ETSI ETS 300 172 ed.2 (1994-01)

Private Telecommunication Network (PTN); Inter-exchange signalling protocol Circuit mode basic services

RE/ECMA-00044

Zasebno telekomunikacijsko omrežje (PTN) – Medcentralni signalizacijski protokol - Vodovne osnovne storitve

General Information

• Status: Published
• Publication Date: 17-Jan-1994
• Technical Committee: Ecma - Standardizing information and communications systems
• Current Stage: 12 - Completion
• Due Date: 07-Jan-1994
• Completion Date: 18-Jan-1994
• Mandate: T-75C.1
• Ref Project: SIST ETS 300 172 E2:2005 - Private Telecommunication Network (PTN); Inter-exchange signalling protocol Circuit mode basic services

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 172 E2:2005
01-maj-2005
Zasebno telekomunikacijsko omrežje (PTN) – Medcentralni signalizacijski protokol
- Vodovne osnovne storitve
Private Telecommunication Network (PTN); Inter-exchange signalling protocol Circuit
mode basic services
Ta slovenski standard je istoveten z: ETS 300 172 Edition 2
ICS:
33.040.35 Telefonska omrežja Telephone networks
SIST ETS 300 172 E2:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 172 E2:2005

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SIST ETS 300 172 E2:2005
EUROPEAN ETS 300 172
TELECOMMUNICATION January 1994
STANDARD Second Edition
Source: ETSI TC-ECMA Reference: DE/ECMA-0004
ICS: 33.080
Key words: PTN, QSIG-BC, ECMA-143
Private Telecommunication Network (PTN);
Inter-exchange signalling protocol
Circuit mode basis 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: [e-mail]
Tel.: [phone] - Fax: [phone]
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 11
Section I - General 13
1 Scope 13
2 Field of application 13
3 Conformance 13
4 References 13
5 Definitions and Acronyms 14
5.1 Definitions 14
5.1.1 General 14
5.1.2 Side, Incoming Side and Outgoing Side (see figure 1) 14
5.1.3 Outgoing Call and Incoming Call 14
5.1.4 Originating PTNX, Terminating PTNX and Transit PTNX (see figure 1) 14
5.1.5 Gateway PTNX, Incoming Gateway PTNX and Outgoing Gateway PTNX (see figure 1) 14
5.1.6 Preceding PTNX and Subsequent PTNX 15
5.1.7 Unrecognised Message 15
5.1.8 Unexpected Message 15
5.1.9 Unrecognised information element 15
5.1.10 information elements with Invalid Contents 15
5.2 Acronyms 16
6 General principles 16
6.1 Protocol Model 17
6.2 Services Provided to Call Control 18
6.3 Services Required of the Data Link Layer 18
6.4 Protocol Control States 18
6.4.1 States for Circuit Mode Call Control 19
6.4.1.1 Null State (0) 19
6.4.1.2 Call Initiated (1) 19
6.4.1.3 Overlap Sending (2) 19
6.4.1.4 Outgoing Call Proceeding (3) 19
6.4.1.5 Call Delivered (4) 19
6.4.1.6 Call Present (6) 19
6.4.1.7 Call Received (7) 19
6.4.1.8 Connect Request (8) 19
6.4.1.9 Incoming Call Proceeding (9) 19
6.4.1.10 Active (10) 19
6.4.1.11 Disconnect Request (11) 19
6.4.1.12 Disconnect Indication (12) 19

