ETSI ETS 300 366 ed.1 (1994-07)

SLOVENSKI STANDARD
SIST ETS 300 366 E1:2005
01-maj-2005
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Private Telecommunication Network (PTN); Inter-exchange signalling protocol ; Call
completion supplementary services
Ta slovenski standard je istoveten z: ETS 300 366 Edition 1
ICS:
33.040.35 Telefonska omrežja Telephone networks
SIST ETS 300 366 E1:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 366 E1:2005
EUROPEAN ETS 300 366
TELECOMMUNICATION July 1994
STANDARD
Source: ETSI TC-ECMA Reference: DE/ECMA-00049
ICS: 33.080
PTN, ECMA-186, QSIG.CC
Key words:
Private Telecommunication Network (PTN);
Inter-exchange signalling protocol
Call completion supplementary services
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
No part may be reproduced except as authorized by written permission. The copyright and the
Copyright Notification:
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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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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Table of contents
Foreword 7
1Scope 9
2 Conformance 9
3 References 10
4 Definitions 11
4.1 External definitions 11
4.2 CC Call 11
4.3 CC Request 11
4.4 Connection release 12
4.5 Connection retention 12
4.6 Path Reservation 12
4.7 Service retention 12
5 List of acronyms 12
6 Signalling protocol for the support of SS-CCBS and SS-CCNR 13
6.1 SS-CCBS/CCNR description 13
6.2 SS-CC operational requirements 13
6.2.1 Requirements on the Originating PTNX 13
6.2.2 Requirements on the Terminating PTNX 13
6.2.3 Requirements on a Transit PTNX 13
6.3 SS-CC coding requirements 14
6.3.1 Operations 14
6.3.2 Information elements 16
6.3.2.1 Facility information element 16
6.3.2.2 Other information elements 17
6.3.3 Messages 17
6.4 SS-CC State definitions 17
6.4.1 States at the Originating PTNX 17
6.4.1.1 CC-Idle 17
6.4.1.2 CC-Wait-Ack 17
6.4.1.3 CC-Invoked-A-RET 17
6.4.1.4 CC-Invoked-A-RLS 17
6.4.1.5 CC-Suspended-A 17
6.4.1.6 CC-Path-Setup 17
6.4.1.7 CC-Wait-User-A-Answer-N 17
6.4.1.8 CC-Wait-User-A-Answer-R 17
6.4.1.9 CC-Ringout 17
6.4.1.10 CC-Wait-User-A-Free 17
6.4.2 States at the Terminating PTNX 18
6.4.2.1 CC-Idle 18
6.4.2.2 CC-Invoked-B 18
6.4.2.3 CC-Await-Call-Completion 18
6.4.2.4 CC-Suspended-B 18
6.4.2.5 CC-Path-Complete 18
6.4.2.6 CC-Wait-User-B-Alert 18
6.5 SS-CC signalling procedures 18
6.5.1 Major options 18

