SIST ETS 300 172 E3:2005

Private Integrated Services Network (PISN); Inter-exchange signalling protocol; Circuit-mode basic services [ISO/IEC 11572 (1994) modified]

This European Telecommunication Standard (ETS) defines the layer 3 protocol for signalling for the support of circuit-mode bearer services (used either on thei 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 ETS 300 475-1.

Zasebno telekomunikacijsko omrežje (PTN) – Medcentralni signalizacijski protokol - Vodovne osnovne storitve [ISO/IEC 11572 (1994) spremenjen]

General Information

• Status: Published
• Publication Date: 30-Apr-2005
• ICS: 33.040.35 - Telephone networks
• Technical Committee: SPN - Services and Protocols for Networks
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-May-2005
• Due Date: 01-May-2005
• Completion Date: 01-May-2005
• Ref Project: ETSI ETS 300 172 ed.3 (1995-11) - Private Integrated Services Network (PISN); Inter-exchange signalling protocol; Circuit-mode basic services [ISO/IEC 11572 (1994) modified]

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 172 E3:2005
01-maj-2005
Zasebno telekomunikacijsko omrežje (PTN) – Medcentralni signalizacijski protokol
- Vodovne osnovne storitve [ISO/IEC 11572 (1994) spremenjen]
Private Integrated Services Network (PISN); Inter-exchange signalling protocol; Circuit-
mode basic services [ISO/IEC 11572 (1994) modified]
Ta slovenski standard je istoveten z: ETS 300 172 Edition 3
ICS:
33.040.35 Telefonska omrežja Telephone networks
SIST ETS 300 172 E3:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 172 E3:2005

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SIST ETS 300 172 E3:2005
EUROPEAN ETS 300 172
TELECOMMUNICATION November 1995
STANDARD Third Edition
Source: ETSI TC-ECMA Reference: RE/ECMA-00117
ICS: 35.020
PISN, PSS1, PTN, QSIG
Key words:
Private Integrated Services Network (PISN);
Inter-exchange signalling protocol;
Circuit-mode basic services
[ISO/IEC 11572 (1994) modified]
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - [e-mail]
X.400: Internet:
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1995. All rights reserved.
New presentation - see History box

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ETS 300 172: November 1995
Foreword
This third edition European Telecommunication Standard (ETS) was produced by the Standardizing
Information and Communication Systems (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 Integrated services Network eXchanges (PINX). The QSIG protocol is known as "Private
integrated Signalling System no. 1" (PSS1) in International Standards.
Whilst this particular ETS defines signalling for the support of circuit-mode bearer services, other ETSs
specify other aspects of the QSIG protocol, e.g. generic procedures for the support of supplementary
services, and individual supplementary services.
The previous (second) edition of this ETS contained a "standalone" definition of the protocol. This edition
endorses an International Standard, ISO/IEC 11572, published since the publication of the second edition
of this ETS.
Transposition dates
Date of adoption of this ETS: 30 November 1995
Date of latest announcement of this ETS (doa): 28 February 1996
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 31 August 1996
Date of withdrawal of any conflicting National Standard (dow): 31 August 1996
Endorsement notice
The text of International Standard ISO/IEC 11572 (1994) was approved by ETSI as an ETS with agreed
modifications as given below.
NOTE: New or modified text is indicated using sidebars. In addition, underlining and/or strike-
out are used to highlight detailed modifications where necessary.
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 172: November 1995
Clause 1
Replace the text of clause 1 by:
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 Integrated services Network eXchanges (PINX) connected together
within a Private Integrated Services Network (PISN). The Q reference point is defined in
ETS 300 475-1 [14].
Service specifications are produced in three stages and according to the method specified in
ETS 300 387 [13]. 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 [10]. The protocol
defined in this ETS satisfies the requirements identified by the stage 1 and stage 2 specifications in
ETS 300 171 [10].
Annexes ZA - ZD are an integral part of this ETS.
Clause 2
After clause 2, add the following new clause:
2bis Conformance
In order to conform to this ETS, a PINX shall satisfy the requirements identified in the Protocol
Implementation Conformance Statement (PICS) proforma in annex A.
Clause 3
Replace the first paragraph by:
This ETS incorporates by dated and undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
Insert the following normative references at the end of clause 3:
[9] ETS 300 102-1 (1990): "Integrated Services Digital Network (ISDN); User-
network interface layer 3 Specifications for basic call control".
[10] ETS 300 171 (1992): "Private Telecommunication Network (PTN); Specification,
functional models and information flows Control aspects of circuit-mode basic
services".
[11] ETS 300 173 (1992): "Private Telecommunication Network (PTN); Specification,
functional models and information flows Identification supplementary services".
[12] ETS 300 189 (1992): "Private Telecommunication Network (PTN); Addressing".
[13] ETS 300 387 (1994): "Private Telecommunication Network (PTN); Method for
the specification of basic and supplementary services".
[14] ETS 300 475-1 (1995): "Private Integrated Services Network (PISN); Reference
configuration Part 1: Reference configuration for PISN eXchanges (PINXs)".
Throughout the text of ISO/IEC 11572
Throughout the text of ISO/IEC 11572, replace references as shown in the table below:

