SIST ETS 300 361 E1:2005

SLOVENSKI STANDARD
01-maj-2005
Zasebno telekomunikacijsko omrežje (PTN) – Specifikacija, funkcijski model in
informacijski pretoki - Dopolnilna storitev: ponudba klica
Private Telecommunication Network (PTN); Specification, functional models and
information flows; Call offer supplementary service
Ta slovenski standard je istoveten z: ETS 300 361 Edition 1
ICS:
33.040.35 Telefonska omrežja Telephone networks
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 361
TELECOMMUNICATION November 1994
STANDARD
Source: ETSI TC-ECMA Reference: DE/ECMA-00008
ICS: 33.080
Key words: CO, PTN, stage 1, stage 2, supplementary service, ECMA-191
Private Telecommunication Network (PTN);
Specification, functional model and information flows
Call offer supplementary service
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: secretariat@etsi.fr
Tel.: +33 92 94 42 00 - Fax: +33 93 65 47 16
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 300 361: November 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 Standards Approval Dept." at the address shown on the title page.

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ETS 300 361: November 1994
Contents
Foreword.5
1 Scope .7
2 Conformance .7
3 References .7
4 Definitions .8
4.1 External definitions.8
4.2 Additional network feature .9
4.3 Automatic Call Offer invocation timer .9
4.4 Busy.9
4.5 Call, Basic call.9
4.6 Consultation timer .9
4.7 Offered call.9
4.8 Path retention.9
5 List of acronyms .9
6 SS-CO stage 1 specification .10
6.1 Description .10
6.1.1 General description .10
6.1.2 Qualifications on applicability to telecommunication services .10
6.2 Procedures .10
6.2.1 Provision/withdrawal .10
6.2.2 Normal procedures.10
6.2.2.1 Activation/deactivation/registration/interrogation.10
6.2.2.2 Invocation and operation.10
6.2.3 Exceptional procedures .11
6.2.3.1 Activation/deactivation/registration/interrogation.11
6.2.3.2 Invocation and operation.12
6.3 Interactions with other supplementary services and ANFs .12
6.3.1 Calling Line Identification Presentation (SS-CLIP).12
6.3.2 Connected Line Identification Presentation (SS-COLP).12
6.3.3 Calling/Connected Line Identification Restriction (SS-CLIR).12
6.3.4 Calling Name Identification Presentation (SS-CNIP) .12
6.3.5 Connected Name Identification Presentation (SS-CONP) .12
6.3.6 Calling/Connected Name Identification Restriction (SS-CNIR) .12
6.3.7 Call Forwarding (SS-CFU/SS-CFB/SS-CFNR) .12
6.3.7.1 Call Forwarding Unconditional (SS-CFU).12
6.3.7.2 Call Forwarding Busy (SS-CFB) .13
6.3.7.3 Call Forwarding No Reply (SS-CFNR) .13
6.3.8 Call Transfer (SS-CT).13
6.3.9 Call Completion to Busy Subscriber (SS-CCBS).13
6.3.10 Call Completion on No Reply (SS-CCNR).13
6.3.11 Do Not Disturb (SS-DND).13
6.3.12 Do Not Disturb Override (SS-DNDO).14
6.3.13 Path Replacement (ANF-PR) .14
6.4 Interworking considerations .14

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6.5 Overall SDL. 14
7 SS-CO stage 2 specification. 19
7.1 Functional model . 19
7.1.1 Functional model description . 19
7.1.2 Description of Functional Entities. 20
7.1.2.1 Calling user's control entity, FE1 . 20
7.1.2.2 Called user's control entity, FE2. 21
7.1.3 Relationship of functional model to Basic Call functional model . 21
7.2 Information flows. 21
7.2.1 Definition of information flows. 21
7.2.1.1 ra-CO-ACTIVATE. 21
7.2.1.2 ra-CO-AVAILABLE. 22
7.2.1.3 ra-CO-INVOKE-IMMEDIATE . 22
7.2.1.4 ra-CO-INVOKE . 22
7.2.1.5 ra-CO-TERMINATED. 23
7.2.2 Relationship of information flows to Basic Call information flows . 23
7.2.3 Information flow sequences. 25
7.2.3.1 Normal operation of SS-CO . 25
7.2.3.2 Failure operation of SS-CO. 28
7.3 Functional Entity actions. 33
7.3.1 Functional Entity actions of FE1 . 33
7.3.2 Functional Entity actions of FE2 . 33
7.4 Functional Entity behaviour. 34
7.4.1 Behaviour of FE1 . 34
7.4.2 Behaviour of FE2 . 41
7.5 Allocation of Functional Entities to physical equipment . 44
7.6 Interworking considerations. 44
History . 45

