This Recommendation presents the general principles for
employing those maintenance features and capabilities of international
transmission systems and equipment which are based on alarm information.
.sp 9p
.RT
.PP
It describes a set of strategies, in addition to the maintenance philosophy in Recommendation\ M.20, to use these alarm\(hybased features and
capabilities in an effective and efficient manner. This Recommendation is also intended to address the interactions between alarms of digital and analogue
transmission systems and equipments.
.PP
Alarm interactions for mixed analogue/digital transmission systems and equipment are under study.
.RT
.PP
1.2
While this Recommendation discusses the strategy to employ
these features and capabilities, the actual arrangements to provide and use
them are left to the discretion of the Administrations.
.sp 9p
.RT
.sp 2P
.LP
\fB2\fR \fBTypes of\fR
\fBalarms and related messages\fR
.sp 1P
.RT
.PP
Alarm information may be categorized as
follows:
.RT
.LP
a)
Prompt maintenance alarm
(PMA);
.LP
b)
Deferred maintenance alarm
(DMA);
.LP
c)
Maintenance event information
(MEI).
.PP
Definitions of PMA, DMA and MEI are found in Recommendation\ M.20, \(sc\ 5.4.1.
.sp 2P
.LP
\fB3\fR \fBGuidance for using alarm information\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIHierarchy\fR
.sp 9p
.RT
.PP
The alarm information from transmission systems and equipment is
based on a hierarchy of:
.RT
.LP
a)
alarms and indications displayed on failed equipment or
systems,
.LP
b)
office audible/visual alarms which alert local staff, and
.LP
c)
remote information which appears on a display monitored by centralized maintenance staff which is not collocated with the
failed equipment or systems.
.PP
This alarm hierarchy is used in failure localization, either
for a maintenance entity, or for specific equipment within a maintenance
entity.
.sp 1P
.LP
3.2
\fIDisplay\fR
.sp 9p
.RT
.PP
Alarm information can be displayed to help in localization in
different ways, such as:
.RT
.LP
a)
locally\ \(em\ on the equipment,
.LP
b)
on site\ \(em\ in the same building as the equipment, or
.LP
c)
remotely\ \(em\ at a building not collocated with the
equipment.
.PP
Both localized and on\(hysite displays are used by on\(hysite
maintenance staff. Remote displays are normally used either for coverage during periods when a building is not staffed or to obtain a wider maintenance
perspective from a single location on a possibly large number of systems.
.PP
For example, the remote maintenance strategy of \(sc\ 3.5 can be
used first to localize a trouble to a maintenance entity. Then, maintenance
staff can obtain further remote (or otherwise made available) information to
localize the failure to specific equipment. After this, the maintenance staff can use the local alarm maintenance strategy of \(sc\ 3.7 to isolate and correct
the failure.
.bp
.RT
.sp 1P
.LP
3.3
\fIConsiderations for local or remote alarm monitoring\fR
.sp 9p
.RT
.PP
Alarm information may be displayed locally on equipment, or on\(hysite in the same building as the monitored equipment using external monitoring
equipment. Use of such displays implies that maintenance staff must be present or visit the site to observe the information.
.PP
Remote alarm monitoring provides a means for staff at a centralized
location, not collocated with the transmission systems and equipment, to
monitor them.
.PP
The choice between local and remote monitoring and the degree of
centralization and automation employed depends on a number of factors,
including the type of maintenance organization, the expected failure rates and the physical locations involved.
.RT
.sp 1P
.LP
3.4
\fIReducing unnecessary maintenance activity\fR
.sp 9p
.RT
.PP
When an equipment failure requiring some maintenance activity
occurs, alarms should, if possible, be generated by the maintenance entity of which the equipment is part. The general rule is that maintenance
activities should be directed only at the maintenance entity in which the
failure exists. Thus, techniques should be used which prevent unwanted alarms (and the resulting unnecessary maintenance activity) beyond the maintenance
entity in which a failure exists. Also, maintenance entities downstream of the failed maintenance entity should have a means of recognizing that a failure has occurred upstream, as part of the aim of reducing maintenance activity.
Provision may be made at a maintenance entity to indicate an upstream failure and/or inhibit unnecessary actions. For example, in digital transmission
systems and equipment, this may be accomplished by the use of:
.RT
.LP
\(em
alarm indication signal (AIS);
.LP
\(em
service alarm (SA);
.LP
\(em
upstream failure indication (UFI).
.PP
For definition of AIS, SA and UFI see Recommendation M.20,
\(sc\ 5.4.2.
.sp 1P
.LP
3.5
\fIConsiderations for\fR
\fIremote maintenance alarm information\fR
.sp 9p
.RT
.PP
Remote maintenance alarm information provides a means for staff not collocated with transmission systems and equipment to nonetheless monitor and control them. The monitored equipment may be located in unstaffed locations.
This section recommends the principles which should be followed if remote
alarm information is provided.
.RT
.PP
3.5.1
Identification and localization are required to determine what
the response should be: start restoration of service by using alternate
routes, dispatch for maintenance of failed equipment, or wait and gather
further information to better identify the nature and/or seriousness of the
problem.
.PP
3.5.2
The decision to send maintenance staff is based upon the
maintenance philosophy in Recommendation\ M.20, \(sc\ 1.1.
.sp 1P
.LP
3.6
\fIMaintenance alarm arrangements\fR
.sp 9p
.RT
.PP
Maintenance alarm arrangements are based on the use of
audible/visual alarm systems. These systems provide alarms which direct on\(hysite staff to the location of the failed equipment. The objective when providing
audible/visual alarm indications is that they should permit on\(hysite
maintenance staff to detect and locate the source of failure in a timely
fashion in line with other priorities. Note that distinctive sounds may be used to differentiate audible alarms. Also, visual signals should be able to direct maintenance staff to the failed equipment or to a point where the location of the failure can be determined.
.RT
.sp 1P
.LP
3.7
\fIUse of\fR
\fIlocal alarm information\fR
.sp 9p
.RT
.PP
3.7.1
Local alarm information is concerned with alerting on\(hysite
maintenance staff to equipment failures. The local maintenance activities
usually entail the location and correction of the failure. To carry this out
effectively and efficiently, information which helps direct the maintenance
staff to the failure should be provided directly from the failed equipment.
