SIST ETS 300 199 E1:2003

• Abstract:

  DE/NA-012204

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.080 - Integrated Services Digital Network (ISDN)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Ref Project: ETSI ETS 300 199 ed.1 (1994-12) - Integrated Services Digital Network (ISDN); Call Forwarding Busy (CFB) supplementary service; Service description

SIST ETS 300 199 E1:2003 is the Slovenian adoption of ETS 300 199 Edition 1, published by SIST from an ETSI European Telecommunications Standard. It specifies the stage 1 service description for the Integrated Services Digital Network (ISDN) Call Forwarding Busy (CFB) supplementary service, including how calls are redirected when the served user is busy. It is aimed at service providers, network engineers, and implementers who need the user-level behavior, subscription options, forwarding rules, and interworking conditions for CFB.

What does SIST ETS 300 199 E1:2003 specify?

SIST ETS 300 199 E1:2003 specifies the overall, user-facing description of the CFB supplementary service for the pan-European ISDN. It also sets the interworking requirements for private ISDNs and describes the base functionality when the service is offered through a private ISDN.

The document is organized into these main clauses:

• Scope
• Normative references
• Definitions
• Symbols and abbreviations
• Description
• Procedures
• Intercommunication considerations
• Interaction with other supplementary services

Clause 6 contains the operating procedures, and Table 1 in clause 6.1 collects the subscription options that control forwarding notifications and number presentation.

The standard applies to all circuit-switched telecommunication services. It excludes charging principles and interactions with supplementary services not listed in clause 8.

What are the key requirements of SIST ETS 300 199 E1:2003?

Service availability and basic behavior

SIST ETS 300 199 E1:2003 says that CFB is available to users connected by basic access or primary rate access. When the served user’s number is busy, the network redirects the incoming call to another user.

In practice, this means the service can be applied to all calls or only to calls associated with selected basic services. The served user’s ability to make outgoing calls is not changed by CFB.

The document also allows a service provider option to notify the served user that CFB is active when that user makes a call. That matters operationally because the user can be aware that calls to their number are being forwarded.

Subscription and activation options

SIST ETS 300 199 E1:2003 allows CFB to be subscribed on a per ISDN number basis or for the whole access, depending on the service provider offer. It also allows the user to apply CFB to all subscribed basic services or to selected basic services.

Clause 6.1 defines four subscription options in Table 1: whether the served user receives notification that a call has been forwarded, whether the calling user receives notification, whether the served user receives a notice that CFB is currently activated, and whether the served user’s ISDN number may be presented to the forwarded-to user.

This matters in practice because those options control what each party sees during forwarding and what information the service provider must store and present.

Forwarding limits and call handling

SIST ETS 300 199 E1:2003 limits the number of diversions per call, with a service provider option and an upper limit of five diversions. All diversion types count toward that limit.

The standard distinguishes between user determined user busy and network determined user busy. If the user is offered the call and indicates busy, the network may then forward it. If the network already knows the user is busy, it forwards the call without offering it first.

This distinction matters because it affects when the served user is alerted, when forwarding starts, and which notification path is used.

Notification to the served user, forwarded-to user, and calling user

SIST ETS 300 199 E1:2003 defines what each party can be told during forwarding. The served user can be informed that CFB has been invoked, the forwarded-to user can be told that the call was forwarded and may receive the served user’s number, and the calling user can receive forwarding notifications depending on the chosen subscription option.

When multiple diversions occur, the information passed onward can include the originally called user’s number, the last diverting user’s number, and the reason for the last diversion. In practice, this lets the network preserve traceability through a chain of forwarding events.

The standard also says that if a number cannot be shown, the user who would have received it is told why it was not available. That is important for user support and for consistent handling of presentation restrictions.

Activation, deactivation, interrogation, and rejection

SIST ETS 300 199 E1:2003 says that activation requires the forwarded-to user’s address, and optionally a subaddress, plus the basic service scope of the activation. Deactivation and interrogation follow similar identification rules when multiple ISDN numbers are present on an access.

The network can reject requests for reasons such as missing information, an invalid forwarded-to number, use of a special service number, or trying to activate CFB for a basic service where it does not apply. If a request is rejected, only the terminal that made the request is informed.

This matters because provisioning systems and customer support tools must validate the request before accepting or changing the service state.

