1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0#/-/.G0G04/G0G0!,!.!,/5%G0G0#!22)%2G1342!.3-)33)/.G0G03934%-3(90/4(%4)#!,G0G02%- three pairs of group modulators, each pair including t
2、ranslation from the basic group to the basic supergroupand vice versa;- six pairs of supergroup modulators, each pair including translation from the basic supergroup to a higher ordermodem and vice versa;- twelve pairs of higher order modulators, each pair providing the necessary modulation stages t
3、o and from theline frequency.Figure 1/G.215 shows the principle of the hypothetical reference circuit.This hypothetical reference circuit consists of 12 homogeneous sections of equal length (seeRecommendation G.212). Two homogeneous sections may be connected in tandem without translating equipment a
4、t thejunction if the transmission system has suitable line regulating capability and does not introduce undesirable noise andcrosstalk into any telephone channel.Note - Each homogenous section has a length of approximately 420 km.FIGURE 1/G.215Diagram of a hypothetical reference circuit of 5000 km2
5、Design objectives for circuit noise1)The same noise values as for the 2500 km HRC apply (Recommendation G.222, 1).Note 1 - This design objective is in line with Recommendation G.123, “Circuit noise in national networks“,which in 2.1.1 recommends that the line noise in channels used to provide very l
6、ong-distance circuits (over 2500 km)should not exceed 2 pW0p/km._1)Although the noise objective for the 5000 km HRC is in principle agreed, some countries will not be soon in the position to installequipment of the desired performance, and will continue to use existing systems on the very long natio
7、nal and international circuits,according to established planning and design practices.2 Fascicle III.2 - Rec. G.215Note 2 - Designers are expected to fit their noise distribution curves fall below all 1.1 and 1.2 ofRecommendation G.222.Note 3 - In applying these design objectives, 2.4 through 2.7 of
8、 Recommendation G.222 should be taken intoaccount.The subdivision of the total noise between the various sources of noise is left entirely to the designer of thesystem, within the limits of 2500 pWOp for the terminal equipment and 7500 pWOp for the line. This allocation isintended to permit the use
9、of modulating equipment meeting the maximum values recommended in Table 1/G.222 ofRecommendation G.222 as indicated in Table 1/G.215.TABLE 1/G.215Equipment Maximum noise contributed bythe send and receive side togetherNumber ofmodulator pairsTotal noiseChannel modulatorsGroup modulatorsSupergroup modulatorsHigher order modulatorsThrough connecting equipment200 pW0p80 pW0p60 pW0p120 pW0p13612200pW0p240 pW0p360 pW0p1440 pW0p260 pW0pTotal: 2500 pW0pNote - This Table assumes two stages of modulation in the higher modulator.
