2 Call Forwarding on mobile subscriber Busy (CFB)

04.823GPPCall Forwarding (CF) Supplementary ServicesStage 3TS

2.1 Normal operation

2.1.1 Served mobile subscriber side

When call forwarding on mobile subscriber busy is active, the following actions are taken by the network:

‑ If the mobile is Network Determined User Busy (NDUB as defined in GSM 02.01), incoming calls for the specified basic service(s) will be forwarded without being offered to the served mobile subscriber.

‑ If the mobile is not NDUB, the incoming call is offered (as a normal or waiting call) to the served mobile subscriber.

‑ if the call is subsequently released by the mobile with the first clearing message containing the cause = "User Busy" before the CONNECT message is received, it will be forwarded by the network, see figure 2.0;

‑ if any other release causes are given, the call will be released;

‑ if one of the call control timers (T303 or T310) elapse, the call will be released.

MS Network

SETUP

<————————————————————————————————————————

….Transaction Identifier (A-B)….

RELEASE COMPLETE/RELEASE/DISCONNECT

————————————————————————————————————————>

….Transaction Identifier (A-B)….

….Cause # 17 (User Busy)….

Figure 2.0: Call which is offered to the served mobile subscriber being released.
The network will invoke call forwarding on mobile subscriber busy in this case,
if CFB is active for the requested basic service

When an incoming call is forwarded on mobile subscriber busy due to NDUB the served mobile subscriber can, as a subscription option, receive a NotifySS operation containing the SS-Notification indicating that a call has been forwarded, see figure 2.1. He will not be able to answer the incoming call.

The transaction identifier employed shall correspond to any call B is having.

MS Network

FACILITY (TI=B-X)

<————————————————————————————————————————

Facility (Invoke = NotifySS (CFB, SS-Notification))

NOTE: X is any party with which B has a call.

Figure 2.1: Notification to the served mobile subscriber that a call is forwarded on mobile subscriber busy

When CFB is active, the ability of the served mobile subscriber to originate calls is not affected. However, a NotifySS operation containing the SS‑Status indicating that a conditional call forwarding supplementary service is currently active and operative will be sent to the served mobile subscriber each time an outgoing call is made, see figure 2.2.

MS Network

SETUP

————————————————————————————————————————>

e.g. ALERTING

<————————————————————————————————————————

Facility (Invoke = NotifySS (SS-Code, SS-Status))

NOTE: The SS‑Code will be the common SS‑Code for all conditional call forwarding services.

Figure 2.2: Notification to the served mobile subscriber
that a conditional call forwarding service is active

2.1.2 Forwarded‑to mobile subscriber side

The forwarded‑to mobile subscriber will receive a NotifySS operation containing the SS‑Notification indicating that the incoming call is a forwarded call. When available, the SS‑Code of the invoked forwarding service is also included, see figure 2.3.

When multiple forwarding occurs the value of the SS‑Code shall relate to the last invoked forwarding service.

In addition the forwarded-to mobile subscriber will receive the redirecting party BCD number and optionally, a redirecting party subaddress.

The redirecting party BCD number information element is made up of a number of information units as indicated in GSM 04.08.

In addition to or instead of the redirecting party’s digits, the subscriber may be given the following information:

– screening indicator;

– presentation indicator.

Indicator values are given in GSM 04.08.

The redirecting party subaddress information element is made up of a number of information units as indicated in GSM 04.08.

MS Network

SETUP

<————————————————————————————————————————

Facility (Invoke = NotifySS (CFB, SS-Notification))

Redirecting party BCD number (screening indicator, presentation indicator, redirecting party digits),

Redirecting party subaddress

NOTE: If the specific call forwarding service is not known the common SS-Code for all forwarding SS will be used.

Figure 2.3: Notification to the forwarded‑to mobile subscriber
that the incoming call is a forwarded call

2.1.3 Calling mobile subscriber side

As a subscription option, the served mobile subscriber can request that the calling mobile subscriber receives a NotifySS operation containing the SS‑Notification indicating that the call has been forwarded. When available, the SS‑Code of the invoked forwarding service is also included, see figure 2.4.

MS Network

SETUP

————————————————————————————————————————>

FACILITY

<————————————————————————————————————————

Facility (Invoke = NotifySS (CFB, SS-Notification))

NOTE: If the specific call forwarding service is not known the common SS‑Code for all forwarding SS will be used.

