Computer

Systems

Technology

U.S. DEPARTMENT OF

COMMERCE

Technology Administration

National Institute of Standards

and Technology

Nisr

NAT'L INST OF STAND S TECH R.I.C.

A111D3 7MDQfll

PUBLICATIONS

-QC

100

.U57

823-1

1992

C.2

NIST Special Publication 823-1

Overview of Integrated

Services Digital Network

Conformance Testing

Leslie A. Collica, Kathleen M. Roberts, and David Su

NIST Special Publication 823-1 lOO

Overview of Integrated ?

Services Digital Network

Conformance Testing

Leslie A. Collica, Kathleen M. Roberts,

and David Su

Advanced Systems Division

Computer Systems Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

March 1992

U.S. DEPARTMENT OF COMMERCE

Barbara Hackman Franklin, Secretary

Technology Administration

Robert M. White, Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS

AND TECHNOLOGY

John W. Lyons, Director

i
Reports on Computer Systems Technology

The National Institute of Standards and Technology (NIST) has a unique responsibility for computer

systems technology within the Federal government. NIST's Computer Systems Laboratory (CSL) develops standards and guidelines, provides technical assistance, and conducts research for computers and

related telecommunications systems to achieve more effective utilization of Federal information technology resources. CSL's responsibilities include development of technical, management, physical, and administrative standards and guidelines for the cost-effective security and privacy of sensitive unclassified

information processed in Federal computers. CSL assists agencies in developing security plans and in improving computer security awareness training. This Special Publication 823 series reports CSL re- search and guidelines to Federal agencies as well as to organizations in industry, government, and

academia.

National Institute of Standards and Technology Special Publication 823-1

Natl. Inst. Stand. Technol. Spec. Publ. 823-1, 20 pages (Mar. 1992)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1992

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
Overview of ISDN Conforaiance Testing

ABSTRACT

This document introduces a series of documents which focus on the conformance test specifications for the various

ISDN Protocols. An overview of the current status of ISDN Conformance Testing, and the issues involved are also

provided.

KEYWORDS

Abstract Test Suite, Basic Rate Interface, BRI, Conformance Testing, Implementation Under Test, ISDN, PICS,

PIXIT, Primary Rate Interface, PRI, Protocol Implementation Conformance Statement, Protocol Implementation

Extra Information for Testing, Tree and Tabular Combined Notation, TTCN

iii
NOTICE OF DISCLAIMER

This document contains NIUF conformance tests as agreed among participating expert technical

personnel to the texts of isdn standards, conhgurations and descriptions that are intended to

promote interoperability and efficiency. these conformance tests were developed and approved by

organizations participating in the north american isdn users' forum (niuf) meetings. neither the

National Institute Of Standards And Technology (NIST) nor any of the participants in the NIUF make

ANY representation OR WARRANTY, EXPRESS OR IMPLIED WITH RESPECT TO THE SUFFICIENCY, ACCURACY, OR USE

OF ANY INFORMATION OR OPINION CONTAINED HEREIN. THE USE OF THIS INFORMATION OR OPINION IS AT THE RISK

OF THE USER. UNDER NO CIRCUMSTANCES SHALL NIST, OR ANY PARTICIPANT IN THE NIUF BE LIABLE FOR ANY

DAMAGE OR INJURY INCURRED BY ANY PERSON ARISING OUT OF THE SUFFICIENCY, ACCURACY, OR USE OF ANY

INFORMATION OR OPINION CONTAINED HEREIN.

NIST does not recommend or endorse products and nothing contained herein is intended as a recommendation or endorsement of any product.

iv
ACKNOWLEDGMENTS

The authors would like to acknowledge Al Koenig and Jerry Linn of NIST for their valuable contributions to this

document.

V

TABLE OF CONTENTS

ABSTRACT iii

NOTICE OF DISCLAIMER iv

ACKNOWLEDGMENTS v

1 INTRODUCTION 1

2 SCOPE OF ISDN CONFORMANCE TESTING 1

3 CONFORMANCE TEST SUITES FOR ISDN 2

3.1 Physical Layer Test Specifications 3

3.2 Data Link Layer Test Speciflcations 3

3.3 Network Layer Test Speciflcations 4

3.4 Additional Test Speciflcations 4

4 ISDN CONFORMANCE TESTING 5

4.1 Conformance Testing Standards 5

4.2 Conformance Testing Development 7

4.2.1 Implementors' Agreements 7

4.2.2 Abstract Conformance Test Suite Development 7

4.2.3 Test Suite Validation 7

5 USE OF PICS AND PIXIT 8

6 CONFORMANCE VS. INTEROPERABILITY TESTING 9

7 THE NIST TTCN TRANSLATOR 9

ANNEX A ABBREVIATIONS 10

ANNEX B REFERENCES 11

vii
List of Figures

Figure 1. ISDN Interface Functional Groups and Reference Points 1 Figure 2. Conformance Testing Steps 5

