1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.180 (03/93) GENERAL CHARACTERISTICS OF INTERNATIONAL TELEPHONE CONNECTIONS AND INTERNATIONAL TELEPHONE CIRCUITS CHARACTERISTICS OF N + M TYPE DIRECT TRANSMISSION RESTORATION SYSTEMS FOR USE ON DIGITAL AND A
2、NALOGUE SECTIONS, LINKS OR EQUIPMENT ITU-T Recommendation G.180 (Previously “CCIlT Recommendation”) ITU-T RECMN*G.LBO (REV*l) 93 W 4862593 0583009 692 W FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecorn- munication Union. The ITU-T i
3、s responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study
4、 by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation G.180 was revised by the ITU-T Study Group XV (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Te
5、lecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRE3 have been replaced by the Radiocommunication Sector. In orde
6、r not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology relat
7、ed to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form
8、or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. CONTENTS Page 1 General . 1 2 Object of Recommendation 1 3 RSE specifications 2 3.1 Interfaces 3 3.2 Operational aspects . 3 4 RSCE specifications . 5 4.1 Interfaces 5 4.2 Ope
9、rational aspects . 6 Annex A 7 A. 1 Maximum permissible intrinsic jitter at output ports of regenerative restoration switching equipment . 7 Annex B . 9 Jitter transfer characteristics recommended for regenerative restoration switching equipment . 9 Appendix I - Examples of alarms and status criteri
10、a for digital systems 11 Appendix II - Examples for monitoring and self-test procedures for digital system 12 B.l Recommendation 6.180 (03/93) i ITU-T RECNN*G.180 (REVr1) 93 m 4862591 05830L1 240 m Recommendation G.180 CHARACTERISTICS OF N + M TYPE DIRECT TRANSMISSION RESTORATION SYSTEMS FOR USE ON
11、DIGITAL AND ANALOGUE SECTIONS, LINKS OR EQUIPMENT (Melbourne, 1988; amended at Helsinki, 1993) 1 General Transmission restoration functions are often implemented in the modern telecommunication networks to improve the availability and quality of service, by minimizing the effects or potential effect
12、s of a transmission failure, and to make the maintenance operations easier. The terminology and general principles of transmission restoration are described in Recommendation M.495. The functional organization for automatic transmission restoration is described in Recommendation M.496. 2 Object of R
13、ecommendation This Recommendation specifies the characteristics of equipment for N + M type direct transmission restoration systems (protection link switchingj for digital and analogue sections, links and equipment (see Recommendations G.701 and G.211). The general arrangement of a system for N + M
14、direct transmission restoration is shown in Figure 1. This Recommendation refers to the equipment labelled as RSE (restoration switching equipment) and RSCE (restoration switching control equipment). This Recommendation is intended also to cover the case where the signals at the interfaces T belong
15、to different hierarchical levels. In this case, each access at one side can be a group of accesses as indicated in the example of Figure 2. The left part of this figure refers to the particular case where the restored path is not on a complete link but just through a multiplex equipment. NOTE - The
16、equipment specified in this Recommendation can possibly be used also for N + M automatic or semi- automatic transmission rerouting (protection network switching) but generally this type of restoration function is implemented by different equipment. often incorporating also other functions (such as,
17、for example, automatic digital distribution frames). Three types of direct transmission restoration systems are considered by this Recommendation: The first one should permit routing of any one of N normal links on to any one of M restoration links. The second type should permit the interconnection
18、of any of the N accesses to any one of the N + M links. The third one should permit routing of any one of N normal links to a single restoration link (in many cases this type can be considered just a special case of the first type). For all the types two options exist: aj to switch the two direction
19、s of transmission independently; and b) to switch the two directions of transmission simultaneously. This Recommendation does not cover the restoration systems fully embedded in transmission systems and the 1 + 1 systems where the switching occurs at the receive end only (see Recommendation G.18 1).