Figure 2.4: Notification to the calling mobile subscriber that the call is forwarded

2.2 Registration

The following information has to be registered in the network:

‑ the ForwardedToNumber which may be accompanied by a ForwardedToSubAddress;

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

2.2.1 Registration by the served mobile subscriber

A CFB registration request from a mobile user shall include the SS‑Code of the forwarding service to be registered, and possibly the BasicServiceCode the request applies to. If the BasicServiceCode is not included, the request applies to all basic services.

If the registration is successful, the CFB service will be registered and activated. The network will then send a return result indicating acceptance of the request, including the ForwardedToNumber and possibly the BasicService (group) Code to which CFB is registered. If the request applied to a single elementary basic service group, the ForwardedToNumber may be accompanied by a ForwardedToSubAddress. In other cases the result shall not contain a ForwardedToSubAddress. The result may also contain an SS‑Status parameter. If the MS does not send an SS Version Indicator in the invocation request then the network shall send an SS‑Status in the result. If the MS does send an SS Version Indicator in the invocation request then the inclusion of SS‑Status in the result is optional. If the SS‑Status is included the network shall set it to reflect the state of the service. The MS shall ignore the contents of the SS‑Status parameter if one is received. See figure 2.5.

Note that the use of SS‑Status is to provide backwards compatibility with phase 1.

If the system cannot accept a registration request, a corresponding error indication is returned to the served mobile subscriber that CFB registration was not successful. Error values are specified in GSM 04.80.

MS Network

REGISTER

————————————————————————————————————————>

Facility (Invoke = RegisterSS (CFB, BasicServiceCode, ForwardedToNumber, ForwardedToSubAddress))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = RegisterSS (BasicServiceCode, SS-Status, ForwardedToNumber, ForwardedToSubAddress))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: If BasicServiceCode is not included it applies to all basic services. The ForwardedToNumber may be accompanied by a ForwardedToSubAddress. The SS‑Status may not be included in all cases, see text.

Figure 2.5: Registration of call forwarding on mobile subscriber busy

The SS‑Code may indicate the code for "all forwarding SS", as specified in subclause 1.2.1.

The SS‑Code may indicate the code for "all conditional forwarding SS". In this case the return result shall contain the information for any conditional call forwarding services which the subscriber has provisioned.

2.3 Erasure

A previous registration can be erased in one of three ways:

‑ the subscriber can specifically erase a previous registration with an appropriate control procedure;

‑ the subscriber can register information for CFB for the specific basic service to another directory number, thus causing the previous registration of CFB to be overridden;

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

2.3.1 Erasure by the served mobile subscriber

A CFB erasure request from a mobile subscriber may include the BasicServiceCode. If this is not the case, the erasure applies to all basic services.

If the erasure is successful, the CFB service will be erased (and automatically deactivated). The network will then send a return result indicating acceptance of the request. The result is formatted according to the options shown below:

‑ The result includes the BasicService (group) Code for which CFB was erased. The result may also contain an SS‑Status parameter. If the MS does not send an SS Version Indicator in the invocation request then the network shall send an SS‑Status in the result. If the MS does send an SS Version Indicator in the invocation request then the inclusion of SS‑Status in the result is optional. If the SS‑Status is included the network shall set it to reflect the state of the service. The MS shall ignore the contents of the SS‑Status parameter if one is received. See figure 2.6.

Note that the use of SS‑Status is to provide backwards compatibility with phase 1.

‑ If the request did not include a BasicServiceCode, and the erasure was successful for all basic services, the network may send an empty return result to the MS. This option applies whether or not an SS Version Indicator is received from the MS.

If the network cannot accept the erasure request, the status of CFB in the network remains unchanged. An error indication will then be returned to the served mobile subscriber that erasure of CFB was unsuccessful. Error values are specified in GSM 04.80.

MS Network

REGISTER

————————————————————————————————————————>

Facility (Invoke = EraseSS (CFB, BasicServiceCode))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = EraseSS (BasicServiceCode, SS-Status))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: If BasicServiceCode is not included it applies to all basic services. The SS‑Code may also indicate the code for "all conditional forwarding SS" or the code for "all forwarding SS". The SS‑Status may not be included in all cases, see text.

Figure 2.6: Erasure of call forwarding on mobile subscriber busy

2.4 Activation

An explicit CFB activation request shall contain the SS‑Code of the supplementary service to be activated and possibly the BasicServiceCode the request applies to. If a BasicServiceCode is not included in the activation request the request applies to all basic services against which CFB forwarded‑to number is registered. The user shall receive appropriate notification of acceptance, rejection or partial acceptance of the CFB activation request, see figure 2.7.

Error values to be used in the two latter situations are specified in GSM 04.80.