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6.5.1.1 Path reservation 18
6.5.1.2 Retention of signalling connection 19
6.5.1.3 Service retention 19
6.5.2 Actions at the Originating PTNX 19
6.5.2.1 Normal procedures 19
6.5.2.1.1 CCBS invocation 19
6.5.2.1.2 CCNR invocation 20
6.5.2.1.3 SS-CC invocation - detailed procedure 20
6.5.2.1.4 Indication that User B is not busy 21
6.5.2.1.5 CC Call without Path Reservation 22
6.5.2.1.6 CC Call with Path Reservation 22
6.5.2.1.7 User A busy, non-reservation method 23
6.5.2.1.8 User A busy before Path Reservation 23
6.5.2.1.9 User A busy after Path Reservation 23
6.5.2.1.10 CCBS/CCNR cancellation 24
6.5.2.2 Exceptional procedures 25
6.5.2.2.1 CCBS/CCNR invocation 25
6.5.2.2.2 Unexpected APDUs 25
6.5.2.2.3 Service duration timer expiry 25
6.5.2.2.4 SS-CC Recall timer expiry 25
6.5.2.2.5 Failure of Path Reservation 25
6.5.2.2.6 Failure of CC Call presentation 26
6.5.3 Actions at the Terminating PTNX 26
6.5.3.1 Normal procedures 26
6.5.3.1.1 CCBS invocation 26
6.5.3.1.2 CCNR invocation 26
6.5.3.1.3 SS-CC invocation - detailed procedure 27
6.5.3.1.4 Indication that User B is not busy 27
6.5.3.1.5 CC Call without Path Reservation 28
6.5.3.1.6 CC Call with Path Reservation 29
6.5.3.1.7 CCBS/CCNR suspension / resumption 29
6.5.3.1.8 CCBS/CCNR cancellation 30
6.5.3.2 Exceptional procedures 30
6.5.3.2.1 CCBS/CCNR invocation 30
6.5.3.2.2 Unexpected APDUs 31
6.5.3.2.3 User B busy again on Path Reservation attempt 31
6.5.3.2.4 User B busy again on CC Call presentation 31
6.5.3.2.5 Interruption of CC Call 31

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6.5.4 Actions at the Transit PTNX 31
6.6 Impact of interworking with public ISDNs 31
6.6.1 Incoming Gateway PTNX procedures: SS-CCBS request from a public ISDN 32
6.6.2 Outgoing Gateway PTNX procedures: SS-CCBS request to a public ISDN 32
6.7 Impact of interworking with non-ISDNs 33
6.7.1 Incoming Gateway PTNX procedures 33
6.7.2 Outgoing Gateway PTNX procedures 33
6.8 Parameter values (timers) 34
6.8.1 Timers at the Originating PTNX 34
6.8.2 Timers at the Terminating PTNX 34
Annex A (normative): Protocol Implementation Conformance Statement (PICS) Proforma 35
A.1 Introduction 35
A.2 Instructions for completing the PICS proforma 35
A.2.1 General structure of the PICS proforma 35
A.2.2 Additional Information 36
A.2.3 Exception Information 36
A.3 PICS proforma for ECMA-186 36
A.3.1 Implementation Identification 36
A.3.2 Protocol Summary 37
A.3.3 General 37
A.3.4 Procedures at the Originating PTNX 38
A.3.5 Procedures at the Terminating PTNX 39
A.3.6 Procedures at a Gateway PTNX 40
A.3.7 Coding 41
A.3.8 Timers 42
Annex B (informative): Examples of message sequences 43
B.1 Successful CCBS 44
B.1.1 With path reservation and connection released 44
B.1.2 Without path reservation 45
B.2 Successful CCNR 45
B.3 User A busy 46
B.3.1 Path reservation case 46
B.3.2 Non-reservation case 47
B.4 User B busy again 48
B.4.1 At path reservation 48
B.4.2 At CC Call presentation - without path reservation, without service retention 49
B.4.3 At CC Call presentation - without path reservation, with service retention 50
Annex C (informative): Specification and Description Language (SDL), representation of procedures 51
C.1 Behaviour of the Originating PTNX 51
C.2 Behaviour of the Terminating PTNX 62
Annex D (informative): Imported Data types 69
History 70

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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 Integrated Services Digital Network (ISDN) concepts as
developed by CCITT and is also within the framework of standards for open systems interconnection as defined by ISO.
This particular ETS specifies the signalling protocol for use at the Q reference point in support of the Call Completion
supplementary services.
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, CCITT, 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 voting process for this ETS it has been agreed that this ETS will not be
converted to the ETSI stylesheet.

