InfoMagic Standards 1993 July/Disc.iso/ccitt/1988/troff/6_1_05.tro

Text File | 1991-12-13 | 112.7 KB | 4,017 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'
.LP
\s9\fBMONTAGE:\ \fR REC.\ Q.31 EN T\* | TE DE CETTE PAGE
.RT
.sp 2P
.LP
\v'33P'
\fBRecommendation Q.32\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBREDUCTION OF THE RISK OF INSTABILITY BY SWITCHING MEANS\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.32''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.32    %'
.ce 0
.sp 1P
.PP
For any connection between two\(hywire terminations, the transmission plan
admits a certain risk of instability. In an international connection,
Recommendation\ G.122 defines for each national network its responsibility in
this respect.
.sp 1P
.RT
.PP
It is recognized in\ \(sc\ 2 of that Recommendation that during certain
phases of the call, the risk of instability could in certain circumstances
become excessive; this refers in particular to conditions other than that
of an established connection, viz. during set\(hyup, clear\(hydown and
changes in
a connection. Appropriate precautions must then be taken by the switching
services.
.bp
.PP
Techniques applicable to analogue exchanges which will afford a
reduction of the risk of instability for a national network have been shown
in earlier versions of Recommendation\ Q.32 (\fIRed\ Book\fR \ 1985 and
earlier). For
digital exchanges these methods are as a rule not equally suitable, however,
it should be noted that, with today's digital networks giving 4\(hywire
transmission down to the local exchanges and with corresponding terminating
losses, the transmission plan may often not require extra loss during
setting\(hyup, etc., conditions.
.PP
Recommendation\ G.121, \(sc\ 6.2 calls for a sum of losses round the a\(hyt\(hyb
path of at least\ 6\ dB; calculating according to Recommendation\ G.122,
\(sc\ 2.2,
this would be some four times the standard deviation, corresponding to
a risk of about\ 3 in\ 10\ 000. (The six calls per thousand risk called
for in
Recommendation\ G.122 corresponds to about\ 3.25 times the standard deviation.)
The switching services thus only need to maintain this minimum loss in
cases
where it is reduced in the conditions mentioned.
.PP
The use of a restricted value of loss (rather than total interruption of
the 4\(hywire loop) allows the passage of information tones or recorded
announcements or of communication with an operator, and of national use for
non\(hychargeable calls. Although as a rule digital pads are deprecated, the
reasons for this are all concerned with their presence in an established
connection, and do not apply to their use for the present purpose.
.RT
.sp 2P
.LP
\fBRecommendation Q.33\fR
.RT
.sp 2P
.ce 1000
\fBPROTECTION AGAINST THE EFFECTS OF FAULTY TRANSMISSION\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.33''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.33    %'
.ce 0
.sp 1P
.ce 1000
\fBON GROUPS OF CIRCUITS\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
1.1
Although certain signalling systems may have the capability to
provide an indication when an individual circuit is faulty, in order to
maintain the required availability of the public network, it is considered
necessary to provide alarm facilities to alert maintenance staff when a
group of circuits provided by a multiplex transmission system is faulty.
.sp 9p
.RT
.PP
1.2
An alarm indication can be initiated on failure of a FDM system by
means of pilot supervision. On failure of a PCM system, and alarm indication
initiated at both ends by the loss of frame alignment (or multiframe alignement
as appropriate) [1], [2].
.sp 9p
.RT
.PP
These failure indicators provide the means whereby the faulty
circuits can be removed from service automatically and, when the fault
condition no longer exists, be restored automatically by the switching
control of an international exchange (see\ \(sc\ 1.4 below).
.PP
Additionally, the existence of such failure indications allow an
end\(hyto\(hyend indication of circuit availability which is a prerequisite
to the
operation of Signalling System No.\ 7 without a per call continuity check
[see Recommendations\ Q.724 (TUP) and\ Q.764 (ISUP)].
.RT
.PP
1.3
Where transmission links comprise several transmission systems in
tandem, the protection against the effects of faulty transmission on groups
of circuits can only be maintained if the primary multiplex structure is
maintained from end\(hyto\(hyend together with a transparency of alarm
indications. In other cases the provisions of \(sc\(sc\ 2 and\ 3 below
apply.