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ETS 300 172: November 1995
Reference in ISO/IEC 11572 Modified reference
CCITT Q.931                        (note) ETS 300 102-1 [9]
CCITT Recommendation Q.931 ETS 300 102-1 [9]
ISO/IEC 11571 ETS 300 189 [12]
ISO/IEC 11572 or ETS 300 172
International Standard ISO/IEC 11572
DIS 11574 or ISO/IEC 11574 ETS 300 171 [10]
DIS 11579 or ISO/IEC 11579 ETS 300 475-1 [14]
NOTE: This replacement should be made through out the text except in table 20, where the term
"CCITT Q.931" is used to describe the protocol discriminator coding.
Throughout the text of ISO/IEC 11572
Throughout the text of ISO/IEC 11572, replace the term "International Standard" by "ETS".
Subclause 4.10
Replace the text "clauses 9.3 and 10" by "clauses 9.3 and 10, and annex ZA".
Subclause 4.12
Insert the following new subclause after subclause 4.12:
4.13 Signalling Carriage Mechanism (SCM)
The infrastructure that transports messages between Protocol Control entities in two interconnected
PINXs.
Subclause 9.1.1
Replace the text "general procedures in 9.2 and 9.3" by "general procedures in subclauses 9.2 and 9.3
and annex ZA".
Subclause 9.2.7.1
Replace the text "(refer to Table 22" by "(refer to Tables 22 and 34".
Subclause 10.5.1
In item (c), replace the text "Calling/Connected Line Identification Restriction" by "Calling/Connected Line
Identification Restriction (see ETS 300 173 [11])".
Subclause 10.6.4
In the second paragraph, replace the text "Calling/Connected Line Identification Restriction" by
"Calling/Connected Line Identification Restriction (see ETS 300 173 [11])".
Subclause 10.7.6
In the last paragraph of 10.7.6, replace the words "no connected number or subaddress information other
than the presentation indicator shall be presented to the other network." by "presentation of the number to
the other network is outside the scope of this ETS, but will depend on such factors as the other network's
commitment to honour the restriction.".
Clause 12, table 4
Replace the text of note 5 (beginning "Timers T301 .") to table 4 by:

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ETS 300 172: November 1995
"NOTE 5: The value of this timer is implementation dependent and shall be equal to, or greater
than, 30 seconds. In the case of operation of certain call handling supplementary
services in a PISN, the receipt of an ALERTING or CONNECT message may be
delayed significantly beyond that expected for a normal call. In order to ensure that
unnecessary failure of these services can be avoided, it is recommended that T310 be
given a value of at least 110 seconds.".
Clause 14
Replace the second paragraph by:
Whenever a message is sent, according to the procedures of clauses 9, 10 and 11, it shall be coded as
specified in this clause, except where the message is segmented according to the procedures of
annex ZA, in which case each message segment shall be coded as specified in that annex.
Subclause 14.4, table 21
Modify table 21 (continued) as follows:
Table 21: Message type (continued)
Bits
  8 7 6 5 4 3 2 1
        0 1 1 0 1 RELEASE
        1 1 0 1 0 RELEASE COMPLETE
        0 0 1 1 0 RESTART
        0 1 1 1 0 RESTART ACKNOWLEDGE
  0 1 1 Miscellaneous messages
        0 0 0 0 0 SEGMENT       (note 2)
        1 1 0 1 1 INFORMATION
        1 1 1 0 1 STATUS
        1 0 1 0 1 STATUS ENQUIRY
NOTE 1: The handling of national/private messages is
outside the scope of this ETS (see annex D).
NOTE 2:    This message type is only used in conjunction
with the message segmentation and re-
assembly procedures defined in annex ZA.
Subclause 14.5.1, table 22
Modify table 22 by inserting a new row before the row for bearer capability, as follows:
0 0 0 0 0 0 0 0 Segmented message annex ZA note 1
0 0 0 0 0 1 0 0 Bearer capability 14.5.5 11
Subclause 14.5.2
Replace the 8th paragraph by:
Codeset 4 is used for ISO defined information elements. Codeset 5 is used by ETSI for information
elements that are defined in addition to those defined by ITU-T or ISO. The rules for handling information
elements of codeset 0 apply to codesets 4 and 5 too. See also subclause 14.6.
Subclause 14.5.3, table 23
Modify table 23 as follows:

