ÿWPCL ûÿ2BJ|xÐ ` ÐÐÌÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿH øÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÌÐÐ °°°è ÐÑ Âx„|ü@Ž ÑÐ Å°6Ø'°6Ø'Å ÐÓÓÃÃRecommendation I.603ÄÄ Áà#ÁAPPLICATION OF MAINTENANCE PRINCIPLES TO ISDN BASIC ACCESSESƒ 1.ÁHÁÃÃScope of applicationÄÄ Ð 8 ÐÁHÁThis Recommendation covers the maintenance of that part of the ISDN subscriber basic access, controlled by the network, follows the maintenance principles as defined in Recommendation M.20 and applies to the basic access directly connected to the local exchange without any multiplexer or concentrator. ÁHÁThe principle of controlled maintenance (as defined in Recommendation M.20) is applied for maintaining the subscriber basic access. ÁHÁControlled maintenance is a method of sustaining a desired technical performance by the systematic application of supervision, testing and performance sampling in order to minimize preventive maintenance and to reduce corrective maintenance. 2.ÁHÁÃÃNetwork configuration for maintenance activitiesÄÄ ÁHÁFigure 1/I.603 is the basis for the general maintenance principles of the subscriber access. ÁHÁSAMC: Subscriber Access Maintenance Centre ÁHÁSIME: Subscriber Installation Maintenance Entities ÁHÁMSP:  Maintenance Service Provider ÃÃNote 1ÄÄ © The subscriber access contains a digital section which can use different varieties of transmission techniques and may also include a regenerator. Ð X ÐÃÃNote 2ÄÄ © In some countries certain maintenance functions within the subscriber access may be controlled by the subscriber installation (SIME). ÁàÀIÁFIGURE 1/I.603ƒ ÁàÀPÁƒ ÁàÀ6ÁÃÃConfiguration for the maintenance of the basic accessÄă 3.ÁHÁÃÃFailure detectionÄÄ 3.1ÁHÁÃÃGeneralÄÄ ÁHÁWhen the digital section (as seen by the exchange) of the ISDN subscriber basic access is in the active state, automatic supervision of the correct functioning of the layer 1 up to the NT1 is operating. This supervision is called continuous automatic supervision on layer 1. ÁHÁWhen the ISDN subscriber basic access is in the active state (as seen by the exchange), automatic supervision of the correct functioning of the        D©Channel layers 2 and 3 is also operating. This supervision is called automatic supervision on layers 2 and 3 of the D©Channel protocol. ÁHÁWhen the ISDN subscriber basic access is not in an active state (as seen by the exchange), the subscriber access may be periodically tested by the exchange. This is called the continuity test. 3.2ÁHÁÃÃAutomatic supervisionÄÄ 3.2.1ÁHÁÃÃContinuous automatic supervision of layer 1ÄÄ 3.2.1.1Á  ÁObjectives ÁHÁThis supervision is realized by permanent automatic mechanisms located in the pieces of equipment of the subscriber basic access (see definition in Figure 1/I.601). ÁHÁThese automatic mechanisms are continuously operational during the active period of the subscriber basic access. ÁHÁThey are designed to detect malfunctioning of particular items, e.g. power supply, quality level of transmission, incoming signal, frame alignment. ÁHÁThe continuous automatic supervision mechanism should be in operation even if there is no subscriber installation connected to the T reference point. For this, it must be possible for the digital section to be placed in a state where the automatic supervision can be performed continuously although the T reference point may not be capable of full activation according to Recommendation I.430. ÂHHÂÁ€Á3.2.1.2Á  ÁDigital section functionsÆÆ ÁHÁFunctions, which are allocated to the digital section are listed below: ÁHÁ©Âà  Âdetection of loss of frame alignment within the digital system;ÆÆ ÁHÁ©Âà  Âdetection of loss of frame alignment on the user©network interface as defined in Recommendation I.430;ÆÆ ÁHÁ©Á  Ásupervision of the power feeding; ÁHÁ©Âà  Âtransmission performance monitoring.ÆÆ ÁHÁTransmission performance monitoring mechanisms are for further study. ÃÃNoteÄÄ © In case the digital section has its own failure detection mechanism, failure indication signals may be sent to and received by the local exchange termination. Alternatively, the detection mechanisms are included in the exchange termination. 