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ETS 300 361: November 1994
Foreword
This European Telecommunication Standard (ETS) has been produced by the European Computer Manufacturers
Association (ECMA) on behalf of its members and those of the European Telecommunications Standards Institute
(ETSI).
This ETS is one of a series of standards defining services and signalling protocols applicable to Private
Telecommunication Networks (PTNs). The series uses the ISDN concepts as developed by the ITU-TS and is also
within the framework of standards for open systems interconnection as defined by ISO.
This ETS specifies the Call Offer supplementary service, which is applicable to various basic services supported by
Private Telecommunication Networks (PTNs).
The ETS is based upon the practical experience of ECMA member companies and the results of their active and
continuous participation in the work of ISO, ITU-TS, ETSI and other international and national standardisation bodies.
It represents a pragmatic and widely based consensus.
This ETS was produced by ECMA using the ECMA guidelines for the production of standards and using the ECMA
stylesheet. In order to avoid undue delays in the approval process for this ETS it has been agreed that this ETS will not
be converted to the ETSI stylesheet.
Transposition dates
Date of latest announcement of this ETS (doa): 28 February 1995
Date of latest publication of new National Standard 31 August 1995
or endorsement of this ETS (dop/e):
Date of withdrawal of any conflicting National Standard (dow): 31 August 1995

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ETS 300 361: November 1994
1 Scope
This European Telecommunication Standard (ETS) specifies the Supplementary Service Call Offer (SS-CO),
which is applicable to various basic services supported by Private Telecommunication Networks (PTNs). Basic
services are specified in ETS 300 171.
SS-CO is a supplementary service which , on request from the calling user (or on that user's behalf), enables a
call to be offered to a busy called user and to wait for that called user to accept this call.
Services specifications are produced in three stages, according to the method described in ETS 300 387. This
ETS contains the stage 1 and stage 2 specifications of SS-CO. The stage 1 specification (clause 6) specifies the
supplementary service as seen by users of PTNs. The stage 2 specification (clause 7) identifies the functional
entities involved in the supplementary service and the information flows between them.
NOTE 1
For this ETS, stage 2 does not consider the split of functionality between a functional terminal and the local PTNX.
Terminal functions and local PTNX functions are included in the same Functional Entity.
2 Conformance
In order to conform to this ETS, a stage 3 standard shall specify signalling protocols and equipment behaviour
that are capable of being used in a PTN which supports the supplementary service specified in this ETS. This
means that to claim conformance, a stage 3 standard is required to be adequate for the support of these aspects
of clause 6 (stage 1) and clause 7 (stage 2) which are relevant to the interface or equipment to which the stage 3
standard applies.
3 References
ETS 300 171 Private Telecommunications Network (PTN); Specification, functional models and
information flows Control aspects of circuit mode basic services (ECMA-BCSD)
ETS 300 173 Private Telecommunications Network (PTN); Specification, functional models and
information flows Identification supplementary services (ECMA-ISSD)
ETS 300 237 Private Telecommunication Network (PTN); Specification, functional models and
information flows Name identification supplementary service; ECMA-NISD
ETS 300 256 Private Telecommunication Network (PTN); Specification, functional models and
information flows Diversion supplementary services
ETS 300 260 Private Telecommunication Network (PTN); Specification, functional models and
information flows Call transfer supplementary service
ETS 300 363 Private Telecommunication Network (PTN); Specification, functional model and
information flows Do not disturb and do not disturb override supplementary services
ETS 300 365 Private Telecommunication Network (PTN); Specification, functional models and
information flows Call completion supplementary services
ETS 300 387 Private Telecommunications Network (PTN); Method for the specification of basic and
supplementary services
ENV 41007-1 Definition of terms in private telecommunication networks (1989)
CCITT Rec. I.112 Vocabulary of terms for ISDNs (1988)
CCITT Rec. I.210 Principles of telecommunication services supported by an ISDN and the means to describe
them (1988)
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CCITT Rec. I.221 Common specific characteristics of services (1988)
CCITT Rec. Z.100 Specification and description language (1988)
4 Definitions
For the purpose of this ETS, the following definitions apply.
4.1 External definitions
This ETS uses the following terms defined in other documents:
− Basic Service (CCITT Rec. I.210)
− Connection (CCITT Rec. I.112)
− Network Determined User Busy (CCITT Rec. I.221)
− Private (ENV 41007-1)
− Private Telecommunication Network Exchange (PTNX) (ENV 41007-1)
− Public (ENV 41007-1)
− Public ISDN (ENV 41007-1)
− Service (CCITT Rec. I.112)
− Signalling (CCITT Rec. I.112)
− Supplementary Service (CCITT Rec. I.210)
− Telecommunication Network (ENV 41007-1)
− Terminal, Terminal equipment (ENV 41007-1)
− User (ETS 300 171)
− User Determined User Busy (CCITT Rec. I.221)
This ETS refers to the following basic call Functional Entities (FEs) defined in ETS 300 171:
− Call Control (CC)
− Call Control Agent (CCA)
This ETS refers to the following basic call inter-FE relationships defined in ETS 300 171:
− r1
− r2
-r3
This ETS refers to the following basic call information flows defined in ETS 300 171:
− SETUP request/indication
− SETUP response/confirmation
− REPORT request/indication
− RELEASE request/indication
− RELEASE response/confirmation