.PP
3.7.2
Local alarm information is derived from local failure
indications, together with the maintenance staff use of tests and relevant
documentation. This should be sufficient to localize the failure within
the failed equipment.
.bp
.PP
3.7.3
Note that a further purpose of local failure indications is to
provide a backup for remote indications, in the event that there is a failure in communications between monitored equipment and a central monitoring
location.
.sp 2P
.LP
\fB4\fR \fBGeneral considerations\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fIMonitoring\fR
.sp 9p
.RT
.PP
In general, failures of equipment should be detected by
continuous (or nearly continuous) automatic monitoring, as opposed to
monitoring or testing involving human intervention. Note that shared, but
automatic, monitoring is considered nearly continuous. Continuous (or
nearly continuous) monitoring is often made feasible by virtue of advances
in technology, and by virtue of the large number of circuits affected or
jeopardized by a transmission system failure. In addition, continuous (or
nearly continuous) monitoring is faster, more reliable, and less labor
intensive than alternative monitoring strategies.
.RT
.sp 1P
.LP
4.2
\fIUses of PMA, DMA and MEI\fR
.sp 9p
.RT
.PP
4.2.1
When reporting or displaying alarms either locally or remotely,
it is important to distinguish between PMA/DMA indications and MEI\ indications. PMA/DMA indications are those which cause maintenance staff to be alerted
(e.g., by ringing a bell), and MEI\ indications are those which are displayed in response to staff interrogations or in conjunction with other indications
(e.g., alarms) which are spontaneously generated.
.PP
4.2.2
These distinctions should be defined for each transmission system and equipment in order for alarm indications to be properly processed.
These distinctions may be of particular importance when using remote alarm
surveillance systems, where large numbers of PMA, DMA and MEI\ indications must be dealt with by maintenance staff.
.PP
4.2.3
MEI indications may be used as aids in failure localization or
verification of remote operations (such as remote control of protection
switching) under manual control. The information conveyed by MEI\ indications
may also be used to supplement that conveyed by PMA/DMA indications.
.PP
4.2.4
Note that detection of failures is accomplished by having
suitable monitors associated with each maintenance entity. The criteria for
activating alarm indications at a maintenance entity should generally be based on limits on the maintenance entities, which will generally be related to the performance objectives of the transmission systems.
.PP
4.2.5
To aid in the dispatch of personnel, remote indications should
include the following information:
.LP
a)
identification of the failed transmission system or
equipment and nature of trouble condition,
.LP
b)
distinction between service\(hyaffecting failures and
non\(hyservice\(hyaffecting failures where such a distinction is
possible, and
.LP
c)
severity of the failure which has occurred.
.sp 1P
.LP
4.3
\fITransmission and presentation of alarm information\fR
.sp 9p
.RT
.PP
4.3.1
There are two basic interface arrangements for transferring
alarm information between monitored and monitoring equipment:
.LP
a)
discrete, parallel, and
.LP
b)
serial data.
.PP
The
parallel method of data gathering and control
uses
discrete wires for implementing each function. The
serial data method of
gathering and control
uses a single pair of wires to carry serial (in time) data points, rather than individual wires for each point. Much new
telecommunications equipment is \*Qintelligent\*U, that is, it employs
microprocessor circuit design, which lends itself more readily to serial data transfer rather than to parallel.
.PP
4.3.2
The presentation of alarm information can be:
.LP
a)
visual (lamp, LED, printer or display indication), and/or
.LP
b)
audible (bell, tones or voice).
.PP
The alarm information may be presented as:
.LP
a)
an indication at an alarm interface (e.g., contact function,
d.c. signal) and/or
.LP
b)
an alarm message on the man\(hymachine interface.
.bp
.PP
This alarm message may contain:
.LP
i)
heading (name of maintenance entity, date, time,\ etc.),
.LP
ii)
category of failure (PMA, DMA, MEI),
.LP
iii)
description of failure, which may include the cause of
failure, location of the failed item(s) and other information
which can be useful in locating the failed item(s),
.LP
iv)
possible consequences of the failure, and
.LP
v)
automatic actions performed by the network (internal
protection and service actions).
.sp 1P
.LP
4.4
\fIPossible use of MEIs\fR
.sp 9p
.RT
.PP
Administrations using MEI may desire to alert maintenance
staff by means of a PMA or DMA. The criteria and arrangements
.FS
The
arrangements to generate such information may take place in the transmission
system or in auxiliary supervision systems.
.FE
for generating PMA or DMA
based on analysis of MEI are left to their discretion.
.RT
.sp 1P
.LP
4.5
\fIConsiderations for\fR
\fIprotection switching and control\fR
.sp 9p
.RT
.PP
To meet transmission system availability objectives or maintenance criteria, transmission systems may be provided with protection
equipment. Such equipment, if provided, may have the following
capabilities:
.RT
.LP
a)
automatic protection switching of service from failed
regular equipment to working standby equipment,
.LP
b)
automatic protection switching of service to overcome
transmission degradation caused, for example, by radio path fading,
.LP
c)
remotely controlled protection switching of service
between regular equipment and standby equipment, and/or
.LP
d)
locally controlled protection switching of service between regular equipment and standby equipment.
This Recommendation presents the general principles for
employing performance monitoring features and capabilities on international
transmission systems and equipment for maintenance purposes. Performance
monitoring data is one category of maintenance information as described in
Recommendation\ M.20, \(sc\ 5.4.
.sp 9p
.RT
.PP
1.2
As an example, the need for performance monitoring may be seen
by considering a defective transmission system or equipment which will
increasingly degrade for a period of time prior to total failure. In the early stages, the failing system or equipment generates errors over isolated short
duration intervals, possibly causing short losses of frame alignment. As the
severity of the degradation increases with time, the quantities and densities of errors and losses of frame alignment increase to more severe levels. Since these error bursts and losses of frame alignment are usually too short in
duration to initiate automatic\(hyprotection switching or to generate alarms, they will propagate through the network unchecked and affect customers. The
degradation process may last for days, weeks or even months if not corrected
before a detectable failure occurs. In many cases, the defective equipment
will never completely fail, but continually generate errors and losses of frame alignment.
.PP
1.3
This Recommendation describes a possible strategy to employ
performance monitoring features and capabilities. The choice of applying this strategy and the actual arrangements to provide it are left to the discretion of the Administrations.
