1、INTERNATIONAL TELECOMMUNICATION UNIONITU-TG.120TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(12/98)SERIES G: TRANSMISSION SYSTEMS AND MEDIA,DIGITAL SYSTEMS AND NETWORKSInternational telephone connections and circuits Generalcharacteristics of national systems forming part ofinternational connections
2、Transmission characteristics of nationalnetworksITU-T Recommendation G.120(Previously CCITT Recommendation)ITU-T G-SERIES RECOMMENDATIONSTRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKSFor further details, please refer to ITU-T List of Recommendations.INTERNATIONAL TELEPHONE CONNECTIONS
3、AND CIRCUITS G.100G.199General definitions G.100G.109General Recommendations on the transmission quality for an entire internationaltelephone connectionG.110G.119General characteristics of national systems forming part of internationalconnectionsG.120G.129General characteristics of the 4-wire chain
4、formed by the international circuits andnational extension circuitsG.130G.139General characteristics of the 4-wire chain of international circuits; international transit G.140G.149General characteristics of international telephone circuits and national extensioncircuitsG.150G.159Apparatus associated
5、 with long-distance telephone circuits G.160G.169Transmission plan aspects of special circuits and connections using the internationaltelephone connection networkG.170G.179Protection and restoration of transmission systems G.180G.189Software tools for transmission systems G.190G.199INTERNATIONAL ANA
6、LOGUE CARRIER SYSTEMGENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMSG.200G.299INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONESYSTEMS ON METALLIC LINESG.300G.399GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONESYSTEMS ON RADIO-RELAY OR SATELLITE LINKS
7、 AND INTERCONNECTIONWITH METALLIC LINESG.400G.449COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499TESTING EQUIPMENTSTRANSMISSION MEDIA CHARACTERISTICSDIGITAL TRANSMISSION SYSTEMSTERMINAL EQUIPMENTS G.700G.799DIGITAL NETWORKS G.800G.899DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999Rec
8、ommendation G.120 (12/98) iITU-T RECOMMENDATION G.120TRANSMISSION CHARACTERISTICS OF NATIONAL NETWORKSSummaryThis Recommendation was revised to consolidate all the characteristics of national networks into oneRecommendation. Additionally, it tightened the requirement for noise induced by power lines
9、 and itnow makes provision for the addition of Asynchronous Transfer Mode (ATM) technology to beintegrated into the PSTN. This Recommendation provides guidance regarding the performance ofnational networks.SourceITU-T Recommendation G.120 was revised by ITU-T Study Group 12 (1997-2000) and wasapprov
10、ed under the WTSC Resolution No. 1 procedure on the 3rdof December 1998.Recommendation G.120 (12/98)iiFOREWORDITU (International Telecommunication Union) is the United Nations Specialized Agency in the field oftelecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanen
11、t organ ofthe ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuingRecommendations on them with a view to standardizing telecommunications on a worldwide basis.The World Telecommunication Standardization Conference (WTSC), which meets every four years,estab
12、lishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendationson these topics.The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down inWTSC Resolution No. 1.In some areas of information technology which fall within ITU-T
13、s purview, the necessary standards areprepared on a collaborative basis with ISO and IEC.NOTEIn this Recommendation the term recognized operating agency (ROA) includes any individual, company,corporation or governmental organization that operates a public correspondence service. The termsAdministrat
14、ion, ROA and public correspondence are defined in the Constitution of the ITU (Geneva, 1992).INTELLECTUAL PROPERTY RIGHTSThe ITU draws attention to the possibility that the practice or implementation of this Recommendation mayinvolve the use of a claimed Intellectual Property Right. The ITU takes no
15、 position concerning the evidence,validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or othersoutside of the Recommendation development process.As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property,
16、protected by patents, which may be required to implement this Recommendation. However, implementors arecautioned that this may not represent the latest information and are therefore strongly urged to consult theTSB patent database. ITU 1999All rights reserved. No part of this publication may be repr
17、oduced or utilized in any form or by any means,electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.Recommendation G.120 (12/98) iiiCONTENTSPage1 Scope 12 References 13 Application of ITU-T Recommendations on telephone performance to nationalnetw