Figure 3. Remote Single Layer Test Method 6

Figure 4. Example of an ISDN Layer 2 (LAPD) test script in TTCN 6

Figure 5. LAPD Test Script Validation System 8

Figure 6. Implementation of a Test System Using the NIST TTCN Translator 9

List of Tables

Table 2.1. Basic Test Configurations 2

• viii
1 INTRODUCTION

Advances in communication networks have increased the complexity of communications protocols and

interfaces significantly, and the correct interpretation of standards has become a critical issue in ensuring

interoperability of equipment from different vendors. The challenge to the telephony industry in providing

high quality Integrated Services Digital Network (ISDN) service and interoperable ISDN products is unprecedented, as the ISDN protocols and interfaces are very complex and more open in terms of how

services are to be provided. Conformance testing is a fundamental task in meeting this challenge.

This document is one of a group of National Institute of Standards and Technology (NIST) Special

Publications that will be issued on Integrated Services Digital Network Conformance Testing. The purpose

of this group of Special Publications is to publish the set of conformance test suites which were agreed upon

in the North American ISDN Users' Forum (NIUF). These documents will be referenced by the Federal

Information Processing Standard (FIPS) which specifies the testing requirements which ISDN equipment

must meet to comply with ISDN protocol standards and agreements reached in the NIUF.

This pubUcation, which is an introduction to the group, provides the general scope of ISDN conformance

testing. Section 3 provides an overview of the abstract test suites in the group, including the test configurations of each suite. Section 4 ouUines conformance testing standard guidelines and describes

conformance testing development. In addition, sections 5 and 6 provide information on the use of

proformas in testing, and conformance and interoperability testing.

2 SCOPE OF ISDN CONFORMANCE TESTING

Conformance testing is the process of determining whether an implementation complies with the

specifications of the standard and exhibits the behaviors mandated by the standard [22]. There are two

classes of testing on an ISDN network-user interface: testing from the direction of the network and testing

from the direction of the user. Figure 1 shows the model of functional groups and reference points across a network-user interface [5].

The functional groups include

the Exchange Termination (ET)

group, the Network Termination

(NTl and NT2) group. Terminal

Equipment of type 1 (TEl), and

the Terminal Adaptor (TA). The

TE2 functional group represents

the existing non-ISDN data

terminals.

U

TEl JnT2

TE2 TA

NTl ET

Reference Points:

R, S, T, U

Figure 1. ISDN Interface Functional Groups and Reference Points.

The functional grouping shown

in figure 1, represents only an

abstract model for easier

reference by protocol standards. This document refers to equipment to the left of the U reference point as

the User Side equipment. An actual implementation of a user side equipment may perform more than one

of these functions, for example, it may perform only the TEl or TA function, the TEl or TA and NT2

combined, the NTl plus NT2, or other combinations. A TEl or TA may be designed to connect directly

to an NTl, in which case the S and T reference points coincide. When the TE and NTl function are combined, only the U reference point is available.

There are several basic test configurations of the System Under Test (SUT) and Tester for conformance

testing, given table 2.1, below. The symbol "TE" in the table 2.1 rs to either a TEl or TA, and S/T refers

to the case where S and T coincide. For testing from the direction of the network side to the user side, one

1
may test an NTl at the U reference point, NT2 at T, or TE at S or S/T. Similarly, for testing from the

other direction, one may test NT2 at S, NTl at T, or ET at U. The tester must often perform more than one role. For example, to test layer 2 or layer 3 implementation of a TE at the S/T reference point, the

tester must provide the layer 1 signals from the NTl and layers 2 or 3 messages from the ET. Furthermore,

additional test equipment might be needed beyond the SUT; for example, when testing an NT2 from the user side at the S reference point, the supports for the NTl and ET must also be provided. The exact test set-up requirements depend on how much of the functional group the SUT supports.

Table 2.1. Basic Test Configurations

Configuration System Under Reference Tester's Role

Test's Role Point

NU.l TE S NT2

NU.2 TE S/T NTl

NU.3 NT2 T NTl

NU.4

• NTl U ET

UN.l NT2 S TE

UN.2 NTl S/T TE

UN.3 NTl T NT2

UN.4 ET U NTl

The NTl function may be embedded in a TE or NT2.

Note that configurations NU.l and UN.l, and configurations NU.l and UN.l each have the same setup, but

the roles of the tester and lUT are reversed. Since the ISDN protocols are not always symmetric across

the network-user interface, one can not share the same test script by simply exchanging roles. Each

configuration requires its own test script.

