1 Call forwarding unconditional (CFU)

23.0823GPPCall Forwarding (CF) Supplementary ServicesRelease 17Stage 2TS

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

1.1 Handling of call forwarding unconditional

1.1.1 Registration

At the beginning of registration subscription to the basic service, provision of the supplementary service and sufficiency of registration information has to be checked (see figure 1.2).

The following information has to be registered in the network:

1) the forwarded-to number (possibly including a sub-address);

2) information as to whether all calls or all calls of a specific basic service group should be forwarded.

The basic service group code

If the registration request received by the HLR does not contain any basic service group code, the registration shall be performed for all subscribed basic service groups for which CFU is provided, see figure 1.2.

The forwarded-to number

If the forwarded-to number is a number in the HPLMN country, it may be entered by the served mobile subscriber in three different formats, independent of his actual location, according to the schemes:

1) national (significant) number;

2) (trunk) prefix plus national (significant) number;

3) international prefix, country code, national (significant) number.

The received number may have to be converted to an international number before further processing.

The network may also validate the forwarded-to number before accepting the call forwarding registration request.

If a served mobile subscriber is provided with the Translation Information Flag (TIF-CSI) as part of the CAMEL subscriber data (refer to TS 23.078), the network shall accept and store the forwarded-to number transparently at the time of registration. In this case the network shall neither convert nor validate the received number. Therefore the forwarded-to number may not comply with the schemes indicated above.

For further details related to the handling of the forwarded-to number refer to figure 1.2.

Supplementary Service interaction

Possible interaction situations between CFU and other call forwarding and barring supplementary services must then be checked. This is described in figure 1.2. Also see technical specifications 3GPP TS 22.004 and 3GPP TS 22.082. For interaction between CFU and other supplementary services (ie not call barring or call forwarding services), the reader is referred to the respective technical specification for those supplementary services.

Interaction with CAMEL Phase 2 or higher

Possible interaction between CFU and CAMEL Phase 2 or higher is described in figure 1.2. If CAMEL Phase 2 or higher is not supported in the HLR, processing continues from the "No" exit of the test "Result=Pass".

Notifications to the subscriber

When the mobile subscriber registers CFU, the network shall attempt to register and activate the service. The network will return notification of acceptance of the request. This notification will include the forwarded-to number and possibly the basic service group code to which CFU is registered.

If the system cannot accept a registration request, the network sends a notification that CFU registration was not successful to the served mobile subscriber.

The information flow for registration of CFU is shown in figure 1.1.

MS MSC VLR HLR

───── ───── ───── ─────

│ │ │ │ │ │ │ │

│ │ Register CFU │ │ │ │ │ │

│ │—————>│ │ │ │ │ │

│ │ │ │Register CFU│ │ │ │

│ │ │ │———–>│ │ │ │

│ │ │ │ │ │Register CFU│ │

│ │ │ │ │ │———–>│ │

│ │ │ │ │ │ │CFU1│

│ │ │ │ │ │ Acknowledge│ │

│ │ │ │ │ │<———–│ │

│ │ │ │ Acknowledge│ │ │ │

│ │ │ │<———–│ │ │ │

│ │Release complete│ │ │ │ │ │

│ │<—————│ │ │ │ │ │

│ │ \Facility │ │ │ │ │ │

Figure 1.1: Registration of call forwarding unconditional

Figure 1.2: CFU1 Call forwarding unconditional registration process

1.1.2 Erasure

A previous registration can be erased in either of the following three ways:

– the subscriber can specifically erase a previous registration (to a basic service group) with an appropriate control procedure;

– the subscriber can register information for CFU (to a basic service group), thus causing previous registrations of CFU to be overridden (in the network this shall be handled as an erasure immediately followed by a registration);

– all information is erased as a result of withdrawal of the supplementary service (administrative handling).

The basic service group code

If the erasure request received by the HLR does not contain any basic service group code, the erasure request applies for all basic service groups for which CFU is registered. See figure 1.4.

