1、INTERNATIONAL STANDARD ISOIIEC 7480 Second edition 1991-12-15 Information technology - Telecommunications and information exchange between systems - Start-stop transmission signal quality at DTElDCE interfaces Technologies de /information - T4l .- X.20 together with V.10 and/or V.ll electrical chara
2、cteristics. The signal quality requirement is limited to start- stop transmission at the interface with asynchro- nous DCEs. or with synchronous DCEs operating in asynchronous mode in accordance with CClTT Rec- ommendations V.14 or V.42. Signal quality pertaining to DTEs working in a synchronous mod
3、e of operation is not part of this international Standard. This international Standard is also applicable when the inlerface as specified in the above CCITT Rec- ommendations is provided at the ISDN Reference point R as defined in CClTT Recommendation 1.411 and as specified in CCITT Recommendations
4、V.110. V.120 and X.30. 1.2 The signal quality characteristics apply re- gardless of whether or not multiplexing equipment is included. They do not apply where there is inter- mediate equipment and no signal regeneration is provided between interconnected sections. 1.3 This International Standard doe
5、s not describe the signal quality of the DCE or the line associated with it. Neither does it describe any requirement for an acceptable bit error rate. 1.4 This International Standard does not specify the speed characteristics. The nominal value of the modulation rate and the character interval are
6、ap- plication dependent. 2 Normative references The following standards contain provisions which, through reference in this text. constitute provisions of this international Standard. At fhe time of publi- cation, the editions indicated were valid. All stan- dards are subject to revision, and patlie
7、s to agreements based on this International Standard are encouraged to investigate the possibility of ap- plying the most recent editions of the standards in- dicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. CCITT Recommendation 1.411:1988, /SDN cl
8、ser- rJetwork interfaces - Reference configurations. CCITT Recommendation V.10 (= X.26):1988. Elec- trical characterislics for unbalanced double-current inferchange circuits for general else wifh infegrafed circuii eqr/ipmenl in fhe field of data com1?J11Ji- cafions. CCITT Recommendation V.ll (= X.2
9、7).1988 Elec- trical characlerisfics for balanced double-current inter-change circuits for genera/ me wifh integraled circuif equipmenl in tllf? field of data CODtmnni- cations. CClTT Recommendation V.14:1988. Tranxmi.ssiort of s/art-stop chracfers over synchronocs bearer chn- nels. 1 ISOllEC 748&l
10、991 (E) CCITT Recommendation V.21:1988, 300 Oils per sec- ond duplex modem standardized for use in the gen- era/ switched telephone network. CCITT Recommendation V.22:1988, 1200 hiIs per second duplex modem standardized for use tn the genera/ switched telephone nefwork and on point- to-point 2-wire
11、leased telephone-type circuits. CCITT Recommendation V.22 bis:1988, 2400 hits per second duplex modem using fhe frequency division technique standardized for use on fhe general switched telephone network and on poinf-lo-point 2-wire /eased telephone-type circuits. CCITT Recommendation V.23:1988, 600
12、/I 200 baud modem standardized for else in the general switched telephone network. CCITT Recommendation V.24:1988, List of definitions for interchange circuits between data terminal equipment and data circuit-ferminating equipment. CCITT Recommendation V.26 ter:1988, 2400 bits per second duplex mode
13、m using the echo cancellation technique standardized for use on the genera/ switched telephone network and on point-fo-point 2-wire /eased telephone-type circuits. CCITT Recommendation V.28:1988, Electrical characteristics for unbalanced double-current inier- change circuits. CCITT Recommendation V.