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1Scope
This European Telecommunication Standard (ETS) specifies the signalling protocol for the support of the Call
Completion supplementary services (SS-CCBS, SS-CCNR) at the Q reference point between Private
Telecommunication Network Exchanges (PTNXs) connected together within a Private Telecommunication
Network (PTN).
SS-CCBS enables a calling User A, encountering a busy destination User B, to have the call completed when
User B becomes not busy, without having to make a new call attempt.
SS-CCNR enables a calling User A, encountering a destination User B that, though alerted, does not answer, to
have the call completed when User B becomes not busy again after a period of activity, without having to make
a new call attempt.
The Q reference point is defined in Standard ISO/IEC 11579.
Service specifications are produced in three stages and according to the method specified in ENV 41005. This
Standard is the output from stage 3, the definition of signalling protocols, for SS-CCBS and SS-CCNR. This
Standard satisfies the requirements identified by the stage 1 and stage 2 specifications in ETS 300 365.
The signalling protocols for SS-CCBS and SS-CCNR operate partly on top of the signalling protocol for basic
circuit switched call control, as specified in ETS 300 172, and partly independently of a basic call. The
protocols use certain aspects of the generic procedures for the control of supplementary services specified in
ETS 300 239.
The impact on the protocol of interactions between the Call Completion services and other supplementary
services is outside the scope of this Standard.
This Standard is applicable to PTNXs which can interconnect to form a PTN.
2 Conformance
In order to conform to this Standard, a PTNX shall satisfy the requirements identified in the Protocol
Implementation Conformance Statement (PICS) proforma in Annex A.

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3 References
ISO/IEC 11579: Information Technology - Telecommunications and Information Exchange between
Systems - Private Integrated Services Network - Reference Configurations for
PISN Exchanges (1994)
ETS 300 172: Private Telecommunication Network (PTN); Inter-exchange signalling protocol;
Circuit mode basic services (1994)
ETS 300 196-1: Integrated Services Digital Network (ISDN); Generic functional protocol for the
support of supplementary services; Digital Subscriber Signalling System No. one
(DSS1) protocol; Part 1: Protocol specification (1992)
ETS 300 239: Private Telecommunication Network (PTN) - Inter-exchange signalling protocol;
Generic functional protocol for the support of supplementary services (1992)
ETS 300 359-1: Integrated Services Digital Network (ISDN); Completion of Calls to Busy
Subscriber (CCBS) supplementary service; Digital Subscriber Signalling System
No. one (DSS1) protocol; Part 1: Protocol specification (1994)
ETS 300 365: Private Telecommunication Network (PTN); Specification, functional model and
information flows; Call completion supplementary services (1994)
ETS 300 171: Private Telecommunication Networks (PTN); Specification, functional model and
information flows; Control aspects of circuit mode basic services (1992)
ENV 41005: Method for the Specification of Basic and Supplementary Services of Private
Telecommunication Networks (1989)
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)
CCITT Rec. Z.100: Specification and description language (SDL) (1988)

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4 Definitions
For the purposes of this Standard the following definitions apply.
4.1 External definitions
This Standard uses the following terms defined in other documents:
− Application Protocol Data Unit (APDU) (ETS 300 239)
− Basic Service (CCITT Rec. I.210)
− Busy (ETS 300 365)
− Call, Basic Call (ETS 300 239)
− Call Independent (ETS 300 239)
− Call Independent Signalling Connection (ETS 300 239)
− Call Related (ETS 300 239)
− End PTNX (ETS 300 239)
− Gateway PTNX (Incoming / Outgoing) (ETS 300 239)
− Interpretation APDU (ETS 300 239)
− Network Facility Extension (NFE) (ETS 300 239)
− Originating PTNX (ETS 300 172)
− Private Telecommunication Network Exchange (ENV 41007-1)
− Public ISDN (ENV 41007-1)
− SS-CC Recall (ETS 300 365)
− Signalling (CCITT Rec. I.112)
− Supplementary Service (CCITT Rec. I.210)
− Supplementary Service Control Entity (ETS 300 239)
− Telecommunication Network (ENV 41007-1)
− Terminal, Terminal Equipment (ENV 41007-1)
− Terminating PTNX (ETS 300 172)
− Transit PTNX (ETS 300 172)
− User (ETS 300 171-1)
− User A (ETS 300 365)
− User B (ETS 300 365)
4.2 CC Call
The re-initiation, in the course of executing a CC Request, of the previously unsuccessful call from User A to
User B on behalf of User A, with or without Path Reservation.
4.3 CC Request
An instance of SS-CCBS or SS-CCNR.

