Internet Standards/CD2.mdf/ccitt/1992/i/i603.asc

Text File | 1993-06-28 | 13KB | 608 lines

Recommendation I.603



APPLICATION OF MAINTENANCE PRINCIPLES TO ISDN BASIC ACCESSES





1.    Scope of application



    This Recommendation covers the maintenance of that part of the ISDN subscriber basic access,
controlled by the network, follows the maintenance principles as defined in RecommendationM.20
and applies to the basic access directly connected to the local exchange without any multiplexer or
concentrator.



    The principle of controlled maintenance (as defined in RecommendationM.20) is applied for
maintaining the subscriber basic access.



    Controlled maintenance is a method of sustaining a desired technical performance by the sys-
tematic application of supervision, testing and performance sampling in order to minimize preventive
maintenance and to reduce corrective maintenance.



2.    Network configuration for maintenance activities



    Figure 1/I.603 is the basis for the general maintenance principles of the subscriber access.



































    SAMC: Subscriber Access Maintenance Centre

    SIME: Subscriber Installation Maintenance Entities

    MSP:Maintenance Service Provider



Note 1 - The subscriber access contains a digital section which can use different varieties of transmission
techniques and may also include a regenerator.



Note 2 - In some countries certain maintenance functions within the subscriber access may be controlled
by the subscriber installation (SIME).



FIGURE 1/I.603



Configuration for the maintenance of the basic access





3.    Failure detection



3.1    General



    When 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.



    When 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.



    When the ISDN subscriber basic access is not in an active state (as seen by the exchange), the sub-
scriber access may be periodically tested by the exchange.  This is called the continuity test.



3.2    Automatic supervision



3.2.1    Continuous automatic supervision of layer 1



3.2.1.1    Objectives



    This 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).



    These automatic mechanisms are continuously operational during the active period of the subscriber
basic access.



    They are designed to detect malfunctioning of particular items, e.g. power supply, quality level of trans-
mission, incoming signal, frame alignment.



    The 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 refer-
ence point may not be capable of full activation according to RecommendationI.430.



3.2.1.2    Digital section functions



    Functions, which are allocated to the digital section are listed below:



    -    detection of loss of frame alignment within the digital         system;



    -    detection of loss of frame alignment on the user-network     interface as defined in Recommen-
dationI.430;



    -    supervision of the power feeding;



    -    transmission performance monitoring.



    Transmission performance monitoring mechanisms are for further study.



Note - 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.



3.2.1.3    Exchange termination functions



    Functions which are allocated to the exchange termination are listed below:



    -    supervision of information related to or received from the digital section;



    -    transmission performance evaluation.



    The transmission performance evaluation is based on a permanent processing of the elementary
results presented by the continuous error monitoring of the digital section.



    The result of the processing will give information on at least one transmission quality level.



    Definition of quality levels and evaluation timing conditions are out of the scope of this Recommen-
dation.



3.2.2    Automatic supervision of layers 2 and 3 of the D-Channel protocol



    This 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).



    There are three categories of automatic supervision which may be performed by layers 2 and 3 of
the D-Channel protocols:



    -    service provision incapability detection (e.g. incapability of layer 2 to establish a data link
connection);



-protocol misoperation detection (e.g. at layer 2, detection of dual TE1 assignment);



    -    error monitoring (e.g. the layer 2 CRC check procedure can      detect the occurrence of an
errored frame).



    These events (defined in RecommendationsI.440 and I.450) should be recorded.



3.3    Continuity test



3.3.1    General



    When 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.



    The test should be a simple go/no go test.



Note - 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     Control of the continuity test



    The continuity test is based on a normal activation of layer 1.  If the activation is confirmed by a pos-
itive result of the continuity test, the subscriber basic access is declared to be in good order for opera-
tion.  No report is given to the SAMC.



    If 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 pro-
cess, and will report to SAMC.



    The 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.    System protection



    When a failure is detected which has an adverse effect on the availability and/or functionality of net-
work 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 RecommendationI.601).  In
this condition, removal of power from the line may be required.



5.    Failure information



    A 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.



    The message could be presented after an automatic identification of a failed maintenance entity
(ME) has been made (see _6).



6.    Failure localization



6.1    Automatic confirmation of failure within the subscriber basic access



    An 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, fol-
lowing abnormal conditions which have been detected by the processes presented above, i.e.  continu-
ous supervision, supervision on layer 2 and layer 3, continuity test.



    The 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.



    If 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.



6.2    Failed maintenance entity identification



6.2.1    General



    Such a function has to be made on demand or automatically following the indication of failed condi-
tions by the network or following a subscriber complaint.  It is necessary, before undertaking the appropri-
ate action, to identify (know) the maintenance entity affected by the failure.



6.2.2    Objectives



    The main objective of this function which is controlled by the SAMC is to indicate to the SAMC if the
failure is:



    -    within the ET and/or the LT;



-within the line and/or the NT1, separated between NT1 and line ifpossible;



    -    within the subscriber installation.



6.3    Loopbacks



6.3.1    Locations of loopbacks within the subscriber basic access



    Loopback locations for failure localization and verification controlled by the local exchange are shown
in Figure 2/I.603.



Note - Other loopbacks might be necessary.



























FIGURE 2/I.603





6.3.2    Characteristics of loopbacks within the subscriber access



    The characteristics of loopbacks within the subscriber access are given in Table 1/I.603.  Other loop-
backs used in support of maintaining the subscriber installation from within the subscriber installation are
specified in Recommendation I.602.



                               TABLE 1/I.603

















































Note 1 - 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.



Note 2 - Network control signals for loopbacks may not be harmonized.



6.3.3    Use of loopbacks



    If 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.



    If loopback 2 cannot be established and/or if faulty network conditions are detected, the exchange:



    -    either goes further in the identification of the failed maintenance entity (see _6.2) and reports to
the SAMC later, once the failed maintenance entity has been identified;



    -    or informs the SAMC that the network is affected by a failure, in the case of non automatic iden-
tification process of the failed maintenance entity is implemented.



6.4    Command controlled tests and measurements



    For 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.



    For further study.



7.    Logistic delay time



    See Recommendation M.20.



8.    Failure correction



    See Recommendation M.20.



9.    Verification



    The verification that the failure has been corrected is made on demand of the staff.



    Tests described in __3, 6 and 11 may be used.



10.    Restoration



    After 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 Rec-
ommendationI.601).



11.    Overall performance measurements



    Overall performance measurements could be made as follows, from the point of view of the exchange:



    -    the measurement may concern a limited number of subscriber accesses at the same time;



    -    the measurement is only made on demand.



    These 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.



    For the performance evaluation of a digital transmission system (over a longer period of time, with per-
manent activation of the subscriber basic access) the Administration network shall have arrangements for
the calculation of the performance levels according to Recommendation G.821.