home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
InfoMagic Standards 1994 January
/
InfoMagic Standards - January 1994.iso
/
ccitt
/
1988
/
troff
/
6_5_02.tro
< prev
next >
Wrap
Text File
|
1991-12-13
|
127KB
|
4,889 lines
.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\" Not Copyright ( c) 1991
.\"
.\" Assumes tbl, eqn, MS macros, and lots of luck.
.TA 1c 2c 3c 4c 5c 6c 7c 8c
.ds CH
.ds CF
.EQ
delim @@
.EN
.nr LL 40.5P
.nr ll 40.5P
.nr HM 3P
.nr FM 6P
.nr PO 4P
.nr PD 9p
.po 4P
.rs
\v | 5i'
.sp 1P
.ce 1000
\v'3P'
SECTION\ 3
.ce 0
.sp 1P
.ce 1000
\fBDESIGN\ OBJECTIVES\ AND\ MEASUREMENTS\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.541\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBDIGITAL\ EXCHANGE\ DESIGN\ OBJECTIVES\fR \fB\ \(em\ GENERAL\fR
.EF '% Fascicle\ VI.5\ \(em\ Rec.\ Q.541''
.OF '''Fascicle\ VI.5\ \(em\ Rec.\ Q.541 %'
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.PP
This Recommendation applies to digital local, combined, transit and international
exchanges for telephony in Integrated Digital Networks (IDN)
and mixed (analogue/digital) networks, and also to local, combined, transit
and international exchanges in an Integrated Services Digital Network (ISDN).
The field of application of this Recommendation is more fully defined in
Recommendation\ Q.500. Some objectives only apply to a certain type (or
types) of exchange. Where this occurs, the application is defined in the
text. Where no such qualification is made, the objective applies to all
exchange
applications.
.RT
.sp 2P
.LP
\fB2\fR \fBGeneral design objectives\fR
.sp 1P
.RT
.PP
The exchange and/or any associated operations and maintenance
systems/centers shall have the capabilities needed to allow the exchange
to be operated and administered efficiently while providing service in
accordance
with an Administration's performance requirements.
.RT
.sp 1P
.LP
2.1
\fIExchange modifications and growth\fR
.sp 9p
.RT
.PP
The exchange should be capable of having hardware and/or software added
or changes made without causing a significant impact on service (see
\(sc\(sc\ 4.4, 4.10.2 \(em\ Planned outages).
.RT
.sp 1P
.LP
2.2
\fIService provisioning and records\fR
.sp 9p
.RT
.PP
There should be efficient means of establishing service, testing, discontinuing
service and maintaining accurate records for:
.RT
.LP
\(em
subscriber lines and services,
.LP
\(em
interexchange circuits.
.sp 1P
.LP
2.3
\fITranslations and routing information\fR
.sp 9p
.RT
.PP
There should be efficient means of establishing, testing and
changing call processing information, such as translation and routing
information.
.RT
.sp 1P
.LP
2.4
\fIResource utilization\fR
.sp 9p
.RT
.PP
There should be efficient means of measuring performance and
traffic flows and to arrange equipment configurations as required to insure
efficient use of system resources and to provide a good grade of service
to all subscribers (e.g.,\ load balancing).
.bp
.RT
.sp 1P
.LP
2.5
\fIPhysical design objectives\fR
.sp 9p
.RT
.PP
The exchange shall have a good physical design that
provides:
.RT
.LP
\(em
adequate space for maintenance activities,
.LP
\(em
conformance with environmental requirements,
.LP
\(em
uniform equipment identification (conforming with the
Administration's requirements),
.LP
\(em
a limited number of uniform power up/down procedures for
all component parts of the exchange.
.sp 2P
.LP
\fB3\fR \fBIntegrated Digital Network design objectives\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIExchange timing distribution\fR
.sp 9p
.RT
.PP
The timing distribution system of an exchange will be derived from a highly
reliable exchange clock system. The distribution of timing within the exchange
must be designed so that the exchange will maintain synchronism on
64\ kbit/s channel timeslots in a connection through the exchange.
.RT
.sp 1P
.LP
3.2
\fINetwork synchronization\fR
.sp 9p
.RT
.PP
Within a synchronized IDN/ISDN, different methods of providing
timing between exchanges may be used. An exchange should be able to be
synchronized:
.RT
.LP
a)
by an incoming digital signal at an interface A (or B,
if provided) as defined in Recommendation\ Q.511; this
applies only to signals derived from a Primary Reference
Source, as defined in Recommendation\ G.811;
.LP
b)
directly by a Primary Reference Source, using an
interface complying with Recommendation\ G.811;
.LP
c)
optionally, by an analogue signal at one of the
frequencies listed in Recommendation\ G.811.
.PP
Plesiochronous operation should also be possible.
.PP
The clock of the local, combined or transit exchange shall be
responsible for maintaining the synchronization in the part of the network
associated with that exchange.
.PP
The timing performance of the clocks in local, combined or transit
exchanges should comply with Recommendation\ G.811. The timing performance of
clocks at subscriber premises, at digital PABXs, in digital concentrators,
at muldexes,\ etc., require further study.
.PP
Synchronized national networks may be provided with exchange clocks
not having the frequency accuracy required for international interworking.
However, when these synchronized networks within national boundaries are
required to interwork internationally as part of the international IDN/ISDN,
it will be necessary to provide means to operate these national networks
to the
internationally recommended value of frequency accuracy in
Recommendation\ G.811.
.RT
.sp 1P
.LP
3.3
\fISlip\fR
.sp 9p
.RT
.PP
The design objective controlled slip rate within a synchronized
region (see Note) controlled by the exchange should be zero provided that
input jitter and wander remain within the limits given in Recommendation\
G.823
and\ G.824.
.PP
The design objective controlled slip rate at a digital exchange in
plesiochronous operation (or operating to another synchronized region)
shall be not more than one slip in 70\ days in any 64\ kbit/s channel,
provided that input jitter and wander remain within the limits given in
Recommendations\ G.823
and\ G.824.
.PP
The operational performance requirements for the rate of octet slips on
an international connection or corresponding bearer channel are covered
in Recommendation\ G.822.
.PP
The occurrence of a controlled slip should not cause loss of frame
alignment.
.PP
\fINote\fR \ \(em\ A synchronized region is defined as a geographic entity
normally synchronized to a single source and operating plesiochronously with
other synchronized regions. It may be a continent, country, part of a country
or countries.
.bp
.RT
.sp 1P
.LP
3.4
\fIRelative Time Interval Error (TIE)\fR \fIat the exchange output\fR
.sp 9p
.RT
.PP
Relative Time Interval Error (TIE) at the exchange output is
defined as the difference in time delay of a given timing signal when
compared to a reference timing signal for a given measurement period
(see Recommendation\ G.811).
.RT
.sp 1P
.LP
3.4.1
\fIInterface V\fI\d\fI1\fR\u
.sp 9p
.RT
.PP
Relative Time Interval Error (TIE) at the exchange output at the
interface to the basic access digital section requires further study.
.RT
.sp 1P
.LP
3.4.2
\fIInterfaces A, B, V\fI\d\fI4\fR\u [ mangled text ].
.PP
The relative TIE at the output of the digital interfaces\ A, B,
V\d2\u, V\d3\uand V\d4\uover the period\ S seconds should not exceed the
following limits:
.RT
.LP
1)
(100 S) ns + 1/8 UI for S < 10.
.LP
2)
1000 ns for S \(>=" 10 (see Figure\ 4/Q.541).
.LP
.rs
.sp 30P
.ad r
\fBFigure 1/Q.541, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
In the case of synchronous operation the limits are specified on the assumption
of an ideal incoming synchronizing signal (no jitter, no wander and no
frequency deviation) on the line delivering the timing information. In
the case of asynchronous operation the limits are specified assuming no
frequency deviation of the exchange clock, (this is equivalent to taking the
output of the exchange clock as the reference timing signal for the relative
TIE measurements).
.PP
It is recognized that the approach of using relative TIE to specify
the performance of an exchange in the case of synchronous operation in some
implementations (e.g.,\ when\ mutual synchronization methods are used)
requires further study.
.bp
.PP
Any internal operation or rearrangement within the synchronization and
timing unit or any other cause should not result in a phase discontinuity
greater than 1/8 of a Unit Interval (UI) on the outgoing digital signal from
the exchange.
.PP
The limits given in Figure 4/Q.541 may be exceeded in cases of
infrequent internal testing or rearrangement operations within the exchange.
In such cases, the following conditions should be met:
.RT
.PP
The Relative Time Interval Error (TIE) over any period up to
2\u1\d\u1\d unit intervals should not exceed 1/8 of a UI. For periods greater
than 2\u1\d\u1\d\ UI, the phase variation for each interval of\ 2\u1\d\u1\d
UI should not exceed 1/8\ UI up to a maximum total Relative TIE defined
in
Recommendation\ G.811 for long time periods.
.sp 1P
.LP
3.5
\fISynchronization requirements when interworking with a digital\fR
\fIsatellite system\fR
.sp 9p
.RT
.PP
On a provisional basis the following should apply:
.PP
The transfer from the timing of the terrestrial digital network to the
timing of the satellite system, if required (plesiochronous operation),
will
not be performed by the digital exchange. The earth station will be equipped
with buffer memories of suitable size to compensate for the time delay
variations due to shifts of the satellite from its ideal position (and
due to any other phenomena with similar effects) and to meet the slip performance
requirements established in CCITT Recommendation\ G.822.
.RT
.sp 2P
.LP
\fB4\fR \fBAvailability\fR \fBdesign objectives\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fIGeneral\fR
.sp 9p
.RT
.PP
Availability is one aspect of the overall quality of service of an exchange.
.PP
Availability objectives are important factors to be considered in
the design of a switching system and may also be used by administrations to
judge the performance of a system design and to compare the performance of
different system designs.
.PP
Availability may be determined by collecting and evaluating data from exchanges
in operation in accordance with draft Recommendation\ E.450. Data
collection may be facilitated by the use of the Telecommunications
Management Network (TMN).
.PP
Availability may be expressed as the ratio of the accumulated time
during which the exchange (or part of it) is capable of proper operation
to a time period of statistically significant duration called the mission
time.
\v'6p'
.RT
.ce 1000
Availability (A) =
@ { ccumulated~up\(hytime } over { ission~time } @ =
@ { ccumulated~up\(hytime } over { ccumulated~up\(hytime~+ } @
.ce 0
.sp 1P
.ce 1000
Availability (A) = accumulated up\(hytime =
accumulated down\(hytime
.ce 0
.sp 1P
.PP
.sp 1
Sometimes it is more convenient to use the term unavailability
(instead of availability) which is defined as:
\v'6p'
.sp 1P
.ce 1000
Unavailability (U) = 1 \(em A.
.ce 0
.sp 1P
.PP
.sp 1
The terms used in this section, when they already exist, are in
accordance with CCITT Recommendation\ G.106.
.sp 1P
.LP
4.2
\fICauses of\fR
\fIunavailability\fR
.sp 9p
.RT
.PP
This Recommendation deals with availability as observed from the
exchange termination point of view. Both planned and unplanned outages
need to be considered, and both types need to be minimized. Unplanned outages
reflect on the inherent reliability of the exchange and are therefore considered
separately from planned outages in this Recommendation.
.PP
Unplanned unavailability counts all failures that cause
unavailability. Thus hardware failure, software malfunctions and unintentional
outages resulting from craftperson activity are to be counted.
.bp
.RT
.sp 1P
.LP
4.3
\fIIntrinsic and operational unavailability\fR
.sp 9p
.RT
.PP
Intrinsic unavailability is the unavailability of an exchange (or part
of it) due to exchange (or unit) failure itself, excluding the logistic
delay time (e.g.\ travel times, unavailability of spare units,\ etc.) and
planned outages.
.PP
Operational unavailability is the unavailability of an exchange (or
part of it) due to exchange (or unit) failure itself, including the logistic
delay time (e.g.\ travel times, unavailability of spare units,\ etc.).
.RT
.sp 1P
.LP
4.4
\fIPlanned outages\fR
.sp 9p
.RT
.PP
Planned outages are those intentionally induced to facilitate
exchange growth or hardware and/or software modifications. The impact of
these activities on service depends on their duration, the time of day
they are
introduced and on the particular system design.
.RT
.sp 1P
.LP
4.5
\fITotal and partial unavailability\fR
.sp 9p
.RT
.PP
Exchange unavailability may be either total or partial. Total
unavailability affects all terminations, and consequently, all traffic
that is offered during the outage is equally affected. A partial outage
has an effect only on some terminations.
.PP
From the point of view of one termination on an exchange (e.g. a
subscriber line termination), the numerical value of mean accumulated downtime
(and hence the unavailability) for a specified period of time should not
depend on the exchange size or its traffic handling capacity. Similarly,
from the
point of view of a group of terminations of size\ \fIn\fR , the mean accumulated
downtime for a specified period of time, \fIin case they are simultaneously\fR
\fIunavailable\fR , should not depend on exchange size. However, for two
groups of
.PP
terminals of differing size\ \fIn\fR and\ \fIm\fR such that\ \fIn\fR is greater
than\ \fIm\fR \ (\fIn\fR \ >\ m), the mean accumulated downtime (and hence the
unavailability) for\ \fIn\fR will be less than the mean accumulated downtime
(MADT) or the unavailability for\ \fIm\fR .
.RT
.LP
Thus:
.sp 1P
.ce 1000
MADT(\fIn\fR ) < MADT(\fIm\fR ) where \fIn\fR \ >\ \fIm\fR
.ce 0
.sp 1P
.LP
and
.sp 1P
.ce 1000
U(\fIn\fR ) < U(\fIm\fR )
.ce 0
.sp 1P
.PP
The lower limit of \fIm\fR is one termination, and it can be
specified as having a mean value of \fIT\fR \ minutes per year.
.sp 1P
.LP
4.6
\fIStatistical basis\fR
.sp 9p
.RT
.PP
Any estimation of unavailability is of necessity a statistical
quantity, because outages are presumed to occur randomly and they are of
random duration. Therefore, availability measurements are significant when
made over a statistically significant number of exchanges. It follows then,
that a single exchange may exceed the unavailability objectives. Further,
to be statistically significant the mission time must be adequate in order
to have sufficient
collected data. The accuracy of the result is dependent on the amount of
collected data.
.RT
.sp 1P
.LP
4.7
\fIRelevant failure events\fR
.sp 9p
.RT
.PP
Different types of failure events may occur in an exchange. In
order to evaluate the unavailability of an exchange (or part of it) only
those events having an adverse effect on the exchange's ability to process
calls as required should be taken into account. A failure event which is
short in
duration and results only in call delay rather than in a call denial can be
disregarded.