.bp
.sp 2P
.LP
\fB2\fR \fBGeneral strategy for using performance monitoring data\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIGeneral\fR
.sp 9p
.RT
.PP
Performance monitoring is generally used to collect data
which may identify degrading systems before they fail and cause alarms. The
maintenance staff response to performance monitoring data does not usually
require the same priority as to other alarm information.
.RT
.sp 1P
.LP
2.2
\fILocal or remote performance monitoring\fR
.sp 9p
.RT
.PP
Performance data may be displayed locally on equipment, or
on\(hysite in the same building as the monitored equipment using external
monitoring equipment (for example, portable test sets). Use of such displays
implies that maintenance staff must visit the site at least periodically to
retrieve the data.
.PP
Remote performance monitoring provides a means for staff at a
centralized location to monitor distant transmission systems and
equipment.
.PP
The choice between local and remote monitoring and the degree of
centralization and automation employed depends on a number of factors,
including the type of maintenance organization, the expected failure rates and the physical locations involved.
.RT
.sp 1P
.LP
2.3
\fIMonitoring strategies\fR
.sp 9p
.RT
.PP
In general, failures of equipment should be detected by continuous automatic performance monitoring, as opposed to monitoring or testing involving human intervention. This capability, however, implies that the performance
monitor feature is built into the digital terminal system, or that dedicated
external performance monitor equipment is provided for each termination.
.PP
An alternative to providing dedicated external performance monitor
equipment is to provide remote access to protected monitor points and share
external performance monitoring equipment with a number of terminal systems.
This alternative of shared, but automatic monitoring is considered
nearly continuous.
.PP
Continuous (or nearly continuous) monitoring is often made
feasible by virtue of advances in technology, and by virtue of the large number of circuits affected or jeopardized by a transmission system failure. While
continuous performance monitoring capabilities built into transmission systems and terminals are clearly the preferred implementation for new systems, the
concept of nearly continuous monitoring offers an efficient and cost\(hyeffective means of providing automatic monitoring capabilities for existing digital
systems not having the built\(hyin capabilities. In addition, continuous (or
nearly continuous) monitoring is faster, more reliable, and less labor
intensive than manual monitoring strategies.
.RT
.sp 1P
.LP
2.3.1
\fIUses of\fR
\fIperformance monitoring data\fR
.sp 9p
.RT
.PP
Three general ways in which performance monitoring data may be used for maintenance purposes are:
.RT
.LP
a)
for routine monitoring of transmission systems and
equipment,
.LP
b)
for demand monitoring initiated by staff,
.LP
c)
for initiating a deferred maintenance alarm when performance has degraded beyond pre\(hydetermined limits.
.PP
2.3.2
For
routine monitoring
, performance data which may be
useful in predicting degrading systems is routinely collected and reported to a person on a scheduled or periodic basis. The reporting of data may provide, for example, daily, weekly or monthly summaries of performance.
.PP
As an example, remotely located monitoring equipment may
continuously observe the performance of a collocated transmission system and
store the significant data until a central computer requests the remote
monitoring equipment to report the data. The central computer may routinely
request data once every day. Then the central computer would convert the data into a report format useful for maintenance staff. Maintenance staff may use
this routine data to determine trends in performance and schedule preventive
maintenance or repairs before a failure has occurred. Or it may use the data
to verify that transmission objectives are being met.
.bp
.PP
2.3.3
For
demand monitoring
, the staff requests performance
data on an essentially real\(hytime basis from a monitored entity. This type
allows the staff to retrieve detailed information from the monitored
entity.
.PP
The main uses of demand monitoring are repair verification,
installation and acceptance testing. However, for some transmission systems
(for example, a radio system), demand monitoring may be used with other test
equipment or signal generators to perform fault localization.
.PP
2.3.4
A deferred maintenance alarm is initiated if performance has
degraded so much that it is important for the staff to be alerted independently of the routine reporting of performance data. The deferred maintenance alarm
should be indicated to the staff as soon as practical. It would be expected
that maintenance staff would respond relatively quickly to this alarm for
restoration and correction.
.sp 1P
.LP
2.3.5
\fICriteria for\fR
\fIselection of performance monitoring data\fR
.sp 9p
.RT
.PP
The general criteria for selection of performance monitoring data are as follows:
.RT
.LP
a)
the data should be chosen depending on their use;
i.e.,\ maintenance (\(sc\ 2), verification (\(sc\ 3.1) or
characterization (\(sc\ 3.2);
.LP
b)
the amount of data and their resolution should be adjusted
so as to minimize the amount of data collected, stored and
reported consistent with the uses of performance monitoring
data in \(sc\ 2.3.1;
.LP
c)
the data should be of a form which allows comparison of
performance among different transmission systems and equipment;
.LP
d)
for each data element it is important to select an
appropriate measurement time interval.
.sp 1P
.LP
2.4
\fITypes of\fR
\fIinterfaces to monitoring equipment\fR
.sp 9p
.RT
.PP
2.4.1
For specific applications, Administrations should consider
using a serial interface for transfer of perfor
mance monitoring data between the monitored entity and the equipment which is monitoring it. To derive
maximum benefit in using the performance monitoring data, very fine resolution for representing each data element may be necessary. This may imply that an
impractically large number of wires may be required if a serial interface is
not used. For other applications where little performance data is transferred or where each performance data element can be represented with few levels of
coarse resolution, a discrete interface may be appropriate (see \(sc\ 4.3 of
Recommendation\ M.32).
.PP
2.4.2
It is recommended that Administrations evaluate both interface
arrangements using the above considerations and use the one which is most
economical and feasible for the specific application.
.sp 1P
.LP
2.5
\fIData collection and report screening\fR
.sp 9p
.RT
.PP
2.5.1
Performance monitoring implies the collection of data from
transmission systems and equipment which may be performing satisfactorily a
large portion of the time they are monitored. To meet the objectives for
performance monitoring, a means of screening the data is desirable so that only useful information is provided. Administrations should base the amount of
screening on the desired maintenance staff responses and the processing,
storage and communications needs related to the data quantities.
.PP
2.5.2
As an example of screening, consider the case where there are
two thresholds available in a remotely located performance monitoring
equipment. For a particular monitored entity, a storage threshold may be used such that performance data for that entity measured over a given time interval need not be stored or reported unless the threshold is exceeded. Then a
deferred maintenance alarm threshold may be used such that when the performance data exceeds this threshold, the monitoring equipment will not only store the data but also generate a deferred maintenance alarm.
