1、Page 1 Recommendation T/CS 50-01 (Montpellier 1984) MAINTENANCE PHILOSOPHY FOR DIGITAL AND MIXED NETWORKS Recommendation proposed by Working Group T/WG 11 “Switching and Signalling” (CS) Text of the Recommendation adopted by the “Telecommiicatos” Commissioit : “The European Conference of Postal and
2、Telecommunications Administrations, considering - that the existing CCITT Recommendations on maintenance philosophy do not cover the whole network and only - that there was no common understanding about what maintenance consists of; - that there was no fundamental and logical description of what mai
3、ntenance is; - that system designers must be aware of the fact that maintenance is one of the major cost-factors of the total life deal with some maintenance aspects; time of a system, recommends that the members of the CEPT recognise the following considerations.” O Edition of May 15, 1986 TICS 50-
4、01 E Page 3 Table of contents Page 1. GENERAL 4 1.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Overall maintenance philosophy . . . . . . . . . . . . .
5、 . . . . . . . . . . . . . . . . , 5 1.3.1, Maintenance entity concept . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3.2. ClassiJication of failiwes . . . . . . . . . . . . . . . . . . . . . . , , . . . . . . . , . 7 2. SUPERVISION . . . . . . . . . . . . . . . . . . . . . . .
6、. . . . . . . . . . . . . 7 3. MAINTENANCE PHASES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . 7 3.2. Failure detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,
7、. 9 3.2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.2. Continuow checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . 9 3.2.3. Routine or periodic testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3
8、.2.4. Checking under zero trafic conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.5. Checking under live traffic conditions , . . . . . . . , . . . . . . . . . . . . . . . . . . 9 3.3. Protection of the system . . . , . . . . . . . . . . . . . . . . - . . . . . . . . . , . . 9
9、3.4. 3.4.1. 3.4.2. 3.4.2.1. 3.4.2.2. 3.4.2.3. 3.4.3. 3.4.4. 3.4.5. 3.4.6. Failure information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 O Alarin itfortnation . . . . . . . . . .
10、. . . . . . . . . . . . . . . . . . . . . . . . . 10 Prompt maintenance alarm (PMA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Deferred maintenance alarm (DMA) . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Maintenance information (MI) . . . . . . . . . . . . . . . . . . .
11、. . . . . . . . . . . 10 Guiding rnaintenance action after MIS . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Alarm indication signal (AIS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Ifornation to the tuer terininal . . . . . . . . . . . . . . . . . . . . . . . . . . .
12、. . . 11 Information for blocking or automatic change over . . . . . . . . . . . . . . . . . , . . . . 11 3.5. Failure localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.6. Logistic delay times . . . . . . . , . . . . . . . . . , . . . . . . . . . . . . . . . . .
13、 11 3.7. Failure correction , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.8. Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . 11 3.9. Restoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4. M
14、AINTENANCE LOGISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5. FAILURE STATISTICS . , , . . . . . , , . . . . . . . . . . . . . . . . . . . . . 12 6. PREVENTIVE MAINTENANCE ACTIONS . . . . . . . . . . . . . . . . . . . . . . . 12 7. SPECIAL ASPECTS OF VARIOUS NETWORK PARTS . .