.RT
.sp 1P
.LP
4.8
\fIAvailability independence\fR
.sp 9p
.RT
.PP
The design objectives for the unavailability of a single
termination or any group of terminations of size \fIn\fR are independent
of exchange size or internal structure.
.RT
.sp 1P
.LP
4.9
\fIIntrinsic downtime and unavailability objectives\fR
.sp 9p
.RT
.PP
The recommended measure for use in determining \fIintrinsic\fR
\fIunavailability\fR is mean accumulated intrinsic down time (MAIDT) for
individual or groups of terminations, for a given mission time, typically
one year.
.bp
.PP
For one termination:
.RT
.sp 1P
.ce 1000
MAIDT(1) \(= 30 minutes per year.
.ce 0
.sp 1P
.PP
For an exchange termination group of size \fIn\fR :
.sp 1P
.ce 1000
MAIDT(\fIn\fR ) < MAIDT(\fIm\fR ) where \fIn\fR \ >\ \fIm\fR .
.ce 0
.sp 1P
.PP
This reflects the consequences (e.g. traffic congestion, social
annoyance, etc.), of the simultaneous outage of a large number of
terminations.
.PP
The above expression is a statement of principle and means that units serving
larger group sizes shall have lower MAIDT.
.RT
.sp 2P
.LP
4.10
\fIOperational unavailability objectives\fR
.sp 1P
.RT
.sp 1P
.LP
4.10.1
\fILogistic delay time\fR
.sp 9p
.RT
.PP
Due to differing national conditions, logistic delay times may vary from
country to country and therefore may not be subject to international
Recommendation.
.PP
Nevertheless, for design guidance, an indication of the
Administration's logistic delays is considered desirable to establish overall
operational performance objectives. It is left for the operating Administration
to determine how it should be accounted for in the determination of operational
unavailability.
.RT
.sp 1P
.LP
4.10.2
\fIPlanned outages\fR
.sp 9p
.RT
.PP
Planned outages are to be minimized to the greatest extent
practicable. They should be scheduled so as to have least impact on service
practicable.
.RT
.sp 1P
.LP
4.11
\fIInitial exchange availability performance\fR
.sp 9p
.RT
.PP
A system rarely meets all long\(hyterm design objectives when first
placed into service. The objectives contained in this Recommendation may
therefore not be fulfilled for a limited period of time after the newly
designed switched system has been put into service; this period of time
should be minimized to the greatest extent practicable.
.RT
.sp 2P
.LP
\fB5\fR \fBHardware reliability design objectives\fR
.sp 1P
.RT
.PP
\fI\fR A bound on the rate of hardware failures is recommended. It
includes all types of hardware failures and the failures counted are
independent of whether or not there is a resulting service degradation.
.PP
An acceptable hardware failure rate for an exchange is a function of the
exchange size and the types of terminations.
.PP
The following formula can be used to verify that the maximum failure rate
does not exceed the Administration's requirements:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIF\fR \dmax
\u = C
\d0\u +
@ pile { fIn\fR above sum above \fIi\fR~=1 } @\fIC
\di\uT
\di\u\fR
.ce 0
.sp 1P
.LP
.sp 1
where:
.LP
\fIF\fR\dm\\da\\dx\u
the maximum acceptable number of hardware
failures per unit of time;
.LP
\fIT\fR\d\fIi\fR\u the number of terminations of type\ \fIi\fR ;
.LP
\fIn\fR the number of distinct types of terminations;
.LP
C\d0\u to be determined taking into account all
failures which are independent of exchange size;
.LP
\fIC\fR\d\fIi\fR\u coefficients for terminations of type\ \fIi\fR , reflecting
the number of failures associated with individual terminations
of that type. Different hardware used with different
types of terminations may result in different values
for \fIC\fR\d\fIi\fR\u.
.bp
.sp 2P
.LP
\fBRecommendation\ Q.542\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBDIGITAL\ EXCHANGE\ DESIGN\ OBJECTIVES\ \(em\ OPERATIONS
AND\ MAINTENANCE\fR
.EF '% Fascicle\ VI.5\ \(em\ Rec.\ Q.542''
.OF '''Fascicle\ VI.5\ \(em\ Rec.\ Q.542 %'
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.PP
This Recommendation applies to digital local, combined, transit and international
exchanges for telephony in Integrated Digital Networks (IDN)
and mixed (analogue/digital) networks, and also to local, combined, transit
and international exchanges in an Integrated Services Digital Network (ISDN).
.PP
The field of application of this Recommendation is more fully defined in
Recommendation\ Q.500. Some objectives only apply to a certain type (or
types) of exchange. Where this occurs, the application is defined in the
text. Where no such qualification is made, the objective applies to all
exchange
applications.
.RT
.sp 2P
.LP
\fB2\fR \fBMaintenance design objectives\fR
.sp 1P
.RT
.PP
The exchange shall be arranged so that normal maintenance
activities can be easily performed by maintenance personnel. It should be
capable of providing all information necessary for the identification of
trouble conditions and the direction of repair activities.
.RT
.sp 1P
.LP
2.1
\fIStatus and other information\fR
.sp 9p
.RT
.PP
The exchange shall provide information to maintenance personnel so that
they can quickly ascertain:
.RT
.LP
\(em
equipment/system status,
.LP
\(em
critical load levels,
.LP
\(em
trouble conditions,
.LP
\(em
network management controls in effect.
.sp 1P
.LP
2.2
\fIInputs and outputs\fR
.sp 9p
.RT
.PP
The exchange shall be able to transmit and receive maintenance
information and respond to commands from on\(hysite and if appropriate, from
remote maintenance centre(s) or systems over the recommended interface(s)
(Recommendation\ Q.513).
.PP
In performing operations and maintenance functions, the exchange shall
use CCITT MML at its input/output terminals as covered in the Z.300\(hyseries
of Recommendations.
.RT
.sp 1P
.LP
2.3
\fIRoutine testing\fR
.sp 9p
.RT
.PP
The exchange shall have facilities for performing or directing
routine test activities on its component parts and possibly with interfacing
equipment or systems.
.RT
.sp 1P
.LP
2.4
\fITrouble localization\fR
.sp 9p
.RT
.PP
The exchange shall have adequate facilities for diagnosing and
locating faults within the exchange.
.RT
.sp 1P
.LP
2.5
\fIFault and alarm detection and actions at interfaces A, B,\fR
\fIV\fR\d\fI4\fR\u
.sp 9p
.RT
.EF '% \fI2,\''
.OF '''\fI2,\ %'
.EF '% \fI3\ and\''
.OF '''\fI3\ and\ %'
.PP
The exchange shall interact with transmission systems as required to detect
fault and alarms and take appropriate actions.
.RT
.sp 1P
.LP
2.5.1
\fIFault detection\fR
.sp 9p
.RT
.PP
The following fault conditions should be detected:
.RT
.LP
\(em
failure of local power supply (if practicable);
.LP
\(em
loss of incoming signal;
.LP
\fINote\fR \ \(em\ The detection of this fault condition is required only
when the fault does not result in an indication of loss of frame
alignment.
.bp
.LP
\(em
loss of frame alignment (see Recommendations G.706; the loss of frame
alignment will also be assumed if no CRC multiframe
alignment can be achieved or if the proportion of corrupted
CRC checks exceeds a certain value);
.LP
\(em
excessive error ratio (without CRC procedure). The criteria for activating
and deactivating the indication of the fault
condition are given in draft Recommendation\ G.707. Consequent
actions are given in \(sc\ 2.5.3;
.LP
\(em
CRC error reporting, if applicable:
.LP
a)
every time a received CRC block is detected
errored by the exchange termination:
.LP
\(em
a report will be transmitted to the error
monitoring function;
.LP
\(em
the information \*Qone multiframe errored\*U is
transmitted in the outgoing signal at the interface
using an E\ bit (see Recommendation\ G.704, \(sc\ 2.3.3.4);
.LP
b)
every time that an E bit in the binary state 0 is
received, a report will be transmitted to the error
monitoring functions.
.LP
(On a provisional basis the considerations related to the
E bit may only apply to V\ interfaces \(em\ for further study.)
.sp 1P
.LP
2.5.2
\fIAlarm signal detection\fR
.sp 9p
.RT
.PP
The following alarm indications should be detected:
.RT
.LP
\(em
Alarm indication (remote alarm) received from the remote
end.
.LP
\(em
AIS (alarm indication signal). The equivalent binary
content of the alarm indication signal (AIS) is a continuous
stream of \*Q1\*Us at 2048 or 8448\ kbit/s.
.PP
The strategy for detecting the presence of the AIS should be such that
the AIS is detectable even in the presence of an error ratio of\ 1
in\ 10\u3\d. However, a signal with all bits except the frame alignment bit in
the 1\ state should not be mistaken as an AIS.
.sp 2P
.LP
2.5.3
\fIConsequent actions\fR
.sp 1P
.RT
.sp 1P
.LP
2.5.3.1
\fIGeneration of alarm signals for action within the\fR
\fIexchange\fR \v'3p'
.sp 9p
.RT
.LP
\(em
The service alarm indication should be generated to
signify that the service is no longer available
(see\ Table\ 1/Q.542).
.LP
\(em
The prompt maintenance alarm indication should be generated
to signify that performance is
below\ acceptable standards
and that immediate maintenance attention is required
locally (see\ Table\ 1/Q.542).
.sp 1P
.LP
2.5.3.2
\fIGeneration of alarm signals transmitted by the exchange\fR \v'3p'
.sp 9p
.RT
.LP
\(em
Alarm signals sent in the outgoing direction at the exchange
interface. The relevant alarm bits for
the\ remote alarm
indication, as recommended in G.704 should be effected as
soon as possible
(see\ Table\ 1/Q.542).
.LP
\(em
Alarm signals sent towards the switching
function. Alarm indication signal applied in all received
time\(hyslots containing speech, data and/or signalling
should be applied as soon as possible and not later than
2\ ms after the detection of the fault condition (see
Table\ 1/Q.542).
.sp 1P
.LP
2.5.3.3
\fIRemoval of alarm indications\fR
.sp 9p
.RT
.PP
When all fault conditions have been cleared and alarm indication
signal is no longer received, the alarm indication signal and remote alarm
indication should be removed within the same respective time limits as
specified in \(sc\ 2.5.3.4 after the conditions have cleared.
.bp
.RT
.ce
\fBH.T. [T1.542]\fR
.ce
TABLE\ 1/Q.542
.ce
\fBFault conditions and alarms detected by exchange termination functions\fR
.ce
\fBand consequent actions\fR
.ce
\fB(excluding interface V\fR\(da\fB1)\fR
.T&
lw(54p) | lw(54p) | lw(48p) | lw(36p) | lw(36p) .
.T&
lw(54p) | cw(54p) | cw(48p) | cw(36p) | cw(36p) .
Failure of power supply Yes Yes Yes, if practicable Yes, if practicable
_
.T&
lw(54p) | cw(54p) | cw(48p) | cw(36p) | cw(36p) .
Loss of incoming signal Yes Yes Yes Yes
_
.T&
lw(54p) | cw(54p) | cw(48p) | cw(36p) | cw(36p) .
Loss of frame alignment Yes Yes Yes Yes
_
.T&
lw(54p) | cw(54p) | cw(48p) | cw(36p) | cw(36p) .
Excessive error ratio Yes Yes Yes Yes
_
.T&
lw(54p) | cw(54p) | cw(48p) | cw(36p) | cw(36p) .
{
Alarm indication received from remote end
} {
2048 | | 448 kbit/s:
Yes
1544 | | 312 kbit/s:
optional
} 1544 | | 312 kbit/s: Yes
_
.T&
lw(54p) | cw(54p) | cw(48p) | cw(36p) | cw(36p) .
AIS received Yes Yes Yes
.TE
.LP
\fINote\fR
\ \(em\ A \fIYes\fR
in the table signifies that an action should be taken. An
open space in the table signifies that the relevant action should \fInot\fR
be
taken if this condition is the only one present. If more than one fault
condition or alarm is simultaneously present, action should be taken if
for at least one of the conditions a \fIYes\fR
is shown, except in the case of AIS
received for which \(sc\ 2.5.3.4 applies. The use of error performance
monitoring in this table is for further study.
.nr PS 9
.RT
.ad r
\fBTable 1/Q.542 [T1.542], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
.sp 5
2.5.3.4
\fIAlarm processing\fR
.sp 9p
.RT
.PP
The following items are required to ensure that equipment is not
removed from service due to short breaks in transmission (e.g.\ due to
noise or transient fault) and to ensure that maintenance action does not
result where no direct maintenance action is required.
.RT
.LP
\(em
The persistence of service alarm and of the prompt
maintenance alarm indications may be verified for 100\ ms
before action is taken.
.LP
\(em
When the AIS is detected, the prompt maintenance alarm
indication, associated with loss of frame alignment and
excessive error rate in the frame alignment pattern, should be
inhibited.
.LP
\(em
When the fault conditions cease, the service alarm and prompt
maintenance alarm indications, if given, should be removed.
Again, the persistence of this change in condition may be
verified for 100\ ms before action is taken.
.bp
.LP
\(em
It is possible that some systems could suffer from frequent
transient faults resulting in an unacceptable quality of
service. For this reason, if a persistence check is provided,
fault rate monitoring should also be provided for each digital
transmission system. This monitoring will result in permanent
removal from service of digital transmission system which are
frequently removed from the service or frequently produce
transient alarm conditions. The threshold for removal from
service needs study. When this action is taken the service alarm
indication and the prompt maintenance alarm indication shall be
given.
.sp 2P
.LP
2.5.4
\fIError performance monitoring using CRC\fR
.sp 1P
.RT
.sp 1P
.LP
2.5.4.1
\fIGeneral\fR
.sp 9p
.RT
.PP
When the CRC procedure is implemented at the interface, the
exchange should monitor the error performance of the interface to report
on the performance (see Recommendation\ G.821).
.RT
.sp 1P
.LP
2.5.4.2
\fIError performance parameters\fR
.sp 9p
.RT
.PP
The exchange should derive the following information from CRC
checks in the incoming signal and received E\ bits:
.RT
.LP
\(em
degraded minutes (DM),
.LP
\(em
severely errored seconds (SES),
.LP
\(em
error\(hyfree seconds (EFS).
.PP
\fINote\ 1\fR \ \(em\ These parameters are defined in Recommendation G.821.
.PP
\fINote\ 2\fR \ \(em\ The definition of a value for the suitable time interval
during which the parameters should be assessed needs further study.
.PP
\fINote\ 3\fR \ \(em\ The choice has to be made between the association of one
type of parameter to each direction of transmission and the integration
of the two directions in one type of parameter. This needs further study.
.PP
\fINote\ 4\fR \ \(em\ The correlation between the results of CRC checks
and the parameters quoted above requires further study.