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4.2 Additional network feature
A capability, over and above that of a basic service, provided by a PTN, but not directly to a PTN user.
4.3 Automatic Call Offer invocation timer
A timer governing the time after which SS-CO is automatically invoked after the calling user has been
informed that a call has failed because of busy at the destination. The duration of the timer is an
implementation option.
4.4 Busy
A property of a user for whom either a Network Determined User Busy or User Determined User Busy
condition exists.
4.5 Call, Basic call
An instance of the use of a basic service.
4.6 Consultation timer
A timer governing the time in which the calling user is allowed to request invocation of SS-CO after being
informed that a call has failed because of busy at the destination. The duration of the timer is an
implementation option.
4.7 Offered call
A call that is in a waiting condition as a result of invocation of SS-CO, against a busy called user.
4.8 Path retention
The retaining of the network connection between the Originating CC and the Destination CC so that a
supplementary service (such as SS-CO) can be invoked without establishing a new connection.
5 List of acronyms
ANF Additional Network Feature
CC Call Control (functional entity)
CCA Call Control Agent (functional entity)
FE Functional Entity
PR Path Replacement
PTN Private Telecommunication Network
PTNX Private Telecommunication Network Exchange
SDL Specification and Description Language
SS-CCBS Call Completion to Busy Subscriber Supplementary Service
SS-CCNR Call Completion on No Reply Supplementary Service
SS-CFB Call Forwarding Busy Supplementary Service
SS-CFNR Call Forwarding No Reply Supplementary Service
SS-CFU Call Forwarding Unconditional Supplementary Service
SS-CLIP Calling Line Identification Presentation Supplementary Service
SS-CLIR Calling/Connected Line Identification Restriction Supplementary Service
SS-CNIP Calling Name Identification Presentation Supplementary Service
SS-CNIR Calling/Connected Name Identification Restriction Supplementary Service
SS-CO Call Offer Supplementary Service
SS-COLP Connected Line Identification Presentation Supplementary Service
SS-CONP Connected Name Identification Presentation Supplementary Service