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6.4.1.13 Release Request (19) 19
6.4.1.14 Overlap Receiving (25) 19
6.4.2 States for Layer Management 20
6.4.2.1 Null State (Rest 0) 20
6.4.2.2 Restart Request (Rest 1) 20
6.4.2.3 Restart (Rest 2) 20
6.5 Message Segmentation and Re-assembly Functions 20
6.5.1 States for Message Segmentation and Re-assembly Procedures 21
6.5.1.1 Null (0) 21
6.5.1.2 Receiving segmented message (1) 21
6.6 Call Control 21
6.6.1 States for Transit PTNX Call Control 21
6.6.1.1 TCC_Idle (0) 21
6.6.1.2 TCC_Await Digits (1) 21
6.6.1.3 TCC_Await Additional Digits (2) 22
6.6.1.4 TCC_Overlap (3) 22
6.6.1.5 TCC_Incoming Call Proceeding (4) 22
6.6.1.6 TCC_Transit Call Proceeding (5) 22
6.6.1.7 TCC_Call Alerting (6) 22
6.6.1.8 TCC_Call Active (7) 22
6.6.1.9 TCC_Await Incoming Release (8) 22
6.6.1.10 TCC_Await Outgoing Release (9) 22
6.6.1.11 TCC_Await Two-Way Release (10) 22
6.6.1.12 TCC_Await Incoming Disconnect (11) 22
6.6.1.13 TCC_Await Outgoing Disconnect (12) 22
6.6.1.14 TCC_Await Two-Way Disconnect (13) 22
Section II - Procedures 23
7 General procedures 23
7.1 Use of the Services of Layer 2 23
7.1.1 Establishment of a Data Link Connection 23
7.1.2 Transfer of Data 23
7.1.3 Data Link Reset 23
7.1.4 Data Link Failure 23
7.2 Message Segmentation Procedures 23
7.2.1 Procedures for Message Segmentation 24
7.2.2 Procedures for Message Re-assembly 24
7.2.3 SDL for Message Segmentation and Re-assembly (informative) 26
7.3 Handling of protocol error conditions 29
7.3.1 Protocol discriminator error 29
7.3.2 Message too short 29
7.3.3 Call reference error 29
7.3.3.1 Invalid Call reference format 29

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7.3.3.2 Call reference procedural errors 29
7.3.4 Message type or message sequence errors 30
7.3.5 General information element errors 30
7.3.5.1 Duplicated information elements 30
7.3.5.2 information elements exceeding maximum length 30
7.3.5.3 information elements out of sequence 30
7.3.6 Mandatory information element errors 31
7.3.6.1 Mandatory information element missing 31
7.3.6.2 Mandatory information element content error 31
7.3.7 Non-mandatory information element errors 32
7.3.7.1 Non-mandatory information element not recognised 32
7.3.7.2 Non-mandatory information element content error 32
7.3.8 Data Link reset 33
7.3.9 Data Link failure 33
7.4 Status and Status Enquiry Protocol Procedures 33
7.4.1 Status Enquiry procedure 33
7.4.2 Receiving a STATUS message 34
7.4.2.1 Receipt of a STATUS message reporting an incompatible Protocol Control state 35
7.4.2.2 Receipt of a STATUS message reporting a compatible Protocol Control state 35
7.4.2.3 Receiving a STATUS message containing the Global Call Reference 35
8 Circuit-Switched Call Control Procedures 35
8.1 Call establishment 36
8.1.1 Call request 36
8.1.2 B- channel selection 36
8.1.3 Overlap sending 37
8.1.4 Call Proceeding 37
8.1.4.1 Call proceeding, en-bloc sending 37
8.1.4.2 Call proceeding, overlap sending 38
8.1.4.3 Expiry Of Timer T310 38
8.1.5 Call confirmation indication 38
8.1.6 Call connected 39
8.1.7 Use of the PROGRESS message 39
8.1.7.1 During Call Establishment 39
8.1.7.2 During Call Failure 39
8.1.8 Failure of Call Establishment 40
8.2 Call clearing 40
8.2.1 Terminology 40
8.2.2 Exception conditions 41
8.2.3 Clearing 41
8.2.4 Clear Collision 41
8.3 Call Collisions 42
8.4 Protocol Control SDL Diagram (informative) 42
8.5 Transit PTNX Call Control requirements 66

