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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 Copyright Inte
10、rnational Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:21:05 MDTNo reproduction or networking permitted without license from IHS -,-,- ISOllEC 748 Generator under test Figure 5 - Test arrangement
11、for V.ll generators I f Equivalent clrcuft of i standard test load ! hcludlng test equipment) I I I Test slgnal generator 1 Y e i s St 3 f P Load under test Figure 6 - Test arrangement for V.11 loads 9 Copyright International Organization for Standardization Provided by IHS under license with ISO Li
12、censee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:21:05 MDTNo reproduction or networking permitted without license from IHS -,-,- ISOllEC 7480:1991 (E) Signal quality at asynchronous transmission interfaces - Mathematical relationship Annex A (informative) between signal qua
13、lity parameters In order to assist users in interpreting the various measurements indicated in this International Stan- dard, attention is drawn to certain mathematical re- lationships that exist. Several of the parameters listed in table 1 can be derived from the others as follows. A.1 For transmit
14、ting equipment, the two funda- mental parameters - synchronous start-stop distortion, N, and - modulation rate accuracy, M, can be used to derive gross start-stop distortion, P, minimum signal element, Q. and character interval requirements. In electronically timed systems operating in contin- uous
15、start-stop mode, the reductions in character interval, minimum, T, and average, R. are related to the cumulative clock error due to modulation rate accuracy and are independent of the number of characters, S, over which it is averaged. A.l.l Gross start-stop distortion, P, is given by P=(N+nM) where
16、 N is the synchronous start-stop distortion; M is the modulation rate accuracy; n is the number of elements in the charac- ter. A.1.2 Minimum signal element, Q, is given by Q = (100 - 2N) % of unit interval where N is the synchronous start-stop distortion A.2 For receiving equipment, the fundamental
17、 parameter synchronous margin, I/. can be used lo derive the practical margin. 11, which is given by Ihe formula V = II - nM where IJ is the synchronous margin; M is the modulation rate accuracy (of the transmitter): n is the number of elements in the charac. ter. 10 Copyright International Organiza
18、tion for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:21:05 MDTNo reproduction or networking permitted without license from IHS -,-,- ISOllEC 7480:1991(E) UDC 681.3:621.391.8 Descriptors: data processing, informat
19、ion interchange, data transmission. start-stop transmission, data terminal equipment, data circuit-terminations, interfaces, computer Interfaces. Price based on 10 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 21:21:05 MDTNo reproduction or networking permitted without license from IHS -,-,-