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SS-CT Call Transfer Supplementary Service
SS-DND Do Not Disturb Supplementary Service
SS-DNDO Do Not Disturb Override Supplementary Service
TE Terminal Equipment
6 SS-CO stage 1 specification
6.1 Description
6.1.1 General description
SS-CO is a supplementary service which, on request from the calling user (or on that user's behalf),
enables a call to be offered to a busy called user and to wait for that called user to accept the call, after the
necessary resources have become available.
The busy called user is given an indication of the offered call. During the time that the call is offered, the
called user may ignore the offered call or may attempt to make the necessary resources available (e.g. by
releasing or placing on hold another call). When and if the necessary resources become available, the call
shall be completed as a normal incoming call.
6.1.2 Qualifications on applicability to telecommunication services
SS-CO is applicable to all circuit mode basic services defined in ETS 300 171.
6.2 Procedures
6.2.1 Provision/withdrawal
SS-CO may be provided or withdrawn after pre-arrangement with the service provider (by means of service
profile control), or may be available generally to all users. In a PTN that offers more than one way of
invoking SS-CO (see 6.2.2.2), one or more of these ways shall be selected at provision time.
6.2.2 Normal procedures
6.2.2.1 Activation/deactivation/registration/interrogation
Not applicable.
6.2.2.2 Invocation and operation
There are four different ways of invoking SS-CO. A PTN shall offer one or more of these ways. These
ways are:
1 Network invocation (immediate): the PTN shall automatically invoke SS-CO whenever the calling
user makes a call to a user that is busy, if required by the service profile of the calling user.
2 Consultation: the calling user, on being informed that a call has failed because of busy at the
destination and that SS-CO may be possible, shall be able, within a defined time period
(consultation timer) to request invocation of SS-CO.
3 Immediate invocation: the calling user shall be able to request invocation of SS-CO as part of the
initial call set up.
4 Network invocation (delayed): the network, having informed the calling user that a call has failed
because of busy at the destination, shall automatically invoke SS-CO unless the calling user
initiates call clearing within a defined time period (automatic call offer invocation timer).