.RT
.sp 1P
.LP
2.5.4.3
\fIError performance evaluation\fR
.sp 9p
.RT
.PP
Each of the performance parameters will be processed separately in order
to evaluate the performance of the interface.
.PP
The following classification of the interface maintenance conditions has
to be made by the exchange (see\ I.600\(hyseries of Recommendations):
.RT
.LP
\(em
correct functioning interface;
.LP
\(em
degraded transmission interface;
.LP
\(em
unacceptable transmission interface.
.PP
\fINote\ 1\fR \ \(em\ This section may only apply to V interfaces (for
study).
.PP
\fINote\ 2\fR \ \(em\ The level at which an interface for ISDN access enters
the degraded transmission condition may be dependent on the quality of
service
provided to the customer.
.PP
\fINote\ 3\fR \ \(em\ The levels at which an interface enters the degraded or
unacceptable transmission conditions are for further study and are outside
the scope of this Recommendation.
.RT
.sp 1P
.LP
2.5.4.4
\fIConsequent actions\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
2.6
\fIFault and alarm signal detection and actions at interface V\fI\d\fI1\fR\u
.sp 9p
.RT
.PP
The exchange shall interact with transmission systems as required to detect
fault and alarm signals and take appropriate actions.
.RT
.LP
a)
Fault\ detection
.LP
b)
Alarm\ detection
\ To be specified
.LP
c)
Consequent\ actions
.bp
.sp 1P
.LP
2.7
\fIFault and alarm signal detection and actions at interface Z\fR \v'3p'
.sp 9p
.RT
.LP
a)
Fault\ detection
.LP
b)
Alarm\ detection
\ To be specified
.LP
c)
Consequent\ actions
.sp 1P
.LP
2.8
\fIFault and alarm signal detection and actions for transmission\fR
\fIsystems\fR
.sp 9p
.RT
.PP
Faults and alarms which cannot be directly detected by the exchange termination
function but which are detected by transmission equipment
(e.g.,\ group pilot failure) should be accepted by the exchange as needed to
take appropriate action.
.RT
.sp 2P
.LP
2.9
\fIFault and alarm signal detection and actions for channel\fR
\fIassociated signalling\fR (2048 and 8448\ kbit/s)
.sp 1P
.RT
.sp 1P
.LP
2.9.1
\fIFault detection\fR
.sp 9p
.RT
.PP
The exchange signalling function should detect the following fault conditions
for each multiplex carrying a 64\(hykbit/s signalling
channel:
.RT
.LP
\(em
failure of local power supply (if practicable),
.LP
\(em
loss of 64\ kbit/s incoming signal,
.LP
\fINote\fR \ \(em\ The detection of this fault condition is required only
when the fault does not result in an indication of loss of
multiframe alignment.
.LP
\(em
loss of multiframe alignment.
.PP
The criteria for activating and deactivating the indication of the fault
condition are given in Recommendations\ G.732 and\ G.744.
.sp 1P
.LP
2.9.2
\fIAlarm detection\fR
.sp 9p
.RT
.PP
The exchange signalling function should detect the alarm indication (remote
alarm) received from the remote end.
.RT
.sp 2P
.LP
2.9.3
\fIConsequent actions\fR
.sp 1P
.RT
.sp 1P
.LP
2.9.3.1
\fIGeneration of alarm signals for action within the\fR
\fIexchange\fR \v'3p'
.sp 9p
.RT
.LP
\(em
The Service Alarm indication should be generated by the
exchange signalling function to signify that the service is no
longer available (see Table\ 2/Q.542).
.LP
\(em
The prompt maintenance alarm indication should be generated to signify
that performance is
below\ acceptable standards and
that immediate maintenance attention is required locally
(see
Table\ 2/Q.542).
.sp 1P
.LP
2.9.3.2
\fIAlarm transmitted by the exchange\fR
.sp 9p
.RT
.PP
An alarm indication (remote alarm) should be applied in the
outgoing direction at the transmission/switching interface as soon as possible
(see Table\ 2/Q.542). The relevant alarm bit for the remote alarm indication
is given in Recommendation\ G.732.
.RT
.sp 1P
.LP
2.9.3.3
\fIRemoval of alarm indication\fR
.sp 9p
.RT
.PP
When all fault conditions have been cleared and AIS is no longer
received, the remote alarm indication should be removed as soon as
possible.
.RT
.sp 1P
.LP
2.9.3.4
\fIAlarm processing\fR
.sp 9p
.RT
.PP
Same as in \(sc 2.5.3.4.
.bp
.RT
.ce
\fBH.T. [T2.542]\fR
.ce
TABLE\ 2/Q.542
.ce
\fBFault conditions and alarms detected by the exchange signalling\fR
.ce
\fBfunction and consequent actions\fR
.T&
lw(60p) | lw(42p) | lw(42p) | lw(42p) .
.T&
lw(60p) | cw(42p) | cw(42p) | cw(42p) .
Failure of power supply Yes Yes Yes, if practicable
_
.T&
lw(60p) | cw(42p) | cw(42p) | cw(42p) .
{
Loss of 64 kbit/s incoming signal
} Yes Yes Yes
_
.T&
lw(60p) | cw(42p) | cw(42p) | cw(42p) .
Loss of multiframe alignment Yes Yes Yes
_
.T&
lw(60p) | cw(42p) | cw(42p) | cw(42p) .
{
Alarm indication received from remote end
} Yes \fINote\fR
.TE
.LP
\ \(em\ A \fIYes\fR
in the table signifies that an action should be taken. An open space in
the table signifies that the relevant action should \fI\fInot\fR
be taken if this condition is the only one present. If more than one fault
condition or
alarm is simultaneously present, action should be taken if for at least
one of the conditions a \fIYes\fR
is shown.
.nr PS 9
.RT
.ad r
\fBTable\ 2/Q.542 [T2.542], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.sp 1P
.LP
2.10
\fIFault and alarm signal detection and actions for channel\fR
\fIassociated channel signalling\fR (1544 kbit/s)
.sp 9p
.RT
.PP
Requires further study.
.RT
.sp 1P
.LP
2.11
\fIFault and alarm signal detection and actions for common channel\fR
\fIsignalling\fR
.sp 9p
.RT
.PP
Requirements specified in relevant Recommendations apply.
.RT
.sp 2P
.LP
2.12
\fIFault and alarm detection and consequent actions \(em other\fR
\fIfunctions of the exchange\fR
.sp 1P
.RT
.sp 1P
.LP
2.12.1
\fIFaulty circuits\fR
.sp 9p
.RT
.PP
The exchange should not switch any new calls to a detected faulty circuit.
.PP
The exchange should remove from service all circuits found to be
permanently faulty as detailed in \(sc\(sc\ 2.5, 2.8, 2.9, 2.10 and\ 2.11.
.RT
.sp 1P
.LP
2.12.2
\fIMaster clock distribution\fR
.sp 9p
.RT
.PP
The absence of timing information distributed from a master clock located
at the exchange or received from an external master clock shall be
recognized and a prompt maintenance alarm shall be given.
.PP
Changeover to an alternate timing source shall be operated so as to
fulfil the requirements of \(sc\(sc\ 2.7.2 and 2.7.3 of Recommendation\ Q.543.
.bp
.RT
.sp 1P
.LP
2.12.3
\fIInternal timing distribution\fR
.sp 9p
.RT
.PP
The distribution of timing information to the major elements of the exchange
shall be supervised as required. A service alarm shall be given when a
failure is detected. A maintenance alarm shall be given if it is appropriate.
.PP
\fINote\fR \ \(em\ Remote elements may have to be taken into consideration.
.RT
.sp 1P
.LP
2.13
\fISupervision or testing of interface function\fR
.sp 9p
.RT
.PP
The exchange shall have the capability of verifying the proper
operation of the interface functions, including the fault detection and
supervision functions.
.PP
Routine tests, statistical tests, manual activities and/or other means
may be used to verify proper operation of these functions.
.PP
Information shall be given to the far end exchange when new calls
cannot be established on the circuits on which routine tests are being
initiated. Established calls, including semi\(hypermanent connections,
must not be interrupted. During the tests, the generation of alarms at
the far end exchange due to the removal of circuits from service should
be avoided, if
possible.
.RT
.sp 1P
.LP
2.13.1
\fIET functions \(em Interfaces A, B, V\fI\d\fI4\fR\u
.sp 9p
.RT
.EF '% \fI2,\''
.OF '''\fI2,\ %'
.EF '% \fI3\ and\''
.OF '''\fI3\ and\ %'
.PP
The verification of the proper operation of exchange termination
functions can be performed by the means of statistical observations or by
testing. Testing may be manual or automatic.
.RT
.sp 1P
.LP
2.13.2
\fIET functions \(em Interfaces C and Z\fR \v'3p'
.sp 9p
.RT
.LP
i)
Failures of codecs (except those covered in ii) below)
should be recognized by the exchange using the criteria defined in
Recommendation\ G.732.
.LP
ii)
Supervision or testing of codecs of one or a small number of channels
may be accomplished according to\ i) above or by
inter\(hyoffice transmission measurement and testing on circuits
between exchanges or by statistical measurements.
.sp 1P
.LP
2.13.3
\fIET functions \(em Interface V\fI\d\fI1\fR\u
.sp 9p
.RT
.PP
To be specified.
.RT
.sp 1P
.LP
2.14
\fISupervision or testing of signalling functions\fR
.sp 9p
.RT
.PP
In addition to fault detection required in \(sc 2.7, the following
applies.
.RT
.sp 1P
.LP
2.14.1
\fIChannel associated signalling\fR
.sp 9p
.RT
.PP
The exchange should be able to verify the proper operation of the signalling
functions by generating and responding to test calls or by a
statistical observation.
.RT
.sp 1P
.LP
2.14.2
\fICommon channel signalling\fR
.sp 9p
.RT
.PP
The exchange should be able to verify the proper operation of the signalling
functions as required by common channel signalling
recommendations.
.RT
.sp 1P
.LP
2.15
\fISupervision or testing of exchange connections\fR
.sp 9p
.RT
.PP
Checking the different portions of the path individually in a
digital exchange network helps to ensure the continuity of the connections
overall. In this respect the exchange has to verify:
.RT
.LP
\(em
the continuity across the exchange, as covered in this
section;
.LP
\(em
the continuity in the transmission links terminating on
the exchange as covered in \(sc\(sc\ 2.16 and\ 2.17.
.bp
.sp 1P
.LP
2.15.1
\fIContinuity across the exchange\fR
.sp 9p
.RT
.PP
A means should be provided to determine that the operational error performance
requirement (i.e.,\ on bit error ratio) is being met. (The design
objective for error performance can be found in Recommendation\ Q.554.)
.PP
The exchange should provide adequate provision of the cross office
path continuity and verify the transmission performance. (The design objective
for transmission performance can be found in Recommendation\ Q.543.) This
will guarantee, in particular, an acceptable transmission quality to its
connections.
.RT
.sp 1P
.LP
2.15.2
\fIVerification depending on the type of connection\fR
.sp 9p
.RT
.PP
The verifications to be performed by the exchange should depend
also on the type of connection. In particular:
.RT
.LP
\(em
for 64 kbit/s switched connections, the transmission
performance requirements of Q.543 may be considered to be
sufficient in order to guarantee the cross office path
continuity;
.LP
\(em
semi\(hypermanent connections may require special supervision
procedures which need further study;
.LP
\(em
supervision of n\ \(mu\ 64 kbit/s requires further study for
both switched and semi\(hypermanent connections.
.sp 1P
.LP
2.16
\fISupervision or testing of digital link performance\fR
.sp 9p
.RT
.PP
The exchange shall have the capability of monitoring digital link performance
to detect when bit error ratio and loss of framing thresholds
exceed operational objectives. The exchange will then take subsequent action
to give appropriate trouble indications or alarms and perform other appropriate
actions, such as removing circuits from service.
.RT
.sp 2P
.LP
2.17
\fISupervision or testing of analogue link performance\fR
.sp 1P
.RT
.sp 1P
.LP
2.17.1
\fIInterexchange circuit continuity check\fR
.sp 9p
.RT
.PP
The exchange should be capable of performing circuit continuity
checks in accordance with appropriate signalling system recommendations.
Circuits failing circuit continuity checks should be removed from service
and repair procedures initiated as required.
.RT
.sp 1P
.LP
2.17.2
\fIInterexchange transmission measurement and testing on circuits\fR
\fIbetween exchanges\fR
.sp 9p
.RT
.PP
The exchange may also be equipped within itself or give access to external
equipment to perform other transmission tests on circuits. Faulty
circuits should be removed from service and repair procedures initiated as
required.
.RT
.sp 2P
.LP
\fB3\fR \fBSubscriber line maintenance and testing design objectives\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIAnalogue subscriber lines\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
3.2
\fIDigital subscriber lines\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 2P
.LP
\fB4\fR \fBOperations design objectives\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fIGeneral\fR
.sp 9p
.RT
.PP
The exchange and/or any associated Operations and Maintenance
Systems/Centres shall have the capabilities necessary to permit it to be
operated, administered, and maintained efficiently while providing service
in accordance with an Administration's performance requirements.
.bp
.PP
The Telecommunications Management Network (TMN) architecture, as
described in Recommendation\ M.30, considers the exchange to be a Network
Element (NE) which can interact with Operations Systems (OS) within a TMN.
Operations systems may be used at the discretion of Administrations to
improve operating efficiencies and service by centralizing and mechanizing
operations, administrative and maintenance functions. The number and variety
of operations systems will depend on the operating practices of the Administration.
.PP
The decision to implement TMN principles rests with the
Administration.
.RT
.sp 2P
.LP
4.2
\fIOperations features\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.1
\fIService provisioning and records\fR
.sp 9p
.RT
.PP
There should be efficient means of establishing service, testing, discontinuing
service and maintaining accurate records for:
.RT
.LP
\(em
subscriber lines and services (in local exchanges);
.LP
\(em
interexchange circuits.
.sp 1P
.LP
4.2.2
\fITranslation and routing information\fR
.sp 9p
.RT
.PP
There should be efficient means of establishing, testing and
changing call processing information, such as translation and routing
information.
.RT
.sp 1P
.LP
4.2.3
\fIResource utilization\fR
.sp 9p
.RT
.PP
There should be efficient means of measuring performance and
traffic flows and to arrange equipment configurations as required to insure
efficient use of system resources and to provide a good grade of service
to all subscribers (e.g.,\ load balancing).
.RT
.sp 1P
.LP
4.2.4
\fIExchange observation and measurements\fR
.sp 9p
.RT
.PP
The exchange should provide means for making observations and
measurements on Quality of Service and network performance, to satisfy, for
example, Grade of Service objectives as covered in Recommendation\ E.500,
or for provisioning purposes. Details of measurements for digital exchanges
are given in Recommendation\ Q.544.