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4.4 Connection release
The release of the call independent signalling connection as soon as SS-CC has been initiated and the
establishment of further call independent signalling connections for subsequent phases of the service.
4.5 Connection retention
The use of a single call independent signalling connection throughout the lifetime of a particular instance of
SS-CC.
4.6 Path Reservation
The reservation of resources prior to the SS-CC Recall, by means of a basic call set up from the Originating
to the Terminating PTNX, in order to have a bearer connection through the PTN available when User A
accepts the SS-CC Recall.
4.7 Service retention
The optional capability to continue with a CC Request after the CC Call failed due to User B being busy
again.
5 List of acronyms
APDU Application Protocol Data Unit
ASN.1 Abstract Syntax Notation no. 1
CC Call Completion
ISDN Integrated Services Digital Network
NFE Network Facility Extension
PICS Protocol Implementation Conformance Statement
PTN Private Telecommunication Network
PTNX Private Telecommunication Network Exchange
SDL Specification and Description Language
SS-CC Supplementary Service Call Completion (i.e. SS-CCBS or SS-CCNR)
SS-CCBS Supplementary Service Call Completion to Busy Subscriber
SS-CCNR Supplementary Service Call Completion on No Reply
TE Terminal Equipment

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6 Signalling protocol for the support of SS-CCBS and SS-CCNR
6.1 SS-CCBS/CCNR description
Call Completion to Busy Subscriber (SS-CCBS) is a supplementary service which allows a calling User A,
on encountering a busy called User B, to request that the PTN monitors User B and indicates to User A when
User B becomes not busy. On response by User A to that indication the PTN will attempt to complete the call
to User B.
Call Completion on No Reply (SS-CCNR) is a supplementary service which allows a calling User A, when
the called User B does not respond to the call request, to request that the PTN monitors User B and indicates
to User A when User B becomes not busy after a subsequent period of activity at User B's TE. On response
by User A to that indication the PTN will attempt to complete the call to User B.
NOTE 1
Which activities at User B's TE would result in a 'B not busy' indication to User A is outside the scope of this
Standard.
These supplementary services are applicable to all circuit mode basic services defined in ETS 300 171.
6.2 SS-CC operational requirements
6.2.1 Requirements on the Originating PTNX
Call establishment procedures for the outgoing side of an inter-PTNX link and call release procedures, as
specified in ETS 300 172, shall apply.
Generic procedures for the call related control of supplementary services, as specified in ETS 300 239 for
an End PTNX, shall apply. Additionally generic procedures for the call independent control (connection
orientated) of supplementary services, as specified in ETS 300 239 for an Originating and a Terminating
PTNX, shall apply.
6.2.2 Requirements on the Terminating PTNX
Call establishment procedures for the incoming side of an inter-PTNX link and call release procedures, as
specified in ETS 300 172, shall apply.
Generic procedures for the call related control of supplementary services, as specified in ETS 300 239 for
an End PTNX, shall apply. Additionally generic procedures for the call independent control (connection
orientated) of supplementary services, as specified in ETS 300 239 for an Originating and a Terminating
PTNX, shall apply.
6.2.3 Requirements on a Transit PTNX
Basic call procedures for call establishment and call clearing at a Transit PTNX, as specified in ETS 300
172, shall apply.
NOTE 2
The use of basic call timer T310 at a Transit PTNX can cause premature clearing of a reserved path if the timer
value is too short. For this reason this Standard specifies the sending of CCITT progress description no. 8
"in-band information or appropriate pattern now available" by the Terminating PTNX, in order to stop timer
T310, even though in-band tones and announcements are not applicable in this situation.
Generic procedures for the call related control and call independent control (connection orientated) of
supplementary services, as specified in ETS 300 239 for a Transit PTNX, shall apply.