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Table 23: Locking/non-locking shift element
Codeset identification
Bits
3 2 1
0 0 0 Codeset 0: CCITT Q.931 information
elements (initially active
codeset)
1 0 0 Codeset 4: Information elements defined by
ISO
1 0 1 Codeset 5: Information elements defined by
ETSI
1 1 0 Codeset 6: Information elements specific to
the local network (public or
private)
1 1 1 Codeset 7: User-specific information
elements
All other values are reserved (note 1)
NOTE 1: The handling of national/private information elements is
outside the scope of this ETS (see annex D).
Subclause 14.5.5, table 24
Modify the coding of the Information transfer capability (octet 3) in table 24 as follows:
Information transfer capability (octet 3)
Bits
5 4 3 2 1
0 0 0 0 0 Speech
0 1 0 0 0 Unrestricted digital information
0 1 0 0 1 Restricted digital information (applicable only
in interworking situations)
1 0 0 0 0 3,1 kHz audio
1 0 0 0 1 Unrestricted digital information with tones /
announcements
All other values are reserved.
Subclauses 14.5.8 and 14.5.10
In subclauses 14.5.8 and 14.5.10:
Add a note at the end of the first paragraph:
NOTE 1: For the definition of subaddress, see ETS 300 189 [12].
Renumber the existing note to be NOTE 2.
Subclause 14.5.12
Replace the text of NOTE 2 by:
NOTE 2: Channel number shall be used unless there is a bilateral agreement to use channel
map.
Subclause 14.5.14
In subclause 14.5.14, add a note at the end of the first paragraph:

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ETS 300 172: November 1995
NOTE 1: For the definition of subaddress, see ETS 300 189 [12].
Renumber the existing note to be NOTE 2.
Subclause 14.5.17, table 32
In table 32, following the first occurrence (i.e., in relation to the codepoints for the Coding standard, octet
3) of the words "All other values are reserved", add the words "(note 5)".
In table 32, following the words "Progress description (octet 4)", add (as underlined text) the words "NOTE
5".
In table 32, following the third occurrence (i.e., in relation to the codepoints for the Progress description,
octet 4) of the words "All other values are reserved", add the words "(note 5)".
In the notes at the end of table 32, add a new note:
NOTE 5:    Additional progress descriptions are specified in annex ZC.
Subclause 14.5.19
Insert the following new subclauses after subclause 14.5.19:
14.6 Information elements of codeset 4
Codeset 4 contains information elements defined by ISO/IEC.
In general the coding rules described in subclause 14.5.1 for codeset 0 apply to codeset 4 also.
Table 34 lists the information element identifiers for information elements of codeset 4 used in this ETS.
Table 34: Information element Identifier coding (Codeset 4)
Coding Ref. Length
8 7 6 5 4 3 2 1
1 : : : - - - - Single Octet information elements:
0 0 0 - - - - Reserved
0 0 1 - - - - Shift 14.5.3 1
0 : : : : : : : Variable length information elements:
0 1 1 0 0 0 1 Transit counter annex ZB 3
All other values are reserved.
14.7 Information elements of codeset 5
Codeset 5 contains information elements defined by ETSI.
In general the coding rules described in subclause 14.5.1 for codeset 0 apply to codeset 5 also.
Table 35 lists the information element identifiers for information elements of codeset 5 used in this ETS.