.RT
.sp 1P
.LP
4.3
\fIExchange functions related to the TMN\fR
.sp 9p
.RT
.PP
Detailed descriptions, definitions, and classifications of TMN
functions to which the exchange will contribute is for further study.
.PP
A partial list of TMN functions is given below. A more complete list is
given in Recommendation\ M.30.
.PP
Exchanges may have requirements for Operations, Administration and
Maintenance functions which are not related to TMN. This is for further
study.
.RT
.sp 1P
.LP
4.3.1
\fIFunctions potentially related to TMN\fR \v'3p'
.sp 9p
.RT
.LP
\(em
Subscriber administration;
.LP
\(em
tariff and charging administration;
.LP
\(em
routing administration;
.LP
\(em
network management;
.LP
\(em
maintenance of subscriber lines;
.LP
\(em
maintenance of circuits between exchanges;
.LP
\(em
exchange maintenance;
.LP
\(em
signalling network maintenance;
.bp
.LP
\(em
administration of hardware configuration;
.LP
\(em
administration of software configuration;
.LP
\(em
external alarms and indications;
.LP
\(em
O&M staff procedures;
.LP
\(em
traffic measurements;
.LP
\(em
quality of service and network performance observation.
.sp 1P
.LP
4.3.2
\fIInformation flows\fR
.sp 9p
.RT
.PP
Generally, information flows will consist of requests/demands to
the exchange and responses from the exchange. There will also be autonomous
information flows from the exchange (e.g.\ alarms, programmed response,\
etc.). Refer to Recommendation\ Q.513 for information on interfaces to
the TMN.
.PP
This subject is for further study.
.RT
.sp 2P
.LP
\fB5\fR \fBNetwork management design objectives\fR
.sp 1P
.RT
.sp 1P
.LP
5.1
\fIGeneral\fR
.sp 9p
.RT
.PP
Network management is the function of supervising the performance of a
network and taking action to control the flow of traffic, when necessary,
to promote the maximum utilization of network capacity.
.PP
These functions have application in exchanges within the IDN, and may or
may not have application in national networks during the transition period
to IDN.
.PP
The implementation of network management features and functions in
national networks and in specific exchanges will be at the option of
Administrations. Likewise the choice of which controls and features
to use will be the option of each Administration.
.RT
.sp 1P
.LP
5.1.1
\fINetwork management objectives\fR
.sp 9p
.RT
.PP
Information on network management objectives can be obtained from Recommendation\
E.410, and from the CCITT \*QHandbook on Service Quality, Network Maintenance
and Management\*U, ITU, Geneva\ 1984.
.RT
.sp 1P
.LP
5.1.2
\fIThe application of network management in exchanges\fR
.sp 9p
.RT
.PP
In addition to the normal engineering and economic factors, the
decision whether or not to provide network management capabilities in a
digital exchange will be based on the following considerations:
.RT
.LP
\(em
the size of the exchange, the size of circuit groups it
serves and the network architecture;
.LP
\(em
the role and importance of the exchange in its own network,
or as an access exchange interfacing other exchanges and
networks (e.g.,\ international or other exchange networks);
.LP
\(em
the requirement for the exchange to interact for network
management purposes with other exchanges and/or network
management centres;
.LP
\(em
the features necessary to provide essential services
in emergency situations, where other means are not
available;
.LP
\(em
alternative approaches such as providing redundancy and
special routing methods;
.LP
\(em
the need for managing network resources effectively when
overload conditions occur in its own or interworking
networks.
.PP
Other factors to be considered are:
.LP
\(em
the network management organization, its equipment and
selected functions;
.LP
\(em
the possible interactions of both the circuit switched and
signalling networks when network management actions are applied
under various traffic conditions or network configurations;
.LP
\(em
the potential impact of network management functions on
the engineering design and administration of the network and the
exchange;
.LP
\(em
the evolution towards IDN and interworking of SPC with
non\(hySPC exchanges in the interim period;
.bp
.LP
\(em
the proportion of automatic and manual features to be
implemented and the rate of introduction of various network
management features;
.LP
\(em
the reduction of exchange processing capacity due to the
additional load imposed by network management (if
appropriate);
.LP
\(em
possible additional holding time of equipment in some
switching and signalling systems where open numbering is
used, if and when certain network management controls are
applied.
.sp 1P
.LP
5.2
\fINetwork management elements\fR
.sp 9p
.RT
.PP
The basic elements of a network management system to be provided by an
exchange or by network management centres are:
.RT
.LP
\(em
collection of information about network status and
performance;
.LP
\(em
processing of information for network management
decisions;
.LP
\(em
delivery to exchanges of network status information and/or
commands for control activities;
.LP
\(em
activation/deactivation of controls resulting from decisions
made in the exchange or a network management centre;
.LP
\(em
feedback of status in response to control actions.
.PP
Descriptions of the functions required in the exchanges to support these
elements are given in \(sc\(sc\ 5.3 and\ 5.4.
.sp 2P
.LP
5.3
\fIInformation provided by an exchange for network management\fR
\fIpurposes\fR
.sp 1P
.RT
.sp 1P
.LP
5.3.1
\fIGeneral\fR
.sp 9p
.RT
.PP
The term \*Qinformation\*U is used here as meaning all messages,
signals or data in any form, used or provided by the exchange or by a network
management centre.
.RT
.sp 1P
.LP
5.3.2
\fISources of information\fR
.sp 9p
.RT
.PP
The information provided by an exchange for network management will be
based on the status, availability and performance and
configuration of:
.RT
.LP
\(em
circuit groups;
.LP
\(em
exchange processes;
.LP
\(em
common channel signalling link sets;
.LP
\(em
other exchanges with direct links to this exchange;
.LP
\(em
destination exchanges.
.PP
Status information is generated by comparing the current value of load
indicators with appropriate threshold values and/or detecting abnormal
conditions. Such type of information assumes discrete values and it can be
used, without other processing, to activate traffic control routines.
.PP
This information should be sent spontaneously in a real\(hytime basis to
other exchanges or to a network management centre.
.PP
Performance information is obtained by means of traffic measurements and
can be used for centralized processing or for network supervision in a
network management centre. Such type of information can be sent in a
near\(hyreal\(hytime basis.
.PP
Configuration information is used for a network management data base at
exchange level. This information could include:
.RT
.LP
\(em
threshold values actually used,
.LP
\(em
list of supervised circuit groups,
.LP
\(em
list of supervised signalling circuits,
.LP
\(em
list of supervised processors,
.LP
\(em
list of supervised destination codes,
.LP
\(em
list of primary and alternate routes for specified
destinations.
.PP
Details of network measurements are given in
Recommendation\ Q.544.
.bp
.sp 1P
.LP
5.3.3
\fIProcessing of network management information in an exchange\fR
.sp 9p
.RT
.PP
Information collected at an exchange for network management
purposes may or may not require some form of sorting and assembly (processing)
before being used for network management.
.PP
Where processing is required, this may be done by the exchange
processor, or by a data processing system serving one or more exchanges,
or by a network management centre.
.RT
.sp 1P
.LP
5.3.4
\fITransmittal of information\fR
.sp 9p
.RT
.PP
Network management information may be sent on a scheduled
near\(hyreal\(hytime basis when triggered by abnormal situations (e.g.,\
overload
conditions, alarms,\ etc.): alternatively, information may be sent on demand,
i.e.,\ in response to an external request. Table\ 3/Q.542 shows the
correspondence between sources of information and their transmission mode.
.RT
.ce
\fBH.T. [T3.542]\fR
.ce
TABLE\ 3/Q.542
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(36p) | cw(36p) | cw(36p) .
{
Data transmission
mode
Source of information
} Real\(hytime On demand Scheduled
_
.T&
lw(90p) | cw(36p) | cw(36p) | cw(36p) .
Status information X X
_
.T&
lw(90p) | cw(36p) | cw(36p) | cw(36p) .
{
Performance and availability
information
} X X
_
.T&
lw(90p) | cw(36p) | cw(36p) | cw(36p) .
Configuration information X
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 3/Q.542 [T3.542], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The destinations of network management information may be:
.LP
\(em
within the originating exchange,
.LP
\(em
to distant exchanges,
.LP
\(em
to a network management centre.
.PP
Information may be carried by the TMN over a dedicated telemetry or data
facility, over a common channel signalling network, or over other
telephony network facilities as appropriate.
.PP
For each mode of transmittal the appropriate interface and protocol
requirements, where covered by CCITT Recommendations, should be satisfied.
.RT
.sp 1P
.LP
5.3.5
\fIPresentation of information\fR
.sp 9p
.RT
.PP
Indications of network management controls in effect in an exchange shall
be presented on visual indicators and/or printing\(hytype or video display
terminals for purposes of advising on\(hysite personnel.
.PP
Similar displays and/or indicators may also be provided in a
co\(hylocated and/or distant network management centre.
.RT
.sp 2P
.LP
5.4
\fIExchange controls for network management\fR
.sp 1P
.RT
.sp 1P
.LP
5.4.1
\fIGeneral\fR
.sp 9p
.RT
.PP
Network management controls provide the means to alter the
flow of traffic in the network, in support of network objectives. Most
network management controls are applied by, or in the exchange; however,
certain actions may be taken external to the exchange. Recommendation\ E.412
provides specific information on network management controls and gives
guidance on their application. Additional information is provided in the
CCITT \*QHandbook on Service Quality, Network Management and Maintenance\*U.
.bp
.RT
.sp 1P
.LP
5.4.2
\fIActivation and deactivation of controls\fR
.sp 9p
.RT
.PP
Controls in an exchange can be activated, or deactivated, by input from
a network management operations system or by direct input from an exchange
man\(hymachine interface terminal. In addition, some controls can be activated
automatically either by external or internal stimulus, or by a threshold
being crossed.
.PP
When automatic control operation is provided, means for human override
should also be provided.
.PP
Controls will usually be activated or deactivated in steps (stages)
that are intended to avoid surge effects in the network that could be caused
by too much control being added or removed too quickly.
.PP
A low level threshold may be required to remove controls as
appropriate, when traffic conditions have been stabilized.
.RT
.sp 1P
.LP
5.4.3
\fITraffic to be controlled\fR
.sp 9p
.RT
.PP
Exchanges should be capable of applying a range of network
management controls (see Recommendation\ E.412).
.PP
The operational parameters of a control can be defined by a set of
traffic attributes. As shown in Figure\ 1/Q.542, these parameters include
distinctions based on the origin of traffic, for example, customer\(hydialed,
operator\(hydialed, transit or other classification as may be specified by the
Administration. These can be further defined by type of service, particularly
by ISDN.
.PP
Additional attributes can be specified, for example, incoming/outgoing
circuit group class, or hard\(hyto\(hyreach status of destinations can
be used.
Further distinctions can be based on the outgoing traffic type, for example,
direct\(hyrouted, alternate\(hyrouted or transit.
.RT
.LP
.rs
.sp 12P
.ad r
\fBFigure\ 1/Q.542, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
5.4.4
\fINetwork management controls\fR
.sp 9p
.RT
.PP
The following is a list of typical network management controls to be considered
for implementation in a given exchange.
.PP
It is desirable that these controls be activated to affect a
variable percentage of traffic (for example, 25%, 50%, 75% or\ 100%).
Alternatively the number of call attempts routed in a particular period
may be controlled (for example 1\ calls per minute). It may also be desirable
to apply controls on a destination code basis.
.PP
These controls are normally activated/deactivated manually from a
man\(hymachine interface in the exchange, or from an operations system. The
automatic operation of these controls and the need for new controls is for
further study.
.PP
It is preferable that these controls be provided in international
transit exchanges and large transit exchanges in national applications.
However, the decision whether or not to provide these controls in local and
combined local/transit exchanges is at the discretion of the
Administration.
.bp
.RT
.sp 1P
.LP
5.4.4.1
\fICode blocking control\fR
.sp 9p
.RT
.PP
This control bars or restricts routing to a specific destination
code. Code blocking can be done on a country code, an area code, an exchange
identifying code and, in some cases, on an individual line number.
.RT
.sp 1P
.LP
5.4.4.2
\fICancellation of alternative routing\fR
.sp 9p
.RT
.PP
There are two types of cancellation of alternative routing control. One
version prevents traffic from overflowing from the controlled route
(Alternate Routed From \(em\ ARF). The other version prevents overflow
traffic from all sources from having access to the controlled route (Alternate
Routed To
\(em\ ART). When cancellation of alternative routing is to be provided,
both types are recommended.
.RT
.sp 1P
.LP
5.4.4.3
\fICall gapping\fR
.sp 9p
.RT
.PP
This control sets an upper limit on the number of call attempts
allowed to be routed towards the specified destination in a particular
period of time (for example, one\ call per minute).
.RT
.sp 1P
.LP
5.4.4.4
\fIRestriction of direct routing\fR
.sp 9p
.RT
.PP
This control limits the amount of direct routed traffic accessing a route.
.RT
.sp 1P
.LP
5.4.4.5
\fISkip route\fR
.sp 9p
.RT
.PP
This control allows traffic to bypass a specific route and advance instead
to the next route in its normal routing pattern.
.RT
.sp 1P
.LP
5.4.4.6
\fITemporary alternative routing\fR
.sp 9p
.RT
.PP
This control redirects traffic from congested routes to routes
not normally available which have idle capacity at the time. This can be
done for subscriber, and/or operator\(hyoriginated traffic.
.RT
.sp 1P
.LP
5.4.4.7
\fICircuit directionalization\fR
.sp 9p
.RT
.PP
This control changes both\(hyway operated circuits to one\(hyway operated
circuits.
.RT
.sp 1P
.LP
5.4.4.8
\fICircuit turndown/busying\fR
.sp 9p
.RT
.PP
This control removes one\(hyway and/or both\(hyway operated circuits from
service.
.RT
.sp 1P
.LP
5.4.4.9
\fIRecorded announcements\fR
.sp 9p
.RT
.PP
These are announcements which give special instructions to
operators and subscribers, such as to defer their call to a later time.
.RT
.sp 2P
.LP
5.5
\fIAutomatic controls for network management\fR
.sp 1P
.RT
.sp 1P
.LP
5.5.1
\fIGeneral\fR
.sp 9p
.RT
.PP
This section provides descriptions of some automatic traffic
control methods that can be provided in digital exchanges for network
management purposes.
.PP
Automatic, and/or dynamic network management controls represent a
significant improvement over static manual controls. These controls, which
are pre\(hyassigned, can respond automatically to conditions internally
detected by
the exchange, or to status signals from other exchanges and can be promptly
removed when no longer required.
