1、 CEPT NET*ZL 92 232b414 OOLL3L7 9Tb NET 21 First edition: 1992 EUROPEAN TELECOMMUNICATION STANDARD Attachments to the Public Switched Telephone Network (PSTN) Category II attachment requirements for 300 bits per second duplex modems standardized for use on the PSTN Published by: CEPT Liaison Office
2、Seilerstrasse 22 CH-3008 Bern Telephone: Facsimile: Telex: 91 1089 CEPT CH + 41 3 1 62 20 8 1 + 41 3 1 62 20 78 CEPT NET*2L 72 m 232b4L4 OOLL3L8 832 m THE EUROPEAN CONFERENCE OF POSTAL AND TELECOMMUNICATIONS ADMINISTRATIONS (CEPT) Copyright 1992 the European Conference of Postal and Telecommunicatio
3、ns Administrations (CEPT). II NET 21 CEPT NET*2L 92 2326414 0011319 779 NORMES EUROPENNES DE TLCOMMUNICATION It is recognized, in the field of telecommunications within Europe, that there is a need to create common European standards for telecommunications equipment. Such harmonization would among o
4、ther things facilitate cooperation between telecommunications equipment manu- facturers and public telecommunications network operators, create a marketplace which naturally transcends that of na- tional frontiers, enhance the efficiency of business and other communication across Europe to bring eco
5、nomic benefits, and help translate the vision of a united Europe into a working reality. In 1985 an initiative by the Conference of European Posts and Telecommunications Administrations (CEPT) re- sulted in the drafting of a Memorandum of Understanding (MOU) agreeing to the mutual recognition of res
6、ults of tests of conformity to a technical specification which would be known as a Norme Europenne de Tlcommunication (or NET). A list of signatories to the MOU is shown at the end of this introductory text. The signatories represent telecommunica- tions Administrations in most countries in Western
7、Europe, including EEC and EFA Administrations. In 1986 the European Community Council Directive 86/361/EEC laid down the principles of the initial stage of the mutual recognition of type approval for telecommunications terminal equipment. The Directive imposes the obligation on EC Member States to i
8、mplement the recognition of tests to common conformity specifications. 1 NETs 1.1 include: - - Guiding principles under which a NET is written are the need to ensure essential requirements are met. These user safety insofar as this requirement is not covered by other legal instruments (e.g. Directiv
9、e 73/23/EEC) safety of employees of public telecommunications network operators insofar as .this requirement is not covered by other legal instruments (e.g. Directive 73/23/EEC) protection of public telecommunications networks from harm interworking of terminal equipment, in justified cases - - 1.2
10、Each NET constitutes part of a series of NETs prepared in response to the MOU and the EC Directive 86/36 1. 1.3 A NET details the requirements, and a specification of interface tests for conformance to those requirements, which a defined type of telecommunications terminal equipment is required to s
11、atisfy in order to obtain authorization for connec- tion of the equipment to a defined European telecommunications network. The NET also includes, where appropriate, re- quirements made necessary in a given State by historical network peculiarities. 1.4 The existence of a NET will make it possible f
12、or an accredited laboratory in a country whose Administration has signed the MOU, to carry out tests, specified in the NET, on terminal equipment submitted to it, and to issue a test report. On the basis of the report, a competent body may then issue a certificate of conformity to the NET. There may
13、 of course be cases where the laboratory itself is the competent certification authority. This certificate is then recognized as valid in all the other signatory countries, avoiding the need for the equipment to have to undergo the same tests over again each time approval is applied for in any of th
14、ose countries. 1.5 The common reference point which a NET represents thus offers the opportunity of substantially reducing the complexity, length and cost of approval formalities. The operators of public networks are required to make reference to relevant NETs in public supply contracts. Manufacture
15、rs are thereby enabled to compete on a more equal technical basis in the supply of terminal equipment covered by NETs. 2 TYPES OF NET The majority of NETs falls into one of the two categories: access NETS and terminal NETs. (a) Access NET Details of the technical characteristics (electrical, mechani
16、cal and access control protocol), to be offered by terminal equipment at the interface to a specific public telecommunications network are covered in an “access NET. The objective of an access NET is to ensure no disturbance occurs to the network and to ensure interworking between network and termin
17、al equipment so that calls can be routed successfully through the network (but without any guarantee of terminal to terminal operation). Indeed, since an access NET may have to serve a number of terminal NETs and applications which have not even been envisaged at present, it is important for the con
18、tent not to include anything which is particular to a specific terminal or otherwise inhibiting to new developments. NET 21 III CEPT NET*21 92 m 2326414 0011320 490 m (b) Terminal NET The objective of a terminal NET is to ensure the end-to-end compatibility of a defined telecommunication ser- vice.