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ETS 300 172: November 1995
Table 35: Information element Identifier coding (Codeset 5)
Coding Ref. Length
8 7 6 5 4 3 2 1
1 : : : - - - - Single Octet information elements:
0 0 0 - - - - Reserved
0 0 1 - - - - Shift 14.5.3 1
0 : : : : : : : Variable length information elements:
0 1 1 0 0 1 0 Party category annex ZD 3
All other values are reserved.
Annex A, subclause A.4.1
Insert a new row at the end of the PICS proforma table in subclause A.4.1, as follows:
Z4 Support of the unrestricted digital information with tones 14.5.5 o Yes [ ]  No [ ]
/ announcements bearer
Annex A (end of)
Insert the following new subclauses at the end of annex A:
A.4.12 Message segmentation / re-assembly procedures
Item Question/feature Reference Status N/A Support
K1 Maximum message size generated ZA.3 m Size [          ]
K2 Maximum message size received ZA.3 m Size [          ]
K3 Is length of signalling carriage mechanism information ZA.3 o Yes [ ]  No [ ]
field < max. generated message size
K4 Is length of signalling carriage mechanism information ZA.3 o Yes [ ]  No [ ]
field < max. received message size
K5 Procedures for messages segmentation ZA.3.1 c.12 Yes [ ]
K6 Procedures for messages re-assembly ZA.3.2 c.13 [ ] Yes [ ]
K7 Message formats and codings for segmented messages ZA.4, ZA.5 c.14 [ ] Yes [ ]
and information elements supported
K8 Implementation of T314 ZA.6 c.13 [ ] Yes [ ]
c.12 If K3, then mandatory else, prohibited
c.13 If K4, then mandatory else, not applicable
c.14 If K3 or K4, then mandatory else, not applicable
A.4.13 Transit counter functionality
Item Question/feature Reference Status N/A Support
L1 Transit counter functionality ZB.2 o Yes [ ]  No [ ]
L2 Behaviour as Originating PINX for Transit counter ZB.2.3.1 c.15 [ ] Yes [ ]
functionality
L3 Behaviour as Incoming Gateway PINX for Transit ZB.2.3.4 c.16 [ ] Yes [ ]
counter functionality
L4 Behaviour as Transit PINX for Transit counter ZB.2.3.3 c.17 [ ] Yes [ ]
functionality
L5 Behaviour as Terminating PINX for Transit counter ZB.2.3.2 c.18 [ ] Yes [ ]
functionality
L6 Behaviour as Outgoing Gateway PINX for Transit ZB.2.3.5 c.19 [ ] Yes [ ]
counter functionality
L7 Sending of a Transit counter information element in a ZB.2.3 c.20 [ ] Yes [ ]  No [ ]
SETUP message
c.15 If B1 and L1 then mandatory else, not applicable
c.16 If B2 and L1 then mandatory else, not applicable
c.17 If B3 and L1 then mandatory else, not applicable
c.18 If B4 and L1 then mandatory else, not applicable

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c.19 If B5 and L1 then mandatory else, not applicable
c.20 If L2 or L3 or L4 then optional else, not applicable
A.4.14 Additional progress descriptions
Item Question/feature Reference Status N/A Support
M1 Up to three Progress indicator information elements annex ZC m Yes [ ]
within the same message
M2 Additional progress descriptions annex ZC m Yes [ ]
A.4.15 Party category functionality
Item Question/feature Reference Status N/A Support
N1 Party category functionality ZD.2 o Yes [ ]  No [ ]
N2 Behaviour as Originating PINX for Party category ZD.2.3.1 c.21 [ ] Yes [ ]
functionality
N3 Behaviour as Incoming Gateway PINX for Party ZD.2.4.1 c.22 [ ] Yes [ ]
category functionality
N4 Behaviour as Transit PINX for Party category ZD.2.3.3 c.23 [ ] Yes [ ]
functionality
N5 Behaviour as Terminating PINX for Party category ZD.2.3.2 c.24 [ ] Yes [ ]
functionality
N6 Behaviour as Outgoing Gateway PINX for Party category ZD.2.4.2 c.25 [ ] Yes [ ]
functionality
N7 Sending of a Party category information element in a ZD.2.3, c.26 [ ] Yes [ ]  No [ ]
SETUP message ZD.2.4
N8 Sending of a Party category information element in an ZD.2.3, c.27 [ ] Yes [ ]  No [ ]
ALERTING message ZD.2.4
N9 Sending of a Party category information element in a ZD.2.3, c.27 [ ] Yes [ ]  No [ ]
CONNECT message ZD.2.4
c.21 If B1 and N1 then mandatory else, not applicable
c.22 If B2 and N1 then mandatory else, not applicable
c.23 If B3 and N1 then mandatory else, not applicable
c.24 If B4 and N1 then mandatory else, not applicable
c.25 If B5 and N1 then mandatory else, not applicable
c.26 If N2 or N3 or N4 then optional else, not applicable
c.27 If N4 or N5 or N6 then optional else, not applicable
Annex G
Add the following bibliographic reference to annex G:
[3bis] CCITT Recommendation Q.931 (1988): "ISDN user-network interface layer 3
specification for basic call control" (Blue Book, Volume VI, Fascicle VI.11).