Interworking and service interactions

SIST ETS 300 199 E1:2003 covers interworking with non-ISDNs and private ISDNs. It says that notifications sent to remote users must use national or international ISDN numbers, and the overall diversion limit still applies across public and private ISDN boundaries.

Clause 8 explains interactions with other supplementary services, including advice of charge, call waiting, call hold, number identification services, closed user group, call forwarding unconditional, call forwarding no reply, call deflection, freephone, malicious call identification, multiple subscriber number, subaddressing, terminal portability, three party, and user-to-user signalling.

For implementers, this section is where the important precedence and information-passing rules are found, especially when more than one supplementary service can affect the same call.

What terms does SIST ETS 300 199 E1:2003 define?

• Integrated Services Digital Network (ISDN) - The network type for which the service is specified, using the CCITT vocabulary for ISDN services and numbering.
• Call Forwarding Busy (CFB) - A supplementary service that redirects calls when the served user is busy.
• served user - The user to whom CFB is provided and whose calls may be forwarded.
• user A - The calling user in a call that is subject to diversion.
• user B - The served user when the incoming call is being considered for CFB.
• user C - The forwarded-to user, meaning the destination to which the call is redirected.
• forwarded-to user - The user who receives the redirected call as a result of forwarding.
• diverted-to user - A general term for a user who receives a redirected call as a result of diversion.

Who uses SIST ETS 300 199 E1:2003?

Public telecommunications operators use SIST ETS 300 199 E1:2003 to define how CFB is offered and how subscribers activate, deactivate, and interrogate it. Network designers and switching engineers use it to implement the forwarding behavior, notification flow, and interaction with other supplementary services.

Private ISDN operators use it for interworking with the public ISDN, especially where forwarding information and numbering format must be passed across networks. Equipment vendors and integrators use it when implementing the service logic in stage 2 and stage 3 systems.

Customer operations teams and service administrators use it as a reference for subscription options, user notifications, and rejection handling during provisioning.

What changed in SIST ETS 300 199 E1:2003 from the previous edition?

SIST ETS 300 199 E1:2003 is identified as the first edition of this European Telecommunications Standard.

Which standards are used with SIST ETS 300 199 E1:2003?

• CCITT Recommendation I.130 - Provides the three-stage method used to describe telecommunication services.
• CCITT Recommendation I.112 - Supplies ISDN vocabulary and core definitions used in the document.
• CCITT Recommendation I.221 - Provides service characteristics and the definitions of busy conditions.
• CCITT Recommendation I.210 - Gives the principles for describing telecommunication services supported by ISDN.
• CCITT Recommendation E.164 - Defines the ISDN numbering plan, address, and subaddress structure.
• CCITT Recommendation Q.9 - Provides switching and signalling vocabulary, including basic access and primary rate access.
• ETS 300 203 - Gives the stage 2 aspects of the ISDN CFB supplementary service.
• ETS 300 207 - Gives the stage 3 aspects of the ISDN CFB supplementary service.

What does the SIST ETS 300 199 E1:2003 document contain?

SIST ETS 300 199 E1:2003 contains the service description, procedure rules, and interaction rules for CFB. Clause 5 describes the service itself, including how forwarding works and which subscription options can shape notifications and number presentation.

Clause 6 gives the operational procedures for provision, activation, deactivation, registration, interrogation, and exceptional cases. Clause 7 covers intercommunication with non-ISDNs and private ISDNs, and clause 8 maps how CFB interacts with other supplementary services such as call waiting, number identification services, closed user group, freephone, malicious call identification, and user-to-user signalling.

Table 1 is the main tabular element and summarizes the subscription choices that affect signaling to the served user, the calling user, and the forwarded-to user. The document also states that no separate test method is provided because conformance is achieved by conforming to the stage 3 standards for the relevant equipment.