.sp 9p
.RT
.PP
1.4
Following a transmission failure a number of specific signalling
actions are required to be carried out by the switching control of an
international exchange. These actions are designed to:
.sp 9p
.RT
.LP
    a)
    prevent failure of new call attempts;
.LP
    b)
    provide appropriate failure indications on established
calls;
.LP
    c)
     provide a means of releasing circuit connections beyond the point of
transmission failure.
.PP
Paragraph 4 below details the actions to be taken for circuits
employing
Signalling Systems Nos.\ 5,\ 6 and\ 7 (TUP and ISUP). For circuits employing
Signalling System\ R2, Recommendation\ Q.416 details the actions to be taken.
.bp
.PP
1.5
The recognition time used by the international exchange to validate the
alarm ON/alarm OFF states shall be\ 20\ \(+-\ 10 milliseconds. The recognition
time is defined as the duration that signals representing the alarm ON/OFF
states must be present at the input of the exchange terminal equipment.
.sp 9p
.RT
.PP
Following recognition of the alarm ON or alarm OFF states the
exchange shall carry out the actions detailed in\ \(sc\ 4.
.sp 2P
.LP
\fB2\fR     \fBMixed transmission systems\fR
.sp 1P
.RT
.PP
2.1
Some transmission links comprise differing transmission systems which for
maintenance purposes are treated separately (see Recommendation\ G.704).
Examples of such transmission links are those with:
.sp 9p
.RT
.LP
    \(em
    analogue/digital conversion via transmultiplexers;
.LP
    \(em
    conversion between 24 and 30 channel PCM systems;
.LP
    \(em
    links via TDMA/DSI satellite systems.
.PP
In these cases, failure indications from the local multiplex
equipment can be used, but alone these do not provide an end\(hyto\(hyend
indication of circuit availability. Since the multiplex systems use different
standards, it is usually impossible to provide a ready conversion of alarms
from one
system to another. In order to retain the benefits of the alarm indications
for groups of circuits it is necessary to carry the fault indications on
a circuit basis. This may be inherent in the normal circuit signalling
(as in the case of the digital version of Signalling System\ R2) but in
the general case some form of individual circuit supervision is required.
.sp 2P
.LP
2.2
    \fICircuit supervision for digital systems\fR
.sp 1P
.RT
.sp 1P
.LP
2.2.1
    \fI2048 kbit/s systems\fR (Recommendations\ G.732, G.734)
.sp 9p
.RT
.LP
    \fI8448 kbit/s systems\fR (Recommendation\ G.744)
.PP
In these systems there are two frame structure possibilities. One supports
channel associated signalling, and the other is intended for common
channel signallig which allows extra time\(hyslots to be used for speech
circuits. In order to provide circuit supervision it is necessary to use
the frame
strcuture for channel associated signalling, even in the case of voice
frequency and common channel signalling systems. This implies a number of
restrictions:
.RT
.LP
    \(em
     in the 2048 kbit/s system time slot 16 is not available for speech. Additionally,
the common channel signalling links of Systems\ No.\ 6
and\ No.\ 7 must use a time slot other than number\ 16;
.LP
    \(em
    similarly, in the 8448\ kbit/s system time slots\ 67\(hy70 are
required for the circuit supervision and cannot be used for speech.
.PP
Other systems of transmitting circuit supervision information (for example,
using a common channel) are for further study.
.sp 1P
.LP
2.2.2
    \fI1544 kbit/s systems\fR (Recommendations\ G.733, G.735)
.sp 9p
.RT
.PP
In this system the S bit is used for circuit supervision in a
similar manner to its use for channel associated signalling.
.RT
.sp 1P
.LP
2.2.3
    \fINon\(hystandard systems\fR
.sp 9p
.RT
.PP
In non\(hystandard transmission systems it will often be necessary to provide
a discrete signalling path for the transmission of circuit supervision
indications. Annex\ A to this Recommendation describes the arrangements
used for circuit supervision on TDMA/DSI satellite systems together with
the interfacing with the terrestrial channels.