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6.3 SS-CC coding requirements
6.3.1 Operations
SS-CC-Operations { ccitt (0)  identified-organization (3)  etsi (0)
qsig-call-completion (366)  operations (0) }
DEFINITIONS EXPLICIT TAGS ::=
BEGIN
IMPORTS
OPERATION, ERROR FROM Remote-Operation-Notation
{ joint-iso-ccitt (2) remote-operations (4) notation (0) }
Extension FROM Manufacturer-specific-service-extension-definition
{ ccitt (0)  identified-organization (3)  etsi (0)
 qsig-generic-procedures (239)  msi-definition (0) }
QSIGInformationElement FROM  Generic-Parameters-Definition
{ ccitt (0)  identified-organization (3)  etsi (0)
 qsig-generic-procedures (239)  qsig-generic-parameters (6) }
PartyNumber, PartySubaddress, PresentedNumberUnscreened  FROM
Addressing-data-elements
{ ccitt (0)  identified-organization (3)  etsi (0)  196
 addressing-data-elements (6) }
supplementaryServiceInteractionNotAllowed  FROM General-Errors
{ ccitt (0)  identified-organization (3)  etsi (0)  196
 general-errors (2) };
ptnOBJECT IDENTIFIER ::=  { iso (1)  identified-organization (3)
icd-ecma (0012)  private-isdn-signalling-domain (9) }
CcbsRequest ::= OPERATION
ARGUMENT CcRequestArg
RESULT CcRequestRes
ERRORS { shortTermRejection, longTermRejection,
 supplementaryServiceInteractionNotAllowed,
 unspecified }
CcnrRequest ::= OPERATION
ARGUMENT CcRequestArg
RESULT CcRequestRes
ERRORS { shortTermRejection, longTermRejection,
 supplementaryServiceInteractionNotAllowed,
 unspecified }
CcCancel ::= OPERATION
ARGUMENT CcOptionalArg
CcExecPossible ::= OPERATION
ARGUMENT CcOptionalArg
CcPathReserve ::= OPERATION
ARGUMENT CcExtension

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RESULT CcExtension
ERRORS    {remoteUserBusyAgain,
failureToMatch,
failedDueToInterworking,
unspecified  }
CcRingout ::= OPERATION
ARGUMENT CcExtension
ERRORS    {remoteUserBusyAgain,
failureToMatch,
unspecified  }
CcSuspend ::= OPERATION
ARGUMENT CcExtension
CcResume ::= OPERATION
ARGUMENT CcExtension
Unspecified ::= ERROR
PARAMETER CcExtension
CcRequestArg ::= SEQUENCE  {
numberA PresentedNumberUnscreened,
numberB PartyNumber,
service QSIGInformationElement,
-- permitted information elements are:
-- Bearer capability;
-- Low layer compatibility;
-- High layer compatibility.
subaddrA [10] PartySubaddress OPTIONAL,
subaddrB [11] PartySubaddress OPTIONAL,
can-retain-service [12]  IMPLICIT  BOOLEAN
DEFAULT FALSE,
retain-sig-connection [13]  IMPLICIT  BOOLEAN
OPTIONAL,
-- TRUE: sign. connection to be retained;
-- FALSE: sign. connection to be released;
-- omission: release or retain sign. conn.
extension CcExtension OPTIONAL  }
CcRequestRes ::= SEQUENCE {
no-path-reservation [0] IMPLICIT BOOLEAN
DEFAULT FALSE,
retain-service [1] IMPLICIT BOOLEAN
DEFAULT FALSE,
extension CcExtension  OPTIONAL  }
CcOptionalArg ::=
CHOICE   { fullArg [0] IMPLICIT SEQUENCE {
numberA PartyNumber,
numberB PartyNumber,
service QSIGInformationElement,
-- permitted information elements are:
-- Bearer capability;