.PP
2.5.3
Note that in a system in which processing is shared between
remotely located monitoring equipment and a central processor, the central
processor may contain thresholds which may be used to further screen or process information reported to the maintenance staff.
.bp
.sp 2P
.LP
\fB3\fR \fBOther possible uses of\fR
\fBperformance monitoring data\fR
.sp 1P
.RT
.PP
In addition to maintenance, performance monitoring data may be used for:
.RT
.LP
a)
verification of transmission system or equipment performance
objectives,
.LP
b)
characterization of transmission systems and
equipment.
.PP
3.1
The verification of objectives is concerned with the
transmission systems and equipment as a whole and how well the analogue or
digital signal streams are being delivered to the aggregate of customers using these systems and equipment. Thus, even if a particular regular equipment is
operating poorly, when a protection equipment is operating properly, signal
streams are still being delivered to customers intact. Thus, monitoring for
verification of objectives should usually be done only when the equipment which is the object of the verification is carrying live traffic. The monitored
verification data can be used to give a general picture of the performance of the transmission system and equipment, construct network measures, and verify that transmission objectives are being met.
.PP
3.2
Characterization includes collection of data that may be used by transmission system and equipment designers. This type of data is often
very specialized, and often must be collected in very large quantities in
order to do an appropriate system characterization. It is also often
collected with monitoring equipment specifically designed for the purpose.
\v'6p'
.sp 2P
.LP
\fBRecommendation\ M.35\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBPRINCIPLES\ CONCERNING\fR |
\fBLINE\(hyUP\ AND\ MAINTENANCE\ LIMITS\fR
.EF '% Fascicle\ IV.1\ \(em\ Rec.\ M.35''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.35 %'
.ce 0
.sp 1P
.PP
The following principles have been adopted in respect of
line\(hyup and maintenance action limits for analogue and digital international
circuits, links and lines:
.sp 1P
.RT
.LP
i)
There should be separate limits for line\(hyup and maintenance action.
.LP
ii)
There should be a single limit specified for maintenance
action, and this limit should be chosen such that, if exceeded,
a fault would be considered to exist. (However, the subject of
prompt and deferred maintenance action requirements is under
study and the result of this study may reflect on the number of
limits required for maintenance action.)
.LP
iii)
After clearance of a fault, an international circuit, link or line should be returned to service within the line\(hyup limit
or, in the circumstances where this is not practical, as close
as possible to the line\(hyup limit. In all cases, the circuit, link
or line should be returned to service within the maintenance
action limit.
.PP
It is intended that, wherever practical, these principles be
embodied in new M and N\ Recommendations, and be taken into account when the M and N\ Recommendations have cause to be reviewed or amended.
The purpose of this Recommendation is to apply general maintenance principles to determine the maintenance strategy to be adopted by
Administrations and other maintenance service providers (MSP) in order
to maintain ISDNs.
.PP
In providing this guidance, due consideration has been given to the
principles identified in Recommendations\ M.20, M.30, M.32 and\ M.34 and to the activities identified in the I.600\(hySeries Recommendations\ [1].
.bp
.RT
.sp 1P
.LP
1.1
\fIScope of application\fR
.sp 9p
.RT
.LP
1)
considering that Recommendation M.20 defines the maintenance
philosophy for telecommunications networks;
.LP
2)
considering that Recommendation M.30 defines the principles
for the telecommunications management network (TMN);
.LP
3)
considering that Recommendation I.601 [2] describes
reference configurations, general architecture for maintenance
of ISDN subscriber access and subscriber installation, which
are applied in:
.LP
\(em
Recommendation I.602 [3] for the ISDN subscriber
installations,
.LP
\(em
Recommendation I.603 [4] for the ISDN subscriber
basic accesses,
.LP
\(em
Recommendation I.604 [5] for the ISDN subscriber
primary rate accesses,
.LP
\(em
Recommendation I.605 [6] for the static multiplexed
basic rate accesses,
.LP
\(em
Recommendation I.606 (under study) for the ISDN
subscriber higher rate access;
.LP
4)
considering that Recommendations Q.940 [7] and Q.942
(under study) describe the model, service elements and
protocols to be provided at the ISDN user/network
interfaces for management;
.LP
5)
considering that Recommendation M.550 provides the
maintenance limits for digital paths and sections to achieve
the performance objectives given in
Recommendation\ G.821\ [8],
.LP
this Recommendation defines the ISDN maintenance concepts to be
applied for the maintenance of subscriber installations, networks, including
the transit network, and interworking between ISDNs and other networks,
including both existing and future public and private networks.
.PP
This Recommendation takes into consideration basic ISDN features such as:
.LP
\(em
open communication via the S/T reference points;
.LP
\(em
portability of terminals between S/T reference points, from
subscriber installation to subscriber installation, and from
ISDN to ISDN.
.sp 2P
.LP
\fB2\fR \fBOverview\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIGeneral maintenance principles for ISDN\fR
.sp 9p
.RT
.PP
The fundamental maintenance strategy is to rely on performance
monitoring wherever possible in order to apply the controlled maintenance
principles of Recommendation\ M.20.
.PP
The maintenance capabilities provided must allow for the clear
differentiation of troubles between subscriber and network equipment.
.PP
The maintenance capabilities provided must allow for clear
differentiation between faults and legitimate subscriber activities.
.PP
A MSP should be able to localize the fault in his domain without
disturbing the network or other domains. This should be possible locally and
remotely, i.e.,\ across networks and between any allowed management entities.
.PP
Testing will be needed both to supplement the performance monitoring for trouble detection and to provide additional trouble localization
ability.
.PP
The subscriber installation should be able to receive failure or
performance information if sent from the network side. The network should be
able to receive failure or performance information from the subscriber
side.
.PP
A capability should be provided to control the status of the
subscriber access and of the subscriber equipment during maintenance
operations.
.PP
The subscriber installation (or its MSP) should be able to receive
information, if sent from the network, about the maintenance status of its
access.
.PP
Only the Administration may initiate maintenance action within the
subscriber access.
.PP
The subscriber or his MSP, either private or Administration, may
initiate maintenance action within the subscriber installation.