Supplementary Service interaction

Possible interaction situations between CFU and other supplementary services must then be checked. This is shown in figure 1.4. Also see technical specifications 3GPP TS 22.004 and 3GPP TS 22.082. For interaction between CFU and other supplementary services (ie not call barring or call forwarding services), the reader is referred to the respective technical specification for those supplementary services.

Notifications to the subscriber

When the mobile subscriber erases CFU, the network shall attempt to erase (and thus deactivate) the service. The network shall send an indication of acceptance or rejection of the erasure request to the served mobile station.

The information flow for erasure of CFU is shown in figure 1.3.

MS MSC VLR HLR

───── ───── ───── ─────

│ │ Erase CFU │ │ │ │ │ │

│ │—————>│ │ Erase CFU │ │ │ │

│ │ │ │———–>│ │ Erase CFU │ │

│ │ │ │ │ │———–>│ │

│ │ │ │ │ │ │CFU2│

│ │ │ │ │ │ Acknowledge│ │

│ │Release complete│ │ Acknowledge│ │<———–│ │

│ │<—————│ │<———–│ │ │ │

│ │ \Facility │ │ │ │ │ │

│ │ │ │ │ │ │ │

Figure 1.3: Erasure of call forwarding unconditional

Figure 1.4: CFU2 Call forwarding unconditional erasure process

1.1.3 Activation

The network initially checks subscription to the basic service and registration status of the supplementary service, see figure 1.6.

Possible interaction situations between CFU and other supplementary services must then be checked. The SDL diagrams in figure 1.6 shows the function to be performed in the HLR in order to deal with the interactions between CFU and the call restriction and conditional call forwarding services. Also see 3GPP TS 22.004 [2] and 3GPP TS 22.082 [3]. For interaction between CFU and other supplementary services (ie not call barring or call forwarding services), the reader is referred to the respective technical specification for those supplementary services.

CFU may be active simultaneously with ACR (see 3GPP TS 23.088 [12]). If CFU and ACR are active simultaneously, then the ACR supplementary service shall take precedence over the CFU supplementary service, i.e. a call which is terminated for the served subscriber when CLI presentation is restricted shall be rejected according to the ACR supplementary service.

The Basic Service Group Code

If the activation request received by the HLR doesn’t contain any basic service group code, the activation request shall apply to all subscribed basic service groups against which a CFU forwarded-to number is registered. If a forwarded-to number is not registered against even a subset of the required basic service group, the request will be rejected.

Note that according to 3GPP TS 22.004 [2], a request for activation shall still be accepted although the CFU supplementary service was already active for all basic service groups.

Notification to the subscriber

The network will return notification of acceptance, partial acceptance or rejection of the request to the mobile station.

The information flow for activation of CFU is shown in figure 1.5.

MS MSC VLR HLR

─── ──── ──── ─────

│ │ Activate CFU │ │ │ │ │ │

│ │—————>│ │ Activate CFU │ │ │ │

│ │ │ │————–>│ │ Activate CFU │ │

│ │ │ │ │ │————->│ │

│ │ │ │ │ │ │CFU3│

│ │ │ │ │ │ Acknowledge │ │

│ │ │ │ │ │<————-│ │

│ │ │ │ Acknowledge │ │ │ │

│ │ │ │<————–│ │ │ │

│ │Release complete│ │ │ │ │ │

│ │<—————│ │ │ │ │ │

│ │ \Facility │ │ │ │ │ │

│ │ │ │ │ │ │ │

Figure 1.5: Activation of call forwarding unconditional

Figure 1.6: CFU3 Call forwarding unconditional activation process

1.1.4 Deactivation

The previous activation can be deactivated in either of the following three ways:

– the subscriber can specifically deactivate a previous activation (to a basic service group) with an appropriate control procedure;

– the subscriber can register information for CFU (to a basic service group), thus causing previous registrations and activations of CFU to be overridden (this shall be handled in the same way as an erasure (implying deactivation) immediately followed by a registration (implying activation));

– the service is deactivated as a result of withdrawal of the supplementary service (administrative handling).