Given a test configuration, conformance testing is further divided into smaller groups by protocol layers —

the Physical Layer (Layer 1) at the S/T [6, 7, 13, 16] and U [12, 14] reference points, the Data Link Layer

(Layer 2) [8, 15], and the Network Layer (Layer 3) [9, 10, 17, 18]. In addition, grouping is necessary by

type of services (bearer circuit switching, bearer packet switching, supplementary services, etc.), and type

of interfaces (basic rate access and primary rate access).

The conformance tests described in this series of documents focus on the basic access characteristics and

signalling protocols specified in the ISDN standards Usted. For thoroughness, conformance testing should

also be done for the bearer services covered by ISDN, e.g., X.25 and Group 4 FAX. However, tests for

these services are beyond the scope of this document.

Currently, most of the ISDN conformance testing activities focus on testing of ISDN terminal equipment,

since there are more terminal devices from different vendors than network switching equipment.

3 CONFORMANCE TEST SUITES FOR ISDN

The ISDN Conformance Testing (ICOT) group of the NIUF has been developing conformance test suites

for the protocol standards for ISDN layers 1, 2, and 3. Separate test suites for the user and networic side

equipment, and for the Basic Rate (BRI) and Primary Rate (PRI) interfaces have been, or will be.

2
developed. It is the intent of this group to submit these industry agreements to the related standard bodies

for adoption as national or international standards, as appropriate.

The following sections outline the abstract test suites which will be published in other documents as part

of this group of NIST Special Publications. Included in this outline are brief descriptions of the test specifications and test configurations, as described in the Scope section of this document, for ISDN layers

1, 2, and 3, that are being developed in the NIUF. Additional test specifications include supplementary

services, terminal adaptor, and packet mode bearer services. With the exception of the layer 1 test suite,

the methodology used in the development of the following test suites is based on International Organization

for Standardization (ISO) 9646 [22], and the test scripts are written in the Tree and Tabular Combined

Notation, TTCN.

3.1 Physical Layer Test Specifications

Layer 1 — Physical Layer — The three parts of this specification will describe the test specifications for

American National Standard (ANS) Tl.605-1989 [16], ANS Tl.601-1988 [14] and ANS Tl.408-1990 [13].

This includes testing of functional, electrical, and mechanical characteristics of devices including TEl, TA,

and NT's on the user side. The tests may include verification of framing, line bit rate, relative bit positions,

D-channel access control, checking ofjitter and phase, impedance, pulse shape and amplitude, pulse balance,

receiver/transmitter performance, power feeding and consumption, start-up procedures, pulse characteristics,

frame structure, M-channel bit functions, etc.

Part 1: Basic Rate S/T Interface, User Side [4] describes a set of test specifications which verify

conformance of TEs and NTs to the ISDN Physical Layer Basic Access at the S/T reference point, as defined in ANS Tl.605-1989 [16], and section 4.1.1.2 of the NIU-Forum Agreements on ISDN

[3]. This test suite is designed for test configurations NU.l through NU.5 and UN.l through UN.3

in table 2.1.

Part 2: Basic Rate U Interface, User Side will describe a set of test specifications which verify

equipment implementation conformance to the ISDN Physical Layer Basic Access at the U

interface, as defined in ANS Tl.601-1988 [14] and section 4.1.1.1 of the NIU-Forum Agreements on ISDN [3]. This test suite will be designed for test configuration NU.4 in table 2.1.

Part 3: Primary Rate Interface, User Side will describe a set of test specifications which verify

equipment implementation conformance to the ISDN Physical Layer Primary Access at the S, T,

and U interface, as defined in ANS Tl.408-1990 [13] and the corresponding NIUF Implementation

Agreement. This test suite will be designed for test configurations NU.l, through NU.3, UN.l

through UN.3 in table 2.1.

3.2 Data Link Layer Test Specifications

Layer 2 — Data Link Layer — The two parts of this specification will cover the protocol states defined

in the International Telegraph and Telephone Consultative Committee (CCITT) Q.921 [8] and ANS T1.602

[15] standards. For each state, three types of tests are specified: valid, inopportune, and invalid tests. The

valid tests cover the exchange of valid frames; the inopportune tests check the lUT's response to correctly

formatted frames received in an unexpected state, and the invalid tests verify the lUT's error recovery

procedures upon receiving an incorrectly formatted frame.

Part 1: Basic Rate Interface, User Side will define the abstract test specifications to verify

equipment implementation conformance to the Layer 2 of an ISDN at the user-network interface,

for the BRI access arrangements, as defined in ANS Tl.602-1989 [15] and section 4.1.3 of the

3
NIU-Forutn Agreements on ISDN [3]. This test suite was designed for test configurations NU.l

and NU.2 in table 2.1. This test suite is currently the base text in CCITT Study Group XI for

consideration as an international reconunendation.