18、orks . 24 National transmission plan . 35 Attenuation distortion. 36 Circuit noise . 56.1 Noise induced by power lines. 56.2 Noise contributed by transmission systems 56.2.1 Analogue systems 56.2.2 Use of companders to control noise on analogue systems 66.2.3 Digital system 66.2.4 Mixed circuits . 6
19、6.3 Noise in a national 4-wire automatic exchange 66.3.1 Analogue 4-wire automatic exchanges . 66.3.2 Digital 4-wire automatic exchanges 66.4 Noise allocation for a national system 66.4.1 General planning assumptions 66.4.2 Noise allocations for planning digital systems 76.4.3 Noise allocations for
20、planning incremental analogue transport systems 77 Error on the reconstituted frequency 78 Group-delay distortion 79 Linear crosstalk of circuits . 810 Non-linear distortion of analogue transmission systems 811 Variations of transmission loss with time 8Annex A Noise allocation for a national system
21、 8A.5 Large countries. 10Recommendation G.120 (12/98) 1Recommendation G.120TRANSMISSION CHARACTERISTICS OF NATIONAL NETWORKS(revised in 1998)1 ScopeThis Recommendation provides transmission performance guidance for national networks that formpart of international connections to provide international
22、 telephony services.2 ReferencesThe following ITU-T Recommendations and other references contain provisions which, throughreference in this text, constitute provisions of this Recommendation. At the time of publication, theeditions indicated were valid. All Recommendations and other references are s
23、ubject to revision; allusers of this Recommendation are therefore encouraged to investigate the possibility of applying themost recent edition of the Recommendations and other references listed below. A list of the currentlyvalid ITU-T Recommendations is regularly published.1 Transmission planning o
24、f switched telephone networks, ITU, Geneva, 1976.2 ITU-T Recommendation G.103 (1998), Hypothetical reference connections.3 ITU-T Recommendation G.111 (1993), Loudness Ratings (LRs) in an internationalconnection.4 ITU-T Recommendation G.113 (1996), Transmission impairments.5 ITU-T Recommendation G.11
25、4 (1996), One-way transmission time.6 Recommendation G.1161, Transmission performance objectives applicable to end-to-endinternational connections.7 ITU-T Recommendation G.121 (1993), Loudness Ratings (LRs) of national systems.8 ITU-T Recommendation G.122 (1993), Influence of national systems on sta
26、bility and talkerecho in international connections.9 ITU-T Recommendation G.131 (1996), Control of talker echo.10 ITU-T Recommendation G.173 (1993), Transmission planning aspects of the speech servicein digital public land mobile networks.11 ITU-T Recommendation G.174 (1994), Transmission performanc
27、e objectives for terrestrialdigital wireless systems using portable terminals to access the PSTN.12 ITU-T Recommendation G.175 (1997), Transmission planning for private/public networkinterconnection of voice traffic.13 CCITT Recommendation G.232 (1984), 12-channel terminal equipments.14 Recommendati
28、on G.235 (1988, withdrawn, Blue Book, Volume III, Fascicle III.2.) 16-channel terminal equipments._1Presently at the stage of draft.Recommendation G.120 (12/98)215 ITU-T Recommendation G.712 (1996), Transmission performance characteristics of pulsecode modulation channels.16 CCITT Recommendation Q.3
29、1 (1988), Noise in a national 4-wire automatic exchange.17 CCITT Recommendation Q.45 (1984), Transmission characteristics of an analogueinternational exchange.18 ITU-T Recommendation Q.551 (1996), Transmission characteristics of digital exchanges.19 ITU-T Recommendation Q.552 (1996), Transmission ch
30、aracteristics at 2-wire analogueinterfaces of digital exchanges.20 ITU-T Recommendation Q.553 (1996), Transmission characteristics at 4-wire analogueinterfaces of digital exchanges.21 ITU-T Recommendation Q.554 (1996), Transmission characteristics at digital interfaces ofdigital exchanges.3 Applicat
31、ion of ITU-T Recommendations on telephone performance to nationalnetworksThe different parts of a national network provided by both analogue and digital transmission systemsto be used for an international connection should meet the following general recommendations:3.1 The national sending and recei
32、ving systems should satisfy the limits recommended in: Recommendation G.113 as regards to transmission impairments; Recommendation G.114 as regards to group delay; Recommendation G.121 as regards to Loudness Rating (LR); Recommendation G.122 as regards to balance return loss and transmission loss; R
33、ecommendation G.131 as regards to echo control2; Recommendation G.120: Clause 5 as regards to attenuation distortion; Clause 6 as regards to circuit noise; Clause 7 as regards to error on the reconstituted frequency; Clause 8 as regards to group delay distortion; Clause 9 as regards to linear crosst
