SIST ETS 300 124 E1:2003

• Abstract:

  Attachment to X 25 interfaces: annexes

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.040.40 - Data communication networks
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Ref Project: ETSI ETS 300 124 ed.1 (1991-04) - Terminal Equipment (TE); Attachment requirements for Data Terminal Equipment (DTE) to connect to Packet Switched Public Data Networks (PSPDN) using CCITT Recommendation X.25 (1984) interface; Requirements applicable to DTEs subscribing to Multilink operation

SIST ETS 300 124 E1:2003 is a Slovenian standard published by SIST and identical to ETS 300 124 Edition 1 from ETSI. It specifies attachment requirements for Data Terminal Equipment (DTE) that connect to Packet Switched Public Data Networks (PSPDN) using the CCITT Recommendation X.25 (1984) interface when the DTE subscribes to Multilink operation. In practice, it adds multilink-specific requirements to the base approval requirements in NET 2.

What does SIST ETS 300 124 E1:2003 specify?

SIST ETS 300 124 E1:2003 specifies the extra attachment requirements for packet mode DTE that use the optional Multilink operation over an X.25 interface. The document is a supplement to the main NET 2 approval requirements, so a reader uses it together with NET 2 rather than on its own.

The structure is straightforward:

• Clause 1 lists normative references.
• Clause 2 gives definitions.
• Clause 3 lists symbols and abbreviations.
• Clause 4 contains the Multilink Procedure (MLP), including general rules and test methods.

The foreword says the text can be used to establish Annex I of NET 2. That tells a buyer or test engineer that this standard is meant to fit into the broader NET 2 approval framework.

What are the key requirements of SIST ETS 300 124 E1:2003?

SIST ETS 300 124 E1:2003 mainly defines how a DTE using MLP is to be checked in test conditions, and how it must behave when links are set up, rerouted, or timed out. The practical focus is not on product design details but on observable behavior during conformance testing.

MLP inherits the SLP base rules

Clause 4.1 says the Single Link Procedure (SLP) requirements from section 9 of NET 2, and the supplement for modulo 128 operation, still apply. The main MLP-specific difference is the encoding of the address field in Link Access Procedure Balanced (LAPB) frames, which must follow CCITT Recommendation X.25 (1984) for multilink operation. In practice, a DTE that already meets the base X.25 approval still needs this extra multilink behavior checked.

The test method is protocol-driven

Clause 4.2 explains that tests work by forcing the DTE into a chosen phase or condition using a Protocol Data Unit (PDU) or a sequence of PDUs. The clause also explains how to read optional PDUs in the test sequences:

• PDUs in square brackets are optional and do not require a specific tester response.
• PDUs in parentheses are optional but do require a protocol-correct tester response.

For a test lab, this means the diagrams are not just examples - they are step-by-step exchange patterns that define what the tester must send and when.

Setup-phase verification checks initialization behavior

Clause 4.2.1 defines verification of the MLP setup phase. Before each test, the tester performs a preamble sequence on both lines, and after each test a post-test sequence confirms that the DTE still responds correctly. The tests cover several cases, including whether the system under test (sut) initializes MLP or not, whether one or both lines are in Disconnected Mode (DM), and whether initialization is confirmed on L1 or L2.

In practice, this is the part that shows whether the DTE can start multilink operation cleanly and still preserve correct behavior on both links.

Re-routing conditions are tested under several failures

Clause 4.2.2 checks MLP re-routing conditions after the DTE has been brought into the Information Transfer Phase with L1 and L2 active. The document then exercises specific cases:

• Disconnected Mode (DM)
• Frame reject (FRMR)
• Retransmission
• Busy condition
• Waiting acknowledgement condition

These tests matter because Multilink operation is only useful if the DTE can move traffic between links when one link is blocked, rejected, or waiting for acknowledgment. The tester also has to acknowledge MLP frames on the same link from which they were received.

Timer behavior is checked explicitly

Clause 4.2.3 verifies MLP timer behavior, especially MT3. The tests cover both cases where the DTE does and does not initialize MLP. The sequence is designed to see whether the timer expires and how the DTE reacts after that expiry.

For implementers and test houses, this is important because timer handling affects setup robustness and recovery behavior, not just nominal data transfer.

The tester must keep the DTE in a known state

Across the test clauses, the tester is instructed to use preamble and post-test sequences, to acknowledge frames correctly, and to use specific link states such as DM, active links, SABM, DISC, RR, and UA. This means the standard is aimed at reproducible laboratory verification, where the DTE’s response can be judged against a controlled exchange.