Part 2: Primary Rate Interface, User Side will define the abstract test specifications to verify

equipment implementation conformance to the Layer 2 of an ISDN at the user-network interface,

for the PRI access arrangements, as defined in ANS Tl .602-1989 [15] and NIU-Forum Agreements on ISDN [3]. This test suite will be designed for test configurations NU.3 and NU.4 in table 2.1.

33 Network Layer Test Specifications

Layer 3 — Network Access Layer — The three specifications involving layer 3 will be based on CCITT

Q.931 [9] and ANS T1.607 [17] and cover the D-channel operations for user side states in the following

functional areas: call setup from user and network, call clearing from user and network, and error recovery

mechanisms (invalid information element and missing mandatory information element). As in the Layer

2 test suites, valid, inopportune, and invaUd tests will be performed. Note that the operations of the B

channels will not be covered in these tests.

Part 1: Basic Rate Interface Circuit Switch Call Control, User Side will define the abstract test specifications to verify equipment implementation conformance to the Layer 3 of an ISDN BRI

at the user-network interface for the Basic Call Control Procedures, as defined by ANS T1.607-

1990 [17], section 4.1.4.1.1 of the NIU-Forum Agreements on ISDN [3], and other corresponding

NIUF Implementation Agreements. This test suite was designed for test configurations NU.l and

NU.2 in table 2.1.

Part 2: Primary Rate Interface Circuit Switch Call Control, User Side will define the abstract test specifications to verify equipment implementation conformance to the Layer 3 of an ISDN PRI at the user-network interface for the Basic Call Control Procedures, as defined by ANS Tl.607-1990

[17], section 4.1.4.1.1 of the NIU-Forum Agreements on ISDN [3], and other corresponding NIUF

Implementation Agreements. This test suite will be designed for test configurations NU.3 and

NU.4 in table 2.1.

Part 3: Packet Switched Call Control will define the abstract test specifications to verify equipment

implementation conformance to the Layer 3 of an ISDN at the user-network interface for the

Packet Switched Call Control Procedures, as defined by ANS Tl.608-1990 [18], section 4.1.4.2

of the NIU-Forum Agreements on ISDN [3], and other corresponding NIUF Implementation

Agreements.

3.4 Additional Test Specifications

Supplementary Services will define the abstract test specifications to verify implementation conformance

to the Supplementary Services at the user-network interface, as defined in ANS T1.610 [19], section

4.1.4.11.2 of the NIU-Forum Agreements on ISDN [3], and other appropriate ANS documents and their

corresponding NIUF Implementation Agreements.

Packet Mode Bearer Services Control Procedures will define the abstract test specifications to verify

implementation conformance to the Packet Mode Bearer Services Control Procedures.

Terminal Adaption will define the abstract test specifications to verify equipment implementation

conformance to the ISDN Circuit-Mode Data Terminal Adaption using Statistical Multiplexing, as defined

by ANS T1.6 12- 1990 [20] and the corresponding NIUF Implementation Agreement.

4
4 ISDN CONFORMANCE TESTING

In order to ensure that conformance tests produce correct and consistent results, it is essential that test suites

be standardized. The costs involved, in terms of time and resources, to develop test scripts, implement

testbeds, and perform tests, is a strong incentive to standardize conformance tests. This section first presents

the standard for guidelines in conformance testing, and briefly describes the conformance test development

process including implementors' agreements, abstract test suite development and validation, and

supplemental information required for testing a vendor's product.

4.1 Conformance Testing Standards

The ISO and the CCITT have developed a standard for Open Systems Interconnection (OSI) conformance

testing. The resulting standards, ISO 9646, "OSI Conformance Testing Methodology and Framework" [22]

and CCITT X.290 [11] (with the same title), cover most aspects of the conformance testing process shown

in figure 2. ISO 9646 is a five part standard consisting of:

Part 1 General Concepts — introduces

conformance testing concepts and

terminology;

Part 2 Abstract Test Suite Specification —

defines test methods for test suite

specification, and types of tests which

should be included in an abstract test

suite;

Part 3 The Tree and Tabular Combined

Notation (TTCN) — defines a

language for writing abstract test

suites;

Part 4 Test Realization — specifies

requirements and gives guidance

concerning the realization of a means

of testing lUTs; and

Part 5 Requirements on Test Laboratories

and CUents for the Conformance

Assessment Process — specifies

requirements on both the test laboratory and the client, for the

conduct of the conformance

assessment process.

Part 2 defines abstract test methods: local,

distributed, coordinated and remote methods.