15、. . . . . . . . . . . . . . . . 12 Edition of May 15, 1986 CEPT T/CS*50-O3*E 4 m 232b1114 0005335 3 m TICS 50-01 E Page 4 I 1. GENERAL 1.1. Introduction Maintenance has to do with failures. In a system where failures are not expected, no maintenance is necessary. So failures are the cause of the mai
16、ntenance. The term maintenance covers all the aspects which have to do with failures, such as: supervision, detection, localization, information, repair, etc. All ideas concerning these aspects are contained in the maintenance philosophy. In order to meet the requirements of availability performance
17、 and through that to meet the requirements of network technical performance, various actions related to failures are necessary. The combination of all these actions, with the intention to retain an item in or to restore it to, a state in which it can perform its required function, is defined as main
18、tenance. Maintenance can be performed according to different principles : Preventive maintenance The maintenance carried out at predetermined intervals or corresponding to prescribed criteria and intended to reduce the probability of failure or the performance degradation of an item. The maintenance
19、 carried out after a failure has occurred and intended to restore an item to a state in which it can perform its required functions. A method for sustaining a desired network technical performance by the systematic application of analysis techniques using centralized supervisory facilities and/or sa
20、mpling to minimize preventive maintenance and to reduce corrective maintenance. In general it is proposed for all three network types (analogue, digital and mixed) to use controlled maintenance principles wherever possible, that is to say that the maintenance actions are determined on the basis of i
21、nformation coming out of the system itself or from auxiliary equipment. The maintenance philosophy in general is such that: the right person can be sent to the right place with the right equipment at the right time to perform the right actions In other words it allows the maintenance personnel to id
22、entify failed equipment, to restore the service and to repair the failed equipment. Furthermore it is important that coherent maintenance principles are applied to the various constituent parts of digital networks (e.g, multiplexers, transmission systems, exchanges, etc.) so that satisfactory equipm
23、ent interworking is guaranteed, unambiguous failure location is possible and unnecessary activities can be avoided. To this end “maintenance entities”, “failure information” and “means to assist in detecting and locating failures”, etc., have been defined. The maintenance philosophy and thus the mai
24、ntenance functions are strongly linked to the availability performance parameters of the network, which parameters have to be defined and quantified. For defintions of concepts and terms used, see Recommendation T/CS 10-13 i. Corrective maintenance Controlled maintenance 1.2. Objectives New technolo
25、gies provide new possibilities for the maintenance not only of individual exchanges, but also of the whole network at low cost. The same technology for both transmission and switching will gradually render an in-built system of operation and maintenance possible. The operation and maintenance functi
26、ons should be implemented in such a way that the lifecost will be minimum for a stated service level. The total cost of the network consists of - investment cost, - operation cost, - maintenance cost (for failures), - cost of lost traffic. It is especially the investment cost, the maintenance cost a
27、nd the cost of lost trafic which depend on the requirements of availability performance of the network and of the network components and thus on the maintenance functions built-in or in separate equipments and the reliability (failure rate). The operation cost is dependent on the requirements for th
28、e operation of the network and of the network parts and thus also on the operational functions built-in or in separate equipments. Edition of May 15, 1986 c-. TICS 50-01 E Page 5 - - - L L L L E E E E Xb DM +- T T+ T T. Digital switch _I - - 1.3. Overall maintenance philosophy 1.3.1. Maintenance ent
29、ity concept In the maintenance philosophy, it is assumed that the different equipments of a telecommunication network are interconnected at easily identifiable points at which the interface conditions defined for these equipments The equipments which occur between two consecutive interfaces constitu
30、te a maintenance entity. In an integrated digital network for example such points may be provided by digital distribution frames. Even in a location where no digital distribution frame is provided, an equivalent point where defined interface conditions apply can normally be identified. Examples are
31、given in Figures 1 and 2. In defining the Maintenance Entities (ME) the following aspects are taken into account: i. When a failure occurs within a network, a maintenance alarm indication must be generated identifying the failed maintenance entity. ii. A failure occurring in an entity should not cau
32、se the generation of alarm indications in other entities. If these two principles are met then the responsible maintenance personnel will be called into action, and usually no unnecessary maintenance activity will be initiated elsewhere. Note: Several MEs can be assembled into a maintenance entity a