Possible interaction situations between CFU and other supplementary services must be checked. The SDL diagram in figure 1.8 shows the function to be performed in the HLR in order to deal with the possible interactions between CFU and the conditional call forwarding services.

The Basic Service Group Code

The CFU deactivation request may specify a basic service group for which deactivation is required. If the deactivation request received by the HLR doesn’t contain any basic service group code, the deactivation request shall apply to all basic services for which CFU is active, see figure 1.8.

If the deactivation request received by the HLR contains a basic service group code, only information related to the specified basic service group(s) is affected. Note that according to 3GPP TS 22.004, a request for deactivation shall still be accepted even if the CFU supplementary service was already deactive for all basic service groups.

The user shall receive a notification of acceptance or rejection of the CFU deactivation request.

The information flow for deactivation of call forwarding unconditional is shown in figure 1.7.

MS MSC VLR HLR

─── ──── ──── ─────

│ │Deactivate CFU │ │ │ │ │ │

│ │—————>│ │Deactivate CFU │ │ │ │

│ │ │ │————–>│ │Deactivate CFU│ │

│ │ │ │ │ │————->│ │

│ │ │ │ │ │ │CFU4│

│ │ │ │ │ │ Acknowledge │ │

│ │ │ │ Acknowledge │ │<————-│ │

│ │Release complete│ │<————–│ │ │ │

│ │<—————│ │ │ │ │ │

│ │ \Facility │ │ │ │ │ │

Figure 1.7: Deactivation of call forwarding unconditional

Figure 1.8: CFU4 Call forwarding unconditional deactivation process

1.1.5 Interrogation

Data request

The data request procedure enables the mobile subscriber to obtain information about the data stored in the PLMN. Interrogation of CFU is handled by the HLR which returns the required information or error to the MS, see figure 1.9.

MS MSC VLR HLR

─── ──── ──── ────

│ │Interrogate CFU │ │ │ │ │ │

│ │—————>│ │ │ │ │ │

│ │ │ │Interrogate CFU│ │ │ │

│ │ │ │————–>│ │ │ │

│ │ │ │ │ │Interrogate CFU│ │

│ │ │ │ │ │————–>│ │

│ │ │ │ │ │ │ │

│ │ │ │ │ │ Acknowledge │ │

│ │ │ │ │ │<————–│ │

│ │ │ │ Acknowledge │ │ │ │

│ │ │ │<————–│ │ │ │

│ │Release complete│ │ │ │ │ │

│ │<—————│ │ │ │ │ │

│ │ \Facility │ │ │ │ │ │

│ │ │ │ │ │ │ │

Figure 1.9: Interrogation of call forwarding unconditional

1.2 Functions and information flows

The following Mobile Additional Function has been identified for the PLMN:

MAF007

Call forwarding unconditional authorizations examination

The ability of a PLMN component to determine the authorizations relating to CFU.

See figure 1.10.

Location: HLR.

The information flow for call forwarding unconditional is shown in figure 1.11.

Figure 1.10: MAF007 Call forwarding unconditional authorisations examination (HLR)