The remote single layer testing, as shown in figure 3, is the most conunon method used for ISDN layer 2

and 3 protocol testing. The Implementation Under Test would be either the layer 2 or layer 3

implementation, which would exchange layer N (2 or 3) Protocol Data Units (PDUs) with the tester through

the lower layer services. The lower layer services for the lUT and lower tester are assumed to be available

and are not under test. The "lower tester" refers to the means of providing indirect control and observation

of the lower boundary of the lUT via the underlying service provider. There is one Point of Control and

Observation (PCO) where the lower tester observes the messages being exchanged between the lower tester and the lUT and assigns verdicts (test results) accordingly.

STANDARDS

PICS: Protocol ImplcmenUtion

Conf6nnmncc Statement PKIT: Protocol Implementatloii

IMPLEMENTORS'

AGREEMENTS

ABSTRACT

CONFORMANCE

TEST SUITE

EXECUTABLE

TEST SUITE

ON TEST

EQUIPMENT

TESTING

OPERATIONS

TEST REPORTS

Extra Information for Teiting

Figure 2. Conformance Testing Steps.

5
Lower

Tester

PCO

TM CMrdlBatUa Tnctimrm

-N PDUImpkmcntatlon

Under Tot

-N-1 ASP

For the remote single layer testing, the

upper layer support of the JUT is not

specified, and no explicit test coordination

procedures are assumed, although they

may be present. As an example, during

testing of the ISDN Layer 2 protocol, the

tester may require the lUT to send a link

setup frame, which would require some

activities from Layer 3. The tester may

only be able to generate a request to the

test oj)erator for necessary manual

intervention to the lUT to trigger the link

setup. The exact method which the tester uses to accomplish the Unk initiation is not defined in an abstract test script. It is outside of the scope of the requirements of this test method in an abstract test script and is dependent on the particular implementation of the lUT.

N-l Serrlce ProTider

Figure 3. Remote Single Layer Test Method.

The TTCN language, defined in Part 3 of ISO 9646, allows one to write a precise description of the

behavior of both the tester and the lUT, as well as the exact contents of the Protocol Data Units exchanged.

TTCN has two forms, the tabular or graphic form (TTCN.GR) for human reading, and the machine

processable form (TTCN.MP) for computer processing. Figure 4 is a sample of a test script written in TTCN.GR taken from the NIUF LAPD test suite. A test case consists of a sequence of frames sent

(indicated by !) and received (indicated by ?) by the tester, and related timing operations specified in the

Behavior Description Column. Each event may specify the PDU name and its exact contents in the

Behavior Description column and the Constraints Reference column, respectively. The PDU and constraint names refer to entries in other tables in the test suite.

Test Case Dynamic Behaviour

Reference: LAPD/MFO/S70/DL70_V14

Identifier DL70_V14

Purpose: Verify tfiat tfie lUT sends a SABME/P=1 in response to a DM/F=0 in Multiple Frame Establisfied state (7.0). The lUT is expected to enter Awaiting

Establishment state after sending the SABME/P=1.

Defaults Reference:

Behaviour Description Label Constraint Reference V Comments

DL70_V14

+DL70_PREAf^/IBLE

\DM DMO_NR F=0

START Td

?SABME L700 SABN/IE1_UC (P) P=1

+DL51_VERIFICATI0N

+DL_POSTAMBLE

+DL70_UNEXPECTED

GOTO L700

70THERWISE (F)

+DL_P0STAMBLE

7TIMEOUT Td (F)

+DL_POSTAMBLE

Figure 4. Example of an ISDN Layer 2 (LAPD) test script in TTCN.

6
4.2 Conformance Testing Development

Several steps are required to develop conformance tests from the protocol specification. These steps, shown

in figure 2, include the development of an abstract conformance test suite, the implementation of executable

test scripts on test equipment, the testing operations, and the preparation of the test reports. The following

sections describe the steps through which the abstract test suites in this series were developed and the initial steps in progressing to an executable test suite. The details of the testing operations and test reporting

requirements may be provided in other publications. The fu-st step in the development of an abstract test suite begins with the precise interpretation of the base standards.

4.2.1 Implementors' Agreements

Protocol and interface standards are specifications for products and services. Most standards are written

in natural language (e.g., EngUsh, French) and are subject to different interpretations. Since a standard may

involve many options and variable fields, the test suite developer may need to rely on additional

implementors' agreements which specify or constrain the choice of options and allowable fields. North

American Implementors' Agreements for ISDN are developed by the Access Signalling Working Group in

the Implementor's Workshop of the NIUF. Implementors' Agreements specify 1) options to be

implemented (or excluded) and the PDU codings; 2) stacks of protocol with options preselected, when

offering specific services; and 3) test suites to be used for assessing conformance of the items above. The

Implementors' Agreements determine the set of test suites required for testing conformance of a stack of

protocols, and the selection of test cases and portions of the test scripts within a test case for a given

standard. Once a set of implementor's agreements are in place for a particular protocol, the development

of an abstract test suite begins.