33、ssembly (MEA) for operational and Maintenance reasons. Typical applications are digital exchanges, digital circuits and facilities. ME can also be subdivided into Maintenance sub-entities (MSE) for operational and maintenance reasons. A typical example is a digital line system consisting of line ter
34、minals, repeaters and cable sections. apply. Digital switch X DM X -J I MEJt-E multiplex ME = Maintenance entity. LTE = Line terminating equipment. X DM = Digital multiplexer/Muldex. = Digital distribution frame or equivalent point. li E- Figure 1. General maintenance entity concept for inter-exchan
35、ge connections. Edition of May 15, 1986 CEPT T/CS*CO-Ob*E 84 m 232b414 0005137 7 m TICS 50-01 E Page 6 I I ET - LT 1 - NT1 I I T NT2 - LT/ET NT ET - LT I I I I I T Analogue subscriber line Digital subscriber line I LT LT ET i LT I LT -1- i Muldex - I Digital local exchange I l-T- I Digital Analogue
36、subscriber line I - ET JZange I- l -ME IME Analogue subscriber line -ME- I A-RSUI I A2x ET - Digital I local exchange I I -E+ I 1 I A-KSU Muldex ET local I exchange I I - -ET Muldex i2 I I- I I I I l ME = Maintenance entity. A-PABX = Analogue PABX. D-PABX = Digital PABX. A-RSU D-RSU = Analogue remot
37、e switching unit. = Digital remote switching unit. Figure 2. Subscribers connection divided in 3 main :nance entities. Edition of May 15, 1986 1.3.2. CEPT T/CS*SO-OL*E 84 M 2326434 0005138 9 W . T/CS 50-01 E Page 7 ClassiJication of failures A failure is defined as the termination of the ability of
38、an item to perform a required function. The severity of the failure depends on the failure effect. This effect can be related to: The network service performance requirements as experienced by the subscribers; The probability that multiple failures will occur thus resulting in the deterioration of t
39、he performance as seen by the customer; Probable loss of revenue to the Administration. The failures can also be classified according to their importance and consequences on the quality of service provided to the subscribers and on the network technical performance: failures which give a complete in
40、terruption of service(s) for one or several subscribers; failures which give a partial interruption of service) (e.g., degradation of transmission quality) to one or several subscribers; failures which decrease the availability performance of the equipment and/or the network, but do not affect the s
41、ubscribers. Another classification distinguishes between permanent and intermittent failures. The severity of failures can be determined by measuring the down time, up time and failure rate of the ME. These terms are defined in Recommendations T/CS 10-13 i and T/CS 58-01 2. 2. SUPERVISION Supervisio
42、n is a process in which the various functions of the various items in a network are looked at (supervised). This is done for operational as well as for maintenance matters. For maintenance this supervision process has to include the following functions: (a) Locating “failed” equipment or the equipme
43、nt in which a failure is suspected. It is generally carried out by analytical or statistical identification processes. (b) Report of failures to operating personnel. (c) Transmission of data to the operating personnel, relating to specific functional features of the network (traffic, state of equipm
44、ent, particular malfunctions for instance). These data are transmitted systemati- cally or on demand. (d) To protect the system by transmitting to all the concerned network equipment any necessary informa- tion for the automatic initialization of internal or external protection mechanisms, e.g., rec
45、onfiguration, traffic re-routing, etc. 3. MAINTENANCE PHASES 3.1. General After the occurrence of a failure in the network, a number of maintenance phases are required to correct the failure and to protect, when possible, the traffic aflected by the failure if it has been interrupted. Figure 3 lists
46、 the maintenance phases which are involved after a failure occurrence in a ME. The parameters determining the different phases are indicated in the figure. It is intended to characterize different mainte- nance strategies with the aid of the maintenance phases. Edition of May 15, 1986 CEPT T/CS*SO-O
47、L*E 84 II 2326414 OOO5L39 O TICS 50-01 E Page 8 a I f 4 O f H c, t t T t L E 9 2 c; f i 7 I e ? m Edition of May 15, 1986 CEPT T/CS*50-01*E 4 2326434 0005140 7 W TICS 50-01 E Page 9 Besides the maintenance phases the following aspects have to be dealt with: 0 Preventive maintenance (see paragraph 6.
48、). x: Maintenance logistics (see paragraph 4.). The recording of all failures = Failure statistics (see paragraph 5.). 3.2. 3.2. 3.2.2. 3.2.3. 3.2.4. 3.2.5. 3.3. Failure detection Introduction The discovery of failures must take place so quickly and with such security that the stated service demands
49、 are fuled. Failures should be discovered by the telephone company, independent of and preferably before the subscriber, i.e. the majority of failures are both detected and remedied without the subscriber having been aware of the failures. Different types of failure detection mechanisms can be used as follows: (a) continuous checking; (b) routine or periodic testing; (c) checking under zero trafic conditions; (d) checking of behaviour under live trafic conditions. The niles governing the detection mechanism must be defined for a system, sinc