SLOVENSKI STANDARD
01-december-2003
Digitalno omrežje z integriranimi storitvami (ISDN) – Dopolnilna storitev: predaja
klica ob zasedenosti (CFB) – Opis storitve
Integrated Services Digital Network (ISDN); Call Forwarding Busy (CFB) supplementary
service; Service description
Ta slovenski standard je istoveten z: ETS 300 199 Edition 1
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 199
TELECOMMUNICATION December 1994
STANDARD
Source: ETSI TC-NA Reference: DE/NA-012204
ICS: 33.080
ISDN, supplementary service
Key words:
Integrated Services Digital Network (ISDN);
Call Forwarding Busy (CFB) supplementary service
Service description
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - [e-mail]
X.400: Internet:
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1994. All rights reserved.
New presentation - see History box

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ETS 300 199: December 1994
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 199: December 1994
Contents
Foreword .5
1 Scope .7
2 Normative references.7
3 Definitions.8
4 Symbols and abbreviations .9
5 Description .9
6 Procedures.9
6.1 Provision and withdrawal .9
6.2 Normal procedures .10
6.2.1 Activation, deactivation and registration.10
6.2.1.1 Activation .10
6.2.1.2 Deactivation.11
6.2.1.3 Registration.12
6.2.2 Erasure.12
6.2.3 Invocation and operation .12
6.2.3.1 Served user is user determined user busy .12
6.2.3.2 Served user is network determined user busy .13
6.2.3.3 Forwarded-to user's view.13
6.2.3.4 Calling user's view .14
6.2.4 Interrogation .15
6.3 Exceptional procedures .16
6.3.1 Activation, deactivation and registration.16
6.3.1.1 Activation .16
6.3.1.2 Deactivation.17
6.3.1.3 Registration.17
6.3.2 Erasure.17
6.3.3 Invocation and operation .17
6.3.4 Interrogation .18
7 Intercommunication considerations.18
7.1 Interworking with non-ISDNs .18
7.2 Interworking with private ISDNs.19
8 Interaction with other supplementary services .19
8.1 Advice of charge services.19
8.1.1 Charging information at call set-up time.19
8.1.2 Charging information during the call.19
8.1.3 Charging information at the end of the call.20
8.2 Call waiting.20
8.3 Call hold .20
8.4 Explicit call transfer.20
8.5 Number identification services.20
8.5.1 Calling line identification presentation .20
8.5.2 Calling line identification restriction .20
8.5.3 Connected line identification presentation.21
8.5.4 Connected line identification restriction.21
8.6 Closed user group.21
8.7 Completion of calls to busy subscribers .21
8.8 Conference services .22
8.8.1 Conference call, add-on .22

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ETS 300 199: December 1994
8.8.2 Meet-me conference. 22
8.9 Direct dialling in . 22
8.10 Diversion services . 22
8.10.1 Call forwarding unconditional. 22
8.10.2 Call forwarding busy . 22
8.10.3 Call forwarding no reply . 22
8.10.4 Call deflection . 22
8.11 Freephone. 23
8.12 Malicious call identification. 23
8.13 Multiple subscriber number . 23
8.14 Subaddressing . 23
8.15 Terminal portability. 23
8.16 Three party. 23
8.17 User-to-user signalling . 24
History. 25

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ETS 300 199: December 1994
Foreword
This European Telecommunication Standard (ETS) has been produced by the Network Aspects (NA)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
In accordance with CCITT Recommendation I.130 [1], the following three level structure is used to
describe the supplementary telecommunications services as provided by European public
telecommunications operators under the pan-European Integrated Services Digital Network (ISDN):
- Stage 1: is an overall service description, from the user's standpoint;
- Stage 2: identifies the functional capabilities and information flows needed to support the
service described in stage 1; and
- Stage 3: defines the signalling system protocols and switching functions needed to implement
the service described in stage 1.
This ETS details the stage 1 aspects (overall service description) for the Call Forwarding Busy (CFB)
supplementary service. The stage 2 and stage 3 aspects are detailed in ETS 300 203 (1994) and
ETS 300 207 (1994) respectively.
Proposed transposition dates
Date of latest announcement of this ETS (doa): 31 March 1995
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30 September 1995
Date of withdrawal of any conflicting National Standard (dow): 30 September 1995

