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)#3G0G0 amended at Geneva, 1976)The CCITT,considering(a) that taking into account Recommendations T.50 1 and X.4 2, this Recom
2、mendation applies to thecharacteristics, from the transmission point of view, at the interchange point between data circuit-terminatingequipment and start-stop data terminal equipment using International Alphabet No. 5. Except where otherwisespecified, data terminal equipment in this Recommendation
3、should be understood to mean start-stop apparatus in thewide sense of the term, as defined in 3 i.e. it includes reperforators, service signals sent by switching equipment,signals from answer-back units, automatic transmitters, etc.;(b) that, bearing in mind the definition of User Class of Service 1
4、 in Recommendation X.1 4, where it isspecified that a signalling rate of 300 bit/s, a structure of 11 units per character and start-stop operation shall be usedfor address selection, call progress signals and data transfer;(c) that the characteristics laid down below are those that should be evident
5、 in service conditions at theinterchange point between data terminal equipment and data circuit-terminating equipment,unanimously declares the view:1 Equipment characteristics1.1 The nominal modulation rate should be:a) 300 bauds; orb) 200 bauds.1.2 The difference between the real mean modulation ra
6、te of the signals when in service and the nominal rateshould not exceed 0.1%.1.3 The nominal duration of the transmitting cycle should be at least 11 units, the stop element lasting for at least 2units.1.4 The receiver must be able to translate correctly in service the signals coming from a source t
7、hat appears to havea nominal transmit cycle equal to or greater than 10 units.2 Transmitter characteristics2.1 The degree of gross start-stop distortion of transmitted signals, measured at the interchange point between dataterminal equipment and data circuit-terminating equipment, must not exceed 5%
8、. This value applies to all workingconditions of the equipment under consideration encountered during normal service, whether the signals aretransmitted separately or whether they succeed one another at the maximum rate compatible with the modulation rate.2.2 It is recommended that the measurement s
9、hould be made with a start-stop distortion measuring set for twoconsecutive periods, each of about 15 seconds (corresponding to about 1200 transitions at 200 bauds or1800 transitions at 300 bauds). Early distortion should be observed during one period and late distortion during theother.3 Receiver c
10、haracteristics3.1 The effective net margin measured at the interchange point between data terminal equipment and data circuit-terminating equipment should not be less than 40% for signals corresponding to a nominal transmit cycle equal to orgreater than 10 units.2 Fascicle VII.1 - Rec. S.313.2 It is
11、 recommended that the measurement should be made under the following conditions, in service: 11-unit cycle for the signals transmitted by the measuring apparatus; use of one of the signal trains specified in Recommendation S.33; first test with an identical distortion rate on all transitions of the
12、signal train, obtained by lengthening thestart element; a second test with the same rate of identical distortion on all the transitions of the signal train, but obtainedin this case by shortening the start element; reading the margin when one error per test sentence is obtained (the margin is the le
13、sser of the two valuesof the degree of distortion obtained from the two measurements); the length of the start element or of any data element must in no case be less than 50% of the theoreticalunit element.Note It will be up to Administrations using some other measuring method to work out for their
14、own usefigures to give equivalent results to those which would have been obtained by the recommended method.References1 CCITT Recommendation International Alphabet No. 5, Rec. T.50.2 CCITT Recommendation General structure of signals of International Alphabet No. 5 code for datatransmission over public data networks, Rec. X.4.3 CCITT Definitions: Start-stop apparatus, Vol. X, Fascicle X.1 (Terms and Definitions).4 CCITT Recommendation International user classes of service in public data networks, Rec. X.1.