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NOTE 2
If method 1 is provided to a user, methods 2, 3 and 4 will not be available to that user.
For consultation and network invocation (delayed), for those basic services for which ETS 300 171
requires an in-band tone or announcement to indicate progress or otherwise of the call, the information
provided by the network that the call has failed because of busy at the destination shall include an in-
band tone or announcement.
If the calling user is provided with both consultation and network invocation (delayed), the calling user
shall be able to request SS-CO during the period of the automatic call offer invocation timer. If, at the
time of expiry of the automatic call offer timer, the calling user has not requested SS-CO and has not
initiated call clearing, the network shall automatically invoke SS-CO.
On successful invocation of SS-CO, the called user shall receive an indication of the offered call, and
the calling user shall be advised that SS-CO has been invoked. Additional information that would
normally accompany an incoming call indication (see ETS 300 171) may optionally be provided to the
called user. During the waiting period, for those basic services for which ETS 300 171 requires an in-
band tone or announcement to indicate progress or otherwise of the call, an in-band tone or
announcement shall be given to the calling user.
If the PTN detects that the necessary resources have become available, it shall transfer an incoming call
indication to the called user.
NOTE 3
The waiting period for the offered call can be subject to time-out. At time-out, the offered call can be
released. Any such procedure is outside the scope of this ETS.
SS-CO shall be considered completed when any one of the following occurs:
− the called user starts alerting;
− the called user accepts the call;
− the calling user releases the offered call;
− the called user rejects the offered call.
If the called user starts alerting, the calling user shall receive an appropriate indication.
If the called user rejects the offered call, the call shall be released with an appropriate indication to the
calling user.
6.2.3 Exceptional procedures
6.2.3.1 Activation/deactivation/registration/interrogation
Not applicable.
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6.2.3.2 Invocation and operation
If the calling user requests invocation of SS-CO as part of the initial call request, and immediate
invocation is not provided to the calling user, then the request shall be ignored and the call shall proceed
as if the request had not been made.
An SS-CO request may be rejected for other reasons, e.g. when the number of calls already offered to
the called user is equal to the maximum allowed for this user or when the call fails due to network
conditions (see clause 9.3.3 of ETS 300 171). If the request has been initiated by means of immediate
invocation, consultation or network invocation (delayed), the calling user shall be informed that the SS-
CO request is rejected.
If consultation applies to the call, the call shall be released either if the calling user does not request
invocation within the defined time period (consultation timer) or if the calling user requests invocation
within the defined time period (consultation timer) and this request is rejected.
If SS-CO is requested and the called user is found to be not busy, the call shall be treated as a normal
incoming call to the called user.
6.3 Interactions with other supplementary services and ANFs
Interactions with other supplementary services and ANFs for which PTN standards were available at the time
of publication of this ETS are specified below.
6.3.1 Calling Line Identification Presentation (SS-CLIP)
The called user shall receive, as part of the offered call, the Calling Line Identification of the calling user,
unless SS-CLIR applies and the called user has no override capability.
6.3.2 Connected Line Identification Presentation (SS-COLP)
No interaction.
6.3.3 Calling/Connected Line Identification Restriction (SS-CLIR)
When Calling Line Identification Restriction has been invoked, the Calling Line Identification shall not be
presented to the called user (as part of the offered call), unless the called user has an override category.
6.3.4 Calling Name Identification Presentation (SS-CNIP)
The called user shall receive, as part of the offered call, the Calling Name Identification of the calling user,
unless SS-CNIR applies and the called user has no override capability.
6.3.5 Connected Name Identification Presentation (SS-CONP)
No interaction.
6.3.6 Calling/Connected Name Identification Restriction (SS-CNIR)
When Calling Name Identification Restriction has been invoked, the Calling Name Identification shall not
be presented to the called user (as part of the offered call), unless the called user has an override category.
6.3.7 Call Forwarding (SS-CFU/SS-CFB/SS-CFNR)
6.3.7.1 Call Forwarding Unconditional (SS-CFU)
SS-CO, if invoked, shall operate on a busy user that has been forwarded to as a result of one or more
invocations of SS-CFU.
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6.3.7.2 Call Forwarding Busy (SS-CFB)
If SS-CO invocation is requested by the calling user as part of the initial call set up or automatically by
the network when a call is made to a user that is busy, and if the called user is busy and has SS-CFB
active, SS-CFB shall be invoked. If the SS-CFB forwarded-to user is also busy, SS-CO shall operate on
the forwarded-to user. If the call undergoes more than one forwarding, at least one of which is SS-CFB,
but excluding SS-CFNR, SS-CO shall operate on the final forwarded-to user if that user is busy.
If the calling user is informed that a call has failed because of busy at the destination, and if SS-CO is
subsequently invoked, SS-CO shall operate on the SS-CFB forwarding user or on the SS-CFB
forwarded-to user. If the call has undergone more than one forwarding, at least one of which is SS-CFB,
but excluding SS-CFNR, then SS-CO shall operate either on the first SS-CFB forwarding user or on the
final forwarded-to user. Choice between the two is an implementation option. An implementation may
permit the calling user to make the choice.
6.3.7.3 Call Forwarding No Reply (SS-CFNR)
SS-CO if invoked, shall not operate on a busy user arrived at as a result of one or more forwardings, at
least one of which is SS-CFNR. The procedures of SS-CFNR shall apply.
SS-CFNR can apply when alerting a user after completion of SS-CO on that user.
6.3.8 Call Transfer (SS-CT)
It shall be possible for a user, after having successfully invoked SS-CO against a busy called user, to
invoke call transfer for transferring a third user to that called user. This shall operate in a similar manner to
Call Transfer during the alerting state, except that the call shall continue as an offered call to the called
user. The third user may be notified that the call is in a waiting condition against a busy called user. If the
called user subsequently enters an alerting phase and a notification that the call is in a waiting condition
against a busy called user has been given to the third user, the third user shall be notified that the waiting
condition has ceased.
6.3.9 Call Completion to Busy Subscriber (SS-CCBS)
While a call is being offered, the calling user may be able to invoke SS-CCBS.
SS-CO invoked against the called user shall have priority over any SS-CCBS requests against that called
user, when resources at the called user become available.
6.3.10 Call Completion on No Reply (SS-CCNR)
No interaction.
6.3.11 Do Not Disturb (SS-DND)
If SS-CO has been invoked:
- as part of the initial call set up (i.e. by SS-CO immediate invocation);
- following consultation (i.e. by SS-CO Consultation); or
- by SS-CO network invocation (delayed).

