generically for GPRS PDP Context State Models shall only be implicitly disarmed at the end of the GPRS dialogue. Explicit disarming is possible.

When EDP’s are armed with MonitorMode ‘Request’ (EDP‑Rs) are encountered, any implicit EDP disarming shall take place before reporting the EDP and transiting the gprsSSF to the WFI state (if not already suspended in the WFI state).

The table entry ‘X’ means that if one DP occurs (independently of arming and reporting to the gsmSCF) the marked one is implicitly disarmed. It shall be possible to rearm explicitly an implicitly disarmed DP.

Table 6.3: Implicit disarming rules for Scenario 1 (the rules apply for non-generically armed DPs)

Encountered DP	Implicit disarmed DPs
	Change of Position GPRS Session	Change of Position Context	Detach	PDP Context Establishment	PDP Context Establishment Acknowledgement	PDP Context Disconnection
Change of Position GPRS Session
Change of Position Context
Detach	X	X	X	X	X	X
PDP Context Establishment
PDP Context Establishment Acknowledgement					X
PDP Context Disconnection		X			X	X

Table 6.4: Implicit disarming rules for Scenario 2 (the rules apply for non-generically armed DPs)

Encountered DP	Implicit disarmed DPs
	Change of Position Context	PDP Context Establishment Acknowledgement	PDP Context Disconnection
PDP Context Establishment Acknowledgement		X
PDP Context Disconnection	X	X	X
Change of Position Context