1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 3 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(9!,0(!“%4)#!,G0G04%,%2!0(G0G04%2-).!,%15)0-%.442!.3-)33)/.G0G0#(!2!#4%2)34)#3/ amended at Geneva, 1976and at Melbourne, 1988)The CCITT,considering(a) that this Recommendation defines the characteristi
2、cs from a transmission point of view of start-stopterminal equipment working at rates up to 300 bauds;(b) that this Recommendation applies except where otherwise specified to start-stop apparatus in general:i.e. it applies to teleprinters, data terminal equipment, multiplexer tributaries, etc.;(c) t
3、hat user classes of service 1 and 2 in Recommendation X.1 1 should be taken into account;(d) that some equipment (using telegraph modems in accordance with Recommendation R.20 2, or singlecurrent working, for instance) cannot be separated during operation from its supply and repeater devices; hence
4、themeasurements under operating conditions must apply to the local end with its termination 3;(e) that the characteristics laid down below are those that should be evident in service conditions on local endswith their terminations that are likely to be connected to the international network. It shou
5、ld be noted however that inthe case of d.c. transmission (including DCEs at the point of interconnection between the DCE and the DTE) theyapply to such local ends with their terminations only if the influence of the line in the local end produces negligibledistortion. In the case of equipment incorp
6、orating telegraph modems the modem-to-modem distorition as given inRecommendation R.20 2 must be included.unanimously declares the view:1 General characteristics1.1 The nominal modulation rate should be chosen from Table 1/S.3.1.2 The difference between the real mean modulating rate of signals when
7、in service and the nominal modulationrate should not exceed 0.1%.Note There is early equipment in service at rates up to 100 bauds with difference of 0.75%.1.3 The nominal duration of the transmitting cycle should be chosen from Table 1/S.3. For 50 and 75-baudworking, the stop element should be at l
8、east 1.4 units (preferably 1.5). For higher rates, the stop element should not beless than its nominal length.1.4 The receiver must be able to translate correctly in service the signals coming from a source that appears to givestop elements equal to or greater than1.0 unit at 50 or 75 bauds1.2 unit
9、at 100 or 200 bauds (when using nominally 7.5 unit characters)1.0 unit at 110 baud1.0 unit at 200 and 300 bauds (when using nominally 11 unit characters)0.8 unit at 100, 150, 200 or 300 bauds (when using nominally 10 unit characters)0.8 unit at 134.5 bauds (when using nominally 9 unit characters)2 F
10、ascicle VII.1 - Rec. S.3TABLE 1/S.3Modulation rateCharacter structure(baud)Character length(units)Stop element(units)5075100100110134.51502002002003003007.57.57.510119107.5101110111.51.51.512111.512122 Transmitter characteristics2.1 Transmit distortion2.1.1 The transmit distortion with a d.c. interf
11、ace should not exceed:a) 5% for equipment working at rates up to 100 bauds.Note A figure of 3% is recommended for new equipment.b) 3% for equipment working at rates between 110 and 300 bauds.2.1.2 The transmit distortion with a scvf interface, measured at the in-station modem, should not exceed:Rate
12、 (baud) 50 75 100 110 134.5 150 200 300Distortion (%) 10* 11* 12* 10 11 12 14 18Note 1 This is derived from the sum of the assumed transmit distortion at a d.c. interface and the modem-to-modem distortion given in Recommendation R.20. (*New equipment, having an assumed distortion of 3% at the d.c.in
13、terface will have a correspondingly lower figure for the resultant transmit distortion from the in-station modem.)Note 2 A higher modem-to-modem (R.20) distortion applies in the case of frequency error, so that acorrespondingly higher resultant transmit distortion from the in-station modem will be o
14、btained.2.2 In all cases “distortion” should be taken as gross start-stop distortion 4, using the appropriate alphabet.It is recommended that the measurement should be made with a start-stop distortion measuring set, for a periodin accordance with Recommendation R.5 5.Fascicle VII.1 - Rec. S.3 33 Re
15、ceiver characteristics3.1 Receive Margin3.1.1 The receive margin with a d.c. interface should not be less than 40%.3.1.2 The receive margin with a scvf interface, as measured at the in-station modem, should not be less than:Rate (baud) 50 75 100 110 134.5 150 200 300Marging (%) 35 34 33 33 32 31 29
16、25Note 1 This is derived from the assumed terminal margin at a d.c. interface of 40% and the modem-to-modemdistortion as given in Recommendation R.20.Note 2 A higher modem-to-modem (R.20) distortion applies in the case of frequency error so that acorrespondingly lower resultant marging at the in-sta
17、tion modem will be obtained.3.2 In all cases “marging” should be taken as effective net margin 6, using the appropriate alphabet.It is recommended that the measurement should be made under the following conditions, in service: character structure appropriate to the equipment under test chosen from T
18、able 1/S.3; use of one of the standardized texts in Recommendation R.52 7; test with the appropriate degree of start element distortion, long and short; reading the margin when one error per test sentence is obtained (the marging is the lesser of two values ofthe degree of distortion obtained from t
19、he two measurements).Note It will be up to Administrations using some other measuring method to work out for their own usefigures to give equivalent results to those which would have been obtained by the recommended method.References1 CCITT Recommendation International user classes of service in pub
20、lic data networks and integrated servicesdigital networks (ISDNs), Rec. X.1.2 CCITT Recommendation Telegraph modem for subscriber lines, Rec. R.20.3 CCITT Recommendation Definition of essential technical terms relating to apparatus for alphabetictelegraphy, Rec. S.140, Definition, No. 26 local end (
21、with its termination).4 CCITT Recommendation Definitions of essential technical terms in the field of telegraph transmission,Rec. R.140, Definition, No. 33.09, degree of gross start-stop distortion.5 CCITT Recommendation Observation conditions recommended for routine distortion measurements onintern
22、ational telegraph circuits, Rec. R.5.6 CCITT Recommendation Definitions of essential technical terms relating to apparatus for alphabetictelegraphy, Rec. S.140, Definitions, Nos. 59 and 60, margin and effective margin (of a given apparatus).7 CCITT Recommendation Standardization of international texts for the measurement of the margin of start-stopequipment, Rec. R.52.