20、 The hierarchical levels at interfaces T are those specified in Recommendation G.702 (hierarchy levels 1 and up). For RSE to be used on analogue transmission systems the frequency bands at interface T are those specified in Recommendation G.211. Recommendation G.180 (03/93) 1 Sections, links or equi
21、pment T T T T ,M LT, N+M + +-.-. .- - - - 7 LT , optional ,. MUX MUX sparelink I : accesses . . , . . . . . . . . -. - - - - 1 LT, LT, Y . 3 MUX MUX y . . . . . - - - . . - - - RSE RSE LT, Y I MUX . MUXi+ , Y LT, LT, Y 2 Y T I t- ” - - 1 MUX MUX Y Y I - - X X +Eq LOCA A + RSCE RSCE 4-. - -. -. . -.
22、-. -. control Z Embedded in the restoration z+ manual control and/or normal links or separate Q TI 51 3480-93/d01 RSE Restoration switching equipment X Non-standardized (or standard Q) interface. If RSE and RSCE are combined interface X does not exist RSCE Restoration switching control equipment Int
23、erface to be standardized in the future (possibly standard Q) Q Optional standard Q interface to the TMN (telecommunication management network) or to a control centre Y Line terminal, digital multiplexing Z Interface possibly to be standardized or analogue translating equipment This link can be repl
24、aced by connection in the TMN MUX .- . _ . T Transmission path interfaces NOTES 1 In this case interface Y may not exist. 2 3 4 5 Recommendation. The faiiing of a section or link can possibly be detected in the RSE and the information transferred to the RSCE. The interworking with the TMN via interf
25、ace Q is at present beyond the scope of the Recommendation. The N + M links or sections can be in the same cable os follow different routes. Spare link accesses may be used to convey low priority traffic. The interface between the RSCE and local manual control is not standardized and it is not cover
26、ed by this FIGURE UG.180 N + M direct transmission restoration system 3 RSE specifications Two types of RSE are considered by this Recommendation: “segenesative” and “non-regenerative”. The first type, where the digital signal undergoes a complete process of retiming and reshaping, is for digital sy
27、stems only. It makes the RSE a digital equipment, and it is sometimes considered to be advantageous, e.g. from the station cabling point of view. 2 Recommendation G.180 (03/93) Optional accesses Regular accesses M 1 N 1 - I RSE I RSE Optional accesses Regular accesses M 1 N 1 - I MUXI XI RSE I RSE I
28、 RSE Restoration switching equipment MUX Digital muitiplexing or analogue translating equipment LT Line terminal equipment T1513490-9kdO2 FIGURE 2/G.180 Examples of restoration systems where the hierarchical levels at the two ends are different The second type, where the output signal is proportiona
29、l to the input signal (except for minor distortion) is considered to be useful for digital systems under some circumstances, e.g. from a reliability and cost point of view, and it is the only one usable for analogue systems. 3.1 Interfaces 3.1.1 Transmission path interfaces (T) The relevant paramete
30、rs and the recommended values are listed in the uppermost part of Table 1 for the non-regenerative RSE, to be used for digital systems. The uppermost part of Table 2 covers the regenerative RSE. The uppermost part of Table 3 is for the non-regenerative RSE to be used for analogue systems. 3.1.2 Cont
31、rol interfaces The only control interface of the RSE is X. This interface is not at present specified by the CCIIIT. However in the future. it may be specified as a Q interface (see Recommendation G.773). If the interface X is not standardized, the separation between the RSE and RSCE (and consequent
32、ly between clauses 3 and 4) will be somewhat arbitrary. 3.2 Operational aspects 3.2.1 Transfer of the switched signals The relevant parameters and the recommended values are listed in the lower part of Table 1 for the non-regenerative RSE to be used for digital systems. The lower part of Table 2 cov
33、ers the regenerative RSE. The lower part of Table 3 is for the non-regenerative RSE to be used for analogue systems. Recommendation G.180 (03/93) 3 TABLE 1/G. 180 Nominal impedance Recommended values for the interface and transfer characteristics of non-regenerative RSE for use on digital systems As
34、 stated in Rec. G.703 terminated on the nominal impedance) 6 dB above the values stated in Rec.G.703 The output levels considered in Rec. G.703 Transfer Transfer function between the input and the output of the RSE (terminated on the nominal impedances) (see Note 2 of Table 2) Crosstalk attenuation
