ISO/IEC 15992:1998

INTERNATIONAL ISO/IEC
STANDARD 15992
First edition
1998-12-15
Information technology —
Telecommunications and information
exchange between systems — Private
Integrated Services Network —
Inter-exchange signalling protocol —
Call priority interruption and call priority
interruption protection supplementary
services
Technologies de l'information — Télécommunications et échange
d'information entre systèmes — Réseau privé à intégration de services —
Protocole de signalisation d'échange — Services supplémentaires
d'interruption de priorité d'appel et de protection d'interruption de priorité
d'appel
Reference number
B C
ISO/IEC 15992:1998(E)

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ISO/IEC 15992:1998(E)
Contents
Foreword v
Introduction vi
1 Scope 1
2 Conformance 1
3 Normative references 1
4 Definitions 2
4.1 External definitions 2
4.2 Called user 3
4.3 Calling user 3
4.4 Call interruption 3
4.5 Call Priority Interruption Capability Level (CPICL) 3
4.6 Call Priority Interruption Protection Level (CPIPL) 3
4.7 Call protection 3
4.8 Established call 3
4.9 Established call user 3
4.10 Established call user's PINX 3
4.11 Forced release 3
4.12 Inter-PINX link 3
4.13 Interrupting PINX 3
4.14 Non-priority call 3
4.15 Priority call 3
4.16 Protected call 3
5 List of acronyms 3
6 Signalling protocol for the support of SS-CPI(P) 3
6.1 SS-CPI(P) description 3
6.2 SS-CPI(P) operational requirements 4
6.2.1 Requirements on the Originating PINX 4
6.2.2 Requirements on the Terminating PINX 4
6.2.3 Requirements on a Transit PINX 4
6.2.4 Requirements on the Interrupting PINX 4
6.2.5 Requirements on the Established call user's PINX 4
6.3 SS-CPI(P) coding requirements 5
6.3.1 Operations 5
6.3.2 Notifications 6
6.3.3 Information elements 6
6.3.4 Messages 6
©  ISO/IEC 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or
utilized in any form or by any means, electronic or mechanical, including photocopying and micro-
film, without permission in writing from the publisher.
ISO/IEC Copyright Office • Case postale 56 • CH-1211 Genève 20 • Switzerland
Printed in Switzerland
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ISO/IEC ISO/IEC 15992:1998(E)
6.4 SS-CPI state definitions 6
6.4.1 States at the Originating PINX 6
6.4.2 States at the Transit PINX 7
6.4.3 States at the Interrupting PINX 7
6.5 SS-CPIP state definitions 7
6.5.1 States at the Originating PINX 7
6.5.2 States at the Transit PINX 7
6.5.3 States at the Terminating PINX 7
6.6 SS-CPI signalling procedures for activation, deactivation and registration 7
6.7 SS-CPIP signalling procedures for activation, deactivation and registration 7
6.8 SS-CPI signalling procedures for invocation and operation 7
6.8.1 Actions at the Originating PINX 8
6.8.2 Actions at a Transit PINX 8
6.8.3 Actions at the Interrupting PINX 8
6.8.4 Actions at the Terminating PINX 10
6.8.5 Actions at the Established call user's PINX 10
6.9 SS-CPIP signalling procedures for invocation and operation 10
6.9.1 Actions at the Originating PINX 10
6.9.2 Actions at a Transit PINX 10
6.9.3 Actions at the Terminating PINX 10
6.10 SS-CPI impact of interworking with public ISDNs 11
6.11 SS-CPIP impact of interworking with public ISDNs 11
6.12 SS-CPI impact of interworking with non-ISDNs 11
6.13 SS-CPIP impact of interworking with non-ISDNs 11
6.14 Protocol interactions between SS-CPI(P) and other supplementary services and ANFs 11
6.14.1 Interaction with Calling Name Identification Presentation (SS-CNIP) 12
6.14.2 Interaction with Connected Name Identification Presentation (SS-CONP) 12
6.14.3 Interaction with Completion of Call to Busy Subscriber (SS-CCBS) 12
6.14.4 Interaction with Completion of Call on No Reply (SS-CCNR) 12
6.14.5 Interaction with Call Transfer (SS-CT) 12
6.14.6 Interaction with Call Forwarding Unconditional (SS-CFU) 12
6.14.7 Interaction with Call Forwarding Busy (SS-CFB) 12
6.14.8 Interaction with Call Forwarding No Reply (SS-CFNR) 12
6.14.9 Interaction with Call Deflection (SS-CD) 12
6.14.10 Interaction with Path Replacement (ANF-PR) 12
6.14.11 Interaction with Call Offer (SS-CO) 13
6.14.12 Interaction with Call Intrusion (SS-CI) 13
6.14.13 Interaction with Do not Disturb (SS-DND) 13
6.14.14 Interaction with Do not Disturb Override (SS-DNDO) 13
6.14.15 Interaction with Advice of Charge (SS-AOC) 13
6.14.16 Interaction with Recall (SS-RE) 13
6.14.17 Interaction with Call Interception (ANF-CINT) 13
6.14.18 Interaction with Transit Counter (ANF-TC) 13
6.14.19 Interaction with Cordless Terminal Location Registration (SS-CTLR) 13
6.14.20 Interaction with Cordless Terminal Incoming Call (ANF-CTMI) 13