4.2.2 Abstract Conformance Test Suite Development

The ISDN Conformance Testing (ICOT) Working Group was formed as a permanent implementor's

subgroup of the NIUF to develop abstract conformance test suites based on the NIUF Implementor's

Agreements. ICOT consists of testing experts from organizations such as AT&T Bell Laboratories, Bell

Atlantic, Bell Northern Research, Bell Communications Research (Bellcore), Corporation for Open Systems

(COS), IBM, IDACOM/Hewlett Packard, NIST, Northern Telecom, NYNEX, TEKELEC, and

Telecommunications Techniques Corporation. Test suite development for the Layer 2 test suite, for

example, began with a complete review of the protocol standard Q.921, to determine the desired coverage

by the test suite. The test scripts were developed in the TTCN, reviewed, and validated by the participating

members during numerous NIUF and interim meetings. The validation process is described below.

4.2.3 Test Suite Validation

The validation of test suites was provided by different means during the development of the abstract test

suite. First, selected groups of test cases were coded into executable test cases for test equipment and

evaluated in parallel to the test suite development. The results of these preliminary tests were reported to ICOT, and refinements were discussed. The entire test suite was coded as executable tests and evaluated

during the fmal development of the test suite.

A second validation method was developed at NIST during the development of the NIUF Layer 2 (LAPD)

test suite, and subsequently used for test suites for other protocols. Figure 5 shows the system development

process. Based on the Q.921 states/events matrix, a protocol model of the LAPD protocol standard, was

developed using the formal description language Estelle [21]. It simulates the behavior of the lUT and can be used to exercise most of the test cases in the test suite. In parallel, a tester was implemented using the

TTCN-to-C translator, described in section 7. The abstract test suite is compiled into an executable test

7
suite in C code. As part of this process, both semantics and

syntax cliecking is perfonned on

each test case. The protocol

model of the implementation and

the tester run concurrently as two

independent processes on a UNIXTM system. The Layer 1 Service Provider function, shown

in figure 3, is simulated by means

of a UNIXTM inter-process

communication facility called

shared memory. In this system, an abbreviated Layer 3 software is implemented to realize the test coordination procedures required

by the lower tester. Thus, no real

ISDN hardware is required. At

the end of each test case, the test log and the simulator execution

trace are compared to find any

discrepancies between the test

script and the behavior of the

lUT.

USE OF PICS AND PIXIT

LAPD Standard Q.921/ri.602

NIU-Fbium

ImpleincntoiB' Agreements

State/Events

Matrix

Test Suite

in TTCN.MP

Reference Model

in ESTELLE

TTCN * C Compiler

ESTELLE CompUci

LAPD Tester

(a UNIX Process)

LAPD Simulator

(a UNDC Process)

Physical Layer Interface (UNIX Interprocess Communication)

Test Log Execution Trace

It is likely that an entire test suite Figure 5. LAPD Test Script Validation System,

is not applicable for all lUTs.

Therefore, a test selection

procedure must be performed to determine the applicability of each test case to a particular TUT. Such

selection is based on the Protocol Implementation Conformance Statement (PICS) and the Protocol

Implementation Extra Information for Testing (PKIT). The guidelines for developing both PICS and PIXIT

are provided in ISO 9646 [22].

The PICS proforma, in the form of a questionnaire, becomes the PICS when completed by a supplier for an ISDN implementation. The PICS specifies the capabilities and options which have been implemented,

and any features which have been omitted, so that the implementation can be tested for conformance against

relevant requirements, and against those requirements only. Static conformance assessment is based upon

information provided about the lUT in the PICS; e.g., are all of the mandatory features implemented, and

are related conditional options implemented when there are inter-dependencies. The conformance testing

guidelines of ISO 9646 recommends that the PICS proforma become part of the protocol standard.