What terms does SIST ETS 300 124 E1:2003 define?

SIST ETS 300 124 E1:2003 relies on a small set of core terms from NET 2 and X.25, and it also lists the abbreviations used throughout the tests.

• Data Terminal Equipment (DTE) - the terminal equipment being attached to the network and tested for compliance.
• Single Link Procedure (SLP) - the base link procedure that remains applicable alongside MLP.
• Multilink Procedure (MLP) - the optional procedure that lets the DTE use more than one link.
• Link Access Procedure Balanced (LAPB) - the link-layer procedure whose frame address field is treated specially in multilink operation.
• Protocol Data Unit (PDU) - the unit used in the test sequences to drive the DTE into specific states.
• Disconnected Mode (DM) - a link state used repeatedly in the setup, rerouting, and timer tests.
• sut - the system under test, meaning the DTE being verified in the laboratory.

Who uses SIST ETS 300 124 E1:2003?

SIST ETS 300 124 E1:2003 is used by DTE manufacturers, conformance test laboratories, and approval or quality teams that need to verify packet-mode equipment against the X.25 multilink attachment requirements. It is also relevant to network equipment buyers and integrators who need to check that a DTE supports the expected multilink behavior before deployment.

In practice, the document is most useful when someone has to design, test, or accept equipment that will connect to PSPDN using X.25 and subscribe to Multilink operation.

Which standards are used with SIST ETS 300 124 E1:2003?

SIST ETS 300 124 E1:2003 is used together with NET 2 and CCITT Recommendation X.25 (1984).

• NET 2 - provides the main approval requirements for data terminal equipment connecting to packet switched public data networks.
• CCITT Recommendation X.25 (1984) - defines the DTE/DCE interface and the multilink-related frame encoding rules used here.

The definitions in the standard also say that the meanings from NET 2 and X.25 apply throughout this document, so readers need both references to interpret the tests correctly.

What does the SIST ETS 300 124 E1:2003 document contain?

SIST ETS 300 124 E1:2003 contains clause-based test material rather than product design guidance. Its main technical content is the set of MLP verification sequences for setup, re-routing conditions, and timer behavior.

The document includes preamble and post-test exchanges, line-by-line message diagrams, and notes that explain how the tester should respond to the DTE. It also shows when the DTE is expected to transmit I-frames and how the tester should use RR, SABM, DISC, DM, FRMR, and other control frames during the tests. For an engineer, that makes the standard a practical script for lab verification; for a quality manager, it is evidence of the observable behaviors that must be checked; and for a buyer, it shows that the standard is aimed at conformance of multilink-capable DTE rather than general network performance.

SLOVENSKI STANDARD
01-december-2003
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QDSDNHWQRNRPXWLUDQDMDYQDSRGDWNRYQDRPUHåMD363'1SUHNYPHVQLNDSR
SULSRURþLOX&,77;±=DKWHYH]D'7(SULQDYH]RYDQMXQDYHþSRYH]DYQR
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Terminal Equipment (TE); Attachment requirements for Data Terminal Equipment (DTE)
to connect to Packet Switched Public Data Networks (PSPDN) using CCITT
Recommendation X.25 (1984) interface; Requirements applicable to DTEs subscribing to
Multilink operation
Ta slovenski standard je istoveten z: ETS 300 124 Edition 1
ICS:
33.040.40 Podatkovna komunikacijska Data communication
omrežja networks
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 124
TELECOMMUNICATION April 1991
STANDARD
ICS: 33.020
DTE, PSPDN, Multilink operation
Key words:
Attachment requirements for Data Terminal Equipment (DTE)
to connect to Packet Switched Public Data Networks (PSPDN)
using CITT Recommendation X.25 (1984) interface
Requirements applicable to DTEs subscribing to Multilink
operation
(the text of this ETS may be utilized for the establishment of Annex I of NET 2)
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 1991. All rights reserved.
New presentation - see History box