14、32:1988, A family of 2-wire, duplex modems operating at data signalling rates of up to 9600 bit/s for use on the general switched telephone network and OIJ leased telephone-type circuits. CCITT Recommendation V.32 bis:1990. A duplex modem operating at data signalling rates of up to 14400 &it/s for u
15、se on the general switched iele- phone network and on leased point-to-point 2-wire telephone-type circuits. CCITT Recommendation V.42:1988, Error-correcting procedures for DCEs using asynchronous-fo- synchronous conversion. CCITT Recommendation V.l10:1988, Support of data terminal equipments (DTEs)
16、with V-series type inter- faces by an integrated services digital network (ISDN). CCITT Recommendation V.l20:1988, Support by an ISDN of data terminal equipment with V-series type interfaces with provision for sfatisfical multiplexing. circuit-terminating equipment (DCE) for start-stop transmission
17、services on public data networks. CCITT Recommendation X.20 bis:lSAR, Use on public data networks of data terminal equipment (DTE) which is designed for inferfacing to aSynChrOfmJS duplex V-series modems. CCITT Recommendation X.24:1988, List of definitions for interchange circuifs between data termi
18、nal equipment (DTE) and data circuit-ferminating equip-. ment (DCE) on public data networks. CCITT Recommendation X.30:1988, Support of X.21, X.21 bis and X.20 bis based data terminal equip- menfs (DTEs) by an inlegrafed services digital nel- work (ISDN). 3 Definitions For the purposes of this Inter
19、national Standard, fhe following definitions apply. 3.1 electronic timing: An implementalion in which a signal serves to determine the duration of signal elements and to achieve synchronkation within a transmission system, and is derived from an elec-. tronic circuit. 3.2 mechanlcal timing: An imple
20、mentation in which a signal serves to determine the duration of signal elements and to achieve synchronization within a transmission system, and is generally derived from the angular velocity of an electric mofor (power fre- quency used as timing source is also included in this category). 3.3 start-
21、stop system: Data transmission system in which each signal representing a character is pre- ceded by a start signal which serves to prepare fhe receiving device for the reception of a character signal and registration of a character, and is fol- lowed by a stop signal which serves to prepare Ihe rec
22、eiving device for the reception of a subsequenl start signal. 3.4 start-stop transmission: Asynchronous trans. mission such that each group of signals represent. ing a character is preceded by a stat-1 signal and is followed by a stop signal. 3.5 continuous start-stop operation: Method of op- eratio
23、n in start-stop transmission in which the signals represeniing a series of characters follow one another contiguously. CCITT Recommendation X.20:1988, Interface be- fween data terminal equipment (DTE) and data 3.6 signal element: Each of the parts constituting a telegraph or data signal and distingu
24、ished from the others by its nature, magnitude, drlration and rela- tive position (or by one or some of these features only). ISOllEC 7480:1991(E) 3.7 unit interval: In a system using an equal length code, or in a System using an isochronous modu- lation. the interval of time such that the theoretic
25、al durations of fhe significant intervals of a telegraph modulation (or restitution) are whole multiples of this interval. 4 Distinction can be made between the degree of late (or positive) distortion and the degree of early (or negative) distortion. 5 The theoretical intervals are related to the me
26、an ac- tual incoming modulation rate and not necessarily to the nominal modulation rate. 3.8 modulation rate: Reciprocal of the unit interval measured in seconds. This rate is expressed in baud. 3.14 degree of gross start-stop distortion: Degree of distortion determined when the unit interval and th
27、e theoretical intervals assumed are exactly those appropriate to the nominal modulation rate. 3.9 character interval: The duration of a character expressed as the total number of unit intervals (in- cluding information and parity check) plus the stat-l and stop signals. 3.10 start signal: In start-s
28、top transmission, a sig- nal at the beginning of a character lhat prepares the receiving device for the reception of the code el- ements. NOTE 1 A start signal is limited to one signal element generally having the duration of a unit interval. 3.11 start transition: In a character transmitted in a st
29、art-stop system, the mark-to-space transition at the beginning of the slat-t signal. 3.12 stop signal: In start-stop transmission. a signal at the end of a character that prepares the receiving device for the reception of a subsequent character. NOTE 2 A stop signal is usually limited to one signal
30、elernent having any duration equal to or greater than a specified minimum value. 3.13 degree of start-stop distortion (1) Ratio to the unit interval of the maximum measured difference, irrespective of sign, between the actual and theoretical intervals separating any significant instant of modulalion
31、 (or of restitution) from the significant instant of the start element in- mediately preceding it. (2) The highest absolute value of individual dis- tortion affecting the significant instants of a start- stop modulation. NOTE 6 The result of the measurement should be com- pleted by an indication of
32、the period, usually limited, of the observation. For a prolonged modulation (or restitution) it will be ap- propriate to consider the probability that an assigned value of the degree of distortion will be exceeded. In accordance with the CCITT definition of the theoretical duration of a significant
33、interval, in practical measure- ments the unit interval and the theoretical intervals as- sumed are those appropriate to the actual mean rate of modulation (or of restitution). 3.15 degree of synchronous start-stop distortion: Degree of distortion determined when Ihe unit in- terval and the theoreti
34、cal intervals assumed are those appropriate to the actual mean rate of modu- lation (or of restitution). NOTES 7 See note 6. 8 The degree of distortion is the time displacement of the transitions between signal states from their ideal in- stants. 3.16 margin: Maximum degree of distortion com- patibl
35、e with a correct translation when the signals are presented to a receiver under the most un- favourahle conditions where the composition of the signals and of the distortion is concerned. The maximum degree of distortion which results in incorrect translation applies without reference to Ihe form of
36、 distortion affecting the signals. In other words, it is the maximum value of fhe most un- favourahle distorlion causing incorrect translation which determines the value of ihe margin The degree of distortion of a start-stop modulaiion (or restitution) is usllally expressed as a percentage. 3.16.1 s
37、ynchronous margin: Margin represented by the degree of distortion for the margin indicated in NOTES 3.16 when ftie mean unit interval of?he modlJlation applied to the apparatus is equal to that which would 3 The result of the measurement should be completed result from a transmission from the apparatus under by an indication of the period, usually limited, of the ob- examination, assuming it to include a transmitter as servation. well as a receiver.