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8.5.1 Receipt of Address Information 67
8.5.2 State TCC_Await Digits 67
8.5.3 State TCC_Await Additional Digits 67
8.5.4 State TCC_Overlap 68
8.5.5 Channel Through Connection Procedures 69
8.5.6 State TCC_Incoming Call Proceeding 69
8.5.7 State TCC_Transit Call Proceeding 70
8.5.8 State TCC_Call Alerting 71
8.5.9 State TCC_Call Active 71
8.5.10 Clearing at a Transit PTNX 72
8.5.10.1 Call Clearing not Initiated by the Transit PTNX 72
8.5.10.2 Call Clearing Initiated by the Transit PTNX 72
8.5.11 Handling of Basic Call information elements at a Transit PTNX 72
8.5.11.1 Mandatory information elements 73
8.5.11.2 Non-Mandatory information elements 73
8.6 Transit Call Control SDL Diagrams (informative) 73
8.7 Originating PTNX Call Control Requirements 90
8.7.1 Transmission of the SETUP message 91
8.7.2 Agreement of the B-channel 91
8.7.3 Receipt of progress indicators 92
8.7.4 Receipt of ALERTING Message 92
8.7.5 Receipt of CONNECT Message 92
8.7.6 Call Clearing Initiated by the Originating PTNX 92
8.7.7 Receipt of an Indication of Call Clearing 92
8.8 Terminating PTNX Call Control Requirements 93
8.8.1 Receipt of the SETUP message 93
8.8.2 Transmission of ALERTING Message 93
8.8.3 Transmission of progress indicators 94
8.8.4 Transmission of CONNECT Message 94
8.8.5 Call Clearing Initiated by the Terminating PTNX 94
8.8.6 Receipt of an Indication of Call Clearing 94
8.9 Incoming Gateway PTNX Call Control Requirements 95
8.9.1 Transmission of the SETUP message 95
8.9.2 Interworking Indications in the SETUP Message 95
8.9.2.1 Interworking Indications Received from a Public ISDN 96
8.9.2.2 Interworking with a Public Network 96
8.9.2.3 Interworking with another Private Network 96
8.9.2.4 Interworking with a Non-ISDN 96
8.9.2.5 Interworking with a Network with Limited Release Capability 96
8.9.3 Agreement of the B-channel 97
8.9.4 Receipt of progress indicators 97
8.9.5 Receipt of ALERTING Message 97
8.9.6 Receipt of CONNECT Message 97
8.9.7 Call Clearing Initiated by the Incoming Gateway PTNX 98

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8.9.8 Receipt of an Indication of Call Clearing 98
8.10 Outgoing Gateway PTNX Call Control Requirements 98
8.10.1 Receipt of the SETUP message 98
8.10.2 Connection of the B-channel 99
8.10.3 Transmission of Interworking Indications 99
8.10.3.1 Interworking Indications Received from a Public ISDN 99
8.10.3.2 Interworking with a Public Network 99
8.10.3.3 Interworking with another Private Network 100
8.10.3.4 Interworking with a Non-ISDN 100
8.10.3.5 Interworking with a Network with Limited Release Capability 100
8.10.4 Transmission of ALERTING Message 100
8.10.5 Transmission of CONNECT Message 101
8.10.6 Call Clearing Initiated by the Outgoing Gateway PTNX 101
8.10.7 Receipt of an Indication of Call Clearing 101
9 Procedures For Layer Management 102
9.1 Restart Procedures 102
9.1.1 Sending RESTART 102
9.1.2 Receipt of RESTART 102
9.1.3 Restart Collision 102
10 Protocol Timers 103
Section III - Messages 105
11 Functional Definition and Content of Messages 105
11.1 Messages for General Procedures 105
11.1.1 STATUS 105
11.1.2 STATUS ENQUIRY 106
11.2 Messages for Circuit Mode Call Control 106
11.2.1 ALERTING 106
11.2.2 CALL PROCEEDING 107
11.2.3 CONNECT 107
11.2.4 CONNECT ACKNOWLEDGE 108
11.2.5 DISCONNECT 108
11.2.6 INFORMATION 108
11.2.7 PROGRESS 109
11.2.8 RELEASE 109
11.2.9 RELEASE COMPLETE 110
11.2.10 SETUP 110
11.2.11 SETUP ACKNOWLEDGE 111
11.3 Messages for Layer Management 111
11.3.1 RESTART 111
11.3.2 RESTART ACKNOWLEDGE 112

