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).4%2#/%#4)/.G0G0/ further amended)The CCITT finds it necessary to define
2、separation points between various types of equipment, both in cablesystems and in radio-relay systems. These separation points are defined below and the CCIR has adopted the samedefinitions when preparing its Recommendation 380 1 (see also Recommendation G.423).1 Definition of telephony input and ou
3、tput points for the line link1)These are points (marked T and T in Figure 1/G.213) located in principle in a main repeater station 1)wherethe standard conditions given below are found at the output and input of a line link (comprising a cable system or radiolink). These standard conditions permit in
4、terconnection with other line links or with telephony equipment (including,where appropriate, direct through-connection filters as well as translating equipment).At such a point, T, on the receiving side, the following conditions apply:1) All the telephony groups (groups, supergroups, mastergroups,
5、etc.) are still assembled in the positions inthe frequency spectrum which they occupy on the line.2) All the line-regulating, monitoring or frequency-comparison pilots on the H.F. line are, or can be,suppressed (the recommended suppression attenuations are given in Recommendations G.242 andG.243), a
6、ccording to whether the station is at the end of a regulated-line section or not2).3) The relative level of all the telephony channels is independent of frequency, i.e. any de-emphasisnetwork is included in the line equipment.4) No special suppression of additional measuring frequencies is foreseen
7、(CCITT Recommendation G.423for cable systems, CCIR Recommendation 381 2 for radio-relay systems).A similar point T is defined for the sending side, where the following conditions are met:a) All the telephony groups (groups, supergroups, mastergroups, etc.) are still assembled in the positions inthe
8、frequency spectrum which they occupy on the line, except where use is made of direct through-connection filters provided as part of the line equipment.b) Follows from the situation at T according to condition 2) above.c) The relative level of all the telephony channels is independent of frequency, i
9、.e. any pre-emphasisnetwork is included in the line equipment.d) The additional measuring frequencies are transmitted._1)See definitions of Recommendation G.211.2)The interconnecting point between a radio-relay system and a long cable system is always the terminal of a regulated-line section(CCIR Re
10、commendation 381 2 and hence all these pilots are suppressed at that point. For the distinction between a “short“ anda “long“ cable system, see Recommendation G.423, 1.2).2 Fascicle III.2 - Rec. G.213A, A = radio-relay system (1) blocking of continuity pilots and, if necessary, of regulating pilotsB
11、, B = line link by means of radio-relay system (2) blocking, if necessary, of regulating pilots, and pilots that must not go beyond the line link.C, C = line link by means of cable systemD, D = boundary of the high-frequency line equipment (3) through-connection filter for regulating pilots, if nece
12、ssary; through-connection filter for telephone groups can, if necessary, be insertedR = radio-relay system outputR = radio-relay system input (4) blocking of unspecified pilots or supervisory signalsPoint P = provided for possible injection of (5) filter for blocking any unwanted frequency before re
13、gulating pilots injecting a pilot, ensuring with (2) the requisite protection against a pilot (or other) frequency coming from another regulated-line section (B or C, as the case may be)Between T and T = telephony terminating equipment and/ordirect through-connection equipmentDA = de-emphasis networ
14、kPA = pre-emphasis networkFIGURE 1/G.213General remarksNote 1 - Figure 1/G.213 gives an example only.Note 2 - If the station is within a regulated line section, provision must be made for the line-regulating pilots tobe passed through, either by means of the telephony direct through-connection filte
15、r itself or by means of a special pilotthrough-connection filter. To cater for this case, and for the case where the station forms a boundary between tworegulated line sections, a pilot input to, and output from, the line link, separate from the telephony input and outputpoints T and T, should be pr
16、ovided; these are points P and P in Figure 1/G.213.Note 3 - (Applicable to all systems, irrespective of the number of channels):When there is direct through-connection of part of the groups, supergroups, etc. with the aid of the directthrough-connection filters fitted into the line equipment for thi
