ISO/IEC INTERNATIONAL STANDARD 7480 Second edition 1991-12-15 Information technology --- Telecommunications and information exchange between systems Start-stop transmission signal quality at DTE/DCE interfaces Technologies de I'information --. Telecommunications et échange d'information entre systemes --- Qualite des signaux de transmission arythmique aux interfaces ETTD/ETCD Reference number ISO/IEC 7480:1991(E) Copyright International Organization for Standardization cing permitted without license from IHS Not for Resale ISO/1EC 7480:1991(E) Foreword Iso (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the specialized system for worldwide standardization. National bodies that are members of Iso or iEC participate in the development of International Standards through technical committees established by the respective organization to dea! with particular fields of technical activity. IsO and 1Ec technicai com- mittees collaborate in fields of mutual interest. Other international or- ganizations, governmental and non-governmental, in liaison with so and IEC, also take part in the work. In the field of information technology. Iso and IEc have established a joint technical committee, iSO/IEC JTC 1. Draft International Standards jes for voting. Publication as an International Standard requires ap. proval by at least 75 % of the national bodies casting a vole. International Standard ISO/IEC 7480 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology. This second edition cancels and replaces the t edition (Iso first 7480:1984), of which it constitutes a technical revision. Annex A of this International Standard is for information only. ISO/IEC 1991 or by any means, olectronlc or mechanlcal, Includlng photocopying and mlcroflm, without permission in writing from the publisher. ISO/IEC Copyright Otfice · Case Postale 56 · CH-1211 Genove 20 · Switzerland Printed in Switzerland Not for Resale from IHS ISO/IEC 7480:1991(E) Introduction The intent of this International Standard is to complement the electrical characteristics specified in CCiTT V-series recommendations, and to provide a measurement for the transmission signal quality charac- teristics not covered in those documents The signal quality requirement that start-stop transmission equipment should meet is in part dependent on the application and in part de- pendent on the mechanism for timing derivation used by the equipment. For early start-stop transmission equipment. timing was derived or controlled from a mechanical source but nowadays an electronic source is commonplace. An additional factor is that, whereas most start-stop transmissicn car- ries the timing informalion inherentiy within the signalling between the ment may interface to a converter which encodes the information within a synchronous transmission system in which case, the required signal quality at the interface to the converter may need to be more tightly controlled To cover both types of equipment in both types of application, the signai quality specification in this International Standard is given separalely for four performance categories, two of which (P1 and P2) are intended for DTEs using mechanical timingt and two for DTEs using electronic tim- ing. By having two mechanical categories, early start-stop transmission equipment with very limited signal quality capability is accomnodated (Category P1). For the two electronic categories. the more stringent (Category Il) is for equipment to be connected to synchronous DCEs operating asynchronous mode in accordance with CCITT Rec- in ommendation V.14. For each of the four categories defined for the transmitting elements of DTEs (1, 1l. P1 and P2), four complernentary categories are defined for the receiving elements of DTEs (A. B. PA, PB) Notwithstanding the ohvious pairings implied by the complementary categories, the intention is that any receiving equipment may operate