Additional information related to the lUT and its environment is needed before a test campaign can commence; this information is contained in a PIXIT and supplements information contained in a PICS. The

PIXIT questionnaire should be completed by the manufacturer of the lUT, or the test laboratory client, when

submitting an lUT for testing. The PIXIT contains information regarding system specific details required

by the test laboratory to run the test suite. Timer values, for example, may be specified in the PICS as a range of values for a particular timer. The PIXIT questionnaire may request a specific timer value. In this way, the PIXIT provides a refinement of the PICS information. The values of test variables and parameters

for conditions regarding test case selection are derived by the test laboratory from the information supplied

in the PIXIT. ISO 9646 recommends that the PIXIT questionnaire be part of the related abstract test suite.
6 CONFORMANCE VS. INTEROPERABILITY TESTING

Since confonnance testing is done in a controlled environment, the fact that equipment passes conformance

tests does not guarantee that it will interoperate without problems. Interoperability may depend on 1) all manufacturers implementing the same set of options; 2) system loads, which may impact the availabiUty

buffers; and 3) implementation and synchronization of timers, i.e., a mismatched timer may cause a call to be aborted. Conformance testing only increases the confidence that the equipment was implemented as specified in the standard. External factors, such as the condition of the communication port, may also affect

the outcomes of the confonnance tests. Furthermore, conformance testing does not imply complete and

exhaustive testing of every aspect of a standard. The dynamic behaviors of ISDN protocols are so complex

that it is not economically feasible to perform exhaustive testing. Conformance testing is the first step in

product quality testing and is supplemented by interoperability tests and system load tests.

7 THE NIST TTCN TRANSLATOR

The purpose of developing the TTCN-to-C language translator was two-fold: 1) to provide a tool to industry which would expedite the process of converting an abstract test suite (specified in TTCN) into an

executable test suite (specified in the C language), and 2) to provide a tool which could be used in the test

suite validation process described above.

The NIST TTCN translator [2] accepts a test script in machine processable form, TTCN.MP, and translates

it into C language statements. It can be used to ttansform an abstract test suite into an executable test system with minimum effort. Figure 6 shows the process needed to implement an executable test system

Protocol dependent

support programs

Abstract

test

suite

TTCN

Editor

Test suite

in TrCN.MP

TTCN

Translator

Test suite in

C source

programs

CompUe &

Link

Testbed machine

dependent support

programs

Real

test

system

Figure 6. Implementation of a Test System Using the NIST TTCN Translator.

using the NIST translator. The abstract test suite in TTCN.MP form is generated using one of the TTCN

tools described above. It is then input into the TTCN translator which produces a set of C language

programs. These programs are compiled on the target testbed and bound with other support programs to make an executable test system. The protocol and system dependent support programs include such items

as formatting and analyzing PDUs, controlling the ISDN ports, and handling timers or clocks. The

translator has been used to validate the correcmess of the NIUF LAPD test suite, and to implement real test systems.

9
ANNEX A ABBREVIATIONS

ANS American National Standard

ASP Abstract Service Primitives

BRI Basic Rate Interface

CCITT International Telegraph and Telephone Consultative Committee

ET Exchange Termination

FIPS Federal Information Processing Standard

ICOT ISDN Confonnance Testing Working Group of NIUF

ISDN Integrated Services Digital Network

ISO International Organization for Standardization

lUT Implementation Under Test

LAPD Link Access Procedure on the D-channel

NIST National Institute of Standards and Technology

NIUF North American ISDN Users' Forum

NT Network Termination (NTl and NT2)

OSI Open Systems Interconnection

PCO Point of Control and Observation

PDU Protocol Data Unit

PICS Protocol Implementation Conformance Statement

PIXIT Protocol Implementation Extra Information for Testing

PRI Primary Rate Interface

TA Terminal Ad^tor

TEl Terminal Equipment of type 1 (ISDN)

TE2 Terminal Equipment of type 2 (Non-ISDN)

TTCN Tree and Tabular Combined Notation

10
ANNEX B REFERENCES

[I] D.H. Su and L.A. Collica, "ISDN Conformance Testing", Proceedings of the IEEE. Vol. 79, No. 2, February

1991.

[2] D.H. Su, "User's Manual for the NIST TTCN Translator, Version 3.0," National Institute of Standards and

Technology, March 1991.

[3] NIST Special Publication 500-195, North American ISDN Users' Forum Agreements on Integrated Services

Digital Networks, NTIS, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, VA 22161,

September, 1991, (NTIS Order Number PB92-102219).

[4] NIST Special Pubhcation 500-194, ISDN Conformance Testing Layer 1 — Physical Layer — Part 1 Basic

Rate S/T Interface, User Side, NTIS, U.S. Department of Commerce, 5285 Port Royal Road, Springfield,

VA 22161, September, 1991, (NTIS Order Number PB92-102201).

[5] CCITT Recommendation 1.411-1988, ISDN User-Network Interfaces — Reference Configurations.

[6] CCITT Recommendation 1.430-1988, Basic User-Network Interface — Layer 1 Specification.

[7] CCITT Recommendation 1.431-1988, Primary Rate User-Network Interface — Layer 1 Specification.

[8] CCITT Recommendation Q.921-1988, ISDN User-Network Interface, Data Link Layer Specification, (Blue

Book).