6.14.21 Interaction with Cordless Terminal Outgoing Call (ANF-CTMO) 13
6.14.22 Interaction with Cordless Terminal Authentication of a CTM user (SS-CTAT) 13
6.14.23 Interaction with Cordless Terminal Authentication of a PISN (SS-CTAN) 14
6.14.24 Interaction with Message Waiting Indication (SS-MWI) 14
6.14.25 Interaction with Common Information (ANF-CMN) 14
6.15 SS-CPI parameter values (timers) 14
6.15.1 Timer T1 14
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ISO/IEC 15992:1998(E) ISO/IEC
Annexes
A - Protocol Implementation Conformance Statement (PICS) Proforma 15
B - Examples of message sequences 23
C - Specification and Description Language (SDL) representation of procedures 28
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ISO/IEC ISO/IEC 15992:1998(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the
specialized system for worldwide standardization. National bodies that are members of ISO or IEC participate in the
development of International Standards through technical committees established by the respective organization to deal with
particular fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work.
In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1. Draft
International Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the national bodies casting a vote.
International Standard ISO/IEC 15992 was prepared by ECMA (as ECMA-264) and was adopted, under a special “fast-track
procedure”, by Joint Technical Committee ISO/IEC JTC 1, Information technology, in parallel with its approval by national
bodies of ISO and IEC.
Annex A forms an integral part of this International Standard. Annexes B and C are for information only.
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ISO/IEC 15992:1998(E) ISO/IEC
Introduction
This International Standard is one of a series of International Standards defining services and signalling protocols applicable to
Private Integrated Services Networks (PISNs). The series uses ISDN concepts as developed by ITU-T and conforms to the
framework of International Standards for Open Systems Interconnection as defined by ISO/IEC.
This International Standard specifies the signalling protocol for use at the Q reference point in support of the Call Priority
Interruption (CPI) and Call Priority Interruption Protection (CPIP) supplementary services. The protocol defined in this
International Standard forms part of the PSS1 protocol (informally known as QSIG).
This International Standard is based upon the practical experience of ECMA member companies and the results of their active
and continuous participation in the work of ISO/IEC JTC1, ITU-T, ETSI and other international and national standardization
bodies. It represents a pragmatic and widely based consensus.
There are currently no equivalent services specified by ITU-T or ETSI for public ISDN.
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©
INTERNATIONAL STANDARD  ISO/IEC ISO/IEC 15992:1998(E)
Information technology - Telecommunications and information exchange between
systems - Private Integrated Services Network - Inter-exchange signalling protocol -
Call priority interruption and call priority interruption protection supplementary
services
1 Scope
This International Standard specifies the signalling protocol for the support of the Call priority interruption (SS-CPI) and Call
Priority Interruption Protection (SS-CPIP) supplementary services at the Q reference point between Private Integrated Services
Network eXchanges (PINXs) connected together within a Private Integrated Services Network (PISN).
Note 1 - This edition of this International Standard does not apply to calls using the circuit-mode multiple rate bearer service.
SS-CPI allows a call request for a priority call to proceed successfully in the case that there is no user information channel
available. This is accomplished by force releasing an established call of lower priority.
SS-CPIP allows for the protection of calls against interruption from priority calls.
The Q reference point is defined in ISO/IEC 11579-1.
Service specifications are produced in three stages and according to the method specified in CCITT Rec. I.130. This
International Standard contains the stage 3 specification for the Q reference point and satisfies the requirements identified by
the stage 1 and stage 2 specifications in ISO/IEC 15991.
The signalling protocol for SS-CPI(P) operates on top of the signalling protocol for basic circuit switched call control, as
specified in ISO/IEC 11572, and uses certain aspects of the generic procedures for the control of supplementary services
specified in ISO/IEC 11582.
