ITU-T R 58-1988 STANDARD LIMITS OF TRANSMISSION QUALITY FOR THE GENTEX AND TELEX NETWORKS《国际公用电报网和用户电报网的传输质量的标准限值》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.34!.$!2$G0G0,)-)43G0G0/ amended at Geneva, 1964)The CCITT,considering(a) that to permit the sharing of responsibility for the maintenance of a high-standard of transmission be

2、tweencountries participating in the establishment of switched connections, it is necessary to specify limiting values ofdistortion at the international terminal exchanges;(b) that on the other hand, to enable national switched networks to be interconnected, it is necessary to have adistribution plan

3、 of the telegraph distortion between national networks and the international junction circuitsconnecting up the international switching centres (international terminal switching centres);(c) that Figure 1/R.58 shows the points of entry and exit of the national network and the ends of theinternationa

4、l junction circuit;(d) that it is difficult to lay down standards applicable both to small and to large national networks. However, ithas been possible to fix limit values for large countries and they could apply to the great majority of telex subscriberstations or gentex stations taking part in the

5、 international service,unanimously declares the following view1 The following standards of transmission quality are observed for the interconnection of 50-baud nationalnetworks set up by means of telegraph channels and start-stop equipment in accordance with CCITT Recommendations(national gentex or

6、telex networks):2 Fascicle VII.1 - Rec. R.58a) Degree of gross start-stop distortion in service (i.e. including the effect of distortion due to the sendingequipment and the exchanges) at the point of exit of the national network: not more than 22%.Note When a terminal country of an international con

7、nection possesses an intercontinental transit centre,that transit centre is considered as forming part of the national network.b) Degree of inherent start-stop distortion of the international junction circuit: not more than 13%.Note 1 In establishing the 13% limit for the degree of start-stop distor

8、tion in the international junctioncircuit, account has been taken of the fact that, in a world telex or gentex chain, the junction circuit mightquite often consist of two VFT channels in tandem. If the international junction circuit is established on asingle channel, the 8% limit mentioned in Recomm

9、endation R.57 is applicable to that circuit.Note 2 No limit for distortion on the entry of the national network at the receiving end has been indicatedin Recommendation R.58. The values mentioned in 1 a) and 1 b) above are adequate for planningpurposes.2 Although the degrees of distortion to be inse

10、rted in the Recommendations relative to the planning of networksare normally conventional degrees of distortion, the maximum values mentioned under 1 above correspond to theresults that would be provided by the routine measurements carried out in accordance with Recommendation R.5.3 These limit valu

11、es are applicable to large countries that are directly connected without switching in a transitcountry. The stations taking part in the international service that cannot satisfy condition 1 a) above will have to bespecially equipped, for example with distortion correctors.4 Small countries (defined

12、as countries in which all stations can be reached with not more than one long-distancetelegraph circuit in the national network) will have to try to obtain values less than the maximum of 22% for themeasurements corresponding to 1 a) above.5 The standard limits mentioned under 1 above can also apply to private switched networks.