3.2.1.3Á  ÁExchange termination functions Ô ñ,ÔŒÁHÁFunctions which are allocated to the exchange termination are listed below: ÁHÁ©Âà  Âsupervision of information related to or received from the digital section;ÆÆ ÁHÁ©Á  Átransmission performance evaluation. ÁHÁThe transmission performance evaluation is based on a permanent processing of the elementary results presented by the continuous error monitoring of the digital section. ÁHÁThe result of the processing will give information on at least one transmission quality level. ÁHÁDefinition of quality levels and evaluation timing conditions are out of the scope of this Recommendation. 3.2.2ÁHÁÃÃAutomatic supervision of layers 2 and 3 of the D©Channel protocolÄÄ ÁHÁThis activity covers supervision of activities of layers 2 and 3 of the D©Channel protocol. Automatic supervision on layers 2 and 3 will be made by self©acting mechanisms implemented in the network (e.g. in the ET). ÁHÁThere are three categories of automatic supervision which may be performed by layers 2 and 3 of the D©Channel protocols: ÁHÁ©Âà  Âservice provision incapability detection (e.g. incapability of layer 2 to establish a data link connection);ÆÆ Ð 8 ÐÂHH©Âà  Âprotocol misoperation detection (e.g. at layer 2, detection of dual TE1 assignment);ÆÆ Ð ` Ð Ð H ÐÁHÁ©Âà  Âerror monitoring (e.g. the layer 2 CRC check procedure can detect the occurrence of an errored frame).ÆÆ ÁHÁThese events (defined in Recommendations I.440 and I.450) should be recorded. 3.3ÁHÁÃÃContinuity testÄÄ 3.3.1ÁHÁÃÃGeneralÄÄ ÁHÁWhen the subscriber basic access is not active (normal case and/or unknown failure condition case) or has not been recently activated, a continuity test may be applied in order to detect possible failure condition. ÁHÁThe test should be a simple go/no go test. ÃÃNoteÄÄ © The periodicity of testing on each access, if performed on a periodical basis, shall be compatible with the failure detection time value (i.e. the time between failure occurrence and failure detection). 3.3.2 ÃÃControl of the continuity testÄÄ ÁHÁThe continuity test is based on a normal activation of layer 1. If the activation is confirmed by a positive result of the continuity test, the subscriber basic access is declared to be in good order for operation. No report is given to the SAMC. ÁHÁIf the activation is not confirmed by a positive result of the continuity test, or if a failure condition is detected during the process, then the exchange will automatically enter into the failure localization process, and will report to SAMC. ÁHÁThe result of the continuity test should be judged to be positive if the NT1 has the capability to signal that there is no failure on the subscriber basic access. 4.ÁHÁÃÃSystem protectionÄÄ ÁHÁWhen a failure is detected which has an adverse effect on the availability and/or functionality of network equipment, the access is considered "out of service due to failure" and call attempts may be rejected to prevent further damage or to remove the adverse effect (see Recommendation I.601). In this condition, removal of power from the line may be required. 5.ÁHÁÃÃFailure informationÄÄ ÁHÁA failure confirmed by the exchange and related to a subscriber basic access and/or subscriber installation shall be reported to the SAMC in a message. ÁHÁThe message could be presented after an automatic identification of a failed maintenance entity (ME) has been made (see ÀÀ 6). 6.ÁHÁÃÃFailure localizationÄÄ 6.1ÂàHÂÃÃAutomatic confirmation of failure within the subscriber basic accessÄÄÆÆ ÁHÁAn automatic test procedure to confirm a detected possible failure condition within the subscriber basic access should be provided. It should be initiated on an automatic reaction of the exchange, following abnormal conditions which have been detected by the processes presented above, i.e. continuous supervision, supervision on layer 2 and layer 3, continuity test. ÁHÁThe process is based on loopback techniques which allows the exchange to verify that there is no failure within the network and that the failure condition, if any, is not of a temporary nature. ÁHÁIf failures are detected in the D©Channel layers 2 and 3 communication clear differentiation between failures within the subscriber installation and within the subscriber access should be possible. 