34、alk of circuits3; Clause 10 as regards to non-linear distortion of analogue transmission systems; and Clause 11 as regards to variations of transmission loss with time.3.2 Long-distance trunk circuits forming part of the main arteries of the national network shouldbe high-velocity propagation circui
35、ts which enable the limits fixed in Recommendation G.114 to berespected._2Recommendation G.131 applies to control of network originated echo. Additional guidance for echocontrol can be found in: Recommendation G.116 for terminals, Recommendation G.173 for connectingdigital public land mobile network
36、s, Recommendation G.174 for connecting terrestrial digital wirelesssystems using portable terminals and Recommendation G.175 for connecting private networks.3Guidance applicable to linear crosstalk on connections can be found in Recommendation G.116.Recommendation G.120 (12/98) 33.3 National trunk c
37、ircuits should have characteristics enabling them to conform toRecommendation G.131.3.4 International centres Plesiochronous Digital Hierarchy (PDH)/Synchronous DigitalHierarchy (SDH) should satisfy Recommendations Q.551, Q.552, Q.553 and Q.554.National automatic analogue 4-wire centres should obser
38、ve the noise limits specified inRecommendation Q.31.4National digital switching centres should satisfy Recommendations Q.551, Q.552, Q.553 and Q.554.International and national switching centres (Asynchronous Transfer Mode) should, in general, meetthe Q.500-series Recommendations.54 National transmis
39、sion planEvery Administration is free to choose whatever method it considers appropriate for specifyingtransmission performance and to adopt the appropriate limits to ensure satisfactory quality fornational calls. Nevertheless, the recommendations relating to Loudness Ratings (LRs),Recommendation G.
40、121, should be satisfied for international calls.NOTE To meet this twofold condition with respect to national and international calls, each Administrationhas to draw up a national transmission plan, i.e. it must specify limits for each part of the national network.The manual cited in 1 contains desc
41、riptions of the transmission plans adopted by various countriesand also some indications concerning the methods that can be used to establish such a plan.In particular, Annexes A and B to Recommendation G.111 contain useful information forAdministrations who wish to apply the LR method to their nati
42、onal connections.5 Attenuation distortionThe circuit performance objectives for attenuation distortion of international circuits and nationalextension circuits were originally selected so that acceptable performance would be obtained onanalogue 4-wire chains of up to 12 circuits. Although it is reco
43、gnized that the network is continuingits evolution to an all digital network, it is recommended that the individual equipment networkperformance objectives as presented in the following Recommendations not be relaxed: G.232(which gives equipment design objectives for analogue 12-channel terminal equ
44、ipments); G.712(which gives equipment design objectives for digital PCM channelizing equipments); and Q.552 andQ.553 (which give equipment design objectives for digital switches).It follows from the Recommendations mentioned above that, as a rule, the frequency band effectivelytransmitted by a telep
45、hone circuit, according to the definition adopted by the ITU-T (i.e. the band inwhich the attenuation distortion does not exceed 9 dB compared with the value for 1020 Hz), will bea little wider than the 300-3400 Hz band, and for a single pair of channel terminal equipments of thistype, the attenuati
46、on distortion at 300 Hz and 3400 Hz should never exceed 3 dB and in a largenumber of equipments should not average more than 1.7 dB. It is recommended that all channelterminal equipments, including digital switches with analogue interfaces, be designed such that theycan comply with the line-up limit
47、s specified in Figure 1. Analogue terminal equipments with_4In accordance with Recommendation Q.31, the limits are the same as those which were specified inRecommendation Q.45 of the Red Book (1984).5For example, the group delay requirement cannot be met if cell assembly of DS-0 rates is performed.R
48、ecommendation G.120 (12/98)43-kHz-channel spacing, i.e. equipment intended to be G.235 compliant (Note that RecommendationG.235 is no longer in force.) is no longer recommended for use in international connections.T1208920-98dB200 3002506004002400 29002700305030003400 HzFrequencyAttenuationCircuits
49、with equipments having 4-kHz spacing(Based on Recommendation G.232 13.) 1.0 0.501.02.02.53.56.510Figure 1/G.120 Line-up limits of circuits with 4-kHz channel equipmentNOTE 1 The ITU-T examined the possibility of recommending a specific frequency below 300 Hz as thelower limit of the frequency band effectively transmitted by network channelizing equipments, taking thefollowing considerations into account:1) The results of subjective tests
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