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12 General message format and coding of information elements 112
12.1 Overview 112
12.2 Protocol discriminator 113
12.3 Call Reference 114
12.4 Message type 115
12.5 Other information elements for Basic Call Control (Codeset 0) 116
12.5.1 Coding rules 116
12.5.2 Extension of codesets 119
12.5.3 Locking shift procedure 119
12.5.4 Non-locking shift procedure 120
12.5.5 Bearer capability 120
12.5.6 Call state 123
12.5.7 Called party number 123
12.5.8 Called party subaddress 125
12.5.9 Calling party number 125
12.5.10 Calling party subaddress 127
12.5.11 Cause 127
12.5.12 Channel identification 132
12.5.13 Connected number 134
12.5.14 Connected subaddress 134
12.5.15 High layer compatibility (Layers 4 - 7) 134
12.5.16 Lower layer compatibility (Layers 1 - 3) 134
12.5.17 Progress indicator 135
12.5.18 Restart indicator 137
12.5.19 Segmented message 138
12.5.20 Sending complete 138
12.6 Information elements of Codeset 5 138
12.6.1 Party category 139
12.6.2 Transit counter 140
Annex A (informative): Use of the Cause information element 141
A.1 Definition of QSIG cause Values 141
A.2 Use of causes for Busy Conditions 143
Annex B (informative): Examples of Message Sequences 144
B.1 Enbloc Sending 144
B.1.1 Successful Call Setup 144
B.1.2 Unsuccessful Call Setup 144
B.2 Overlap Sending 145
B.2.1 Successful Call Setup 145
B.2.2 Unsuccessful Call Setup 146
B.3 Call Clearing 147
B.3.1 Normal Call Clearing (from originator) 147
B.3.2 Call Abort By a Transit PTNX 147

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Annex C (informative): Manufacturer Specific Information 148
Annex D (normative): Protocol Implementation Conformance Statement (PICS) Proforma 149
D.1 Introduction 149
D.2 Instructions for completing the PICS proforma 149
D.2.1 General structure of the PICS proforma 149
D.2.2 Additional Information 150
D.2.3 Exception Information 150
D.3 PICS Proforma for ETS 300 172 151
D.3.1 Implementation Identification 151
D.3.2 Protocol Summary 151
D.3.3 Bearers Supported 152
D.3.4 General Procedures 152
D.3.4.1 Use of the Services of Layer 2 152
D.3.4.2 Message Segmentation Procedures 152
D.3.4.3 Handling of Protocol Error Conditions 153
D.3.4.4 Status and Status Enquiry Protocol Procedures 153
D.3.5 Circuit-Switched Call Control 154
D.3.6 Call Control at a Transit PTNX 155
D.3.7 Call Control at an Originating PTNX 155
D.3.8 Call Control at a Terminating PTNX 155
D.3.9 Call Control at an Incoming Gateway PTNX 155
D.3.10 Call Control at an Outgoing Gateway PTNX 156
D.3.11 Procedures for Layer Management 156
D.3.12 Timers 157
D.3.13 Message and Information Elements for General Procedures 158
Annex E (informative): Relationship to ETS 300 172 First Edition 161
History 162

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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).
The protocol defined in this ETS is the basis for the QSIG protocol for signalling at the Q reference point between Private
Telecommunication Network Exchanges (PTNXs). Whilst this particular ETS defines signalling for the support of circuit mode
bearer services, other ETS's specify other aspects of QSIG, e.g. generic procedures for the support of supplementary services
and individual supplementary services.
QSIG is independent of the scenario used to interconnect PTNXs (see ENV 41006), and is based on Digital Subscriber
Signalling System No. 1 (DSS1), adapted for intra-PTN use. In particular, this ETS is based on a symmetrical form of
ETS 300 102.
This 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.
The differences between this edition and the first edition of ETS 300 172 are detailed in Annex E of this ETS.
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 publication of this ETS it has been agreed that this ETS will not be converted to the ETSI
stylesheet.