This International Standard also specifies additional signalling protocol requirements for the support of interactions at the Q
reference point between SS-CPI(P) and other supplementary services and ANFs.
Note 2 - Additional interactions that have no impact on the signalling protocol at the Q reference point can be found in the relevant stage 1 specifications.
This International Standard is applicable to PINXs that can interconnect to form a PISN.
2 Conformance
In order to conform to this International Standard, a PINX shall satisfy the requirements identified in the Protocol
Implementation Conformance Statement (PICS) proforma in annex A.
Conformance to this International Standard includes conforming to those clauses that specify protocol interactions between
SS-CPI(P) and other supplementary services and ANFs for which signalling protocols at the Q reference point are supported in
accordance with the stage 3 standards concerned.
3 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International
Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to
agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent
editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International
Standards.
ISO/IEC 11572:1997,
Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Circuit mode bearer services - Inter-exchange signalling
procedures and protocol.
ISO/IEC 11574:1994,
Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Circuit-mode 64 kbit/s bearer services - Service description,
functional capabilities and information flows.
ISO/IEC 11579-1:1994,
Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Part 1: Reference configuration for PISN Exchanges
(PINX).
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ISO/IEC 15992:1998(E) ISO/IEC
ISO/IEC 11582:1995, Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Generic functional protocol for the support of
supplementary services - Inter-exchange signalling procedures and protocol.
ISO/IEC 13869:1995, Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Inter-exchange signalling protocol - Call transfer
supplementary service.
ISO/IEC 13873:1995, Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Inter-exchange signalling protocol - Call diversion
supplementary services.
ISO/IEC 13874:1995, Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Inter-exchange signalling protocol - Path replacement
additional network feature.
ISO/IEC 15054:1997, Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Inter-exchange signalling protocol - Call interception
additional network feature.
1)
ISO/IEC 15431:— , Information technology - Telecommunications and informtion exchange between systems - PISN -
Inter-exchange signalling protocol - Wireless terminal call handling additional network features.
ISO/IEC 15991:1998, Information technology - Telecommunications and information exchange between systems -
Private Integrated Services Network - Specification, functional model and information flows - Call
priority interruption and call priority interruption protection supplementary services.
ITU-T Rec. I.112:1993, Vocabulary of terms for ISDNs.
CCITT Rec. I.130:1988, Method for the characterization of telecommunication services supported by an ISDN and network
capabilities of an ISDN.
ITU-T Rec. I.210:1993, Principles of telecommunication services supported by an ISDN and the means to describe them.
ITU-T Rec. Q.950:1993, Digital Subscriber Signalling System No. 1 (DSS 1) - Supplementary services protocols, structure
and general principles.
ITU-T Rec. Z.100:1993, Specification and description language.
4 Definitions
For the purposes of this International Standard, the following definitions apply.
4.1 External definitions
This International Standard uses the following terms defined in other documents:
− Adjacent PINX (ISO/IEC 11582)
− Application Protocol Data Unit (APDU) (ISO/IEC 11582)
− Basic Service (ITU-T Rec. I.210)
− Call, Basic Call (ISO/IEC 11582)
Coordination Function (ISO/IEC 11582)
−
− Notification (ISO/IEC 11582)
− Originating PINX (ISO/IEC 11572)
− Preceding PINX (ISO/IEC 11572)
− Private Integrated Services Network (PISN) (ISO/IEC 11579-1)
− Private Integrated Services Network Exchange (PINX) (ISO/IEC 11579-1)
− Signalling (ITU-T Rec. I.112)
____________
1)  To be published.
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ISO/IEC ISO/IEC 15992:1998(E)
− Subsequent PINX (ISO/IEC 11572)
− Supplementary Service (ITU-T Rec. I.210)
− Terminating PINX (ISO/IEC 11572)
− Transit PINX (ISO/IEC 11572)
− User (ISO/IEC 11574)
4.2 Called user : The user that receives a request to accept an incoming call and who may request SS-CPIP.
4.3 Calling user : The user that originates a call attempt and who may request SS-CPI and/or SS-CPIP.
4.4 Call interruption : An invocation procedure of SS-CPI whereby the calling user indicates that a "priority call" is to be
made.
4.5 Call Priority Interruption Capability Level (CPICL) : A parameter indicating the priority of a call.
4.6 Call Priority Interruption Protection Level (CPIPL) : A parameter indicating a level of protection of a call against
interruption from other calls.