.PP
The following are a basic set of automatic methods for use in the
telephone network:
.RT
.LP
\(em
Automatic Congestion Control system (ACC);
.LP
\(em
Selective Circuit Reservation control (SCR);
.LP
\(em
Hard\(hyto\(hyReach process (HTR);
.LP
\(em
Temporary Trunk Blocking (TTB).
.bp
.PP
The above list of methods is not exhaustive, but will provide a
framework for more advanced controls which may be required in the ISDN.
.PP
In the following four sections the typical operation of each control is
described, and guidance on the application of the controls is given in
\(sc\ 5.5.6.
.RT
.sp 1P
.LP
5.5.2
\fIAutomatic Congestion Control system\fR
.sp 9p
.RT
.PP
The Automatic Congestion Control (ACC) system allows a congested
exchange to send a congestion indicator in a backward direction to the
preceding exchange. The exchange receiving the congestion indication should
respond by reducing the amount of traffic offered to the congested exchange.
.PP
The preferred method of conveying the congestion indication is via the
relevant common channel signalling system.
\v'3p'
.RT
.LP
a)
\fIDetection and transmission of congestion status\fR
.LP
An exchange should establish a critical operating system
benchmark, e.g.,\ the time required to perform a complete basic
cycle of operations. The exchange should continously monitor
this benchmark and, when continued levels of nominal
performance are not achieved, a state of congestion is declared.
Thresholds should be established so that two levels of
congestion can be identified, with congestion level\ 2 (C2)
indicating a more severe performance degradation than
congestion level\ 1 (C1). When either level of congestion is
detected, the exchange should have the capability to
.LP
1)
code an ACC indication in the appropriate signalling messages, and
.LP
2)
notify its network management support system of its current
congestion status.
.LP
The system can offer benefit, however, by recognizing
a single level of congestion. Where this situation exists,
it should be regarded as congestion level\ 2.
.LP
b)
\fIACC control operation\fR
.LP
Exchanges receiving an ACC indication from an affected
exchange or network operations centre should have the
capability to institute the appropriate ACC controls and to
notify its network management support system of the receipt
of an ACC indication.
.LP
An exchange receiving an ACC indicator from a congested
exchange should activate the assigned ACC controls and start
a timer. (The provisional value of the timer is five seconds
and is for further study.) Subsequent received ACC indicators
restart the timer, when the timer expires, the ACC controls
in the exchange are removed. One or more different response
categories should be available from which to choose.
.LP
To avoid the incorrect application of controls, it is
important that an exchange receiving an ACC indication
should not re\(hytransmit that indication to a preceding
exchange.
.LP
c)
\fIACC response\fR
.LP
An exchange should have the capability of assigning an
ACC response category to individual circuit groups. There should
be several categories available from which to choose. Each
category would specify how much traffic should be controlled
in response to each of the received ACC indicators. The
categories should be structured so as to present a wide range
of response options to received ACC indicators.
.LP
The control options for further processing of calls denied access to
the circuit group may be SKIP or CANCEL. The SKIP
response allows a call to alternate route to the next circuit
group in the routing pattern (if any) while the CANCEL response
blocks the call.
.LP
\fINote\fR \ \(em\ ACC response categories can be set locally in the
exchange or by input from a network management center.
.PP
Table 4/Q.542 is an example of the flexibility that could be
achieved in a control's response to an exchange that is experiencing
congestion.
.PP
In this example, different control actions would be taken based
upon the distinction between Alternate Routed To (ART) and Direct Routed
(DR) traffic types. In the future, other distinctions between traffic could
be
identified that would expand the number of traffic types in Table\ 4/Q.542.
These additional traffic types could be assigned different control percentages
(or excluded from ACC control, as in the case of priority calls), to give
them different treatment during periods of congestion. An example would
be to
control hard\(hyto\(hyreach traffic as indicated in \(sc\ 5.5.4.
.PP
Methods used to achieve the percentages are implementation specific. Additional
response categories could also be added to Table\ 4/Q.542 to give
greater flexibility and more response options to the ACC control.
.bp
.RT
.ce
\fBH.T. [T4.542]\fR
.ce
TABLE\ 4/Q.542
.ce
\fBAn example of 2\(hycongestion level ACC percentage
.ce
control response table\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(24p) sw(24p) sw(24p) , ^ | ^ | c | c | c.
Congestion level Traffic type Response category
A B C
_
.T&
cw(48p) | lw(48p) | cw(24p) | cw(24p) | cw(24p) .
CL1 ART \ \ 0 \ \ 0 100
.T&
cw(48p) | lw(48p) | cw(24p) | cw(24p) | cw(24p) .
DR \ \ 0 \ \ 0 \ \ 0
_
.T&
cw(48p) | lw(48p) | cw(24p) | cw(24p) | cw(24p) .
CL2 ART 100 100 100
.T&
cw(48p) | lw(48p) | cw(24p) | cw(24p) | cw(24p) .
DR \ \ 0 \ 75 \ 75
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 4/Q.542 [T4.542], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 5
.sp 1P
.LP
5.5.3
\fISelective Circuit Reservation control\fR
.sp 9p
.RT
.PP
The Selective Circuit Reservation (SCR) Network Management control enables
a digital exchange to automatically give preference to a specific type
(or types) of traffic over others (e.g.,\ direct routed calls over alternate
routed calls) when circuit congestion is present or imminent. A digital
exchange should provide either the single threshold of multi\(hythreshold
version of the countrol, with the latter being preferred due to its greater
selectivity.
.RT
.sp 1P
.LP
5.5.3.1
\fIGeneral characteristics\fR
.sp 9p
.RT
.PP
A Selective Circuit Reservation control may be defined, for a given circuit
group, by the following parameters:
.RT
.LP
\(em
a reservation threshold(s), and
.LP
\(em
a control response.
.PP
The reservation threshold defines how many circuits should be
reserved for those traffic types to be given preferred access to the circuit
group. The control response defines which traffic types should be given a
lesser preference in accessing the circuit group, the quantity of each type
of traffic to control, and how those calls denied access to the circuit
group should be handled. Examples of possible traffic types are Direct
Routed (DR), Alternate Routed To (ART), Hard\(hyTo\(hyReach (HTR), and
various combinations
thereof. The quantity of each type of traffic to be controlled when the
threshold is exceeded may be represented by a percentage of the total traffic
of that type. The control action options for further processing of calls
denied access to the circuit group may be SKIP or CANCEL.
.PP
When the number of idle circuits in the given circuit group is less
than or equal to the reservation threshold the exchange would, for that
call, check the specified control response to determine if the call should
be
controlled. The SKIP response allows a call to alternate route to the next
circuit group in the routing pattern (if any) while the CANCEL response
blocks the call.
.PP
These parameters should be able to set locally in the exchange or by input
from a network management centre. In addition, the network manager should
have the capability to enable and disable the control, and to enable the
control but place it in a state where the control does not activate (e.g.,\
by setting the reservation threshold to zero).
.bp
.RT
.sp 1P
.LP
5.5.3.2
\fISingle\(hythreshold Selective Circuit Reservation control\fR
.sp 9p
.RT
.PP
In this version of the control, only a single reservation threshold would
be available for the specified circuit group.
.PP
Table\ 5/Q.542 is an example of the flexibility that could be achieved
in the control's response to circuit group congestion. Consider, for example,
a case in which a network manager assigns response category\ \*QB\*U, a
reservation
threshold of 5\ circuits (RT1\ =\ 5), and a control action of SKIP to a circuit
group. Then, when the control is enabled, every time the number of idle
circuits in the circuit group is less than or equal to five, the exchange
SKIPs 50\ percent of the alternate routed traffic attempting to access
the circuit
group. Direct routed traffic has full access to the circuit group because
the quantity of direct routed traffic to be controlled is zero percent.
Note that the reservation threshold (in this example RT1\ =\ 5) is the
same for any of the response categories (A, B and\ C) that can be assigned
to a circuit group. One or more response categories should be available
from which to choose.
.PP
In the future, other distinctions between traffic could be identified that
would expand the number of traffic types in Table\ 5/Q.542. An example
would be to control Hard\(hyTo\(hyReach traffic, as indicated in \(sc\
5.5.4, or to give preference to priority calls.
.RT
.LP
.sp 3
.ce
\fBH.T. [T5.542]\fR
.ce
TABLE\ 5/Q.542
.ce
\fBAn example of a single threshold selective circuit
.ce
reservation percentage control response table\fB\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(36p) | cw(30p) sw(30p) sw(30p) , ^ | ^ | c | c | c.
{
Circuit group reservation threshold
} Traffic type {
Response category
assigned to circuit group
}
A B C
_
.T&
cw(48p) | lw(36p) | cw(30p) | cw(30p) | cw(30p) , ^ | l | c | c | c.
RT1 ART 25 50 100
DR \ 0 \ 0 \ 25
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 5/Q.542 [T5.542], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
.sp 6
5.5.3.3
\fIMulti\(hythreshold Selective Circuit Reservation control\fR
.sp 9p
.RT
.PP
The multi\(hythreshold control would support two reservation
thresholds for the specified circuit group. The purpose of multiple reservation
thresholds would be to allow a gradual increase in the severity of the
control response as the number of idle circuits in the circuit group decreased.
The
only restriction on the reservation thresholds would be that a reservation
threshold associated with a more stringent control must always be less
than or equal to the reservation threshold of any less stringent control,
in terms of the number of reserved circuits [RT2\ \(=\ RT1 in Table\ 6/Q.542].
.PP
Table\ 6/Q.542 is an example of the flexibility that could be achieved
in the control's response to circuit group congestion with two reservation
threshold control. In the future, other distinctions between traffic could
be identified that would expand the number of traffic types in Table\ 6/Q.542,
or to give preference to priority calls.
.bp
.RT
.ce
\fBH.T. [T6.542]\fR
.ce
TABLE\ 6/Q.542
.ce
\fBAn example of a two threshold selective circuit reservation\fR
.ce
.ce
\fBpercentage control response table with HTR capability\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(39p) | cw(27p) sw(33p) sw(27p) sw(27p) sw(27p) , ^ | ^ | c | c | c | c | c.
{
Circuit group reservation threshold
} Traffic type {
Response category assigned to circuit group
}
A B C D E
_
.T&
cw(48p) | lw(39p) | cw(27p) | cw(33p) | cw(27p) | cw(27p) | cw(27p) , ^ | l | l | l | l | l | l
^ | l | l | l | l | l | l
^ | l | l | l | l | l | l.
RT1 {
ART\(hyHTR
DR\(hyHTR
ART\(hyETR
DR\(hyETR
} \ 50 \ \ 0 \ \ 0 \ \ 0 \ 75 \ \ 0 \ 25 \ \ 0 100 \ \ 0 \ 50 \ \ 0 100 \ \ 0 \ 75 \ \ 0 100 \ \ 0 100 \ \ 0
_
.T&
cw(48p) | lw(39p) | cw(27p) | cw(33p) | cw(27p) | cw(27p) | cw(27p) , ^ | l | l | l | l | l | l
^ | l | l | l | l | l | l
^ | l | l | l | l | l | l.
RT2 {
ART\(hyHTR
DR\(hyHTR
ART\(hyETR
DR\(hyETR
} 100 \ \ 0 \ 50 \ \ 0 100 \ 25 \ 50 \ \ 0 100 \ 50 \ 75 \ 25 100 \ 75 100 \ 50 100 100 100 \ 75
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 6/Q.542 [T6.542], p.
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
5.5.4
\fIHard\(hyto\(hyreach (HTR) process\fR
.sp 9p
.RT
.PP
The Hard\(hyto\(hyReach process for network management allows exchanges
to automatically make more efficient use of network resources during periods
of network congestion.
.PP
Part of the improved performance of automatic controls can be derived from
the ability to distinguish between destinations that are easy\(hyto\(hyreach
(ETR) and destinations that are hard\(hyto\(hyreach (HTR), i.e.,\ destinations
with a low answer bid ratio, and applying heavier controls to HTR destinations.
This distinction can be based on:
.RT
.LP
i)
internal performance measurements within the
exchange/Network Management Operations System (OS) (for
example, low Answer Bid Ratio (ABR) to a destination);
.LP
ii)
similar information gathered by other exchanges;
.LP
iii)
historical observations of network performance by
network managers.
.PP
The network manager should have the ability to set the threshold for HTR
determination and to assign manually a destination code as HTR.
.sp 1P
.LP
5.5.4.1
\fISimplified HTR process components\fR
.sp 9p
.RT
.PP
To provide the fundamental elements of a simplified HTR process,
the following capabilities must exist:
.RT
.LP
a)
HTR administration,
.LP
b)
HTR determination,
.LP
c)
manually controlling calls as if hard\(hyto\(hyreach.
.PP
Items a) and b) may be entirely provided by the exchange or by a Network
Management (OS) in cooperation with the exchange(s). Item\ c) can only
be provided in the exchange.
\v'3p'
.LP
a)
\fIHTR administration\fR
.LP
Network managers will administer the HTR process to optimize the information
obtained about current network performance. In
order to properly administer the HTR system, network managers
need four capabilities. These capabilities are listed below.
.LP
1)
\fICodes to be observed\fR
.LP
An exchange should automatically collect ABR data for some destination
areas, e.g.,\ countries, area codes,\ etc.
In addition, network managers should have the capability
to designate/change destinations an exchange should
monitor in greater
.bp
.LP
detail. An exchange should accept at
least three network management designated sets of digits
that identify a specific destination area and
automatically begin surveillance of the specified
destination areas. The specific number of digits to be
analyzed is left to the discretion of the
administration and may be exchange dependent.
.LP
2)
\fIAdministration of HTR thresholds\fR
.LP
There should be a set of thresholds used to monitor
destination areas and another set for use when
monitoring destinations in greater detail. Network
managers should be able to specify/change the values
of \*QB\*U and\ \*QT\*U for the pre\(hyestablished threshold sets
and the HTR hysteresis modifiers (see\ b, sub\(hysection\ 3),
below).
.LP
3)
\fIAdministration of HTR determination exclusion\fR
.LP
A network manager should have the capability to
exclude destination codes from being determined as HTR.
This should prevent these destination codes from
automatically being calculated as HTR and prevent
these destination codes from being automatically
placed on the \*QHTR Control\*U list. A network manager
should also have the ability to restore destination
codes to the fully automatic HTR determination function.
.LP
4)
\fIAdministrative review of HTR list\fR
.LP
Network managers should have the capability to view
the contents of the \*QHTR Control\*U list, either via a
terminal at the exchange or remotely through a
Network Management OS. The list should indicate which
destination codes have been manually designated as HTR
(see c) below). In addition, network managers should
have access to a list of those destination codes which
have been manually excluded from automatic HTR
determination.
.LP
b)
\fIHTR determination\fR
.LP
The capability should exist to determine automatically which destination
codes are HTR. This is based on three capabilities.