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6.3.12 Do Not Disturb Override (SS-DNDO)
If the called user has SS-DND active, and SS-DNDO is successfully invoked, then:
− if CO network invocation (immediate), immediate invocation or network invocation (delayed) is
applicable to the call, then the invocation of CO shall apply to the call after SS-DND has been
overridden,
− if CO consultation is applicable to the call, it shall apply after SS-DND has been overridden.
6.3.13 Path Replacement (ANF-PR)
No interaction.
6.4 Interworking considerations
When interworking with another network which supports an equivalent feature, it may be possible to
cooperate with the other network in order to provide SS-CO.
If a call is made with invocation of SS-CO to a destination in a network that does not support SS-CO, then the
invocation of SS-CO shall be rejected and the call shall proceed normally as if there was no SS-CO
invocation.
6.5 Overall SDL
Figure 1 contains the dynamic description of SS-CO using the Specification and Description Language (SDL)
defined in CCITT Rec. Z.100 (1988). The SDL process represents the behaviour of the network in providing
SS-CO to a calling user.
Input signals from the left and output signals to the left represent primitives from and to the calling user.
Input signals from the right represent either primitives from the called user, or inputs from the basic call
process, or inputs from an internal process.
Output signals to the right represent primitives to the called user.

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Process SS-CO 1(4)
CI-Idle
Call request Call request
with without
CO request CO request
immediate
invocation
implemented?
YES NO
NO
immediate
invocation
provided?
YES
Network
invocation
(immediate)
implemented?
YES NO
NO
Network
invocation
(immediate)
provided?
Consultation
YES implemented?
YES NO
NO
Consultation
provided?
YES
Network
invocation
(delayed)
implemented?
NO
YES
NO
Network
invocation
(delayed)
provided?
YES
Basic call
to proceed
normally
CO-wait-2 CO-wait-1 CI-Idle
Figure 1 (sheet 1 of 4) - SS-CO, overall SDL

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Process SS-CO 2(4)
CO-wait-2
Called user Called user Basic call
not busy busy cleared
YES NO
able to
offer call
?
NO
Network
invocation
(immediate)
Call to be
offered
YES
Notification
CO
Basic call is rejected
Notification
to proceed
CO is invoked
normally
Call to fail
CO-active
following basic
call procedures
Resources Called user Basic call
available rejects call cleared
Basic call
Basic call
indication of
to release
incoming call to
the called user
CO-active-
resources-
available
Called user Called user Basic call
starts alerting accepts call cleared
Notification Notification
CO offered call
terminated is rejected
CO-idle
Figure 1 (sheet 2 of 4) - SS-CO, overall SDL

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Process SS-CO 3(4)
CO-wait-1
Called user Called user Basic call
not busy busy cleared
Basic call
Consultation
CO-idle
to proceed
implemented?
normally
YES NO
CO-idle
NO
Consultation
provided?
Network invocation
YES
(delayed) shall then
apply
Start automatic
CO invocation
timer
Notification
CO
is possible Notification
CO
will happen
Network invocation
(delayed)
implemented?
CO-enabled-A
YES NO
NO
Network invocation
(delayed)
provided?
Start automatic
Start consultation
CO invocation
timer
timer
Notification
CO
will happen
CO-enabled-CA CO-enabled-C
Figure 1 (sheet 3 of 4) - SS-CO, overall SDL

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Process SS-CO 4(4)
CO-enabled-CA
automatic CO
CO basic call
invocation
request cleared
timer expiry
Stop automatic Stop automatic
CO invocation CO invocation
timer timer
NO
called
CO-idle
user busy?
YES
1 2
CO-enabled-C
consultation CO basic call
timer expiry request cleared
Call to fail Stop Stop
following basic consultation consultation
call procedures timer timer
NO
called
CO-idle CO-idle
user busy?
YES
1 2
CO-enabled-A
automatic CO
basic call
invocation
cleared
timer expiry
NO
Stop automatic
called
CO invocation
user busy?
timer
YES
1 2 CO-idle
Figure 1 (sheet 4 of 4) - SS-CO, overall SDL