MS Network

REGISTER

————————————————————————————————————————>

Facility (Invoke = ActivateSS (CFB, BasicServiceCode))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = ActivateSS (SS-Status))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: The SS‑Code may also indicate the code "all conditional forwarding SS" group, as specified in subclause 2.2.1, or the "all forwarding SS" group, as specified in subclause 1.2.1.

Figure 2.7: Activation of call forwarding on mobile subscriber busy

2.5 Deactivation

An explicit CFB deactivation request shall contain the SS‑Code of the supplementary service to be deactivated and possibly the BasicServiceCode the request applies to. If a BasicServiceCode is not included in the deactivation request the request applies to all basic services against which CFB is activated. The user shall receive appropriate notification of acceptance or rejection of the CFB deactivation request, see figure 2.8.

Error values to be used in the latter situation are specified in GSM 04.80.

Deactivation shall not lead to erasure of the information registered in the network.

MS Network

REGISTER

————————————————————————————————————————>

Facility (Invoke = DeactivateSS (CFB, BasicServiceCode))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = DeactivateSS (SS-Status))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: The SS‑Code may also indicate the "all conditional forwarding SS" group or the "all forwarding SS" group.

Figure 2.8: Deactivation of call forwarding on mobile subscriber busy

2.6 Interrogation

Data request

The data request procedure enables the mobile subscriber to obtain information about the data stored in the PLMN. After having requested this procedure the network shall return the following information:

‑ in response to a general data request (i.e. not including a BasicServiceCode) the served mobile subscriber should be given the following data for each basic service group to which CFB is registered:

‑ the SS‑Status indicating whether the supplementary service is "not active", "active and operative" or "active and quiescent";

‑ the associated ForwardedToNumber which shall not be accompanied by a ForwardedToSubAddress,

see figure 2.9.

If CFB is not registered for any basic service groups, only the SS‑Status parameter indicating "not registered" is returned.

MS Network

REGISTER

————————————————————————————————————————>

Facility (Invoke = InterrogateSS (CFB))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = InterrogateSS (BasicServiceCode, SS-Status, ForwardedToNumber))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: The ForwardedToNumber shall not be accompanied by a ForwardedToSubAddress. The return result may consist of a list of parameters, each relating to a specific basic service group.

Figure 2.9: Interrogation of active call forwarding on mobile subscriber busy for all basic services

‑ in response to a specific request (i.e. containing one particular BasicService (group) Code, the served mobile subscriber should receive the SS‑Status parameter, indicating whether or not CFB is registered, including information as to whether or not it is active and operative or active and quiescent for that basic service group. If CFB is registered, the associated ForwardedToNumber shall be given, see figure 2.10. If the request applied to a single elementary basic service group, the ForwardedToNumber may be accompanied by a ForwardedToSubAddress. In other cases the result shall not contain a ForwardedToSubAddress.

If CFB is not registered for the interrogated BasicService (group) code, only the SS‑Status parameter indicating "not registered" is returned.

MS Network

REGISTER

————————————————————————————————————————>

Facility (Invoke = InterrogateSS (CFB, BasicServiceCode))

RELEASE COMPLETE

<————————————————————————————————————————

Facility (Return result = InterrogateSS (BasicServiceCode, SS-Status, ForwardedToNumber, ForwardedToSubAddress))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Return error (Error))

RELEASE COMPLETE

<- – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Facility (Reject (Invoke_problem))

NOTE: The ForwardedToNumber may be accompanied by a ForwardedToSubAddress.

Figure 2.10: Interrogation of active call forwarding on
mobile subscriber busy for one particular basic service

The values "all forwarding SS" and "all conditional forwarding SS" shall not be sent over the air interface by the MS in an interrogation. If an interrogation is received containing one of these codes the network shall send a return error component.

2.7 Cross phase compatibility

2.7.1 Network only supports protocol version 1 control of SS by the subscriber

A CFB registration request which contains a ForwardedToSubaddress shall be rejected by the network if any network element involved is of protocol version 1.

Note that a CFB activation or deactivation request will be rejected by the network is any network element involved is of protocol version 1.

2.7.2 MS only supports protocol version 1 control of SS by the subscriber

In response to a CFB interrogation request, where the SS Version Indicator is not received from the MS, the network shall only return data for basic service groups to which CFB is activated and operative. Data shall not be returned for basic service groups to which CFB is deactivated. This means that the subscriber is not always aware of the true state of the service.

In response to a CFB registration or erasure request, where the SS Version Indicator is not received from the MS, the network shall always include the SS‑Status parameter.