.LP
1)
\fICode measurements\fR
.LP
The HTR/ETR status of a destination is based on
analyzing the data for groupings of routing digits.
An exchange should take measurements based
on a sufficient number of routing digits to identify
a destination. The exchange should take those measurements
necessary to calculate the ABR for each such destination.
.LP
2)
\fIHTR calculations\fR
.LP
Periodically, the ABR for these destination codes
under surveillance should be calculated. A recommended time
interval is every 5\ minutes.
.LP
3)
\fIDetermining destination code HTR/ETR status\fR
.LP
For each destination code, the capacity should be
provided to compare the number of bids and the calculated
ABR to a set of pre\(hyestablished thresholds. There should
be a set of thresholds applicable to determining HTR
destination areas and another set for destinations being
monitored in greater detail.
.LP
A set of pre\(hyestablished threshold consists of:
.LP
\(em
B: Bids; the number of calls received by an
exchange for a given destination code. This count
includes calls that are successfully forwarded to the
succeeding exchange as well as calls that fail within
the current exchange.
.LP
\(em
T: ETR threshold; the threshold above which a
destination code's ABR should be considered ETR.
.LP
A destination code would be considered HTR if,
based on the 5\(hyminute calculations, the measured number
of bids to the code is greater than or equal to
threshold\ \*UB\*U and the ABR is less than or equal
to threshold\ \*QT\*U.
.LP
A destination code that is determined to be HTR
should be placed on a \*QHTR Control\*U list in the
exchange.
.LP
To avoid having destination codes oscillate on and
off the \*QHTR Control\*U list, hysteresis modifiers should
be applied to determine when destination codes should be
removed from the \*QHTR Control\*U list. In succeeding
5\(hyminute periods, these hysteresis modifiers should be
applied to both values \*QB\*U and\ \*QT\*U when it is time to
recalculate the HTR/ETR status of the destination code.
.LP
At the beginning of each 5\(hyminute period, the
\*QHTR Control\*U list should be reviewed. If a destination
code that was calculated to be HTR is determined to
be no longer than HTR, then it should be removed from the
\*QHTR Control\*U list.
.LP
c)
\fIManually controlling calls as if HTR\fR
.LP
A network manager should have the capability of specifying any destination
code as HTR so as to cause automatic network
management control actions to take place within the exchange
as indicated in \(sc\ 5.5.4.2 below. The manually specified
destination code(s) may
.bp
.LP
go on the \*QHTR Control\*U list. They
should not, however, be subject to the 5\(hyminute review and
removal procedure described above. They should be removed
upon request of a network manager. To this end, a network
manager should have the capability of ending this stimulus
to identifying a destination code as HTR.
.LP
Whenever a network manager adjusts the HTR status of a
destination code, that manual action should take precedence
over any automatic actions for that destination code.
.sp 1P
.LP
5.5.4.2
\fIControlling calls based on HTR status\fR
.sp 9p
.RT
.PP
When a call to a destination code that is on the \*QHTR Control\*U list
is being routed and a manual or automatic network management control is
encountered during the processing of the call, the control should take into
account the fact that the destination code is HTR. If a destination code
is on the \*QHTR Control\*U list, then the call should be considered HTR
for all outgoing circuit groups.
.PP
As an example of an automatic network management control incorporating
HTR, the Automatic Congestion Control (ACC) Response Percentage Table
(Table\ 4/Q.542) could be expanded to apply more stringent controls to HTR
traffic, as shown in Table\ 7/Q.542. A similar application of the Selective
Circuit Reservation Control is possible (see \(sc\ 5.5.3).
.RT
.ce
\fBH.T. [T7.542]\fR
.ce
TABLE\ 7/Q.542
.ce
\fBExample of automatic congestion control response
.ce
percentages with HTR\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(39p) | cw(27p) sw(33p) sw(27p) sw(27p) sw(27p) , ^ | ^ | c | c | c | c | c.
Congestion level Traffic type Response category
A B C D E
_
.T&
cw(48p) | lw(39p) | cw(27p) | cw(33p) | cw(27p) | cw(27p) | cw(27p) , ^ | l | l | l | l | l | l
^ | l | l | l | l | l | l
^ | l | l | l | l | l | l.
CL1\fR {
ART\(hyHTR
DR\(hyHTR
ART\(hyETR
DR\(hyETR
} \ \ 0 \ \ 0 \ \ 0 \ \ 0 \ \ 0 \ \ 0 \ \ 0 \ \ 0 100 \ \ 0 \ \ 0 \ \ 0 100 100 \ \ 0 \ \ 0 100 100 \ \ 0 \ \ 0
_
.T&
cw(48p) | lw(39p) | cw(27p) | cw(33p) | cw(27p) | cw(27p) | cw(27p) , ^ | l | l | l | l | l | l
^ | l | l | l | l | l | l
^ | l | l | l | l | l | l.
CL2 {
ART\(hyHTR
DR\(hyHTR
ART\(hyETR
DR\(hyETR
} 100 \ \ 0 \ \ 0 \ \ 0 100 100 \ \ 0 \ \ 0 100 100 \ \ 0 \ \ 0 100 100 100 \ \ 0 100 100 100 \ 75
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 7/Q.542 [T7.542], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 3
.sp 1P
.LP
5.5.5
\fITemporary Trunk Blocking\fR
.sp 9p
.RT
.PP
Temporary Trunk Blocking (TTB) is an alternative method of
exchange congestion control for application in national networks.
.PP
When an exchange is in a low level overload condition, a Temporary
Trunk Blocking signal may be sent to a preceding exchange to indicate that
the release or re\(hyoccupation of a trunk should be delayed for a short
(e.g.,\ 100\ s) period of time. This may permit an overall level of up
to the maximum possible load in the overloaded exchange without need to
generate ACC signals. The
preferred method of conveying the TTB signal is via the relevant common
channel signalling system.
.PP
The exchange receiving the Temporary Trunk Blocking signal will delay the
release or the re\(hyoccupation of the concerned trunk for a short time.
This time should be made changeable by operating personnel command.
.PP
The duration of trunk blocking is limited by a timer in the exchange receiving
the Temporary Trunk Blocking signal. Therefore, an unlimited blocking of
the trunk is avoided.
.bp
.RT
.sp 2P
.LP
5.5.6
\fIApplication\fR
.sp 1P
.RT
.sp 1P
.LP
5.5.6.1
\fIACC\fR
.sp 9p
.RT
.PP
Generally, where an Administration has introduced or is planning to introduce
network management controls, it is considered appropriate for digital transit
and large digital combined local/transit exchanges to be provided with
full ACC capabilities. Digital local and smaller combined local/transit
exchanges should only be provided with ACC receive and control
capabilities.
.RT
.sp 1P
.LP
5.5.6.2
\fISCR\fR
.sp 9p
.RT
.PP
It is considered appropriate for digital transit and large digital combined
local/transit exchanges to be provided with a two\(hythreshold Selective
Circuit Reservation Network Management Control. Network Management of digital
local and smaller combined local/transit exchanges could benefit from having
available, ideally, the two threshold or the single threshold Selective
Circuit Reservation Network Management Control. The decision whether or
not to provide this control in these exchanges is left to the discretion
of the various
Administrations.
.RT
.sp 1P
.LP
5.5.6.3
\fIHTR\fR
.sp 9p
.RT
.PP
It is considered appropriate for digital transit and large digital combined
local/transit exchanges (optionally in conjunction with a Network
Management OS) to be provided with full HTR capabilities. Digital local and
smaller combined local/transit exchanges should only be provided with the
manual HTR and HTR controlling (based on HTR status) capabilities, i.e.,\
those capabilities found in \(sc\(sc\ 5.5.4.1 subsection\ c, and 5.4.4.2
of this
Recommendation. It is also recommended that control modifications, based
on HTR status, be added to both the ACC and Selective Circuit Reservation
capabilities.
.RT
.sp 1P
.LP
5.5.6.4
\fITTB\fR
.sp 9p
.RT
.PP
It is considered appropriate for TTB to be provided in digital
transit and large digital combined local/transit exchanges in national
applications. It may be particularly useful in exchanges that may not be
provided with ACC capabilities, such as local exchanges.
.RT
.sp 1P
.LP
5.6
\fIOrder of application of controls\fR
.sp 9p
.RT
.PP
The order in which various network management controls shall be
applied in an exchange is for further study.
\v'1P'
.RT
.sp 2P
.LP
\fBRecommendation\ Q.543\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBDIGITAL\ EXCHANGE\ PERFORMANCE\ DESIGN\ OBJECTIVES\fR
.EF '% Fascicle\ VI.5\ \(em\ Rec.\ Q.543''
.OF '''Fascicle\ VI.5\ \(em\ Rec.\ Q.543 %'
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.PP
This Recommendation applies to digital local, combined, transit and international
exchanges for telephony in Integrated Digital Networks (IDN)
and mixed (analogue/digital) networks, and also to local, combined, transit
and international exchanges in an Integrated Services Digital Network (ISDN).
.PP
The field of application of this Recommendation is more fully defined in
Recommendation\ Q.500. As to the application in an ISDN, transit connections
and exchange connections types\ I, II, III and\ IV as defined in
Recommendation\ Q.522 are covered (Notes\ 1\ and 2). Other types of connection
and variants of these connections may be feasible in ISDN and will be the
subject of further study.
.bp
.PP
These performance design objectives are applicable to all exchange
implementations at all points in the growth cycle up to the maximum size.
These reference loads and performance objectives may be used by manufacturers
in
designing digital switching systems and by Administrations in evaluating a
specific exchange design or for comparing different exchange designs for
potential use in the Administration's intended implementation.
.PP
These recommended performance design objectives relate to the
technical capabilities of exchange design. They are intended to assure that
exchanges operating in their intended implementation will be capable of
supporting the network grades of service recommended in the E.500\(hyseries of
Recommendations and will offer a level of performance consistent with the
overall network performance objectives given in the I\(hyseries of
Recommendations. The recommended parameters are \fIdesign objectives\fR which
should not be construed to be grade of service or operating requirements. In
actual operation, exchanges will be engineered to provide adequate grades of
service as economically as possible and the \fIperformance requirements\fR
(delays, blocking,\ etc.) of the exchange in operation will \fIdiffer from\fR
the recommended values for these performance \fIdesign objectives\fR .
.RT
.sp 2P
.LP
\fB2\fR \fBPerformance design objectives\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIReference loads\fR
.sp 9p
.RT
.PP
The given reference loads are traffic load conditions under which the performance
design objectives stated in \(sc\(sc\ 2.2\ to 2.7 are to be met. In
order to have a comprehensive characterization of exchange reference loads,
supplementary services and other types of services must be taken into account.
Administrations may specify hypothetical models for use in computing exchange
loading. These models should characterize the sets of traffic parameters
and
services that are considered to be typical in the intended application
of the exchange, and should include the traffic mix (originating\(hyinternal,
originating\(hyoutgoing, incoming\(hyterminating, transit, abandoned, busy
non\(hyanswer,\ etc.), the mix of service classes (residential, business, PABX,
coin,\ etc.), the types and volume of supplementary services (call waiting,
call forwarding,\ etc.) and any other pertinent characteristics. Using
the above
information, it should be possible to \*Qengineer\*U the exchange to produce
the
model. It should also be possible to determine the maximum size of the
exchange by the computations discussed in \(sc\ 2.1.4.
.PP
Reference load A is intended to represent the normal upper mean level of
activity which Administrations would wish to provide for on customer lines
and inter\(hyexchange activities. Reference load\ B is intended to represent
an
increased level beyond normal planned activity levels. (Recommendations\
E.500 and\ E.520 recommended that the normal provisioning of international
circuits in automatic and semi\(hyautomatic operation be based on a particular
loss
probability during the mean busy hour and the average traffic estimated
for the \*Qfive busiest days\*U as set down in Recommendation\ E.500.)
.PP
\fINote\ 1\fR \ \(em\ For the time being, the following definitions and
corresponding values are only applicable to 64\ kbit/s circuit switched
connections, i.e.,\ including transit connections and connection types\ I, II
and\ III option\ a). Other rates and transfer modes require further study.
.PP
\fINote\ 2\fR \ \(em\ The applicability of this document to connections
originating or terminating on PABXs is for further study.
.RT
.sp 1P
.LP
2.1.1
\fIReference load on incoming interexchange circuits\fR \v'3p'
.sp 9p
.RT
.LP
a)
\fIReference load A\fR
.LP
\(em
0.7 erlangs average occupancy on all incoming circuits
.sp 1P
.ce 1000
Call attempts/h =
@ { .7\~\(mu\~number~of~incoming~circuits } over { verage~holding~time~in~hours } @
.ce 0
.sp 1P
.LP
\fINote\fR \ \(em\ Ineffective call attempts must be included in
reference call attempts.
\v'3p'
.LP
b)
\fIReference load B\fR
.LP
\(em
0.8 erlangs average occupancy on all incoming circuits
.LP
with 1.2 times the call attempts/h for reference load A.
.bp
.sp 1P
.LP
2.1.2
\fIReference load on subscriber lines (originating traffic)\fR
.sp 9p
.RT
.PP
Characteristics of traffic offered to local exchanges vary widely depending
upon factors such as the proportions of residence and business lines that
are served. The following Table\ 1/Q.543 provides reference load
characteristics for lines typical of four possible local exchange applications.
Also provided are representative ISDN cases which are discussed below.
Administrations may elect to use other models and/or loads that are more
suitable for their intended application.
.PP
In the following text, ISDN lines will be referred to as digital lines
and non\(hyISDN lines as analogue lines.
.RT
.sp 1P
.LP
2.1.2.1
\fIReference load A\fR
.sp 9p
.RT
.ce
\fBH.T. [T1.543]\fR
.ce
TABLE\ 1/Q.543
.ce
\fBSubscriber line traffic model\fR
.ce
a)
.ce
\fINon\(hyISDN subscriber lines with or without supplementary\fR
.ce
.ce
\fIservices\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(48p) .
Exchange type\fR Average traffic intensity Average BHCA
_
.T&
cw(48p) | cw(48p) | cw(48p) .
W 0.03 | 1.2
.T&
cw(48p) | cw(48p) | cw(48p) .
X 0.06 | 2.4
.T&
cw(48p) | cw(48p) | cw(48p) .
Y 0.10 | 4\fB.8\fR
.T&
cw(48p) | cw(48p) | cw(48p) .
Z 0.17 | 6.8
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 1/Q.543 a) [T1.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
b)
\fIISDN digital subscriber access 2B\ +\ D\fR
.PP
The following ISDN models and traffic parameters are provisional and may
be revised in subsequent study periods.
.ce
\fBH.T. [T2.543]\fR
.ce
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(48p) | cw(48p) | cw(84p) .