4.7 Call protection : An invocation procedure of SS-CPIP whereby the calling user or the called user indicates that a call is to
be protected.
4.8 Established call : The active call that is selected for interruption.
4.9 Established call user : A user in the established call.
4.10 Established call user's PINX : The PINX serving one of the users in the established call.
4.11 Forced release : The release of the established call during interruption.
4.12 Inter-PINX link : The totality of a signalling channel and a number of user information channels at the Q reference
point.
4.13 Interrupting PINX : The PINX that selects an established call for interruption.
Note 3 - The Originating PINX or any Transit PINX involved in a call may also be an Interrupting PINX.
4.14 Non-priority call : A call that has not been assigned a CPICL value.
4.15 Priority call : A call that has a CPICL value greater than zero.
Note 4 - A priority call may also be a protected call.
4.16 Protected call : A call that has a CPIPL value greater than zero.
Note 5 - A protected call may also be a priority call.
5 List of acronyms
ANF Additional Network Feature
APDU Application Protocol Data Unit
ASN.1 Abstract Syntax Notation no. 1
CPICL Call Priority Interruption Capability Level
CPIPL Call Priority Interruption Protection Level
ISDN Integrated Services Digital Network
NFE Network Facility Extension
PICS Protocol Implementation Conformance Statement
PINX Private Integrated Services Network eXchange
PISN Private Integrated Services Network
SDL Specification and Description Language
SS-CPI Call Priority Interruption Supplementary Service
SS-CPIP Call Priority Interruption Protection Supplementary Service
6 Signalling protocol for the support of SS-CPI(P)
6.1 SS-CPI(P) description
SS-CPI is a supplementary service that allows a call request for a priority call to proceed successfully in the case that there is
no user information channel available. SS-CPI may be invoked by the calling user.
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ISO/IEC 15992:1998(E) ISO/IEC
SS-CPIP is a supplementary service that allows for the protection of calls against interruption. SS-CPIP may be invoked by
either the calling user or the called user.
A priority interruption only occurs if the call originating from the calling user has a higher Call Priority Interruption Capability
Level (CPICL) than the Call Priority Interruption Protection Level (CPIPL) of at least one of the established calls on the
selected inter-PINX link.
SS-CPI(P) is applicable to all circuit mode basic services defined in ISO/IEC 11574.
6.2 SS-CPI(P) operational requirements
6.2.1 Requirements on the Originating PINX
Call establishment procedures for the outgoing side of an inter-PINX link and call release procedures, as specified in ISO/IEC
11572, shall apply.
Generic procedures for the call-related control of supplementary services, as specified in ISO/IEC 11582 for an End PINX,
shall apply.
6.2.2 Requirements on the Terminating PINX
Call establishment procedures for the incoming side of an inter-PINX link and call release procedures, as specified in ISO/IEC
11572, shall apply.
For the support of SS-CPIP, generic procedures for the call-related control of supplementary services, as specified in ISO/IEC
11582 for an End PINX, shall apply.
6.2.3 Requirements on a Transit PINX
Basic call procedures, as specified in ISO/IEC 11572 for a Transit PINX, shall apply.
Generic procedures for the call-related control of supplementary services, as specified in ISO/IEC 11582 for a Transit PINX,
shall apply. In addition, for the support of SS-CPI, the generic procedures for notification, as specified in ISO/IEC 11582 shall
apply.
6.2.4 Requirements on the Interrupting PINX
Call establishment procedures for the outgoing side of an inter-PINX link and call release procedures, as specified in ISO/IEC
11572, shall apply.
Generic procedures for the call-related control of supplementary services, as specified in ISO/IEC 11582 for both an End
PINX and a Transit PINX, shall apply. In addition, the generic procedures for notification, as specified in ISO/IEC 11582 shall
apply.
6.2.5 Requirements on the Established call user's PINX
Generic procedures for notification, as specified in ISO/IEC 11582 for a Receiving End PINX, shall apply.
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ISO/IEC ISO/IEC 15992:1998(E)
6.3 SS-CPI(P) coding requirements
6.3.1 Operations
The operations defined in Abstract Syntax Notation number 1 (ASN.1) in table 1 shall apply.