19、The terminal NET should include any requirements which must be added to the corresponding access NET(s) to ensure end-to-end communication. 3 DATE OF APPLICATION The date of application of a NET is that date at which the NET is recognized as being applicable, in the signatory Administrations, for th
20、e purposes of type approval, under the terms of Directive 86/36 1EEC. 4 TRANSITION PERIOD 4.1 which there will be coexistence between the NET and any national requirements which relate to the Scope. The transition period commences at the date of application. The transition period is a period of flex
21、ibility during After the expiry of the transition period the only applicable standard within the Scope for type approval purposes will be that of the particular NET. The end of the transition period is fixed by TRAC as an objective for all signatory countries of the MOU. In some cases, however, for
22、example when a new network has to be set up, all network operators may not be in a position to meet the objective. In such cases, the end of the transition period will be a date which is individual to the given country, and Administrations will publish the projected date by which the end of the tran
23、sition period can be achieved. 4.2 transition period: The following notes are offered as guidance on conformance testing of telecommunications equipment during the During the transition period, new telecommunications equipment offered by manufacturers under the Scope of this NET may be tested at a c
24、ertified laboratory located within the signatory countries, either under this NET or under the exist- ing national requirements, at the choice of the manufacturer. Testing under the NET rather than under the old requirements might offer the manufacturer the opportunity of a larger marketplace in whi
25、ch to sell the equipment. The transition period is also an opportunity for the public network operators to update their network. However, a national approval authority would have the facility of refusing the approval of terminal equipment, for which a certificate of conformance to a NET had been iss
26、ued, if the network were not yet compatible with the terminal equipment to be con- nected. 4.3 already been approved either before application of this NET or during the transition period. The following note is offered as guidance on the supply and connection of telecommunications equipment that has
27、After the application date of this NET, that is, during and after the transition period, the supply and connection of equipment already approved to earlier standards may continue unless the national authority terminates the validity of approvals to earlier standards for whatever reason. Figure 1 is
28、a diagnammatic representation of the above points. 5 APPROVAL PROCEDURES Details of national type approval procedures are not contained within NETs, but are decided by national Adminis- trations. 6 REQUIREMENTS TO BE SATISFIED The scope statement defines which types of equipment must meet the requir
29、ements of each NET. In addition, equip- ment may also have to satisfy the requirements in other NETs (as defined in their scope statements) or, in the absence of hannonised NETs, one or more published national standards. In the absence of any requirements in other NETs or in pub- lished national sta
30、ndards, no additional tests may be sought by any approval authority in the countries whose Administra- tion has signed the MOU. 7 LEGAL BASIS OF THIS INTRODUCTION TEXT This introductory text is provided for guidance, and to aid interpretation. Readers are advised that the legally binding document in
31、 the EC countries is the EEC Directive 86/361. IV NET 21 CEPT NET*? subclause 5.5.1 (Response times of the received line signal detector) and subclause 5.5.2 (Response times of the Ready For Sending RFS indicator) where a restricted range of values have been inserted to assist interoperability. Addi
32、tionally, requirements are included which relate to end-to-end interoperability over PSTN connections. These requirements are in excess of the CCITT Recommendations. A modem which complies with CCITT Recom- mendation V.21 4 should always meet the requirements of this NET which relate to parameters s
33、pecified in that CCITT Recommendation except in the case of some of the intentional deviations identified above. Clause 4 of this ETS references the requirements which are common to both Category I and Category II modems, which are contained in NET 20, Clause 4. Clause 5 of this ETS contains Categor