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7 SS-CO stage 2 specification
The stage 2 specification provides two different methods for the operation of SS-CO within the network. With
the path retention method, if a busy called user is encountered the network connection between the Originating
CC and the Destination CC is not released in accordance with ETS 300 171 but instead is retained awaiting a
possible request for SS-CO. With the non-retention method, if a busy called user is encountered and the basic
call SETUP request/indication was not accompanied by a request for SS-CO, the network connection is released
in accordance with ETS 300 171. Therefore, with the non-retention method, if SS-CO is requested after
encountering a busy called user a new network connection has to be established.
Either of the methods can be used to support any of the four methods of invoking SS-CO described in 6.2.2.2.
− Immediate invocation and network invocation (immediate) can be supported by the non-retention method by
accompanying the SETUP request/indication with a request for SS-CO.
− Immediate invocation and network invocation (immediate) can be supported by the path retention method
by accompanying the SETUP request/indication with a request for path retention and then, when the path is
retained because the called user is busy, requesting SS-CO.
− Consultation or network invocation (delayed) can be supported by the non-retention method by
accompanying the SETUP request/indication with a request for SS-CO and then, when the connection is
released because the called user is busy, consulting the calling user or applying a delay. SS-CO can then be
requested if necessary by repeating the SETUP request/indication, this time accompanied by a request for
SS-CO.
− Consultation or network invocation (delayed) can be supported by the path retention method by not
accompanying the SETUP request/indication with a request for path retention and then, when the path is
retained because the called user is busy, consulting the calling user or applying a delay. SS-CO can then be
requested if necessary using the retained connection. If it is determined that SS-CO is not required, the
connection is released.
The stage 3 standard for SS-CO at the Q reference point shall support both options, shall permit a PTNX
supporting FE1 functionality (see 7.1) to support either path retention or non-retention or both, and shall require
a PTNX supporting FE2 functionality to support both path retention and non-retention.
7.1 Functional model
7.1.1 Functional model description
The functional model shall comprise the following Functional Entities (FEs):
FE1 Calling user's control entity
FE2 Called user's control entity
The following functional relationship shall exist between these FEs:
ra between FE1 and FE2
Figure 2 shows these FEs and the relationship.
ra
FE 1
FE 2
Figure 2 - Functional model for SS-CO

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The further division of FE1 into an FE that is collocated with the Originating CCA (and therefore
allocatable to a functional TE) and an FE that is collocated with the Originating CC (and therefore
allocatable to a PTNX) is outside the scope of this ETS. The further division of FE2 into an FE that is
allocatable to a functional TE and an FE that is collocated with the Destination CC (and therefore allocated
to a PTNX), is outside the scope of this ETS.
7.1.2 Description of Functional Entities
7.1.2.1 Calling user's control entity, FE1
This functional entity:
− at the time of the original call request:
• receives and validates request from the calling user for immediate invocation of SS-CO;
• determines if immediate invocation, network invocation (immediate), network invocation
(delayed) or consultation is applicable to the call;
• if SS-CO is applicable to the call, determines if the path retention method or the non-retention
method is to be used and, as appropriate, sends a path retention request or immediate
invocation request to FE2 at the time of the original basic call r2-SETUP request/indication,
or retains the call setup information;
− if consultation applies to the call and the conditions for performing consultation are met:
• informs the calling user that the called user is busy and SS-CO may be requested;
• limits the length of the consultation by clearing the call if the calling user has not responded
(by requesting SS-CO or clearing the call) within the consultation time;
• receives request (during consultation) from the calling user for invocation of SS-CO, sends an
appropriate SS-CO invocation request (depending on the method used) to FE2, and sends the
result of the invocation request to the calling user;
− if network invocation (delayed) applies to the call and the conditions for performing this are met:
• informs the calling user that the called user is busy and SS-CO will be invoked unless the
calling user clears the call;
• on expiry of the automatic call offer invocation timer or on earlier request from the calling
user, sends an appropriate SS-CO invocation request (depending on the method used) to FE2,
and sends the result of the invocation request to the calling user;
− if immediate invocation or network invocation (immediate) applies and the path retention method is
used, on receipt of the information from FE2 that the called user is busy and SS-CO is allowed,
sends a SS-CO invocation request to FE2.