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ETS 300 124: 1991
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 300 124: 1991
Contents
Foreword.5
1 Normative references .7
2 Definitions.7
3 Symbols and abbreviations.7
4 Multilink procedure (MLP) .7
4.1 General.7
4.2 Tests .8
4.2.1 Verification of MLP setup phase .9
4.2.1.1 The system under test (sut) does not initialize the MLP.10
4.2.1.1.1 Initialization through L1, L2 in DM. (MN(S) = 0).10
4.2.1.1.2 Initialization through L1, L2 in DM.(MN(S)>0).10
4.2.1.1.3 Initialisation through L1, MLP frame with C=1 is sent
immediately after MLP frame when R=1. L2 in DM.10
4.2.1.1.4 Initilization through L1, L2 active.11
4.2.1.1.5 Initialization through L1, confirmation by L2.11
4.2.1.2 The sut does not initialize the MLP.12
4.2.1.2.1 Initialization through L1, L2 in DM. (MN(S) = 0) .12
4.2.1.2.2 Initialization through L1, L2 in DM. (MN(S)>).12
4.2.1.2.3 Initialization through L1, MLP frame when C=1 is sent
immediately after MLP frame when R=1. L2 in DM.12
4.2.1.2.4 Initialization through L1, L2 active.13
4.2.2 Verification of MLP re-routing conditions .14
4.2.2.1 Disconnect Mode (DM) condition .15
4.2.2.2 Frame reject (FRMR) condition.16
4.2.2.3 Retransmission condition.17
4.2.2.4 Busy condition .18
4.2.2.5 Waiting aknowledgement condition.19
4.2.3 Verification of MLP timers.20
4.2.3.1 The DTE does not initialise the MLP. 21
4.2.3.2 The DTE does initialise the MLP .21
History.22

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ETS 300 124: 1991
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ETS 300 124: 1991
Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS contains attachment requirements applicable to packet mode Data Terminal Equipment (DTEs)
which subscribe to the optional application of multilink operation. These attachment requirements are
additional to those contained in the main body of NET 2 [1].
The text of this ETS may be utilised for the establishment of Annex I to NET 2 [1]. Copies of NET 2 [1]
may be obtained from:
CEPT Liaison Office
Seilerstrasse 22
CH - 3008 Bern
Telephone: [phone]
Facsimile: [phone]
Telex: 911089 CEPT CH
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ETS 300 124: 1991
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ETS 300 124: 1991
1 Normative references
This European Telecommunication Standard (ETS) incorporates by dated or 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.
[1] NET 2 (First edition, 1988): "Approval requirements for data terminal equipment
to connect to packet switched public data networks using CCITT
Recommendation X.25 (1984) interface".
[2] CCITT Recommendation X.25 (1984): "Interface between data terminal
equipment (DTE) and data circuit-terminating equipment (DCE) for terminals
operating in the packet mode and connected to public data networks by
dedicated circuit".
2 Definitions
For the purpose of this ETS the definitions provided in NET 2 [1] and CCITT Recommendation X.25 [2]
shall apply.
3 Symbols and abbreviations
DTE Data Terminal Equipment
SLP Single Link Procedure
MLP Multilink Procedure
LAPB Link Access Procedure Balanced
PDU Protocol Data Unit
DM Disconnected Mode
sut system under test
SABM Set Asynchronous Balanced Mode
DISC Disconnect
FRMR Frame Reject
RNR Receive Not Ready
RR Receive Ready
4 Multilink procedure (MLP)
4.1 General
This subclause contains the additional requirements to be satisfied by a DTE which subscribes to the
multilink procedure.
The requirements established for Single Link Procedure (SLP) in section 9 of NET 2 [1] or in the
supplement for modulo 128 operation are applicable. The only difference is in respect of the address field
of Link Access Procedure Balanced (LAPB) frames where the encoding shall be as reflected in CCITT
Recommendation X.25 (1984), paragraph 2.4.2 [2], for multilink operation.

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ETS 300 124: 1991
4.2 Tests
To execute a test, the tester shall attempt to force the DTE to an appropriate phase or condition by
transmitting a particular Protocol Data Unit (PDU) or a sequence of PDUs. However, some DTEs may
initialize the link or send a particular PDU that requires an appropriate answer from the tester to be in
accordance with the protocol procedures.
To represent those situations in the test descriptions, the following notation shall be used:
- PDUs within [ ] denote optional PDUs from the DTE that shall not require a
specific answer from the tester;
- PDUs within ( ) denote optional PDUs from the DTE that shall require a specific
answer from the tester according to the protocol procedures.
The following requirements shall be applied along the whole section:
a) in many tests the DTE has to transmit an I-frame. The DTE can be forced to
transmit an I-frame, e.g. by receiving:
- RESTART INDICATION (in state r1),
- RESET INDICATION on an LC, as assigned as a PVC, in any state
except d2 and d3,
- CLEAR INDICATION on an LC, assigned as an SVC, in any state except
p.6 and p.7.
It depends on the characteristics of the DTE what packet should be used;
b) if for any reason both SLPs become in Disconnected Mode (DM), the MLP
resetting can be possible. If MLP were reset then MLP frames to be transmitted
by the DTE may be lost.
c) the following tests are defined under the assumption that both SLPs are
configured with the same system parameters.