6.2ÁHÁÃÃFailed maintenance entity identificationÄÄ 6.2.1ÁHÁÃÃGeneralÄÄ ÁHÁSuch a function has to be made on demand or automatically following the indication of failed conditions by the network or following a subscriber complaint. It is necessary, before undertaking the appropriate action, to identify (know) the maintenance entity affected by the failure. 6.2.2ÁHÁÃÃObjectivesÄÄ ÁHÁThe main objective of this function which is controlled by the SAMC is to indicate to the SAMC if the failure is: ÁHÁ©Á  Áwithin the ET and/or the LT; Ð Ð ÐÂHH©Âà  Âwithin the line and/or the NT1, separated between NT1 and line ifÔ ñ,Ô possible;ÆÆ Ð ` Ð ÁHÁ©Âà  Âwithin the subscriber installation.ÆÆ 6.3ÁHÁÃÃLoopbacksÄÄ 6.3.1ÁHÁÃÃLocations of loopbacks within the subscriber basic accessÄÄ Ð X ÐÁHÁLoopback locations for failure localization and verification controlled by the local exchange are shown in Figure 2/I.603. ÃÃNoteÄÄ © Other loopbacks might be necessary. ÁàÀIÁFIGURE 2/I.603ƒ 6.3.2ÁHÁÃÃCharacteristics of loopbacks within the subscriber accessÄÄ ÁHÁThe characteristics of loopbacks within the subscriber access are given in Table 1/I.603. Other loopbacks used in support of maintaining the subscriber installation from within the subscriber installation are specified in Recommendation I.602. TABLE 1/I.603 ÃÃNote 1ÄÄ © Whether the loopback is transparent or non©transparent is for further study. Whether or not a transparent loopback is used, the loopback should not be affected by configurations and conditions beyond the point at which the loopback is provided, e.g. by the presence of short circuits, open circuits or foreign voltages. ÃÃNote 2ÄÄ © Network control signals for loopbacks may not be harmonized. 6.3.3ÁHÁÃÃUse of loopbacksÄÄ ÁHÁIf the loopback 2 is established, the network part of the subscriber basic access is considered to be correctly functioning. No report is given to the SAMC. ÁHÁIf loopback 2 cannot be established and/or if faulty network conditions are detected, the exchange: ÁHÁ©Âà  Âeither goes further in the identification of the failed maintenance entity (see ÀÀ 6.2) and reports to the SAMC later, once the failed maintenance entity has been identified;ÆÆ ÁHÁ©Âà  Âor informs the SAMC that the network is affected by a failure, in the case of non automatic identification process of the failed maintenance entity is implemented.ÆÆ 6.4ÁHÁÃÃCommand controlled tests and measurementsÄÄ ÁHÁFor more precise failure localization it would be necessary to obtain line parameter measurements indicating that the value of an electrical parameter is within a certain margin or showing the precise value of the parameter. ÁHÁFor further study. 7.ÁHÁÃÃLogistic delay timeÄÄ ÁHÁSee Recommendation M.20. 8.ÁHÁÃÃFailure correctionÄÄ ÁHÁSee Recommendation M.20. 9.ÁHÁÃÃVerificationÄÄ ÁHÁThe verification that the failure has been corrected is made on demand of the staff. ÁHÁTests described in ÀÀÀÀ 3, 6 and 11 may be used. 10.ÁHÁÃÃRestorationÄÄ ÁHÁAfter the failure has been rectified and the correct operation of the access verified (during which time the access will be in either the "out of service due to failure" or "degraded transmission" conditions), the access shall be returned to the "in service" condition. The mechanism/procedure for returning the access to the "in service" condition (e.g. automatic or manual) is not a subject of this Recommendation (see Recommendation I.601). 11.ÁHÁÃÃOverall performance measurementsÄÄ ÁHÁOverall performance measurements could be made as follows, from the point of view of the exchange:Ô ñ,ÔŒ ÁHÁ©Âà  Âthe measurement may concern a limited number of subscriber accesses at the same time;ÆÆ ÁHÁ©Âà  Âthe measurement is only made on demand.ÆÆ ÁHÁThese tests and/or measurements shall not influence the conditions of the subscriber installation for incoming and outgoing calls. This gives the advantage of enabling measurement of the performance independently of the activity in the different channels of the subscriber basic access and also over a longer period of time. ÁHÁFor the performance evaluation of a digital transmission system (over a longer period of time, with permanent activation of the subscriber basic access) the Administration network shall have arrangements for the calculation of the performance levels according to Recommendation G.821.