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Section I - General
1 Scope
This European Telecommunication Standard (ETS) defines the Layer 3 protocol for signalling for the support of circuit
mode bearer services (used either on their own or in support of teleservices) at the Q reference point between Private
Telecommunication Network Exchanges (PTNX) connected together within a Private Telecommunication Network
(PTN). The Q reference point is defined in ENV 41004.
Service specifications are produced in three stages and according to the method specified in ENV 41005. The
definition of signalling protocols is stage 3 of the method. Stage 1 and stage 2 specifications of the basic circuit mode
bearer services are to be found in ETS 300 171. The protocol defined in this ETS satisfies the requirements identified
by the stage 1 and stage 2 specifications in ETS 300 171.
2 Field of application
This ETS is applicable to PTNXs which interconnect to form a PTN.
3 Conformance
In order to conform to this ETS, a PTNX shall satisfy the requirements identified in the Protocol Implementation
Conformance Statement (PICS) Proforma in annex D.
4 References
ECMA-133 Reference Configurations for Calls through Exchanges of Private Telecommunication
Networks (1989)
ECMA-134 Method for the Specification of Basic and Supplementary Services of Private
Telecommunication Networks (1989)
ECMA-135 Scenarios for Interconnections between Exchanges of Private Telecommunication
Networks (1989)
ECMA-141 Data Link Layer Protocol at the Q Reference Point for the Signalling Channel between
Two Private Telecommunication Network Exchanges (1990)
ECMA-142 Specification, Functional Model and Information Flows for Control Aspects of Circuit
Mode Basic Services in Private Telecommunication Networks (1990)
ECMA-148 Identification Supplementary Services in Private Telecommunication Networks -
Specification, Functional Model and Information Flows (1990)
ECMA-155 Addressing in Private Telecommunication Networks (1991)
ETS 300 102-1:1990 Integrated Services Digital Network (ISDN); User-network interface layer 3;
Specifications for basic call control
ETS 300 170:1992 Private Telecommunication Network (PTN); Inter-exchange signalling, Data link layer
protocol
ETS 300 171:1992 Private Telecommunication Network (PTN); Specification, functional models and
information flows, Control aspects of circuit mode basic services
ETS 300 173:1992 Private Telecommunication Network (PTN); Specification, functional models and
information flows, Identification supplementary services
ETS 300 189:1992 Private Telecommunication Network (PTN); Addressing
ENV 41004:1989 Reference configuration for connectivity relations of private telecommunication network
exchanges
ENV 41005:1989 Method for the specification of basic and supplementary services of private
telecommunication networks

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ENV 41006:1989 Scenarios for interconnections between exchanges of private telecommunication networks
ENV 41007-1:1989 Definition of terms in private telecommunication networks. Part 1: Definition of general
terms
CCITT Rec. E.163:1988 Numbering plan for the international telephone service
CCITT Rec. E.164:1988 Numbering plan for the ISDN era
CCITT Rec. I.112:1988 Vocabulary of terms for ISDNs
CCITT Rec. I.330:1988 ISDN numbering and addressing principles
CCITT Rec. Q.930:1988 ISDN user-network interface layer 3 - general aspects
CCITT Rec. Q.931:1988 ISDN user-network interface layer 3 specification for basic call control
CCITT Rec. T.50:1988 International alphabet no. 5
NOTE 1
Some of the ETSs and ENVs above are based on ECMA Standards, although there is not always complete technical
alignment. The relationships are as follows:
  ETS/ENV ECMA Standard
ETS 300 170  ECMA-141
ETS 300 171  ECMA-142
ETS 300 173  ECMA-148
ETS 300 189  ECMA-155
ENV 41004  ECMA-133
ENV 41005  ECMA-134
ENV 41006  ECMA-135
5 Definitions and Acronyms
5.1 Definitions
5.1.1 General
For the purpose of this ETS the special terminology defined in ENV 41007-1 and I.112 applies. If there is
conflict, the definitions in ENV 41007-1 shall take precedence.
5.1.2 Side, Incoming Side and Outgoing Side (see figure 1)
The term Side is used to describe either of the two PTNXs at each end of an inter-PTNX link, and in particular to
describe the protocol entity within a PTNX.
In the context of a call, the Outgoing Side is the Side which routes the call over the inter-PTNX link and the
Incoming Side is the Side which receives the call.
5.1.3 Outgoing Call and Incoming Call
From the point of view of the Outgoing Side a call is an Outgoing Call.
From the point of view of the Incoming Side a call is an Incoming Call.
5.1.4 Originating PTNX, Terminating PTNX and Transit PTNX (see figure 1)
Within the context of a call, the PTNX to which the calling user is attached is known as the Originating PTNX.
Within the context of a call, the PTNX to which the called user is attached is known as the Terminating PTNX.
Within the context of a call, any PTNX through which the call passes, excluding the Originating PTNX or
Incoming Gateway PTNX and the Terminating PTNX or Outgoing Gateway PTNX, is known as a Transit
PTNX.
5.1.5 Gateway PTNX, Incoming Gateway PTNX and Outgoing Gateway PTNX (see figure 1)
Within the context of a call, a PTNX which performs interworking between the signalling system specified in this
ETS and another signalling system, either ISDN or non-ISDN, is known as a Gateway PTNX.