.bp
.RT
.sp 1P
.LP
2.2
\fISupervision of the subscriber access and end\(hyto\(hyend performance\fR
\fImeasuring\fR
.sp 9p
.RT
.PP
For maintenance purposes, each maintenance entity (ME) and
maintenance entity assembly (MEA) provides its own performance measuring
according to Recommendation\ M.20. The generated anomaly and defect informations allows decision and identification of ME or MEA in the degraded or unacceptable functioning state, and reporting that state to the associated management
entity.
.PP
The network can only measure the performance of MEs and MEAs. The
problem of how to combine the performance of the MEs and MEAs of the transit
network with that of the subscriber accesses to determine the end\(hyto\(hyend
performance as seen by the subscriber is for further study.
.RT
.LP
2.3
\fIManagement reference models\fR
.sp 1P
.RT
.sp 2P
.LP
2.3.1
\fIReference definitions\fR
.sp 1P
.RT
.sp 1P
.LP
2.3.2
\fBsubscriber access maintenance center (SAMC)\fR
.sp 9p
.RT
.PP
An SAMC represents a group of functions, network equipment
elements and staff controlled by the Administration, which together have the
responsibility and capability for maintenance functions and maintenance actions within the subscriber access.
.RT
.sp 1P
.LP
2.3.2.1
\fBsubscriber access maintenance entity (SAME)\fR
.sp 9p
.RT
.PP
The SAME controls the subscriber access maintenance functions and provides communications for such activities. The SAME might be
distributed.
.PP
Example of SAME functions:
.RT
.LP
\(em
control loopbacks in an NT1 or LT;
.LP
\(em
supervise the service state of the subscriber access;
An SIME represents a group of dedicated functions contained within the functional groups (as specified in Recommendation\ I.411\ [9]) of the
subscriber installation (i.e.\ TE1 and NT2) which have, for example, the
following purposes:
.RT
.LP
\(em
interaction with the (human) user;
.LP
\(em
handling of maintenance protocol from the SAME and/or
a MSP;
.LP
\(em
control of internal testing and maintenance
mechanisms.
.PP
It is considered that the functions of the SIME may be distributed throughout the protocol layers implemented in the subscriber equipment and
management/maintenance entities, including NT1 functions in some applications, but the precise architecture and protocol of the SIME is not a subject of this Recommendation.
.PP
Examples of SIME functions:
.RT
.LP
\(em
control TE loopbacks;
.LP
\(em
identify TE service capability;
.LP
\(em
control generation of test signals for maintenance of
subscriber installation wiring;
.LP
\(em
provide access to performance data within subscriber
installation, e.g.\ layer two and three protocol
performance;
.LP
\(em
security screen requests from MSPs.
.sp 1P
.LP
2.3.2.3
\fBmaintenance service provider (MSP)\fR
.sp 9p
.RT
.PP
The MSP represents a group of functions, equipment and maintenance staff, that together have the responsibility for maintaining the subscriber
installation or a part of the subscriber installation. A MSP cannot control the maintenance functions of the subscriber access. If authorized, it can request information from the SAMC about the subscriber access.
.RT
.LP
1)
Agreement and responsibility for maintenance between the
subscriber and the MSP for each part or parts of the subscriber
installation should be made at the time of subscription to
the maintenance service (this may take the form of a
commercial contract). In any case, provision to allow a
customer to change the maintenance service provider(s)
is recommended. The subscriber may choose not to make such
an agreement with a MSP.
.bp
.LP
2)
Maintenance service providers can be
.LP
\(em
private providers,
.LP
\(em
the Administration,
.LP
\(em
the subscriber.
.LP
3)
Private MSPs that are connected to ISDN by a S/T interface
are referred to as external MSPs. Administration MSPs may also
be connected via S/T interface or by other means as described
below.
.LP
4)
The interfaces between ISDNs and MSPs are for further
study.
.LP
5)
It is the sole responsibility of a subscriber installation
and not of the network to ensure that an unauthorized MSP
cannot obtain access to maintenance functions in the
subscriber installation.
.PP
Examples of MSP functions:
.LP
\(em
request SIME maintenance activity;
.LP
\(em
request SAMC maintenance information that is allowed;
.LP
\(em
provide test responders.
.sp 1P
.LP
2.3.2.4
\fBoperation, administration and maintenance centre (OAMC)\fR
.sp 9p
.RT
.PP
The OAMC is an Administration's centre with the responsibility for the general operation, administration and maintenance of the network. It
includes both staff and associated operations systems. The functions may be
distributed among many centres and OSs.
.PP
Examples of OAMC functions:
.RT
.LP
\(em
request SAME to control loopback activation;
.LP
\(em
supervise the bringing into service of subscriber access;
.LP
\(em
obtain performance information on the subscriber access
from the SAME;
.LP
\(em
manage teleservices provided to a subscriber;
.LP
\(em
screen requests from MSPs for authorization.
.PP
The SAMC is composed of the SAME and part of the OAMC.
.sp 1P
.LP
2.3.2.5
\fIManagement entities\fR
.sp 9p
.RT
.PP
Management entities are groups of capabilities that collectively
provide management functions, such as operations, administration, maintenance and provisioning. For the network part, the functions may be implemented by a combination of capabilities in network elements and operations systems. For the subscriber part, management functions may be contained within the subscriber
installations.
.RT
.sp 1P
.LP
2.3.3
\fIReference maintenance configuration\fR
.sp 9p
.RT
.PP
Shown in Figure 1/M.36 is the reference maintenance configuration, which gives the relationship between the subscriber installation and subscriber access to be maintained and the various maintenance centers, entities and
providers.
.PP
This reference model shows the possible physical interconnection
between Terminal Equipment (TE), Local Exchanges (LE), OAMC and MSPs.
.PP
The lines between physical devices containing each functional entity represent physical communications paths over which the management information may flow. It is envisioned that the higher layer protocols for management and maintenance would be the same. See Figure\ 7/I.601\ [2] for another
representation
of this communication. Service primitives are required to facilitate
interworking with a variety of lower layer protocols. Further study is needed to define these service primitives. Thus, the connections between the various entities could be provided by D\(hychannels, X.25 networks, Signalling System
No.\ 7, or leased lines.