35、10% of the interconnecting pair loss and phase distortion allowed in Rec. G.703 for the relevant hierarchical level, or the complement thereof, plus or minus 0.5 dB flat loss. It is assumed that the loss vs frequency distortion approximates to the Jf law 2 40 dB from any channel 2 30 dB multi-channe
36、l interference evaluated on a voltage-sum basis. These values apply up to a frequency value equal to the nominal bit-rate TABLE 2/G.180 Recommended values for the interface and transfer characteristics of regenerative RSE Interface (Note 2) Transfer (Note 2) Connecting pairs Test impedance and retur
37、n loss at the input ports Pulse shape and levels Tolerable input jitter Intrinsic output jitter Jitter transfer Error performance Others As stated in Rec. G.703 As stated in Annex A As stated in Annex B 99.99% error-free seconds (Note 1) The paths across each switch shall maintain bit sequence indep
38、endence and integrity NOTES 1 2 Evaluated under maximum loading condition and excluding any external source of interference. The nominal bit rate and tolerance are as stated in Recommendation G.703. 4 Recommendation G.180 (03/93) TABLE 3/G. 180 Nomind relative levels in switching points Nominal impe
39、dance at the input/output ports Return lo ut the input/output ports Longitudinal balance conversion loss hertion loss Frequencj response as stated in Recommendation G.211 rnterface Tramfer Noiw referred to the voice-frequency channel bandwith Intelligible crosstalk ratio between ports within the sam
40、e RSE As stated in Recommendation G.233 (Note) 2 46 dB 50.3 dB f 0.2 dB I 20 pwo for a pair of RSEs loaded by the signal of maximum power averaged over one minute interval 2 90 dB 3.2.2 Response For RSE providing M storation paths to N nornial paths (M = 1 included) it is recommended that in respons
41、e to a RSCE conimand the RSE should apply the incoming interface signal belonging to a given normal link to the input port of a given restoration link. The signal should not be removed from the input port of the concerned normal link, except that it may be replaced by a test signal. For RSE providin
42、g N + M link to N accesses it is recommended that in response to a RSCE command, the RSE should apply the incoming interface signal belonging to a given access from 1 to N to a given link from 1 to N + M. The time required for the above response is the restoration transfer time, as defined in Recomm
43、endation M.495. 3.2.3 Other operational aspects A recognized failure of the RSCE or its disconnection from the RSE at interface X (when applicable) should either: a) Cause the RSE to route all the signals on the N normal links. After the failure of the RSCE is cleared or the RSCE is reconnected to t
44、he RSE, normal restoration operations will resume. Kot alter the state of the RSE. The cross-connection pattern of the RSE should be available by interrogation from the RSCE to enable it to update, when the failure is cleared or it is reconnected to the RSE, its own record on the cross-connection pa
45、ttern. b) For the restoration systems of the second type (as defined alternative in b) only holds. For the systems of the first aiid third types both alternatives are applicable. 4 RSCE specifications 4.1 Interfaces Interface5 Y. Z of the RSCE (see Figure 1) are at present non standardized. However
46、they may be standardized in the future. Recommendation G.180 (03/93) 5 4.2 Operational aspects 4.2.1 Responses A switching to a restoration link should be initiated under a request coming from interfaces Y, Z, Q (and X where the faults are detected within the RSE) or on command from the local manual
47、 control. When decided in the RSCE the allocation of a restoration link can optionally take place according to defined priority rules based on: - defined priority for each normal link; - request type (low or high priority request). Otherwise the allocation should be specified by the information comi
48、ng from interfaces Z, Q or local manual control. For the restoration systems providing M restoration links (M = 1 included) on N normal links, when a successful restoration request clears, traffic should be returned to the pertinent normal link and the pertinent restoration link should be released.
49、It should be possible from interfaces Z, Q and under local manual control to lock in a working link (e.g. during system maintenance). The time required for the above response is the sum of the waiting time and the restoration procedure time, as defined in Recommendation M.495. 4.2.2 Alarm and status criteria The alarm and status criteria provided by the RSCE are not standardized. Examples are reported in Appendix I. 4.2.3 Monitoring and self-test procedures The monitoring and self-test procedures of the RSCE are not standardized. Examples are reported in Appendix I