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1 Scope
This standard defines the stage one of the Call Forwarding Busy (CFB) supplementary service for the
pan-European Integrated Services Digital Network (ISDN) as provided by European public
telecommunications operators. Stage one is an overall service description from the user's point of view
(see CCITT Recommendation I.130 [1]), but does not deal with the details of the human interface itself.
This standard defines the interworking requirements of private ISDNs with the public ISDN.
In addition this standard specifies the base functionality where the service is provided to the user via a
private ISDN.
This standard does not specify the additional requirements where the service is provided to the user via a
telecommunications network that is not an ISDN but does include interworking requirements of other
networks with the public ISDN.
Charging principles are outside the scope of this standard.
Interaction with supplementary services not listed in clause 8 are outside the scope of this standard.
The CFB supplementary service enables a served user to have the network redirect to another user calls
which are addressed to the served user's ISDN number and meet busy. The CFB supplementary service
may operate on all calls, or just those associated with specified basic services. The served user's ability to
originate calls is unaffected by the CFB supplementary service.
The CFB supplementary service is applicable to all circuit-switched telecommunication services.
This standard is applicable to the stage two and stage three standards for the ISDN CFB supplementary
service. The terms "stage two" and "stage three" are also defined in CCITT Recommendation I.130 [1].
Where the text indicates the status of a requirement, (i.e. as strict command or prohibition, as
authorization leaving freedom, as a capability or possibility), this shall be reflected in the text of the
relevant stage two and stage three standards.
Furthermore, conformance to this standard is met by conforming to the stage three standards with the
field of application appropriate to the equipment being implemented. Therefore, no method of testing is
provided for this standard.
2 Normative references
This standard incorporates, by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to, or revisions of, any of these publications
apply to this standard only when incorporated in it by amendment or revision. For undated references the
latest edition of the publication referred to applies.
[1] CCITT Recommendation I.130 (1988): "Method for the characterization of
telecommunication services supported by an ISDN and network capabilities of
an ISDN".
[2] CCITT Recommendation I.112 (1988): "Vocabulary of terms for ISDNs".
[3] CCITT Recommendation I.221 (1988): "Common specific characteristics of
services".
[4] CCITT Recommendation I.210 (1988): "Principles of telecommunication
services supported by an ISDN and the means to describe them".
[5] CCITT Recommendation E.164 (1991): "Numbering plan for the ISDN era".
[6] CCITT Recommendation Q.9 (1988): "Vocabulary of switching and signalling
terms".
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3 Definitions
For the purposes of this standard, the following definitions apply:
Integrated Services Digital Network (ISDN): See CCITT Recommendation I.112 [2], § 2.3, definition
308.
(basic) service; telecommunications service: See CCITT Recommendation I.112 [2], § 2.2, definition
201.
served user: The user to whom the CFB supplementary service is provided.
user A: The calling user in a call which is subject to diversion.
user B: The served user when a call (from user A) is subject to the CFB supplementary service.
NOTE: In the context of multiple diversions, a suffix is used, e.g. 1, 2, . n, n+1, . m, to
denote the successive diverting users. For example, user B3 is also the diverted-to
user with respect to the diversion applied at user B2.
user C: The forwarded-to user in a call which is subject to the CFB supplementary service. In the case of
a call which is subject to multiple diversions, user C is the forwarded-to user with respect to the final call
forwarding.
forwarded-to user: A user to whom the call is redirected as a result of forwarding.
diverted-to user: A user to whom a call is redirected as a result of diversion.
busy: See CCITT Recommendation I.221 [3], § 3.1.5.
supplementary service: See CCITT Recommendation I.210 [4], paragraph 2.4.
ISDN number: A number conforming to the numbering plan and structure specified in CCITT
Recommendation E.164 [5].
basic access: See CCITT Recommendation Q.9 [6], § 1, definition 1551.
primary rate access: See CCITT Recommendation Q.9 [6], § 1, definition 1552.
address: See CCITT Recommendation E.164 [5], § 12.
subaddress: See CCITT Recommendation E.164 [5], § 12.2.
user determined user busy: see CCITT Recommendation I.221 [3], § 3.1.4.
network determined user busy: See CCITT Recommendation I.221 [3], § 3.1.4.
(call) forwarding: A general term applied to any functionality whereby a call is redirected automatically by
the service provider to another user. The forms of forwarding are: unconditional, whereby all calls are
redirected; busy, whereby calls encountering busy are redirected; and, no reply, whereby calls which are
not answered within a time period are redirected.
diversion: A general term which includes all forms of forwarding, and includes deflection whereby calls
are redirected by the user instead of being answered.