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Add the following new annex ZA:
Annex ZA (normative): Message segmentation / re-assembly procedures
ZA.1 Message segmentation and re-assembly functions
Message segmentation and re-assembly functions shall be employed where the size of a message
exceeds the maximum size of the SCM information field.
The architectural relationship of segmentation and re-assembly functions to other Protocol Control
functions is shown in figure ZA.1.
Call Control

Other Functions
Protocol
Segm entation and
Re-assembly Functions Control
Protocol
Discrim inator Filter
Signalling Carriage
Mechanism

Figure ZA.1: Logical architecture of Protocol Control
showing segmentation and re-assembly functions
Segmentation and re-assembly, where provided, effectively constitute a lower sublayer of Protocol
Control.
NOTE: The only function of Protocol Control below the segmentation and re-assembly
functions is protocol discriminator filtering. This function filters out messages
containing a protocol discriminator that does not match the one specified in this ETS.
The primitives across the boundary between segmentation and re-assembly functions and other functions
are the same as those between the Signalling Carriage Mechanism and Protocol Control (see subclause
6.3). The segmentation functions act upon DL-DATA-REQUEST primitives by converting, where
necessary, a single primitive into two or more primitives before passing to the Signalling Carriage
Mechanism. The re-assembly functions act upon DL-DATA-INDICATION primitives from the Signalling
Carriage Mechanism by converting, where necessary, two or more primitives into a single primitive for
passing up to the other functions of Protocol Control. Other primitives to and from the Signalling Carriage
Mechanism are not affected by the segmentation and re-assembly functions.
ZA.2 States for message segmentation / re-assembly
Message segmentation and re-assembly procedures are each specified in terms of a state machine.
Message segmentation uses a single state, Null (0). Message re-assembly uses two states, as listed
below.

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ZA.2.1 Null (0)
No message is being reassembled.
ZA.2.2 Receiving segmented message (1)
One or more segments of a segmented message have been received and one or more further segments
are awaited.
ZA.3 Segmentation and re-assembly procedures
This clause specifies message segmentation and re-assembly procedures for messages the length of
which exceeds the maximum size of the Signalling Carriage Mechanism information field. The Signalling
Carriage Mechanism information field size is dependent on the PINX interconnection scenario.
A PINX shall conform to the segmentation procedures specified in subclause ZA.3.1 if, for a given PINX
interconnection scenario supported by the PINX, it is capable of transmitting a message that exceeds the
maximum size of the Signalling Carriage Mechanism information field for that scenario. Segmentation
procedures shall not be applied to messages that do not exceed the maximum size of the Signalling
Carriage Mechanism information field.
A PINX that claims conformance to this ETS shall declare the maximum size of message that it is able to
receive. The declared maximum size shall not be less than 260 octets. If, for a given PINX interconnection
scenario supported by the PINX, the maximum size of Signalling Carriage Mechanism information field is
less than the declared maximum size of message the PINX can receive, the PINX shall conform to the re-
assembly procedures specified in subclause ZA.3.2.
NOTE: If a segmented message is received by a PINX that does not support re-assembly
procedures, the procedures specified in subclause 9.2.4 for message type errors will
apply to each received segment.
ZA.3.1 Procedures for segmentation
The following rules apply when a message for transmission exceeds the maximum size of the SCM
information field:
a) The maximum number of message segments is 8. If a message is too long to be segmented, the
action taken shall be an implementation option.
b) The first message segment shall begin with the Protocol discriminator information element
immediately followed by the Call reference information element, the SEGMENT message type, the
Segmented message information element, and octets starting with the first octet following the
message type of the message being segmented, subject to the maximum length of the segment not
exceeding the maximum size of the SCM information field.
c) Each subsequent message segment shall begin with the Protocol discriminator information
element, immediately followed by the Call reference information element, the SEGMENT message
type, the Segmented message information element, and one or more octets of the message being
segmented, starting with the first octet following the last octet transmitted in the previous segment
and subject to the maximum length of the segment not exceeding the maximum size of the SCM
information field.
d) The first segment indicator field of the Segmented message information element shall be set to
ONE (the first segment of a segmented message) in the first segment of a segmented message
and set to ZERO (subsequent segment to the first segment) in each subsequent segment of that
message.
e) The number of segments remaining field of the Segmented message information element shall
indicate how many more segments are to be sent.
f) The segmented message type field of the Segmented message information element shall indicate
the message type of the original message.