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A Gateway PTNX which routes an incoming call from a route employing another signalling system on to an
inter-PTNX link employing the signalling system specified in this ETS is known as an Incoming Gateway PTNX.
A Gateway PTNX which routes an incoming call from an inter-PTNX link employing the signalling system
specified in this ETS on to a route employing another signalling system is known as an Outgoing Gateway
PTNX.
Originating PTNX Term inating PTNX
or Outgoing
or Inc om ing
Gateway PTNX
Gateway PTNX
Transit P TNX
Inter-P TNX link Inter-PTNX link
Outgoing Incom ing Outgoing Incoming
side side side side
Figure 1 - Illustration of Terminology through Example of a Call Routed over Two Inter-PTNX Links
5.1.6 Preceding PTNX and Subsequent PTNX
Within the context of a call, from the point of view of a PTNX acting as the Incoming Side of an inter-PTNX
link, the PTNX at the other end of the link, acting as the Outgoing Side, is known as the Preceding PTNX.
Within the context of a call, from the point of view of a PTNX acting as the Outgoing Side of an inter-PTNX
link, the PTNX at the other end of the link, acting as the Incoming Side, is known as the Subsequent PTNX.
5.1.7 Unrecognised Message
A message which is not specified in Clause 11 of this ETS or in any other ETS that extends the protocol defined
in this ETS to which the PTNX claims conformance (e.g. a ETS specifying generic procedures for supplementary
services).
5.1.8 Unexpected Message
Within the context of a particular Protocol Control state, a message which is recognised, but for which no
procedures are defined in 7.2, 7.4 and 8 of this ETS (or in any other ETS that extends the protocol defined in this
ETS to which the PTNX claims conformance) for receipt in that Protocol Control state.
5.1.9 Unrecognised information element
An information element received in a particular message which is not specified as part of that message in Clause
11 of this ETS or in any other ETS that extends the protocol defined in this ETS to which the PTNX claims
conformance (e.g. a ETS specifying generic procedures for supplementary services).
5.1.10 information elements with Invalid Contents
An information element which is recognised, but whose contents cannot be interpreted as valid using the rules
specified in Clause 12 of this ETS, or the ETS in which the information element is defined, or contains field
values which are marked as 'reserved'.