MSa/TEa GMSC HLRb MSCb LEc ß

─────── ─────── ─────── ───── ───────

│ │ │ │ │ │ │ │ │ │

│ │ Set-up │ │ │ │ │ │ │ │

│ │————->│ │ Info request │ │ │ │ │ │

│ │ │ │————->│ │ │ │ │ │

│ │ │ │ │ │ │ │ │ │

│ │ │ │ Info ack │MAF007│ │ │ │ │

│ │ │ │<————-│ │ │ │ │ │

│ │ │ │ │ │ │ │ │ │

│ │ │ │ Set-up │ │ │ │ │ │

│ │ │OR1:N │—————————>│ │ │ │

│ │ │ │ │ │ │ │ │ │

│ │ │ │ Set-up │ │ │ │ │ │

│ │ │OR1:Y │————————————–>│ │

│ │ │ │ │ │ │ │ │ │

│ │ Notification │ │ │ │ │ │ │ │

│ │<————-│OR2:Y │ │ │ │ │ │ │

│ │ │ │ │ │ │ │ │ │

MSa/TEa GMSC HLRb MSCb HLRc SCcß

───── ─────── ─────── ─── ─── ───

│ │ │ │ │ │ │ │ │ │ │ │

│ │ Set-up │ │ │ │ │ │ │ │ │ │

│ │————->│ │ Info request │ │ │ │ │ │ │ │

│ │ │ │————->│ │ │ │ │ │ │ │

│ │ │ │ │ │ │ │ │ │ │ │

│ │ │ │ Info ack │MAF007│ │ │ │ │ │ │

│ │ │ │<————-│ │ │ │ │ │ │ │

│ │ │ │ │ │ │ │ │ │ │ │

│ │ │ │ Set-up │ │ │ │ │ │ │ │

│ │ │OR1:N │————————–>│ │ │ │ │ │

│ │ │ │ │ │ │ │ │ │ │ │

│ │ │ │ Information request │ │ │ │ │ │

│ │ │OR1:Y │———————————->│ │ │ │

│ │ │ │ │ │ │ │ │ │ │ │

│ │ │ │ Information acknowledge │ │ │ │ │ │

│ │ │ │<———————————-│ │ │ │

│ │ │ │ │ │ │ │ │ │ │ │

│ │ │ │ Set-up │ │ │ │ │ │ │ │

│ │ │ │——————————————–>│ │

│ │ Notification │ │ │ │ │ │ │ │ │ │

│ │<————-│OR2:Y │ │ │ │ │ │ │ │ │

│ │ │ │ │ │ │ │ │ │ │ │

NOTE: info: information Y: Yes
req: request N: No
ack: acknowledge
OR1: Forwarding requested
OR2: Notification to calling subscriber required

Figure 1.11: Information flow for call forwarding unconditional

1.3 Information stored in the HLR

The following logical states are applicable for CFU
(refer to 3GPP TS 23.011 for an explanation of the notation):

Provisioning State	Registration State	Activation State	HLR Induction State
(Not Provisioned,	Not Registered,	Not Active,	Not Induced)
(Provisioned,	Not Registered,	Not Active,	Not Induced)
(Provisioned,	Registered,	Not Active,	Not Induced)
(Provisioned,	Registered,	Active and Quiescent,	Not Induced)
(Provisioned,	Registered,	Active and Operative,	Not Induced)

The registration and activation state may be different for each applicable elementary basic service group.

The provisioning state shall be on a per subscriber basis, and hence the same for all basic service groups.

The HLR shall store:

– the state of CFU (which shall be one of the valid states listed above) for each applicable elementary basic service group;

– the subscription option "notification to the calling party" on a per subscriber basis;

This subscription option takes one of the following values:

– no notification;

– notification.

– the subscription option "MSISDN of the served subscriber can be presented to the forwarded-to subscriber" on a per subscriber basis;

This subscription option takes one of the following values:

– presentation restricted;

– presentation allowed.

– the registration parameter "forwarded-to number" (possibly including a forwarded-to sub-address) for each applicable elementary basic service group.

– the default forwarded-to number (containing less than 16 digits) for each applicable elementary basic service group.

Note that the value "Active and Quiescent" of the activation state is required in case of interaction with Operator Determined Barring (see 3GPP TS 23.015).

1.4 State transition model

The following figure shows the successful cases of transition between the applicable logical states of CFU. The state changes are either caused by actions of the service provider, the mobile user or the network.

Note that error cases are not shown in the diagram as they normally do not cause a state change. Additionally, some successful requests may not cause a state change. Hence, they are not shown in the diagram.

The diagram only shows operations on an elementary basic service group.

Figure 1.12: State transition model for CFU

1.5 Transfer of information from HLR to VLR

If the provisioning state for CFU is "Provisioned" then, when the subscriber registers on a VLR, the HLR shall send that VLR information about the logical state of CFU for all relevant elementary basic service groups.