34、y II requirements specific to 300 bits per second duplex modems. In the case of certain functions common to a number of different types of modem (e.g. Auto-answering sequence), reference is made to Clause 5 of NET 20, which contains the relevant requirements, etc. NET 21 3 CEPT NETt21 92 2326414 001
35、1325 T2 W 1 Scope This NET specifies the technical characteristics to be offered by modems seeking Category II approval for duplex operation over the PSTN at 300 bits per second. The modulation scheme specified is the one described in CCITT Recommendation V.21 4. The term ?modem? in the context of t
36、his ETS includes all physical implementation practices for voice-band modems which are galvanically connected to the PSTN. This NET specifies two modes of operation: answer mode and call mode. Note -Modems can provide either simply one of the above modes or provide both modes together with facilitie
37、s for selecting either of the two modes. This NET also contains descriptions of the tests to be performed in order to confirm compliance with the functional requirements contained herein. A general description of the test conditions and test requirements is given in Annex A (Normative). 2 Normative
38、references This NET incorporates, by dated or undated references, 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 p
39、ublications apply to this NET only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. i11 Pl i31 i41 VI 61 71 3 3.1 Draft prETS 300 001: ?Attachments to Public Switched Telephone Network (PSTN); General technical requir
40、ements for equipment connected to an analogue subscriber interface in the PSTN?. NET 20: ?Attachments to the Public Switched Telephone Network (PSTN); Basic attachment requirements for modems standardized for use on the PSTN?. CCITT Recommendation S.33 (1984): ?Standardization of an international te
41、xt for the measurement of the margin of start-stop machines using International Alphabet No. 5?. CCITT Recommendation V.21 (1984): ?300 bits per second duplex modem standardized for use on the General Switched Telephone Network?. CCITT Recommendation V.24 (1984): ?List of definitions for interchange
42、 circuits between Data Terminal Equipment and Data Circuit-Terminating Equipment?. CCITT Recommendation V.25 (1 984): ?Automatic answering equipment and/or parallel automatic calling equipment on the General Switched Telephone Network including procedures for disabling of echo control devices for bo
43、th manually and automatically established calls?. CCITT Recommendation V.54 (1984): ?Loop Test devices for modems?. Definitions and abbreviations The definitions and abbreviations of NET 20 apply, together with the following. De$nitions Answer mode: when calls are established with automatic faciliti
44、es, a standard answer mode shall be used by the modem at the answering station. This mode consists of conventional characteristics (e.g. use of high channel carrier frequency or particular scrambler generating polynomial) complementary to those used in the standard call mode by the modem at the call
45、ing station, in order to ensure proper connection and interworking. If calls are established on the PSTN by operators, or for leased line operation, bilateral agreement on the use of call mode and answer mode shall be necessary. Call mode: when calls are established with automatic facilities, a stan
46、dard call mode shall be used by the modem at the calling station. This mode consists of conventional characteristics (e.g. use of low channel carrier frequency or particular scrambler generating polynomial) complementary to those used in the standard answer mode by the modem at the answering station
47、, in order to ensure proper connection and interworking. If calls are established on the PSTN by operators, or for leased line operation, bilateral agreement on the use of call mode and answer mode shall be necessary. Data Terminal Equipment (DTE): is used to define the origin and destination of sig
48、nals present at the digital interface of a modem. This expression does not require that a ?commercial data terminal? be present to receive or generate such signals; a tester or any other suitable device may monitor or generate such signals. Degree of start-stop distortion: in start-stop transmission
49、 the ratio of the maximum measured difference, irrespective of sign, between the actual and theoretical intervals separating any significant instant from the significant instant of the start element immediately preceding it, to the unit interval. The highest absolute value of degrees of individual distortion of the significant instants of a stop-start signal is reached within a specific time interval. 4 NET 21 CEPT NET*2L 92 m 232b414 001132b 909 m The degree of distortion of start-stop modulation, restitution or signal shall be expresse