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7.1.2.2 Called user's control entity, FE2
This functional entity:
− on an incoming call with CO request to the called user who is busy, checks if SS-CO is possible; if
so, offers the call to the called user; if not, rejects the CO request;
− on an incoming call without CO request but with path retention request to a called user who is busy,
checks if SS-CO would be possible; if so, retains the path, offers FE1 the possibility of invoking
SS-CO, and, if required, applies an in-band tone or announcement to the calling user;
− having retained the path and offered FE1 the possibility of invoking SS-CO, and on receipt of an
SS-CO request from FE1, checks if SS-CO is still possible and if so, offers the call to the called
user; if not, rejects the request;
− if the call is offered to the called user, applies an in-band tone or announcement to the calling user,
if required;
− if the called user becomes not busy while a call is being offered, presents the call to the called user.
7.1.3 Relationship of functional model to Basic Call functional model
Functional entity FE1 is collocated with calling user's CCA/CC.
Functional entity FE2 is collocated with called user's CC.
An example of relationship between the FEs for SS-CO and FEs for the basic call is shown in figure 3.
r1 r2 r2 r1
CCA CC CC CC CCA
FE 2
FE 1
ra
Calling user
Called user
Figure 3 - Example relationship between model for SS-CO and Basic Call
7.2 Information flows
7.2.1 Definition of information flows
In the tables listing the elements in information flows, the column headed "Request" indicates which of
these elements are mandatory (M) and which are optional (O) in a request/indication information flow, and
the column headed "Confirm" indicates which of these elements are mandatory (M) and which are optional
(O) in a response/confirmation information flow.
7.2.1.1 ra-CO-ACTIVATE
ra-CO-ACTIVATE is an unconfirmed information flow across ra from FE1 to FE2 which is used to
request path retention if the called user is busy and if SS-CO is possible, in order to give the calling user
the opportunity to invoke SS-CO. There are no elements within the ra-CO-ACTIVATE information
flow.
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7.2.1.2 ra-CO-AVAILABLE
ra-CO-AVAILABLE is an unconfirmed information flow across ra from FE2 to FE1 that is used to
inform FE1 that the path has been retained and SS-CO is possible. There are no elements within the ra-
CO-AVAILABLE information flow.
7.2.1.3 ra-CO-INVOKE-IMMEDIATE
ra-CO-INVOKE-IMMEDIATE is a confirmed information flow across ra from FE1 to FE2 which is
used to invoke immediately (as part of the call establishment between FE1 and FE2) SS-CO if the called
user is busy and SS-CO is possible. The response indicates one of the following:
− short term denial, e.g. because of maximum number of offered calls already reached at FE2;
− long term denial, e.g. because of SS-CO not provided;
− not applicable, e.g. because of called user not busy;
− success.
Table 1 lists the elements within the ra-CO-INVOKE-IMMEDIATE information flow.
Table 1 - Content of ra-CO-INVOKE-IMMEDIATE
Element Request Confirm Note
CO-INVOKE-IMMEDIATE-result - M 4
NOTE 4
This element takes one of the values: short-term-denial, long-term-denial, not-applicable, success.
7.2.1.4 ra-CO-INVOKE
ra-CO-INVOKE is a confirmed information flow across ra from FE1 to FE2 which is used to invoke SS-
CO in the case where path retention has been successfully invoked (by ra-CO-ACTIVATE). The
response indicates one of the following:
− short term denial, e.g. because of maximum number of offered calls already reached at FE2;
− not applicable, e.g. because of called user not busy;
− success.
Table 2 lists the elements within the ra-CO-INVOKE information flow.
Table 2 - Content of ra-CO-INVOKE
Element Request Confirm Note
CO-INVOKE-result - M 5
NOTE 5
This element takes one of the values: short-term-denial, not-applicable, success.

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7.2.1.5 ra-CO-TERMINATED
ra-CO-TERMINATED is an
...