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-- Low layer compatibility;
-- High layer compatibility.
subaddrA [10] PartySubaddress OPTIONAL,
subaddrB [11] PartySubaddress OPTIONAL,
extension CcExtension OPTIONAL },
extArg CcExtension  }
CcExtension ::=
CHOICE   { none NULL,
single [14] IMPLICIT Extension,
multiple [15] IMPLICIT SEQUENCE OF Extension }
ccbsRequest CcbsRequest ::= { ptn  ccbs-request (40) }
ccnrRequest CcnrRequest ::= { ptn  ccnr-request (27) }
ccCancel CcCancel ::= { ptn  cc-cancel (28) }
ccExecPossible CcExecPossible ::= { ptn  cc-exec-possible (29) }
ccPathReserve CcPathReserve ::= { ptn  cc-path-reserve (30) }
ccRingout CcRingout ::= { ptn  cc-ringout (31) }
ccSuspend CcSuspend ::= { ptn  cc-suspend (32) }
ccResume CcResume ::= { ptn  cc-resume (33) }
shortTermRejection ERROR ::= { ptn 1010 }
longTermRejection ERROR ::= { ptn 1011 }
remoteUserBusyAgain ERROR ::= { ptn 1012 }
failureToMatch ERROR ::= { ptn 1013 }
failedDueToInterworking ERROR ::= { ptn 1014 }
unspecified Unspecified ::= { ptn 1008 }
END -- of SS-CC-Operations
6.3.2 Information elements
6.3.2.1 Facility information element
The operations defined in subclause 6.3.1 shall be coded in the Facility information element in
accordance with 11.3.3 of ETS 300 239.
The Facility information element shall always contain an NFE. When the Facility information element is
sent in a call related message and conveys an invoke APDU the destinationEntity element of the NFE
shall contain value endPTNX.
A Facility information element conveying a ccPathReserve invoke APDU shall also contain an
Interpretation APDU with value clearCallIfAnyInvokePduNotRecognised. In all other cases the
Interpretation APDU shall either be omitted or included with value rejectAnyUnrecognisedInvokePdu.
Within elements of type QSIGInformationElement information elements (e.g. Bearer capability) shall
be coded in accordance with ETS 300 172.

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6.3.2.2 Other information elements
Any other information elements (e.g. Calling party number, Called party number) shall be coded in
accordance with the rules of ETS 300 172 and ETS 300 239.
6.3.3 Messages
The Facility information element shall be conveyed in the messages as specified in Clause 10 of ETS 300
239.
6.4 SS-CC State definitions
6.4.1 States at the Originating PTNX
The procedures for the Originating PTNX are written in terms of the following conceptual states existing
within the SS-CC Supplementary Service Control entity in that PTNX in association with a particular CC
Request.
6.4.1.1 CC-Idle
This state exists if SS-CC is not active.
6.4.1.2 CC-Wait-Ack
This state exists during SS-CC invocation.
6.4.1.3 CC-Invoked-A-RET
This state exists for an active CC Request while waiting for the indication that User B is not busy,
using the connection retention method.
6.4.1.4 CC-Invoked-A-RLS
This state exists for an active CC Request while waiting for the indication that User B is not busy, using
the connection release method.
6.4.1.5 CC-Suspended-A
This state exists when a CC Call without Path Reservation has been postponed because User A is busy.
6.4.1.6 CC-Path-Setup
This state exists during Path Reservation.
6.4.1.7 CC-Wait-User-A-Answer-N
This state exists while waiting for SS-CC Recall acceptance from User A if no path has been reserved.
6.4.1.8 CC-Wait-User-A-Answer-R
This state exists while waiting for SS-CC Recall acceptance from User A after a path has been reserved.
6.4.1.9 CC-Ringout
This state exists when User A has accepted the SS-CC Recall but completion of the call to User B is
still pending.
6.4.1.10 CC-Wait-User-A-Free
This state exists when Path Reservation is delayed because User A is busy.
6.4.2 States at the Terminating PTNX
The procedures for the Terminating PTNX are written in terms of the following conceptual states existing
within the SS-CC Supplementary Service Control entity in that PTNX in association with a particular CC
Request.