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ETS 300 199: December 1994
basic call procedures: The procedures by which a call (as an instance of a basic telecommunication
service) is established and terminated.
diverting user: A user for whom the call is subjected to diversion.
4 Symbols and abbreviations
CFB Call Forwarding Busy
ISDN Integrated Services Digital Network
PSTN Public Switched Telephone Network
5 Description
The CFB supplementary service shall be available to users who are connected to the network via a basic
access or a primary rate access.
The CFB supplementary service enables a served user to have the network redirect to another user calls
which are addressed to the served user's ISDN number and meet busy. The CFB supplementary service
may operate on all calls, or just those associated with specified basic services. The served user's ability to
originate calls is unaffected by the CFB supplementary service.
As a service provider option, a subscription option can be provided to enable the served user to receive an
indication that the CFB supplementary service has been activated. This indication shall be provided when
the served user originates a call if the CFB supplementary service has been activated for the served
user's ISDN number and for the basic service requested for the call.
The maximum number of diversions permitted for each call is a service provider option with an upper limit
of five diversions. When counting the number of diversions, all types of diversion are included.
6 Procedures
6.1 Provision and withdrawal
The CFB supplementary service shall be provided after prior arrangement with the service provider.
As a service provider option, the CFB supplementary service can be provided on a per ISDN number
basis, or the CFB supplementary service can apply to the whole access. If a service provider offers both
of these options, then it shall be a subscription option to choose which of these options applies.
In addition, the CFB supplementary service (including options) can be subscribed to for all basic services
subscribed to by the user, or as a service provider option, the user can identify particular basic service(s)
for which the CFB supplementary service shall apply.
As a service provider option, the service can be offered with one or more of four subscription options,
which can apply separately to each basic service subscribed to. If the CFB supplementary service is
provided on a per ISDN number basis, then these options can apply separately to each ISDN number. For
each subscription option, only one value can be selected. Subscription options are summarized in table 1.

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Table 1
Subscription options Value
Served user receives notification -no
that the call has been forwarded - yes
Calling user receives notification -no
that the call has been forwarded - yes, without the ISDN
number of the forwarded-to
user
- yes, with the ISDN number of
the forwarded-to user
Served user receives notification -no
that the CFB supplementary service - yes
is currently activated
The served users ISDN number can-no
be presented to the forwarded-to - yes
user
As a service provider option, a subscription option can be offered to served users, to enable the CFB
supplementary service to be activated, deactivated and interrogated for all ISDN numbers on the same
access. ISDN numbers for which the CFB supplementary service is not subscribed to shall not be
affected.
The CFB supplementary service shall be withdrawn by the service provider upon request of the
subscriber, or for service provider reasons.
6.2 Normal procedures
6.2.1 Activation, deactivation and registration
6.2.1.1 Activation
The served user shall supply the following information when requesting the activation of the CFB
supplementary service:
- the ISDN number of the forwarded-to user, which can be accompanied by a subaddress for
additional identification of the forwarded-to user; and
- information as to whether the activation of the CFB supplementary service is for all basic services to
which the CFB supplementary service applies, or for a specific basic service out of the basic
services to which the CFB supplementary service applies.
When subscription applies on a per ISDN number basis and more than one ISDN number is allocated to
the access, then:
- the served user shall also supply the ISDN number for which the activation of the CFB
supplementary service shall apply, or;