17、s purpose, it is up to each Administration to fix therelative levels at the filter access points (which are different from the access point T and T mentioned above).Fascicle III.2 - Rec. G.213 3Note 4 - The levels at points T and T have been chosen so as to permit the insertion of the various direct
18、through-connecting and translating equipments which may be necessary in the main station. The difference in levelbetween points R and T and between points T and R allows for the cabling interconnecting these points, which may beat some distance from each other and, in favourable circumstances, for a
19、 blocking filter having only a small loss in thepassband.2 Definition of the points of international connection at baseband frequencies of a radio-relay systemThe points of international interconnection at baseband frequencies, called R and R, form the input and outputof a radio-relay system, confor
20、ming to CCITT Recommendation G.423 and CCIR Recommendation 380 1.At the output of the radio-relay system (point R), the following conditions are found in the baseband:1) All the telephony groups (groups, supergroups, mastergroups, etc.), and the pilots (line regulating,frequency comparison and monit
21、oring pilots) included in the baseband are assembled in the position inwhich they are transmitted, as defined in the CCITT and CCIR Recommendations mentioned above.2) All the continuity and switching pilots and other signals transmitted in a radio-relay system outside thetelephony band, inherent to
22、the radio equipment, are suppressed in accordance with CCIRRecommendation 381 2.3) Any radio-relay protection switching shall be performed as part of the radio-relay system. With diversityreception, the combined output of the receivers used corresponds to point R.4) Any de-emphasis networks are part
23、 of the radio equipment, so that the relative levels of the telephonechannels are independent of frequency, within the limits of the tolerances stated in Note 7 of CCIRRecommendation 380 1 ( 2 dB relative to the nominal value).A similar point R is defined for the baseband input of a radio-relay syst
24、em, where similar conditions are to bemet.3 Relative levels recommended by the CCITT at the telephony output and input (Points T and T in Figure 1/G.213)At the interconnection points T and T for telephony defined in 1 above, Table 1/G.213 shows the relativelevels which are recommended for cable syst
25、ems, each of which is defined by the maximum number of telephonechannels that it can provide. (Similar levels are recommended by the CCITT and the CCIR for radio systems ofcorresponding capacity - see Recommendation G.423 and CCIR Recommendation 380 1.)The cable systems to which this Recommendation
26、applies are modern systems with transistor equipment andto new versions of other systems previously standardized by the CCITT.The recommended levels at T and T make it possible to insert all the translating or direct through connectingequipment which may be necessary; this does not define the relati
27、ve levels in translating and direct through-connectingequipment, which depend on other considerations.4 Fascicle III.2 - Rec. G.213TABLE 1/G.213Recommended relative levels for interconnection of various cable systemsRelative power level per channelat a main stationMaximum numberof telephone channels
28、Impedance(ohms)Receiving(Point T)(dBr)Sending(Point T)(dBr)Remarks24, 36, 48 150 (bal.) -23 -3660120150 (bal.)or 75 (unbal.)-23 -36300 75 (unbal.) -23 -36600, 960,1200126075 (unbal.)-23or-33-36or-33See note2700 75 (unbal.) -33 -33 See alsoRecommendations G.33and J.77 33600 75 (unbal.) -33 -33 See al
29、soRecommendations G.334and J.77 410 800 75 (unbal.) -33 -33Note - For 600, 960, 1200 and 1260 channel systems Administrations have the choice between the alternative pairs of level shownfor points T and T which apply in the following circumstances:1) - 23 dBr at point T,- 36 dBr at point T,where con
30、formity with well-established equipment using similar levels is necessary;2) - 33 dBr at each of the points T and T,in other cases, for example, to new stations wholly equipped with transistor equipments.References1 CCIR Recommendation Interconnection at baseband frequencies of radio-relay systems f
31、or telephony usingfrequency-division multiplex, Vol. IX, Rec. 380, Dubrovnik, 1986.2 CCIR Recommendation Conditions relating to line regulating and other pilots and to limits for the residues ofsignals outside the baseband in the interconnection of radio-relay and line systems for telephony, Vol. IX,Rec. 381, Dubrovnik, 1986.3 CCITT Recommendation Use of a 12-MHz system for the simultaneous transmission of telephony andtelevision, Vol. III, Rec. J.73.4 CCITT Recommendation Characteristics of the television signals transmitted over 18-MHz and 60-MHzsystems, Vol. III, Rec. J.77.