If the logical state of CFU is changed while a subscriber is registered on a VLR then for the affected basic service groups, the HLR shall inform the VLR of the new logical state of CFU.

1.6 Information stored in the VLR

For CFU the VLR shall store the service state information received from the HLR for all relevant elementary basic service groups.

1.7 Handover

Handover will have no impact on the control procedure and the operation of the service.

1.8 Cross phase compatibility

1.8.1 MS, MSC, VLR or HLR only support Phase 1 control of SS by the subscriber

In response to a CFU interrogation request, if the MS or any network element involved is of Phase 1, only information concerning basic service groups for which the activation state has the value "Active and Operative" will be returned. This means, for example, that the subscriber will not be aware that the forwarded to number is registered if CFU is deactivated. A subaddress (if registered) will not be included in the response.

Note that if any network element involved is of Phase 1, CFU Registration requests which use a subaddress and all CFU Activation and Deactivation requests will be rejected, as these are not specified in Phase 1.

1.8.2 HLR only supports Phase 1 updating of subscriber information

The VLR shall ignore the subscription option "notification to the calling party" and the registration parameter "forwarded to number" when received from a Phase 1 HLR.

If the VLR receives the SS-Status parameter from a Phase 1 HLR it shall act if it has received the SS-Status parameter with the values shown in the following:

1) Activated => A bit = 1, Q bit = 0;

2) Deactivated => A bit = 0, Q bit = 0 or 1

1.8.3 VLR only supports Phase 1 updating of subscriber information

When passing CFU information to a Phase 1 VLR, the HLR shall send the service state information in a form which the VLR can accept, based on the logical state held in the HLR, as follows:

1) (Provisioned, Not Registered, Not Active, Not Induced)

=> Erased, Deactivated;

2) (Provisioned, Registered, Not Active, Not Induced)

=> Registered, Deactivated;

3) (Provisioned, Registered, Active and Operative, Not Induced)

=> Registered, Activated;

4) (Provisioned, Registered, Active and Quiescent, Not Induced)

=> Registered, Deactivated.

The HLR shall not pass a subaddress to a Phase 1 VLR.

1.8.4 GMSC only supports Phase 1 call handling

When a call is forwarded unconditionally, the HLR shall not pass the subaddress to a Phase 1 GMSC. Calls shall be forwarded without the subaddress.

1.8.5 GMSC does not support CAMEL or supports CAMEL Phase 1 only

If the activation state of CFU is "Active and Operative" and if the forwarded-to number is registered in a format other than international and if the GMSC does not support CAMEL or supports CAMEL Phase 1 only, then when a request for routeing information for a mobile terminated call is received in the HLR, CFU shall not be invoked, i.e. the mobile terminated call establishment will be continued towards the served mobile subscriber.

1.9 Contents of Messages

1.9.1 Messages on the C interface (MSC-HLR)

1.9.1.1 Send Routing Info

This message is specified in 3GPP TS 23.018.

Send Routing Info contains the following IE
specific to Long Forwarded-to Numbers:

Information element name	Required	Description
Long FTN supported	C	Shall be present if the GMSC supports Long Forwarded-to Numbers; otherwise shall be absent.

1.9.1.2 Send Routing Info ack

This message is specified in 3GPP TS 23.018.

Send Routing Info ack contains the following amendment to the Forwarded-
to number IE and an additional IE specific to Long Forwarded-to Numbers:

Information element name	Required	Description
Forwarded-to number	C	E.164 number of the C subscriber. Shall be present if the HLR has determined that the call is to be forwarded and at least one of the HLR and GMSC does not support Long Forwarded-to Numbers; otherwise shall be absent.
Long forwarded-to number	C	Number of the C subscriber. Shall be present if the HLR has determined that the call is to be forwarded and Long Forwarded-to Numbers are supported by the HLR and the GMSC; otherwise shall be absent.

1.9.2 Messages on the Um, B and D interfaces (MS – network)

1.9.2.1 RegisterSS

This message corresponds to the MAP_REGISTER_SS service
specified in 3GPP TS 29.002.