.PP
In this reference configuration, the subscriber access is maintained by a SAMC. Local or remote users or MSPs may communicate with the SAMC to
request certain maintenance functions under its control. The SAME provides the communications interface for network local management functions and contains
the control functions for such local activity. The SAME functions may either be entirely part of the local exchange or may be distributed between the LE and an OAMC.
.bp
.RT
.LP
.rs
.sp 35P
.ad r
\fBFigure 1/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.3.4
\fIRelationship to telecommunications management network\fR
.sp 9p
.RT
.PP
The telecommunications management network (TMN) is intended to
provide an Administration with an independent communications network to carry its management (operations, administration and maintenance) messages to and
from its operations system (OSs) to the telecommunications network it manages, including its ISDN and associated network elements. Figure\ 2/M.36 shows an
example of one possible relationship of a TMN to the ISDN that is shown in
Figure\ 1/M.36.
.PP
In Figure 2/M.36, the TMN would carry management messages between the OAMC (including an Administration MSP, if provided) and the ISDN over a Q\(hytype TMN interface (see Recommendation\ M.30 for a description of the TMN
interfaces). The TMN would also provide the communications for an
Administration's externally provided MSP using the TMN PQ\(hyDCN protocol suite
(as defined in Recommendation\ M.30) over a T\(hytype physical ISDN
interface.
.PP
A private MSP may be connected directly to the ISDN via a T\(hytype
interface. It may also be connected to the TMN by interworking via other
network interworking interfaces that are under study.
.PP
While supporting the ISDN, the TMN is also supporting other management functions for the Administration, including the maintenance of transmission
system equipment.
.bp
.RT
.LP
.rs
.sp 29P
.ad r
\fBFigure 2/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.3.5
\fICommunications reference models\fR
.sp 9p
.RT
.PP
Communications between functional groups is required for the
maintenance of ISDNs. The communications configurations for maintenance of the subscriber access and the subscriber installation are shown in
Recommendation\ I.601\ [2]. Configurations for the transit part and for
end\(hyto\(hyend ISDN maintenance are for further study.
.RT
.sp 2P
.LP
2.4
\fIISDN management protocol principles\fR
.sp 1P
.RT
.sp 1P
.LP
2.4.1
\fIGeneral review\fR
.sp 9p
.RT
.PP
The different management functions which may be contained, for
example,
in the SAMC, SIME, MSP,\ etc., are implemented in one or several real systems. A \fBreal system\fR is a set of one or more computers, associated software,\ etc., that form an autonomous whole capable of performing information processing
and/or information transfer. Each real system contains one or more management entities that supports management functions. A
real open system
is a
real system which complies with the requirements of Recommendation\ X.200\ [10] in its communication with other real systems.
.PP
\fINote\fR \ \(em\ Two different modeling concepts are applicable to ISDN
management protocol:
.RT
.LP
\(em
ISDN protocol reference model (ISDN PRM), as defined in
Recommendation\ I.320\ [11];
.LP
\(em
reference model of open systems interconnection for
CCITT Applications (OSI PRM), defined in
Recommendation\ X.200\ [10].
.bp
.PP
These two reference models have the following commonalities:
.LP
\(em
both the ISDN PRM and the OSI PRM organize communications
functions into layers and describe the relation of these
layers with respect to each other;
.LP
\(em
the concepts and the associated terminology, which have been
introduced in Recommendations\ X.200\ [10] and X.210\ [12] are
fully applicable to the ISDN PRM. They include the concept of
layer, layer service, and the notions of service primitives,
peer entities and peer protocol.
.sp 1P
.LP
2.4.2
\fIRequirements for ISDN maintenance activities\fR
.sp 9p
.RT
.PP
Maintenance of ISDN equipments and interfaces is part of the
general management process in an ISDN management entity. It is intended that
maintenance of ISDN equipments by remote MPS through ISDN interfaces should
follow the principles of Recommendation\ X.200 and of open systems management, which are under study.
.PP
Systems management is achieved through a set of application processes running in different management entities that communicate together and play
complementary roles to provide management activities.
.PP
Within a management entity, system management functions are controlled and performed by the \fIsystem management element\fR . The system management element can be seen as a set of application processes communicating with remote
application processes by the use of one or more application layer entities. An application process is an element within a management entity which performs the information processing for a particular application.
.PP
The definitions of the functions among management entities needed to maintain the ISDNs according to the principles stated in this Recommendation
are for further study.
.RT
.sp 2P
.LP
\fB3\fR \fBBasic rate access\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIBasic rate access maintenance models\fR
.sp 9p
.RT
.PP
Three access configurations are described below, along with a
common subscriber equipment arrangement that applies to all three models. For each model, the maintenance entities are identified using reference points to delimit them. Some of these reference points are or may become standard
interfaces. The ownership boundaries between network and customer are outside the scope of this Recommendation.
.PP
Because the D\(hychannels shown in the models below all route through
several MEs (maintenance entities), they are not MEs themselves but will be
treated as maintenance entity assemblies. The D\(hychannels carry several protocol layers that will be treated using the management and maintenance protocols that are under study. These include a definition of a layer management entity
concept for each of the layers.
.PP
Other models are possible, but only a few, representative models are included here. Models including leased lines and digital crossconnect systems are left for further study.
.RT
.sp 1P
.LP
3.1.1
\fISimple model\fR
.sp 9p
.RT
.PP
This model, shown in Figure 3/M.36, is similar to that shown in
Figure\ 2/M.20. In the model, the V\d1\uinterface may be replaced by a function, such as a loopback point in a combined LT/ET, while still providing a boundary between MEs.
.RT
.sp 1P
.LP
3.1.2
\fISubscriber equipment arrangements\fR
.sp 9p
.RT
.PP
This model is shown in Figure 4/M.36.
.RT
.sp 1P
.LP
3.1.3
\fIMultiplexed interface\fR
.sp 9p
.RT
.PP
This model is shown in Figure 5/M.36.
.PP
In this case, several basic rate accesses using V\d1\ureference points are multiplexed or concentrated to interface the exchange termination. For
static multiplexing, a V\d6\uinterface is applied. For dynamic multiplexing
(multiplexing on the D\(hychannel) or concentrating (dynamic assignment of the
B\(hychannels), a V\d2\uinterface is applied. The V\d2\uand V\d6\uinterfaces are defined in Recommendation\ Q.512\ [13]. Performance monitoring is applied to the digital section of the basic rate access (between T interface and V\d1\ureference point) and between the multiplex/concentrator and the exchange
termination.