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- as a service provider option, the served user can, if subscribed to, indicate that the activation of the
CFB supplementary service shall apply for all ISDN numbers for which the CFB supplementary
service is subscribed to. In this case, this activation shall replace any previous activation of the CFB
supplementary service which may be in force on individual ISDN numbers on the access, for the
basic services indicated at activation.
When subscription applies for the whole access, or only one ISDN number is allocated to the access, the
served user need not provide an ISDN number to identify the served user. If the served user includes an
ISDN number allocated to that access, or indicates that the activation of the CFB supplementary service
shall apply to all ISDN numbers (if this functionality is offered by the service provider and subscribed to by
the served user) then the ISDN number, or the indication of all ISDN numbers, shall be ignored. Activation
of the CFB supplementary service shall proceed as normal.
The served user can separately activate the CFB supplementary service for each basic service to which
the CFB supplementary service applies and thereby request a different ISDN number and/or subaddress
to identify the forwarded-to user for each basic service to which the CFB supplementary service applies.
When the CFB supplementary service is activated for all basic services, this activation shall replace any
previous activation of the CFB supplementary service which may be in force on individual basic services.
Verification of the ISDN number of the forwarded-to user can be carried out before accepting the request
to activate the CFB supplementary service. This verification can be limited, e.g. a simple check of the
ISDN number of the forwarded-to user to see if the ISDN number is within the allowed number range.
When the served user's request to activate the CFB supplementary service is accepted, the service
provider shall inform the served user. The information shall include the address of the forwarded-to user
to whom the served user has activated the CFB supplementary service. All affected users shall be
informed.
6.2.1.2 Deactivation
The CFB supplementary service can be deactivated in any of the following ways:
- the served user can request the deactivation of the CFB supplementary service for individual basic
services. The service provider shall inform the served user that the previous activation of the CFB
supplementary service has been deactivated. All affected users shall be informed;
- the served user can request the deactivation of the CFB supplementary service for all basic
services. The service provider shall inform the served user that the previous activation of the CFB
supplementary service has been deactivated. All affected users shall be informed;
- the served user can request the activation of the CFB supplementary service indicating a basic
service for which the CFB supplementary service has already been activated. This shall replace the
previous information registered for that basic service. In this case, users shall not be specifically
informed of the deactivation. The procedures of subclause 6.2.1.1 for informing the served user
apply;
- the served user can request the activation of the CFB supplementary service for all basic services.
This shall replace the information registered for all of the basic services for which the CFB
supplementary service has already been activated. In this case, users shall not be specifically
informed of the deactivation. The procedures of subclause 6.2.1.1 for informing the served user
apply.
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When subscription applies on a per ISDN number basis and more than one ISDN number is allocated to
the access, then:
- the served user shall also supply the ISDN number for which the deactivation of the CFB
supplementary service shall apply, or;
- as a service provider option, the served user can, if subscribed to, indicate that the deactivation of
the CFB supplementary service shall apply for all ISDN numbers for which the CFB supplementary
service is subscribed to.
When subscription applies for the whole access, or only one ISDN number is allocated to the access, the
served user need not provide an ISDN number to identify the served user. If the served user includes an
ISDN number allocated to that access, or indicates that the deactivation of the CFB supplementary
service shall apply to all ISDN numbers (if this functionality is offered by the service provider and
subscribed to by the served user) then the ISDN number, or the indication of all ISDN numbers, shall be
ignored. Deactivation of the CFB supplementary service shall proceed as normal.
6.2.1.3 Registration
Registration of information is performed on activation of the CFB supplementary service.
There are no separate registration procedures for the CFB supplementary service.
6.2.2 Erasure
Not applicable.
6.2.3 Invocation and operation
When the CFB supplementary service has been activated and the served user is network determined user
busy or user determined user busy, then an incoming call to the served user, indicating a basic service for
which the CFB supplementary service has been activated, shall be forwarded.
The maximum number of diversions for each call shall be limited. The maximum number of diversions is a
service provider option with an upper limit of five diversions for each call. When counting the number of
diversions, all types of diversions shall be included.
6.2.3.1 Served user is user determined user busy
The call shall be offered to the served user by means of basic call procedures.
If the served user responds to the offered call by indicating that the user is busy (user determined user
busy), then the network shall attempt to forward the call. According to the value of a subscription option,
the served user shall be informed that the CFB supplementary service has been invoked on the call.
NOTE: The call offering information associated with the subscription option to inform the
served user that a call is being forwarded will have already been given by the network
as part of offering the call. This information includes the following information about the
call that has been forwarded:
- the telecommunications service information;
- user-to-user information (if any);
- the address of the served user;
- the address of user A (provided that the served user has subscribed to the
calling line identification presentation supplementary service, and the calling line
identification restriction supplementary service is not applied).

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If multiple diversions have occurred, the information also includes:
- the ISDN number of the originally called user;
- the ISDN number of the last diverting user;
- reason for last diversion (e.g. invocation of the CFB supplementary service).
6.2.3.2 Served user is network determined user busy
In the case of network determined user busy, the call is forwarded without being offered to the served
user.
According to the value of a subscription option, the served user shall be informed that the CFB
supplementary
...