Table 1 - Operations in support of SS-CPI(P)
Call-Interruption-Operations
{iso (1) standard (0) pss1-call-interruption (15992) call-interruption-operations (0) }

DEFINITIONS EXPLICIT TAGS::=
BEGIN
IMPORTS OPERATION FROM Remote-Operation-Notation
{joint-iso-ccitt (2) remote-operations (4) notation (0)}
Extension FROM Manufacturer-specific-service-extension-definition
{iso (1) standard (0) pss1-generic-procedures (11582) msi-definition (0)};
-- The following operations are defined:
CallInterruptionRequest ::= OPERATION
ARGUMENT CPIRequestArg
CallProtectionRequest ::= OPERATION
ARGUMENT CPIPRequestArg
-- The following arguments are defined:

CPIRequestArg ::= SEQUENCE{
cpiCapabilityLevel CPICapabilityLevel,
argumentExtension CHOICE{
extension [1] IMPLICIT Extension,
sequenceOfExtn [2] IMPLICIT SEQUENCE OF
Extension} OPTIONAL}
CPIPRequestArg ::= SEQUENCE{
cpiProtectionLevel CPIProtectionLevel
argumentExtension CHOICE{
extension [1] IMPLICIT Extension,
sequenceOfExtn [2] IMPLICIT SEQUENCE OF
Extension} OPTIONAL}
CPICapabilityLevel ::= ENUMERATED{
interruptionLowPriority (1),
interruptionMediumPriority (2),
interruptionHighPriority (3)}
CPIProtectionLevel ::= ENUMERATED{
noProtection (0),
lowProtection (1),
mediumProtection (2),
totalProtection (3)}
callInterruptionRequest CallInterruptionRequest ::= 87
callProtectionRequest CallProtectionRequest ::= 88
END -- of Call-Interruption-Operations

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6.3.2 Notifications
The following notifications, defined in Abstract Syntax Notation number 1 (ASN.1) in table 2 shall apply.
Table 2 - Notifications in support of SS-CPI(P)
Call-Interruption-Notifications
{iso (1) standard (0) pss1-call-interruption (15992) call-interruption-notifications (1) }

DEFINITIONS ::=
BEGIN
IMPORTS NOTIFICATION FROM Notification-Data-Structure
{iso (1) standard (0) pss1-generic-procedures (11582) notification-data-structure (7)};
-- The following notifications are defined:
InterruptionIsImpending ::= NOTIFICATION
ARGUMENT NULL
InterruptionTerminated ::= NOTIFICATION
ARGUMENT NULL
InterruptionForcedRelease ::= NOTIFICATION
ARGUMENT NULL
interruptionIsImpending InterruptionIsImpending ::= 2008
interruptionTerminated InterruptionTerminated ::= 2009
interruptionForcedRelease InterruptionForcedRelease ::= 2010
END --of Call-Interruption-Notifications

6.3.3 Information elements
6.3.3.1 Facility information element
The operations defined above shall be coded in the Facility information element in accordance with ISO/IEC 11582.
When conveying an APDU of operation callInterruptionRequest or operation callProtectionRequest the NFE shall be included
and shall contain value anyTypeOfPINX.
When conveying the invoke APDU of operation callInterruptionRequest or operation callProtectionRequest the Interpretation
APDU shall be included and shall contain value discardAnyUnrecognisedInvokePdu.
6.3.3.2 Notification indicator information element
The notifications defined above shall be coded in the Notification indicator information element in accordance with
ISO/IEC 11582.
6.3.3.3 Other information elements
Any other information elements (e.g., Progress indicator) shall be coded in accordance with the rules of ISO/IEC 11572.
6.3.4 Messages
Messages used for call establishment and release shall be as specified in ISO/IEC 11572.
The Facility information element and the Notification indicator information element shall be conveyed in the messages as
specified in clause 10 of ISO/IEC 11582.
6.4 SS-CPI state definitions
6.4.1 States at the Originating PINX
The procedures for the Originating PINX are written in terms of the following conceptual states existing within the SS-CPI
Supplementary Service Control entity in that PINX in association with a particular call.
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ISO/IEC ISO/IEC 15992:1998(E)
6.4.1.1 State CPI-Idle
SS-CPI is not operating.
6.4.2 States at the Transit PINX
Th e procedures for the Transit PINX are written in terms of the following conceptual states existing within the SS-CPI
Supplementary Service Control functional entity in that PINX in association with a particular call.
6.4.2.1 State CPI-Idle
SS-CPI is not operating.
6.4.3 States at the Interrupting PINX
The procedures for the Interrupting PINX are written in terms of the following conceptual states existing within the SS-CPI
Supplementary Service Control functional entity in that PINX in association with a particular call.
6.4.3.1 State CPI-Idle
SS-CPI is not operating.