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ETS 300 124: 1991
4.2.1 Verification of MLP setup phase
A preamble verification sequence shall be executed before each test in both lines (L1 and L2) which link
the DTE and the Tester:
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜¿
‡   Tester                DTE        ‡
‡                               ‡
‡L1&L2   DISC/P=1 --------------->             ‡
‡                               ‡
‡          <-------------- UA/F=1 or DM/F=1  L1&L2‡
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�
A post-test sequence shall be executed after each test to verify the correct status of the DTE:
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜¿
‡   Tester                DTE        ‡
‡                               ‡
‡L1 or L2 I, MN(O) ----------->               ‡
‡                               ‡
‡               <---------- I, MN(O) L1 or L2 ‡
‡                               ‡
‡L1&L2   RR/P=1  ----------->               ‡
‡                               ‡
‡               <---------- RR/F=1  L1&L2   ‡
‡                               ‡
‡                               ‡
‡NOTE: The tester shall acknowledge each MLP frame sent by the‡
‡   DTE with an SLP frame (I or RR) on the same link on  ‡
‡   which the MLP frame was received.           ‡
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�

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ETS 300 124: 1991
4.2.1.1 The system under test (sut) does not initialize the MLP
4.2.1.1.1 Initialization through L1, L2 in DM. (MN(S) = 0)
<-------------- (SABM/P1) L1 & L2
L1 SABM/P=1 --------------------->
L1 (UA/F=1) --------------------->
L2 (DM/F=1) --------------------->
<-------------- UA/F=1 L1
L1 MLP/R=1 (MN(S)=0) ----------->
<-------------- [RR] L1
<-------------- MLP/R=1 L1
L1 RR --------------------->
L1 MLP/C=1 --------------------->
<-------------- [RR] L1
<-------------- MLP/C=1 L1
4.2.1.1.2 Initialization through L1, L2 in DM.(MN(S)>0)
<-------------- (SABM/P1) L1 & L2
L1 SABM/P=1 --------------------->
L1 (UA/F=1) --------------------->
L2 (DM/F=1) --------------------->
<-------------- UA/F=1 L1
L1 MLP/R=1 (MN(S)>0) ----------->
<-------------- [RR] L1
<-------------- MLP/R=1 L1
L1 RR -------------------->
L1 MLP/C=1 -------------------->
<-------------- [RR] L1
<-------------- MLP/C=1 L1
4.2.1.1.3 Initialisation through L1, MLP frame with C=1 is sent immediately after MLP frame
when R=1. L2 in DM
<-------------- (SABM/P1) L1 & L2
**)
L1 SABM/P=1 --------------------->
L1 (UA/F=1) --------------------->
L2 (DM/F=1) --------------------->
<-------------- UA/F=1 L1
L1 MLP/R=1 --------------------->
L1 MLP/C=1 --------------------->
<-------------- MLP/R=1 L1
<-------------- [MLP/C=1] L1
L1 RR --------------------->
<-------------- MLP/R=1 L1 *)
L1 MLP/R=1 --------------------->
<-------------- MLP/C=1 L1
L1 MLP/C=1 --------------------->
*) MT3 expires.
**) If the DTE reacts on R=1 MLP frame before treating C=1 MLP frame MT3 shall not expire. In that
case the test shall be considered successful.

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ETS 300 124: 1991
4.2.1.1.4 Initilization through L1, L2 active
<--------------- (SABM/P=1) L1 & L2
L1 & L2 SABM/P=1 ---------->
L1 & L2 (UA/F=1) ---------->
<--------------- UA/F=1 L1 & L2
L1 MLP/R=1 ---------->
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜¿
‡<-------------- RR         L1‡
‡<-------------- MLP/R=1      L2‡
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�
**)
or
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜¿
‡<-------------- [RR]        L1‡
‡<-------------- MLP/R=1      L2‡
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�
*)
RR ---------->
L1 MLP/C=1 ---------->
<--------------- [RR] L1
<--------------- MLP/C=1 L1 or L2
4.2.1.1.5 Initialization through L1, confirmation by L2
<---------------- (SABM/P=1) L1 & L2
L1 & L2 SABM/P=1 ---------->
L1 & L2 (UA/F=1) ---------->
<---------------- UA/F=1 L1 & L2
L1 MLP/R=1 ---------->
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜¿
‡<-------------- [RR]        L1‡
‡<--
...