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6.4.2.1 CC-Idle
This state exists if SS-CC is not active.
6.4.2.2 CC-Invoked-B
This state exists while User B is monitored as a result of a CC Request received.
6.4.2.3 CC-Await-Call-Completion
This state exists while waiting for the incoming CC Call after having indicated that User B is not busy.
6.4.2.4 CC-Suspended-B
This state exists when a CC Call has been postponed because User A is busy.
6.4.2.5 CC-Path-Complete
This state exists when a path has been successfully reserved and CC Call completion is pending.
6.4.2.6 CC-Wait-User-B-Alert
This state exists after a CC Call has been extended to User B, while waiting for acceptance (alerting or
connect).
6.5 SS-CC signalling procedures
The following procedures are a combination of call related and call independent signalling. The latter uses
the connection-oriented APDU transport mechanism specified in ETS 300 239, which provides call
independent signalling connections for supplementary service control.
All SS-CC control information is exchanged between Originating PTNX and Terminating PTNX.
Examples of message sequences are shown in Annex B.
6.5.1 Major options
The signalling protocol contains the following major options. These are negotiated between the
Originating and Terminating PTNXs at SS-CC invocation time, using specific elements in the argument
and result of operations ccbsRequest and ccnrRequest.
6.5.1.1 Path reservation
There are two methods of establishing the CC Call:
• path reservation method - a bearer connection between the Originating and Terminating PTNXs is
established before recalling User A, to avoid the possibility of encountering network congestion
after User A responds to SS-CC Recall;
• non-reservation method - a bearer connection between the Originating and Terminating PTNXs is
established after User A responds to SS-CC Recall and the service is cancelled if network
congestion is encountered.
As described in subclause 6.5.2, it is an option of the Originating PTNX which of these methods is
used. The procedures specified in subclause 6.5.3 mandate from a Terminating PTNX the support of
both methods. In interworking situations, an Outgoing Gateway PTNX can force the use of the
non-reservation method if the other network cannot support path reservation; see subclauses 6.6 and
6.7.

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6.5.1.2 Retention of signalling connection
There are two ways in which SS-CC uses call independent signalling connections:
• connection retention method - the signalling connection is maintained until completion or
cancellation of SS-CC;
• connection release method - the signalling connection is cleared after each phase of call
independent signalling and a new signalling connection is established for each subsequent phase of
call independent signalling.
If the path reservation method is used, both methods above are possible. The procedures specified in
subclauses 6.5.2 and 6.5.3 leave the decision on the method to the Terminating PTNX, but permit the
Originating PTNX to ask for the use of the connection release method if possible, in order to avoid
occupying network resources for the duration of the service. Similarly, subclause 6.7 permits an
Incoming Gateway PTNX to ask for the use of the connection release method for compatibility with
other networks.
If the non-reservation method is used connection retention is required. Subclauses 6.6 and 6.7 provide a
means by which an Incoming Gateway PTNX or Outgoing Gateway PTNX can force the use of the
connection retention method for compatibility with public ISDNs and other networks that operate with a
retained connection.
6.5.1.3 Service retention
There are two possible behaviours when User B is found to be busy again after User A responds to
SS-CC Recall.
• service retention method - the CC Request remains in force at the Originating and Terminating
PTNXs and the Terminating PTNX commences the monitoring of User B again;
• service cancellation method - the CC Request is cancelled at the Originating and Terminating
PTNXs.
Either PTNX can force the use of the service cancellation method. The service retention method will be
used if both PTNXs agree.
6.5.2 Actions at the Originating PTNX
The SDL representation of procedures at the Originating PTNX is shown in Clause C.1 of
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