6.4.3.2 State CPI-Impending
Following invocation of call interruption, the Interrupting PINX has notified an impending interruption to the users in the
established call and is waiting for the end of the impending phase before starting interruption.
6.4.3.3 State CPI-Releasing
The Interrupting PINX has forced released the established call and is waiting for completion of the clearing process.
6.5 SS-CPIP state definitions
6.5.1 States at the Originating PINX
The procedures for the Originating PINX are written in terms of the following conceptual states existing within the SS-CPIP
Supplementary Service Control entity in that PINX in association with a particular call.
6.5.1.1 State CPIP-Idle
SS-CPIP is not operating.
6.5.2 States at the Transit PINX
The procedures for the Transit PINX are written in terms of the following conceptual states existing within the SS-CPIP
Supplementary Service Control functional entity in that PINX in association with a particular call.
6.5.2.1 State CPIP-Idle
SS-CPIP is not operating.
6.5.3 States at the Terminating PINX
The procedures for the Terminating PINX are written in terms of the following conceptual states existing within the SS-CPIP
Supplementary Service Control functional entity in that PINX in association with a particular call.
6.5.3.1 State CPIP-Idle
SS-CPIP is not operating.
6.6 SS-CPI signalling procedures for activation, deactivation and registration
Not applicable.
6.7 SS-CPIP signalling procedures for activation, deactivation and registration
Not applicable.
6.8 SS-CPI signalling procedures for invocation and operation
Annex B contains some examples of message sequences.
Note 6 - SS-CPI may be invoked by the calling user to identify a call attempt as being a "priority call", and to give it the capability to interrupt other calls as
a means of obtaining the resources needed for successful call establishment.
Calls with an associated Call Priority Interruption Capability Level (CPICL) in which the CPICL value is greater than 0 are known as "priority calls".
Priority calls have the capability to interrupt other calls, both protected and non-protected; with the exception of calls having "total protection" (CPIPL=3).
Priority calls may also be protected calls if SS-CPIP was invoked at the same time as SS-CPI.
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6.8.1 Actions at the Originating PINX
6.8.1.1 Procedure for invocation of SS-CPI
For a given call, the Originating PINX may invoke SS-CPI using the procedures specified below.
The SDL representation of procedures at the Originating PINX is shown in C.1 of annex C.
6.8.1.1.1 Normal procedures
To invoke SS-CPI, the Originating PINX shall send a callInterruptionRequest invoke APDU, and re-enter state CPI-Idle. The
APDU shall be sent in the SETUP message that establishes the call. The argument of the invoke operation shall convey the
CPICL of the calling user.
Note 7 - The method by which the value of the CPICL is assigned is outside the scope of this International Standard.
6.8.1.1.2 Exceptional procedures
If the basic call fails for reasons other than those covered in 6.8.1.2 below (e.g., on calling user release, call failure, etc.), SS-
CPI shall terminate, and state CPI-Idle shall be entered.
6.8.1.2 Procedure for operation of SS-CPI
W hile attempting to establish a new call in accordance with the procedures of ISO/IEC 11572, the inter-PINX link to the
Subsequent PINX may be found to be congested (i.e., no B-channel available).
6.8.1.2.1 Normal procedures
If the calling user invoked SS-CPI, the Originating PINX shall not reject the calling user's call request, but shall check whether
call interruption is possible. It shall do this by behaving as an Interrupting PINX, as specified in 6.8.3.1 below. On completion
of these procedures the behaviour of the PINX shall revert to that of an Originating PINX.
6.8.1.2.2 Exceptional procedures
The exceptional procedures of an Interrupting PINX, as specified in 6.8.3.2 below, shall apply; with the modification that
where "Preceding PINX" is referred to, this shall be interpreted to mean "calling user".
On completion of those procedures the behaviour of the PINX shall revert to that of an Originating PINX.
6.8.2 Actions at a Transit PINX
The SDL representation of procedures at the Transit PINX is shown in C.2 of annex C.
6.8.2.1 Normal procedures
W hile processing, in accordance with the procedures of ISO/IEC 11572, an incoming SETUP message containing a
callInterruptionRequest invoke APDU, the Transit PINX may determine that the inter-PINX link to the Subsequent PINX is
congested (i.e., no B-channels are available). In this case the Transit PINX shall not release the call in the direction of the
Preceding PINX, but shall behave as an Interrupting PINX, as specified in 6.8.3.1 below. On completion of these procedures
the behaviour of the PINX shall revert to that of a Transit PINX.
6.8.2.2 Exceptional procedures
While
...