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g) Once the first segment has been transmitted on a particular SCM connection, then all remaining
segments of that message shall be sent (in order) before any other message (segmented or not) for
any other call reference is sent on that SCM connection. Only failure conditions (e.g., SCM failure)
shall cause the transmission of a segmented message to be aborted.
h) The octet order of the segmented message shall be preserved regardless of segment boundary.
ZA.3.2 Procedures for re-assembly
The following rules apply to the receipt and re-assembly of segmented messages:
a) A re-assembly function, on receiving a message of type SEGMENT containing the Segmented
message information element as the first information element after the message type, shall treat
that message as a segment.
b) A re-assembly function in the Null state, on receiving a segment in which the first segment indicator
field of the Segmented message information element is set to ONE (first segment of segmented
message) and the number of segments remaining field of the Segmented message information
element is set to a value greater than 0 and not exceeding 7, shall enter the Receiving segmented
message state and save the segment contents. Timer T314 shall be initialised. Timer T314 is used
to prevent the re-assembly function waiting indefinitely to receive the next message segment.
c) A re-assembly function in the Receiving segmented message state, on receiving a segment in
which the call reference is equal to the call reference of the first segment received, the first segment
indicator field of the Segmented message information element is set to ZERO (subsequent
segment to first segment), the number of segments remaining field of the Segmented message
information element is set to a value one less than the value in the previously received segment,
and the segmented message type field has a value equal to the value of that field in the first
segment received, shall treat the segment as a valid next segment.
d) A re-assembly function in the Receiving segmented message state, on receiving a valid next
segment in which the number of segments remaining field has a value greater than zero, shall save
the segment contents along with the saved contents of the previous segment or segments, restart
timer T314, and remain in the Receiving segmented message state.
e) A re-assembly function in the Receiving segmented message state, on receiving a valid next
segment in which the number of segments remaining field has a value equal to zero, shall stop
timer T314, deliver the accumulated segments, including the last segment, as a single message for
further Protocol Control processing, and enter the Null state. The message delivered shall have a
call reference equal to that in each received segment and a message type equal to that in the
segmented message type field of the Segmented message information element of each received
segment. Octets following the Segmented message information element in each received segment
shall be included in the delivered message in the order received.
f) A re-assembly function in the Null state shall deliver for further Protocol Control processing any
received message of type other than SEGMENT or that is too short to contain a message type.
g) A re-assembly function in the Null state shall discard any received message of type SEGMENT that
is not a valid first segment. Any other action taken shall be an implementation option. This applies
to the following:
- Messages of type SEGMENT without a valid Segmented message information element
following the message type;
- Segments in which the first segment indicator field of the Segmented message information
element is set to ZERO (subsequent segment to first segment);
- Segments in which the number of segments remaining field of the Segmented message
information element has a value 0 or a value exceeding 7.

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SIST ETS 300 172 E3:2005
Page 13
ETS 300 172: November 1995
h) A re-assembly function in the Receiving segmented message state shall discard any saved
segments, stop timer T314 and enter the Null state on receipt of any message which is not a valid
next segment. This applies to the following:
- Messages with a different call reference from that in the first received segment;
- Messages of type other than SEGMENT;
- Messages of type SEGMENT without a valid Segmented message information element
following the message type;
- Segments in which the first segment indicator field of the Segmented message information
element is set to ONE (first segment of segmented message);
- Segments in which the number of segments remaining field of the Segmented message
information element has a value which is not one less than the value in the previously
received segment;
- Segments in which the segmented message type field of the Segmented message
information element has a value which is not equal to the value in the first received segment.
In the case of a message with a different call reference from that in the first received segment or a
me
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