Line type {
Average traffic intensity per B\ channel
} Average BHCA per B channel {
Average packets per second per D channel
}
_
.T&
cw(36p) | cw(48p) | cw(48p) | cw(84p) .
Y` 0.05 | 2 {
0.05
(signalling) + Data packets | ua\d\u)\d
}
_
.T&
cw(36p) | cw(48p) | cw(48p) | cw(84p) .
Y`` 0.10 | 4 {
0.1\
(signalling) + Data packets | ua\d\u)\d
}
_
.T&
cw(36p) | cw(48p) | cw(48p) | cw(84p) .
Y``` 0.55 | 2 0.05 (signalling) + Data packets | ua\d\u)\d
BHCA\ Busy hour call attempts.
.TE
.LP
\ua\d\u)\d
Data packet rates are for further study. These include teleaction and packet services data.
.nr PS 9
.RT
.ad r
\fBTable 1/Q.543 b) [T2.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
Even though only limited ISDN traffic data is available, the
specification of the corresponding reference loads remains an important
factor in exchange evaluation. For the case of digital subscriber lines
in
Table\ 1/Q.543 | ), access is assumed to utilize the Basic Access with 2B\ +\ D
channels. The B\ channels are available for circuit\(hyswitched calls,
while the
D\ channel is used to carry signalling information or may be used to carry
teleaction data and packet switched data. It is assumed that digital lines
typically carry traffic comparable with the heavy\(hytraffic analogue lines
designated as case\ Y in Table\ 1/Q.543 | ). Three cases representing likely
ISDN applications are included in the table.
.LP
Case\ Y`
traffic per pair of B channels comparable to 1
Case Y line.
.LP
Case\ Y``
traffic per pair of B channels comparable
to 2 Case Y lines.
.LP
Case\ Y```
traffic per pair of B channels
comparable 1 Case Y line plus some very high traffic (e.g.,\ circuit switched
data traffic at 1\ erlang).
.PP
Each of these digital lines also carries the associated ISDN
signalling and data services on the D\ channel. For the circuit switched
calling rates specified in Table\ 1/Q.543 | ), ISDN signalling is expected
to contribute less than 0.05\ packet per second per digital subscriber
line. The packet rates for D\ channel ISDN data services can be much larger
than this; however, these are left for further study.
.sp 1P
.LP
2.1.2.2
\fIReference load B\fR
.sp 9p
.RT
.PP
Reference load B is defined as a traffic increase over
reference load A of:
.PP
+25% in erlangs, with +35% in BHCA.
.PP
Reference load B levels for D channel activity are for further
study.
.RT
.sp 1P
.LP
2.1.3
\fIImpact of supplementary services\fR
.sp 9p
.RT
.PP
If the reference model exchange assumes that significant use is
made of supplementary services, the performance of the exchange can be
strongly affected, especially in exchange designs where processor capacity
can become a limiting item. The performance delays recommended in \(sc\(sc\
2.3 and\ 2.4 can be
significantly lengthened at a given call load under such circumstances. The
Administration or Operating Agency defining the reference model should
estimate the fractions of calls which use various supplementary services
so that an
average processor impact relative to a basic telephone call can be calculated
(e.g.,\ possibly by a methodology similar to that of Annex\ A to this
Recommendation).
.RT
.sp 1P
.LP
2.1.4
\fIExchange capacity\fR
.sp 9p
.RT
.PP
In order to evaluate and compare exchange designs, an
Administration will usually want to know the maximum possible size of the
exchange for the intended implementation. While several factors may limit
exchange capacity, processing capacity will frequently be the limiting
factor. The maximum possible number of lines and circuits served by an
exchange,
\fIwhile meeting performance objectives\fR , will depend on the mix, volumes
and
types of traffic and the services expected in the particular implementation.
.PP
Two methods of determining exchange processing capacity are provided in
the annexes to this Recommendation:
.RT
.LP
\(em
Annex A provides an example of methodology for computing
processing capacity of an exchange using information provided
by the manufacturer and estimates of traffic mix and load
provided by the Administration.
.LP
\(em
Annex B provides an example of methodology for estimating
the capacity of an exchange by making projections from
measurements made on a functioning exchange in the
laboratory or in the field. The test exchange must be
representative of mix and load of traffic and services
expected at maximum size.
.sp 1P
.LP
2.1.5
\fIReference loads on other accesses and interfaces\fR
.sp 9p
.RT
.PP
At this time, other applications, such as n \(mu 64 kbit/s on the
Primary Rate Interface, are left for further study.
.bp
.RT
.sp 2P
.LP
2.2
\fBinadequately handled call attempts\fR
.sp 1P
.RT
.sp 1P
.LP
\fI\fR 2.2.1
\fIDefinition\fR
.sp 9p
.RT
.PP
Inadequately handled call attempts are attempts which are blocked (as defined
in the E.600\(hyseries of Recommendations) or are excessively delayed within
the exchange. \*QExcessive delays\*U are those that are greater than three
times the \*Q0.95 probability of not exceeding\*U values recommended in
the tables in \(sc\(sc\ 2.3\ and 2.4. (See Note.)
.PP
For originating and transit calls, this inadequately handled call
attempt parameter applies only when there is at least one appropriate outlet
available.
.PP
\fINote\fR \ \(em\ Provisionally, call request delay is not included in this
parameter. Further study is required.
.RT
.sp 1P
.LP
2.2.2
\fIProbability of inadequately handled call attempts occurring\fR
.sp 9p
.RT
.PP
The values in Table 2/Q.543 are recommended.
.RT
.ce
\fBH.T. [T3.543]\fR
.ce
TABLE\ 2/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(54p) | cw(54p) | cw(54p) .
Type of connection Reference load A \fR Reference load B
_
.T&
lw(54p) | cw(54p) | cw(54p) .
Internal 10\uD\dlF261\u2\d 4 \(mu 10\uD\dlF261\u2\d
_
.T&
lw(54p) | cw(54p) | cw(54p) .
Originating 5 \(mu 10\uD\dlF261\u3\d 3 \(mu 10\uD\dlF261\u2\d
_
.T&
lw(54p) | cw(54p) | cw(54p) .
Terminating 5 \(mu 10\uD\dlF261\u3\d 3 \(mu 10\uD\dlF261\u2\d
_
.T&
lw(54p) | cw(54p) | cw(54p) .
Transit 10\uD\dlF261\u3\d 10\uD\dlF261\u2\d
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 2/Q.543 [T3.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.sp 1P
.LP
2.3
\fIDelay probability\fR \fI \(em non\(hyISDN or mixed (ISDN \(em non\(hyISDN)\fR
\fIenvironment\fR
.sp 9p
.RT
.PP
The non\(hyISDN environment is composed of analogue subscriber lines and/or
circuits that use either channel associated or common channel
signalling.
.PP
The ISDN environment is composed of digital (ISDN) subscriber lines
and/or circuits that use common channel signalling.
.PP
This section defines delay parameters related to non\(hyISDN environment
and mixed (ISDN \(em non\(hyISDN) environment.
.PP
When a delay parameter in this section is also applicable to the pure ISDN
environment, a reference to the appropriate part of \(sc\ 2.4 (delay
probability \(em\ ISDN environment) is provided.
.PP
In the following delay parameters, it is understood that delay timing begins
when the signal is \*Qrecognizable\*U, that is, after the completion of
signal verification, where applicable. It does not include line\(hydependent
delays for the recognition of induced voltage conditions or line transients.
.PP
The term \*Qmean value\*U is understood to be the expected value in the
probabilistic sense.
.PP
Where several messages are received at the exchange from a digital
subscriber line signalling system (e.g.,\ several alert messages are received
from a multi\(hyuser configuration), the message that is accepted for call
handling is the one considered in determining the start of a given delay
interval.
.bp
.PP
Where common channel signalling (including inter\(hyexchange and
subscriber line signalling) is involved, the terms \*Qreceived from\*U
and \*Qpassed to\*U the signalling system are used. For CCITT Signalling
System No.\ 7, this is designated as the instant the information is exchanged
between the signalling data link (layer\ 1) and the signalling link functions
(layer\ 2). For digital
subscriber line signalling, this is designated as the instant the information
is exchanged by means of primitives between the data link layer (layer\
2) and the network layer (layer\ 3). Thus, the time intervals exclude the
above layer\ 1 (CCITT Signalling System No.\ 7), and layer\ 2 (D\ channel)
times. They do,
however, include queuing delays that occur in the absence of disturbances
but not any queuing delays that occur in the absence of disturbances but
not
any queuing delays caused by re\(hytransmission.
.RT
.sp 1P
.LP
2.3.1
\fBincoming response delay\fR \fB\(em transit and terminating\fR
\fBincoming traffic connections\fR
.sp 9p
.RT
.PP
Incoming response delay is a characteristic that is applicable
where channel associated signalling is used. It is defined as the interval
from the instant an incoming circuit seizure signal is recognizable until
a
proceed\(hyto\(hysend signal is sent backwards by the exchange.
.PP
The values in Table\ 3/Q.543 are recommended.
.RT
.ce
\fBH.T. [T4.543]\fR
.ce
TABLE\ 3/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms 600 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 3/Q.543 [T4.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.sp 1P
.LP
2.3.2
\fBlocal exchange call request delay\fR \fB \(em originating\fR
\fBoutgoing and internal traffic connections\fR \v'3p'
.sp 9p
.RT
.PP
2.3.2.1
For ANALOGUE SUBSCRIBER LINES, call request delay is defined as
the interval from the instant when the off\(hyhook condition is recognizable at
the subscriber line interface of the exchange until the exchange begins
to apply dial tone to the line. The call request delay interval is assumed
to correspond to the period at the beginning of a call attempt during which
the exchange is unable to receive any call address information from the
subscriber.
.PP
The values in Table\ 4/Q.543 are recommended.
.ce
\fBH.T. [T5.543]\fR
.ce
TABLE\ 4/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms 1000 ms
.TE
.LP
\fINote\fR
\ \(em\ The above values are understood to apply when a continuous
tone, i.e.,\ without a cadence, is used and do not include delays caused
by functions such as line tests, which may be used in national
networks.
.nr PS 9
.RT
.ad r
\fBTable\ 4/Q.543 [T5.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
2.3.2.2
For DIGITAL SUBSCRIBER LINES using overlap sending, call request delay
is defined as the interval from the instant at which the SETUP message
has been received from the subscriber signalling system until the SETUP
ACKNOWLEDGE message is pased back to the subscriber signalling system.
.PP
\fINote\fR \ \(em\ In this case this parameter is equivalent to the user
signalling acknowledgement delay (see \(sc\ 2.4.1).
.PP
The values in Table\ 5/Q.543 are recommended.
.RT
.ce
\fBH.T. [T6.543]\fR
.ce
TABLE\ 5/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms 1000 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 5/Q.543 [T6.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
.sp 2
2.3.2.3
For DIGITAL SUBSCRIBER LINES using en\(hybloc sending, call request delay
is defined as the interval from the instant at which the SETUP message
is received from the subscriber signalling system until the call proceeding
message is passed back to the subscriber signalling system.
.PP
The values in Table\ 6/Q.543 are recommended.
.ce
\fBH.T. [T7.543]\fR
.ce
TABLE\ 6/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms 1200 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 6/Q.543 [T7.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
.sp 2
2.3.3
\fBexchange call set\(hyup delay\fR \fB \(em transit and originating\fR
\fBoutgoing traffic connections\fR
.sp 9p
.RT
.PP
Exchange call set\(hyup delay is defined as the interval from the
instant that the information is required for outgoing circuit selection is
available for processing in the exchange, or the signalling information
required for call set\(hyup is received from the signalling system, until the
instant when the seizing signal has been sent to the subsequent exchange
or the corresponding signalling information is passed to the signalling
system.
.bp
.RT
.sp 1P
.LP
2.3.3.1
\fIExchange call set\(hyup delay for transit connections\fR \v'3p'
.sp 9p
.RT
.LP
2.3.3.1.1\ \ For transit traffic connections that involve circuits that use
channel associated signalling or a mix of channel associated and common
channel signalling, the values in Table\ 7/Q.543 are recommended.
.LP
.sp 2
.ce
\fBH.T. [T8.543]\fR
.ce
TABLE\ 7/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 50 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 7/Q.543 [T8.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 8
.LP
2.3.3.1.2\ \ For transit traffic connections between circuits that use CCITT
Signalling System No.\ 7 signalling exclusively, the requirements of the
appropriate signalling system Recommendation should apply, e.g.\ CCITT
Recommendations\ Q.725 and\ Q.766 for T\dc\\du\uvalue (case of a processing
intensive message).
.sp 1P
.LP
2.3.3.2
\fIExchange call set\(hyup delay for originating outgoing traffic\fR
\fIconnections\fR \v'3p'
.sp 9p
.RT
.LP
2.3.3.2.1\ \ For outgoing traffic connections originating from ANALOGUE
SUBSCRIBER LINES, the values in Table\ 8/Q.543 are recommended.
.LP
.sp 2
.ce
\fBH.T. [T9.543]\fR
.ce
TABLE\ 8/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 8/Q.543 [T9.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
2.3.3.2.2\ \ For outgoing traffic connections originating from DIGITAL
SUBSCRIBER LINES using overlap sending, the time interval starts when the
INFORMATION
message received contains a \*Qsending complete indication\*U or when the
address information necessary for call set\(hyup is complete.
.PP
The values in Table\ 9/Q.543 are recommended.
.ce
\fBH.T. [T10.543] \fR
.ce
TABLE\ 9/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms 1000 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 9/Q.543 [T10.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
2.3.3.2.3\ \ For outgoing traffic connections originating from DIGITAL
SUBSCRIBER LINES using en\(hybloc sending, the time interval starts when
the SETUP message has been received from the digital subscriber signalling
system.
.PP
The values in Table\ 10/Q.543 are recommended.
.ce
\fBH.T. [T11.543]\fR
.ce
TABLE\ 10/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
\fR Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00\ ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms 1200 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 10/Q.543 [T11.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.sp 1P
.LP
2.3.4
\fBthrough\(hyconnection delay\fR
.sp 9p
.RT
.PP
Through\(hyconnection delay is defined as the interval from the
instant at which the information required for setting up a through\(hyconnection
is available for processing in an exchange, or the signalling information
required for setting up a through\(hyconnection is received from the signalling
system, to the instant at which the appropriate transmission path is available
for carrying traffic between the incoming and outgoing exchange terminations.
.PP
The exchange through\(hyconnection delay does not include an inter\(hyoffice
continuity check, if provided, but does include a cross\(hyoffice check
if one
occurs during the defined interval.
.PP
When the through\(hyconnection is established during call set\(hyup, \fIthe\fR
\fIrecommended values for exchange call set\(hyup delay apply\fR . When
the
through\(hyconnection in an exchange is not established during the exchange
call set\(hyup interval, the through\(hyconnection delay may then contribute
to the
network call set\(hyup delay.