.bp
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure 3/M.36, (N), p. 16\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 13P
.ad r
\fBFigure 4/M.36, (N), p. 17\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 13P
.ad r
\fBFigure 5/M.36, (N), p. 18\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.1.4
\fIRemote multiplexed interface\fR
.sp 9p
.RT
.PP
The model is shown in Figure 6/M.36.
.PP
This is similar to the previous model except that it is extended
between the multiplex and the ET by one or more digital links which may route over higher order links.
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure 6/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
3.1.5
\fIBasic rate leased lines\fR
.sp 9p
.RT
.PP
This is for further study.
.RT
.sp 2P
.LP
3.2
\fIRequired capabilities\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.1
\fITransmission format maintenance features (layer 1)\fR
.sp 9p
.RT
.PP
The format will be such as to support performance monitoring in
both directions of transmission. Specifically, there will be error detection in each direction computed across the digital signal, for example, with CRC
(cyclic redundancy check) or other error detection methods.
.PP
Transmission errors detected at the LT are converted to near\(hyend
error (NEE) indications. Transmission errors detected at the NT are converted to far\(hyend error (FEE) indications and sent back to the LT. This enables
performance for both directions to be assessed by the Administration.
.PP
A function of the C\(hychannel may be to provide support of maintenance functions such as loopback activation and performance monitoring data
gathering.
.RT
.sp 1P
.LP
3.2.2
\fIMaintenance states and control\fR
.sp 9p
.RT
.PP
This is an area for further study, including:
.RT
.LP
\(em
restricting access to some capabilities to network or
It shall be possible to report the performance information from the exchange to the OAMC (see \(sc\ 3.2.3.2). It shall be possible to reset the
parameter counts. Other issues under study include:
.RT
.LP
\(em
combining all links in subscriber access;
.LP
\(em
parameter consistency;
.LP
\(em
identifying maintenance phases impacted by PM (performance
monitoring).
.sp 1P
.LP
3.2.3.1
\fIMaintenance entities monitored\fR
.sp 9p
.RT
.PP
It shall be possible to monitor the NT to LT links.
.bp
.RT
.sp 1P
.LP
3.2.3.2
\fIRequired performance monitoring parameters and history\fR
.sp 9p
.RT
.PP
The following principles apply to performance monitoring parameters and history:
.RT
.LP
a)
parameters should be counted separately in each direction
when feasible to help isolate troubles and to better estimate
network service provided to users;
.LP
b)
to support different maintenance uses, parameters should be
counted for short durations (e.g.,\ 15\ minutes to one hour) and
longer durations (e.g.\ 24\ hours) as specified in
Recommendation\ M.550;
.LP
c)
error counts and when they occur should be retained to help
deal with intermittent troubles;
.LP
d)
thresholding, covered in Recommendations M.34 and M.550;
.LP
e)
the threshold values should be settable by the OAMC;
.LP
f
)
performance information should be reported from the
exchange to the OAMC:
.LP
\(em
when threshold crossings occur;
.LP
\(em
on demand from the OAMC.
.sp 1P
.LP
3.2.4
\fITesting capabilities\fR
.sp 9p
.RT
.PP
Testing should introduce minimal disruption on other B\(hy and
D\(hychannels, and should not disrupt the subscriber's terminal equipment. Other testing capabilities are for further study.
.RT
.sp 1P
.LP
3.4.2.1
\fILoopbacks\fR
.sp 9p
.RT
.PP
The loopback capabilities for basic rate access, including types, locations, and control domains, are given in Recommendations\ I.602\ [3] and
I.604\ [4].
.RT
.sp 1P
.LP
3.2.4.2
\fITest lines\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
3.2.4.3
\fITest and monitor points\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
3.2.4.4
\fISelf tests and diagnostics\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
3.2.5
\fISupervision and verification of protocol implementations\fR
.sp 9p
.RT
.PP
The principles for the supervision and verification of ISDN access protocol implementations are:
.RT
.LP
a)
Protocol errors due to implementation problems or other
failures need to be detected. This may be based on the logging
and counting of protocol violations;
.LP
b)
Protocol problems need to be sectionalized, analyzed, and
isolated. The following techniques may be used:
.LP
\(em
access to log of protocol violation information;
.LP
\(em
monitoring of the layer 2 frames and the layer\ 3
messages;
.LP
\(em
test access and protocol testing.
.PP
See Recommendation I.603\ [4] for more information.
.sp 2P
.LP
\fB4\fR \fBPrimary rate access\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fIPrimary rate access maintenance models\fR
.sp 9p
.RT
.PP
Four primary rate access configurations are shown below, along with one figure showing four customer premises configurations, that can apply to any of the access models.
.PP
Maintenance entries are not indicated for these configurations,
because there are several different implementations of primary rate access. The definitions of MEs is for further study.
.bp
.RT
.sp 1P
.LP
4.1.1
\fISimple access model\fR
.sp 9p
.RT
.PP
The simple case of primary rate access from the NT2 directly to the exchange is shown in Figure\ 7/M.36. A variant of this model includes higher
order links.
.RT
.LP
.rs
.sp 12P
.ad r
\fBFigure 7/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.1.2
\fISubscriber configurations\fR
.sp 9p
.RT
.PP
There are several subscriber configurations that can appear behind any of the NT1s shown in the primary rate cases, as shown in Figure\ 8/M.36.
.PP
The first is the simplest case of separate NT1 and NT2, followed by a primary rate TE. Another case is with the NT1 and NT2 combined into one unit. A third case is a NT2 which is a PBX on which terminate several basic rate
access lines connecting TEs to the PBX. A final case is one in which the NT2 is a multiplexer on which terminate several basic rate access lines connecting\ TEs to the multiplex.
.RT
.LP
.rs
.sp 25P
.ad r
\fBFigure 8/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.1.3
\fIDigital crossconnect system (DCS)\fR
.sp 9p
.RT
.PP
A model introducing a new network element, the
digital
crossconnect system (DCS)
, in the simple access model is shown in
Figure\ 9/M.36.
.PP
The DCS is a static crossconnect of B\(hychannels, routing some to the
exchange and some to the leased circuit network. Processing of the D\(hychannel by the DCS is for further study, as discussed in Annex\ A.