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5.2 Acronyms
ANF Additional Network Feature
DSS1 Digital Subscriber Signalling System No. 1
IE Information Element
ISDN Integrated Services Digital Network
MP Mapping (functional grouping)
MSI Manufacturer Specific Information
PICS Protocol Implementation Conformance Statement
PTN Private Telecommunication Network
PTNX Private Telecommunication Network Exchange
TE Terminal Equipment
6 General principles
The basic call is a single invocation of a basic service. This ETS specifies the signalling procedures for establishing,
maintaining and clearing a circuit mode basic call at an interface between two PTNXs. These signalling procedures are
defined in terms of messages exchanged over a data link connection within the D-channel of the inter-PTNX link. The
result of successful basic call establishment is a connection for the purpose of user information transfer. This
connection uses a B-channel of the inter-PTNX link.
Throughout this ETS, the term B-channel is used to indicate any channel other than the D-channel, e.g. a single
64 kbit/s B-channel, multiple 64 kbit/s B-channels, or an H-channel.
Conceptually, an inter-PTNX link is attached to the Switching and Call Handling functional groupings of a PTNX at
the Q reference point, and comprises a D-channel and one or more B-channels. In practice, these channels are provided
by bearer services of an intervening network (ISDN or non-ISDN) according to any of the scenarios identified in ENV
41006, e.g. dedicated transmission system, permanent or on demand circuit-switched B and D channels, permanent or
on demand circuit-switched B channels and packet-switched D channel. Inter-PTNX signalling relates to the Control
Plane of the PTN and is conveyed in the User Plane of the intervening network.
A physical interface does not necessarily exist at the Q reference point. The protocol specified in this ETS is the Layer
3 protocol which would exist at the Q reference point if there were a physical interface. It is therefore independent of
the scenario for PTNX interconnection.
The layer 3 protocol at the Q reference point is visible at an interface at the C reference point, subject to any provisions
of the relevant ETS for the Inter-PTNX connection scenario concerned. Underlying protocols at the interface at C are
dependent on the scenario which the intervening network supports, i.e., on the nature of the intervening network and
the bearer service(s) provided. The Mapping (MP) functional grouping (see Standard ECMA-133) maps the conceptual
D- and B- channels at the Q reference point to physical circuits, timeslots and channels at the interface at the C
reference point, and terminates the underlying scenario dependent protocols.
With some scenarios a single physical interface from a PTNX to the intervening network may support links to several
other PTNXs. Also some scenarios permit the use on the same interface of other services of the intervening network
(i.e. for communication with subscribers of the intervening network other than other PTNXs within the same PTN).
Figure 2 illustrates these concepts. Such shared use of a physical interface at C has no impact on the Layer 3 signalling
protocol at Q.
For some scenarios, inter-PTNX connections may be established and released, on demand, by the PTNXs concerned.
Although protocols exist for this purpose at interfaces at the C reference point, such protocols relate to the Control
Plane of the intervening network. They are terminated within the MP functional grouping and do not appear at the Q
reference point.

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PTNX
ISDN
ISDN
PTN
PTNX
(B)
T Interface
Subscriber
user
C
(A) (A)
PTNX
C Interface
PTNX
C Interface
Legend:
(A) Examples of service providing closed communication between two PTNXs in a PTN.
(B) Example of service providing communication between a PTN user and a subscriber in the open ISDN.
Figure 2 - Shared Use of an ISDN Interface
The basic call signalling procedures specified in this ETS apply to circuit mode bearer services, used either on their
own or in support of teleservices.
In addition, this ETS includes signalling procedures for layer management, including restart procedures.
6.1 Protocol Model
Figure 3 shows the relationship, within the Control Plane, between the Layer 3 protocol at Q and the adjacent layers.
PTNX PTNX
Call Call
Control Control
Protocol defined
Protocol Protocol
Control Control
in this standard
Data Link
Data Link
Layer
Layer
Physical
Physical
Layer
Layer
PTNX to PTNX
Connection
Figure 3 - Control Plane Protocol Model
The Protocol Control entity provides services to Call Control. Call Control corresponds to the Call Control
functional entity identified for the basic call at Stage 2 (see ETS 300 171). Primitives exchanged across the

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boundary between Call Control and Protocol Control correspond to the information flows exchanged between the
Call Control functional entities, as identified at Stage 2. Protocol Control provides the mapping between these
primitives and the messages transferred across the inter-PTNX link.
In order to transfer messages, Protocol Control uses the services of the Data Link Layer, which in turn uses the
services of the Physical Layer. The actual Data Link Layer and Physical Layer protocols visible at the C reference
point are dependent upon the PTNX interconnection scenario.
6.2 Services Provided to Call Control
Protocol Control provides services to Call Control whereby Call Control can send information flows to and receive
information flows from the peer Call Control. A primitive from Call Control to Protocol Control of type "request" or
"response" normally results in the associated information flow being presented to the peer Call Control as a
primitive of type "indication" or "confirmation" respectively. The following primitives are used:
− SETUP-REQUEST/INDICATION/RESPONSE/CONFIRMATION for the establishment of a call;
− MORE_INFORMATION-REQUEST/INDICATION for requesting more destination addressing information
during call establishment;
− INFORMATION-REQUEST/INDICATION for providing more destination addressing information during call
establishment;
− PROCEED-REQUEST/INDIC
...