.bp
.RT
.sp 1P
.LP
2.3.4.1
\fIFor transit and originating outgoing traffic connections\fR
.sp 9p
.RT
.PP
The values in Table\ 11/Q.543 are recommended.
.RT
.LP
.sp 1
.ce
\fBH.T. [T12.543]\fR
.ce
TABLE\ 11/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(72p) | cw(66p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(39p) | cw(33p) | cw(33p) | cw(33p) .
Without ancillary equipment With ancillary equipment Without ancillary equipment With ancillary equipment
_
.T&
lw(90p) | cw(39p) | cw(33p) | cw(33p) | cw(33p) .
Mean value \(= | 50 ms \(= | 50 ms \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(39p) | cw(33p) | cw(33p) | cw(33p) .
{
0.95% probability of not exceeding
} \(= | 00 ms \(= | 00 ms \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 11/Q.543 [T12.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
.sp 6
The requirements for multi\(hyslot connections require further
study.
.sp 1P
.LP
2.3.4.2
\fIFor internal and terminating traffic connections\fR
.sp 9p
.RT
.PP
For connections terminating on ANALOGUE SUBSCRIBER LINES, the
through\(hyconnection delay is the interval from the instant at which the
called subscriber off\(hyhook condition (answer) is recognizable at the
subscriber line interface of the exchange until the through\(hyconnection
is established and
available for the carrying traffic or a consequent signal is sent backwards
by the exchange.
.PP
The maximum values applying to this parameter are included with those for
incoming call indication sending delay in \(sc\ 2.3.5.
.PP
For connections terminating on DIGITAL SUBSCRIBER LINES, the
through\(hyconnection delay is the interval from the instant at which the
CONNECT message is received from the signalling system until the through\(hyconnection
is established and available for carrying traffic as those indicated by
passing to the respective signalling systems of the ANSWER and CONNECT
ACKNOWLEDGE
messages.
.PP
The values in Table\ 12/Q.543 are recommended.
.RT
.LP
.sp 1
.ce
\fBH.T. [T13.543]\fR
.ce
TABLE\ 12/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 50 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 12/Q.543 [T13.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.3.5
\fBincoming call indication sending delay\fR \fB \(em (for\fR
\fBterminating and internal traffic connections)\fR \v'3p'
.sp 9p
.RT
.PP
2.3.5.1
For calls terminating on ANALOGUE SUBSCRIBER LINES, the
incoming call indication sending delay is defined as the interval from the
instant when the last digit of the called number is available for processing
in the exchange until the instant that ringing signal is applied by the
exchange to the called subscriber line.
.PP
It is recommended that the sum of the values for ringing signal
sending delay and through\(hyconnection delay for internal and teminating
traffic connection should not exceed the values in Table\ 13/Q.543. In
addition, it is recommended that the value of the incoming call indication
sending delay should not exceed 90% of these values nor the though\(hyconnection
delay exceed 35% of
these values.
.LP
.sp 1
.ce
\fBH.T. [T14.543]\fR
.ce
TABLE\ 13/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 50 ms \(= | 000 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 600 ms
.TE
.LP
\fINote\fR
\ \(em\ The above values assume that \*Qimmediate\*U ringing is applied and
do not include delays caused by functions such as line tests, which may
be used in national networks.
.nr PS 9
.RT
.ad r
\fBTable\ 13/Q.543 [T14.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 6
.PP
2.3.5.2
For calls terminating on DIGITAL SUBSCRIBER LINES, the incoming
call indication sending delay is defined as the interval from the instant at
which the necessary signalling information is received from the signalling
system to the instant at which the SETUP message is passed to the signalling
system of the called digital subscriber line.
.PP
In the case of overlap sending in the incoming signalling system, the values
in Table\ 14/Q.543 are recommended.
.LP
.sp 1
.ce
\fBH.T. [T15.543]\fR
.ce
TABLE\ 14/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00\ ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00\ ms 1000 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 14/Q.543 [T15.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
In the case of en\(hybloc sending in the incoming signalling system, the
values in Table\ 15/Q.543 are recommended.
.ce
\fBH.T. [T16.543]\fR
.ce
TABLE\ 15/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | rw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms 1200 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 15/Q.543 [T16.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.sp 2P
.LP
2.3.6
\fIAlerting sending delay\fR \fI\(em terminating and internal\fR
\fItraffic connections\fR
.sp 1P
.RT
.sp 1P
.LP
2.3.6.1
\fBalerting sending delay for terminating traffic\fR \v'3p'
.sp 9p
.RT
.LP
2.3.6.1.1\ \ For calls terminating on ANALOGUE SUBSCRIBER LINES,
alerting sending delay is defined as the interval from the instant when the
last digit is available for processing in the exchange until the ringing
tone is sent backwards toward the calling user.
.PP
The values in Table\ 13/Q.543 are recommended.
.LP
2.3.6.1.2\ \ For calls termining on DIGITAL SUBSCRIBER LINES, the
alerting sending delay is defined as the interval from the instant that an
ALERTING message is received from the digital subscriber line signalling
system to the instant at which an ADDRESS COMPLETE message is passed to
the
interexchange signalling system or ringing tone is sent backward toward the
calling user.
.PP
The values in Table\ 16/Q.543 are recommended.
.ce
\fBH.T. [T17.543]\fR
.ce
TABLE\ 16/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 00 ms \(= | 50 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 16/Q.543 [T17.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.sp 1P
.LP
2.3.6.2
\fBalerting sending delay for internal traffic\fR \v'3p'
.sp 9p
.RT
.LP
2.3.6.2.1\ \ For calls terminating on ANALOGUE SUBSCRIBER LINES, alerting
sending delay is defined as the interval from the instant that the signalling
information is available for processing in the exchange until ringing tone
is applied to an ANALOGUE calling subscriber line or an ALERTING message
is
sent to a DIGITAL calling subscriber line signalling system.
.PP
For calls from ANALOGUE SUBSCRIBER LINES to ANALOGUE SUBSCRIBER
LINES, the values in Table\ 13/Q.543 are recommended.
.bp
.PP
For calls from DIGITAL SUBSCRIBER LINES to ANALOGUE SUBSCRIBER LINES, the
values in Table\ 17/Q.543 are recommended.
.RT
.ce
\fBH.T. [T18.543]\fR
.ce
TABLE\ 17/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 00 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 17/Q.543 [T18.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
2.3.6.2.2\ \ For internal calls terminating on DIGITAL SUBSCRIBER LINES
originating from ANALOGUE SUBSCRIBER LINES, alerting sending delay is defined
as the interval from the instant that an alerting message is received from
the signalling system of the called subscriber's line until ringing tone
is applied to the calling subscriber line.
.PP
The values in Table\ 13/Q.543 are recommended.
.PP
Alerting sending delay on internal calls between DIGITAL SUBSCRIBER
LINES are covered by Table\ 28/Q.543.
.RT
.sp 1P
.LP
2.3.7
\fBringing tripping delay\fR \fB \(em internal and terminating
traffic connections\fR
.sp 9p
.RT
.PP
Ringing tripping delay is a characteristic that is applicable for calls
terminating on ANALOGUE SUBSCRIBER LINES only. It is defined as the
interval from the instant that the called subscriber off\(hyhook condition is
reconizable at the subscriber line interface until the ringing signal at the
same interface is suppressed.
.PP
The values in Table\ 18/Q.543 are recommended.
.RT
.ce
\fBH.T. [T19.543]\fR
.ce
TABLE\ 18/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 00 ms \(= | 50 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 50 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 18/Q.543 [T19.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.sp 1P
.LP
2.3.8
\fBexchange call release delay\fR
.sp 9p
.RT
.PP
Exchange call release delay is the interval from the instant at
which the last information required for releasing a connection is available
for processing in the exchange to the instant that the switching network
through\(hyconnection in the exchange is no longer available for carrying
traffic and the disconnection signal is sent to the subsequent exchange,
if applicable. This interval does not include the time taken to detect
the release signal,
which might become significant during certain failure conditions,
e.g.,\ transmission system failures.
.bp
.RT
.PP
2.3.8.1\fR For transit traffic connections involving circuits using
channel associated signalling or a mix of channel associated and common
channel signalling, the values in Table\ 19/Q.543 are recommended.
.sp 9p
.RT
.ce
\fBH.T. [T20.543]\fR
.ce
TABLE\ 19/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 50 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 19/Q.543 [T20.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 5
.PP
For transit traffic connections involving circuits using CCITT
Signalling System No.\ 7 signalling exclusively, the values in Table\ 35/Q.543
are recommended.
.PP
2.3.8.7
For originating, terminating and internal traffic connections, the values
in Table\ 20/Q.543 are recommended.
.sp 9p
.RT
.ce
\fBH.T. [T21.543]\fR
.ce
TABLE\ 20/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 50 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 20/Q.543 [T21.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
.sp 5
2.3.9
\fBexchange signalling transfer delay\fR \fB \(em other than
answer signal\fR
.sp 9p
.RT
.PP
Exchange signalling transfer delay is the time taken by the
exchange to transfer a signal, no other exchange action being required.
It is defined as the interval from the instant that the incoming signal
is
recognizable, or the signalling information is received from the signalling
system, until the instant when the corresponding outgoing signal has been
transmitted, or the appropriate signalling information is passed to the
signalling system.
.bp
.RT
.PP
2.3.9.1
For transit traffic connections involving circuits using
channel associated signalling or a mix of channel associated and common
channel signalling, the values in Table\ 21/Q.543 are recommended.
.sp 9p
.RT
.ce
\fBH.T. [T22.543]\fR
.ce
TABLE\ 21/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 00 ms \(= | 50 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 50 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 21/Q.543 [T22.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
.sp 5
For transit traffic connections between circuits that use CCITT
Signalling System No. 7 signalling exclusively, the requirements of the
appropriate signalling system Recommendations should apply, e.g.,\ CCITT
Recommendations\ Q.725/Q.726 for T\dc\\du\uvalue (case of a simple message).
.PP
2.3.9.2
Exchange signalling transfer delay for originating, terminating and internal
traffic involving a mix of ANALOGUE and DIGITAL SUBSCRIBER LINES is left
for further study. Exchange signal transfer delay between DIGITAL
SUBSCRIBER signalling systems or between DIGITAL SUBSCRIBER LINE signalling
systems and CCITT Signalling System No.\ 7 is covered in \(sc\ 2.4.2.
.sp 9p
.RT
.sp 1P
.LP
2.3.10
\fBanswer sending delay\fR
.sp 9p
.RT
.PP
Answer sending delay is defined as the interval from the instant that the
answer indication is received at the exchange to the instant that the answer
indication is passed on by the exchange toward the calling user. The
objective of this parameter is to minimize the possible interruption of the
transmission path for any significant interval during the initial response
by the called user.
.RT
.sp 1P
.LP
2.3.10.1\ \ For transit traffic involving circuits that use channel associated
signalling or a mix of channel associated and common channel signalling,
the
values in Table\ 22/Q.543 are recommended.
.sp 9p
.RT
.ce
\fBH.T. [T23.543]\fR
.ce
TABLE\ 22/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 00 ms \(= | 50 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 50 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 22/Q.543 [T23.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
More stringent values are recommended where in\(hyband line
signalling may be encountered in the national part of a built\(hyup connection.
The recommended values are given in Table\ 23/Q.543.
.ce
\fBH.T. [T24.543]\fR
.ce
TABLE\ 23/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | rw(60p) | rw(60p) .
Mean value \(= | 0 ms \(= | 0 ms
_
.T&
lw(90p) | rw(60p) | rw(60p) .
{
0.95 probability of not exceeding
} 100 ms 180 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 23/Q.543 [T24.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
.sp 3
For transit traffic connections involving circuits that use CCITT Signalling
System No.\ 7 exclusively, the requirements of the appropriate
signalling system Recommendations should apply, e.g.,\ CCITT
Recommendations\ Q.725 and Q.766 for T\dc\\du\uvalue (case of a simple
message).
.sp 1P
.LP
2.3.10.2\ \ For connections in a terminating exchange, exchange answer
sending delay is defined as the interval from the instant that the off\(hyhook
condition is recognizable at the ANALOGUE SUBSCRIBER LINE interface on
an incoming call or a CONNECT message is received from a DIGITAL SUBSCRIBER
LINE signalling
system until the instant that an answer indication is sent back toward the
calling user.
.sp 9p
.RT
.PP
The values in Table\ 24/Q.543 are recommended.
.ce
\fBH.T. [T25.543]\fR
.ce
TABLE\ 24/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 50 ms \(= | 50 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 24/Q.543 [T25.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 3
.sp 1P
.LP
2.3.10.3\ \ For connections in an originating exchange, exchange answer
sending delay is defined as the interval from the instant that the answer
indication is received from the outgoing circuit signalling system or in the
case of an internal call, from the called subscriber's line, until the
instant that the answer indication is sent to the calling user. In the
case of a call originated from a DIGITAL SUBSCRIBER LINE, the answer indication
is a CONNECT message that is sent to the DIGITAL SUBSCRIBER LINE signalling
system. If an
ANALOGUE SUBSCRIBER LINE originated the call, the answer indication may
not be sent.
.bp
.sp 9p
.RT
.PP
The values in Table\ 25/Q.543 are recommended.
.ce
\fBH.T. [T26.543]\fR
.ce
TABLE\ 25/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 50 ms \(= | 00 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 00 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 25/Q.543 [T26.543], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
For ISDN operation involving DIGITAL SUBSCRIBER LINES and CCITT
Signalling System No. 7 exclusively, the values in Table\ 28/Q.543 are
recommended.
.sp 1P
.LP
2.3.11
\fBtiming for start of charging (circuit switched calls)\fR
.sp 9p
.RT
.PP
When required, timing for charging at the exchange where this
function is performed, shall begin after receipt of an ANSWER indication
from a connecting exchange or the called user. The start of timing for
charging
should occur within the intervals recommended in Table\ 26/Q.543.
.RT
.ce
\fBH.T. [T27.543]\fR
.ce
TABLE\ 26/Q.543
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(90p) | cw(60p) | cw(60p) .
Reference load A Reference load B
_
.T&
lw(90p) | cw(60p) | cw(60p) .
Mean value \(= | 00 ms \(= | 75 ms
_
.T&
lw(90p) | cw(60p) | cw(60p) .
{
0.95 probability of not exceeding
} \(= | 00 ms \(= | 50 ms
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 26/Q.543 [T27.543], p.36\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 19P
.sp 2P
.LP
\fBMONTAGE: \(sc 2.4 SUR LE RESTE DE CETTE PAGE\fR
.sp 1P
.RT
.LP
.bp