.RT
.LP
.rs
.sp 10P
.ad r
\fBFigure 9/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.1.4
\fIPrimary rate leased circuits\fR
.sp 9p
.RT
.PP
In this case, all the B\(hy and D\(hychannels traverse the network from one NT2 to the other, without being terminated on a network switch. The network simply provides transport for a private ISDN, as shown in Figure\ 10/M.36.
.RT
.LP
.rs
.sp 7P
.ad r
\fBFigure 10/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
4.2
\fIRequired capabilities\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.1
\fITransmission format maintenance features\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
4.2.2
\fIMaintenance states and control\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 2P
.LP
4.2.3
\fIPerformance monitoring capabilities\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.3.1
\fIMaintenance entities monitored\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
4.2.3.2
\fIRequired performance monitoring parameters and history\fR
.sp 9p
.RT
.PP
For further study. Includes layer 1 and layer 2
monitoring.
.bp
.RT
.sp 2P
.LP
4.2.4
\fITesting capabilities\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.4.1
\fILoopbacks\fR
.sp 9p
.RT
.PP
The loopback capabilities for primary rate access, including types, locations, and control domains, are given in Recommendations\ I.602\ [3]
and\ I.604\ [5].
.RT
.sp 1P
.LP
4.2.4.2
\fITest lines\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
4.2.4.3
\fITest and monitor points\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
4.2.4.4
\fISelf tests and diagnostics\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
4.2.5
\fISupervision and verification of protocol implementations\fR
.sp 9p
.RT
.PP
The principles for the supervision and verification of ISDN access protocol implementations are:
.RT
.LP
a)
protocol errors due to implementation problems or other
failures need to be detected. This may be based on the logging
and counting of protocol violations;
.LP
b)
protocol problems need to be sectionalized, analyzed, and
isolated. The following techniques may be used:
.LP
\(em
access to log of protocol violation information;
.LP
\(em
monitoring of the layer 2 frames and the layer 3
messages;
.LP
\(em
test access and protocol testing.
.PP
See Recommendation I.604\ [5] for more information.
.sp 2P
.LP
\fB5\fR \fBBroadband ISDN access\fR
.sp 1P
.RT
.PP
For further study.
.RT
.sp 2P
.LP
\fB6\fR \fBEnd\(hyto\(hyend maintenance\fR
.sp 1P
.RT
.sp 1P
.LP
6.1
\fIEnd\(hyto\(hyend models\fR
.sp 9p
.RT
.PP
This section provides two examples of end\(hyto\(hyend ISDN connections. Figure\ 11/M.36 shows connection examples where a call from one subscriber
access (primary or basic rate) is switched through the public network to
another subscriber access.
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure 11/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
Figure 12/M.36 shows an end\(hyto\(hyend leased circuit arrangement
example where at each end a subscriber primary rate access is connected to a
DCS. From the DCSs, B\(hychannels are connected both to the switched and to
provide an end\(hyto\(hyend connection between the subscriber locations.
.PP
A variation on this example would have a second primary rate access, without a D\(hychannel, connected end\(hyto\(hyend via a DCS. In this case there is a
possibility of a hidden fault between the DCSs that is not reported to either end and is not detected via the loss of the D\(hychannel. Thus, this is a
configuration where a continuity check is required to detect the
fault.
.RT
.LP
.rs
.sp 15P
.ad r
\fBFigure 12/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
6.2
\fIISDN interworking model\fR
.sp 9p
.RT
.PP
Primary or basic rate subscribers via their ISDN access may wish to interwork with other networks \(em with the public switched telephone network
(PSTN), with a packet switched data network (PSDN) and with another public or private ISDN. A model for this interworking is shown in Figure\ 13/M.36.
.PP
An example of the interworking unit (IWU) would be a modem pool used in the PSTN case. Maintenance of interworking is for further study.
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure 13/M.36, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
6.3
\fITerminal equipment functions for remote operations\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
6.4
\fINetwork to network interworking functions for maintenance\fR
.sp 9p
.RT
.PP
For further study.
.bp
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation M.36)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDigital crossconnect system considerations for ISDN\fR
.sp 1P
.RT
.ce 0
.PP
DCSs may also process the D\(hychannel. They may break the
D\(hychannel layer 2, so that there are two tandem layer\ 2 links between the NT2 and the ET. The DCS routes layer\ 3 packets from the NT2 either to the exchange or to the leased network based on the routing of the associated B\(hychannel.
Thus, the DCS may also act as a packet crossconnect for the D\(hychannel.
.sp 1P
.RT
.PP
However, the DCS does not perform switch functions. Its
crossconnect function is controlled over a separate administrative link, not
over the D\(hychannel with Q.931\ [14] call control. This model also includes
leased circuits.
.PP
The B\(hychannels traverse the network without terminating on a switch. The associated D\(hychannel information can be carried in the leased network in
the same digital paths as the B\(hychannels, or separately from the B\(hychannels, on the Signalling System No.\ 7 signalling network.
.RT
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
CCITT Recommendations of the I.600\(hySeries \fIMaintenance principles for\fR \fIISDN\fR , Vol. III.
.LP
[2]
CCITT Recommendation \fIGeneral maintenance principles of ISDN subscriber\fR \fIaccess and subscriber installation\fR , Vol.\ III, Rec.\ I.601.
.LP
[3]
CCITT Recommendation \fIApplication of maintenance principles to ISDN\fR
\fIsubscriber installation\fR , Vol.\ III, Rec.\ I.602.
.LP
[4]
CCITT Recommendation \fIApplication of maintenance principles to ISDN\fR
\fIbasic accesses\fR , Vol.\ III, Rec.\ I.603.
.LP
[5]
CCITT Recommendation \fIApplication of maintenance principles to ISDN\fR
\fIprimary rate access\fR , Vol.\ III, Rec.\ I.604.
.LP
[6]
CCITT Recommendation \fIApplication of maintenance principles to static\fR \fImultiplexed ISDN basic accesses\fR , Vol.\ III, Rec.\ I.605.
.LP
[7]
CCITT Recommendation \fIISDN user network interface protocol for\fR
\fImanagement\fR , Vol.\ VI, Rec.\ Q.940.
.LP
[8]
CCITT Recommendation \fIError performance of an international digital\fR
\fIconnection forming part of an integrated services digital network\fR ,