[9] CCITT Recommendation Q.931-1988, ISDN User-Network Interface Layer 3 Specification for Basic Call

Control, (Blue Book).

[10] CCITT Recommendation X.25- 1988, Interface Between Data Terminal Equipment (DTE) and Data CircuitTerminating Equipment (DCE)for Terminals Operating In The Packet Mode and Connected to Public Data

Networks by Dedicated Circuit.

[II] CCITT Recommendation X.290-1988, OSI Conformance Testing Methodology and Framework.

[12] ANS Tl.403- 1989, Telecommunications - Carrier to Customer Installation, DSI Metallic Interface

Specification.

[13] ANS Tl.408-1990, Telecommunications - ISDN Primary Rate - Customer Installation Metallic Interfaces - Layer 1 Specification.

[14] ANS Tl.601-1988, Telecommunications - ISDN - Basic Access Interface for Use on Metallic Loops for

Application on the Network Side of the NT, Layer I Specification.

[15] ANS Tl.602-1989, Telecommunications - ISDN - Data Link Layer Signaling Specification for Application

at the User-Network Interface.

[16] ANS Tl.605-1989, Telecommunications - ISDN - Basic Access Interface for S and T Reference Points,

Layer 1 Specification.

[17] ANS Tl .607-1990, Telecommunications - ISDN - Digital Subscriber Signaling System No. I (DSSI) - Layer

3 Signaling Specification for Circuit Switched Bearer Service.

[18] ANS Tl.608-1990, Telecommunications - ISDN - Digital Subscriber Signaling System No. I (DSSI) -

Signaling Specification for X.25 Packet Switched Bearer Service.

[19] ANS Tl.610-1990, Telecommunications - ISDN - Digital Subscriber Signaling System No. I DSSI - Generic

Procedures for the Control of ISDN Supplementary Services.

[20] ANS Tl .612- 1990, Telecommunications - ISDN - Terminal Adaptation Using Statistical Multiplexing.

[21] ISO 9074, Information Processing Systems, Estelle: A Formal Description Technique Based on an Extended

State Transition Model, 1987.

[22] ISO 9646, Information Processing Systems, OSI Conformance Testing Methodology and Framework. Parts

1-5, 1989.

11

NIST-114A U.S. DEPARTMENT OF COMMERCE

(REV. 3-90) NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

BIBLIOGRAPHIC DATA SHEET

1. PUBUCATION OR REPORT NUMBER

NIST/SP-823/1

2. PERFORMINQ ORQANIZATION REPORT NUMBER

3. PUBUCATION DATE

March 1992

4. TITLE AND SUBTITLE

Overview of Integrated Services Digital Network Conformance Testing

S. AUTHOR(S)

Leslie A. Collica, Kathleen M. Roberts, David Su

6. PERFORMINQ ORQANIZATION (IF JOINT OR OTHER THAN NIST, SEE INSTRUCTIONS)

U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

QAITHERSBURQ, MD 20899

7. CONTRACT/GRANT NUMBER

8. TYPE OF REPORT AND PERIOD COVERED

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (STREET, CITY. STATE, ZIP)

Same as item #5

10. SUPPLEMENTARY NOTES

11. ABSTRACT (A 200-WORD OR LESS FACTUAL SUMMARY OF MOST SIGNIFICANT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBUOQRAPHY OR

UTERATURE SURVEY, MENTION IT HERE.)

This document introduces a series of documents which focuses on the conformance test

specifications for the various ISDN Protocols. It provides both an outline of the

abstract test suites in this series and an overview of the current status of ISDN

Conformance Testing and related issues.

12. KEY WORDS (6 TO 12 ENTRIES; ALPHABETICAL ORDER; CAPITAUZE ONLY PROPER NAMES; AND SEPARATE KEY WORDS BY SEMICOLONS)

Abstract Test Suites; Basic Rate Interface; Conformance Testing; Implementation Under Test;

ISDN; NeLwork Termination; Primary Rate Interface; Protocol Implementation Conformance

Statements; Protocol Implementation Extra Information for Testing; Terminal Equipment; Tree

and Tabular Combined Notationj_ TTCN

13. AVAILABIUTY

X

UNUMITED

FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE TO NATIONAL TECHNICAL INFORMATION SERVICE (NTIS).

ORDER FROM SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE,

WASHINGTON, DC 20402. ORDER FROM NATIONAL TECHNICAL INFORMATION SERVICE (NTIS), SPRINGFIELD. VA 22161.

14. NUMBER OF PRINTED PAGES

20

IS. PRICE

ELECTRONIC FORM * U.S. G. P. 0. : 1992-311-891 : 6001

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