Information element name	Required	Description
Long FTN supported	C	Shall be present if the MS supports Long Forwarded-to Numbers; otherwise shall be absent.

1.9.2.2 ActivateSS

This message corresponds to the MAP_ACTIVATE_SS service
specified in 3GPP TS 29.002.

Information element name	Required	Description
Long FTN supported	C	Shall be present if the MS supports Long Forwarded-to Numbers; otherwise shall be absent.

1.9.2.3 InterrogateSS

This message corresponds to the MAP_INTERROGATE_SS service
specified in 3GPP TS 29.002.

Information element name	Required	Description
Long FTN supported	C	Shall be present if the MS supports Long Forwarded-to Numbers; otherwise shall be absent.

1.9.3 Information flows on the J interface (HLR – gsmSCF)

1.9.3.1 Any Time Subscription Interrogation

This IF is specified in 3GPP TS 23.078.

Any Time Subscription Interrogation contains
the following IE specific to Long Forwarded-to Numbers:

Information element name	Required	Description
Long FTN supported	C	Shall be present if the gsmSCF supports Long Forwarded-to Numbers; otherwise shall be absent.

1.9.3.2 Any Time Subscription Interrogation ack

This IF is specified in 3GPP TS 23.078.

The Call forwarding SS data IE within the Any Time Subscription Interrogation ack IF contains the following amendment to the Forwarded-to number IE and an additional IE specific to Long Forwarded-to Numbers:

Information element name	Required	Description
Forwarded-to number	C	Shall be present if at least one of the HLR and the gsmSCF does not support Long Forwarded-to Numbers; otherwise shall be absent.
Long forwarded-to number	C	Shall be present if the HLR and the gsmSCF support Long Forwarded-to Numbers; otherwise shall be absent.

1.9.3.3 Any Time Modification

This IF is specified in 3GPP TS 23.078.

Any Time Modification contains the following IE specific to Long Forwarded-to Numbers:

Information element name	Required	Description
Long FTN supported	C	Shall be present if the gsmSCF supports Long Forwarded-to Numbers; otherwise shall be absent.

1.9.3.4 Any Time Modification ack

This IF is specified in 3GPP TS 23.078.

The Call forwarding SS data IE within the Any Time Modification ack IF contains the following amendment to the Forwarded-to number IE and an additional IE specific to Long Forwarded-to Numbers.

Information element name	Required	Description
Forwarded-to number	C	Shall be present if at least one of the HLR and the gsmSCF does not support Long Forwarded-to Numbers; otherwise shall be absent.
Long forwarded-to number	C	Shall be present if the HLR and the gsmSCF support Long Forwarded-to Numbers; otherwise shall be absent.

1.10 Exceptional Procedures

1.10.1 MS does not support Long Forwarded-to Numbers

The MS shall indicate whether it supports Long Forwarded-to Numbers in the RegisterSS, ActivateSS and InterrogateSS messages.

If the MS does not support Long Forwarded-to Numbers, and a long forwarded-to number is registered, the acknowledgement message shall not contain a forwarded-to number.

1.10.2 HLR does not support Long Forwarded-to Numbers

The HLR shall not allow a subscriber to register a long forwarded-to number.

1.10.3 GMSC does not support Long Forwarded-to Numbers

The HLR can determine from the Send Routing Info message whether the GMSC supports Long Forwarded-to Numbers.

If the GMSC does not support Long Forwarded-to Numbers and the HLR identifies that CFU should be invoked, then:

– If the registered forwarded-to number contains a maximum of 15 digits then the HLR shall populate the Forwarded‑to number parameter in the Send Routing Info ack message with the registered forwarded-to number.

– If the registered forwarded-to number contains more than 15 digits then

– If a default forwarded-to number (containing a maximum of 15 digits) is stored in the HLR, the HLR shall populate the Forwarded-to number parameter in the Send Routing Info ack message with the default forwarded-to number

– Otherwise, the HLR shall instruct the GMSC to release the call.