.RT
.sp 2P
.LP
\fB3\fR     \fBSignalling of circuit supervision indications\fR
.sp 1P
.RT
.PP
3.1
In integrated digital transmission systems interfacing directly with exchanges
(e.g. Recommendations\ G.734, G.744) and where systems connect to the other
Administrations, it is recommended that a standard form of circuit
supervision be used. This is detailed below for 2048\ kbit/s PCM systems and
1544\ kbit/s PCM systems.
.bp
.sp 9p
.RT
.sp 1P
.LP
3.2
    \fI2048 kbit/s PCM systems\fR
.sp 9p
.RT
.PP
Signalling bits \*Qa\*U and \*Qb\*U of time slot 16 are used. Under
abnormal (alarm) conditions both\ a and\ b bits are set to\ 1. The normal
(no\(hyalarm) condition is when \*Qa\*U and \*Qb\*U bits are not both equal
to\ 1.
.RT
.sp 1P
.LP
3.3
    \fI1544 kbit/s PCM systems\fR
.sp 9p
.RT
.PP
In this system the circuit supervision information is
generated:
.RT
.LP
    \(em
    by forcing bit 2 in every channel time slot to the value\ 0,   or
.LP
    \(em
    by modifying the S bit as described in\ \(sc\ 3.1.3.2.2 of
Recommendation\ G.704 for the 12 frame multiframe, or
.LP
    \(em
    by sending a frame alignment alarm sequence
(1111111100000000) as described in\ \(sc\ 3.1.1.3 of Recommendation\ G.704
for the 24 frame multiframe
.FS
The third method proposed cannot ensure a proper end to
end supervision if a TDMA system with multidestination of multiplexes or
a CME is involved in the connection.
.FE
.
.sp 2P
.LP
\fB4\fR     \fBActions in Signalling Systems Nos. 5, 6 and 7 when a
transmission alarm occurs\fR
.sp 1P
.RT
.PP
This section details the actions which should be taken on circuits using
Signalling Systems\ No.\ 5, No.\ 6 and No.\ 7 when a transmission alarm
occurs concerning the speech path. This annex is intended to be applied
to new exchange equipment only.
.PP
It is split into two broad areas dealing firstly with Signalling
System\ No.\ 5 and then with Signalling Systems No.\ 6 and No.\ 7. This
split is
required because the actions taken for inband signalling systems is slightly
different to that taken for common channel signalling systems.
.RT
.sp 1P
.LP
4.1
    \fISignalling System No.\ 5\fR
.sp 9p
.RT
.PP
The action taken if a transmission alarm occurs during the states shown
below is as follows:
.RT
.sp 2P
.LP
4.1.1
    \fIOutgoing circuit failure\fR
.sp 1P
.RT
.sp 1P
.LP
4.1.1.1
    \fIIDLE STATE\fR
.sp 9p
.RT
.PP
Take the circuit out of service to outgoing traffic. Return to
service when transmission is restored.
.RT
.sp 1P
.LP
4.1.1.2
    \fIREGISTER STATE\fR
.sp 9p
.RT
.PP
The register state is assumed to start with sending of seizure
signal and to end with sending of end of pulsing signal (ST).
.RT
.LP
    \(em
    Send clear forward.
.LP
    \(em
    Send a call unsuccessful indication on incoming circuit or
possibly carry out a repeat attempt.
.LP
    \(em
    If clear forward release guard sequence fails, inhibit the
repeat clear forward sequence. Resume the repeat clear forward sequence when
the transmission is restored limiting the number of simultaneous signals
to a value which will prevent overload of the transmission system.
.LP
    \(em
    If the clear forward release guard sequence is successful,
take the circuit out of service to outgoing traffic.
.sp 1P
.LP
4.1.1.3
    \fISEIZED BUT AFTER REGISTER STATE\fR
.sp 9p
.RT
.LP
    \(em
    Wait for calling party to clear and send clear forward.
.LP
    \(em
    If answer signal has not been returned from called party,
send a call unsuccessful indication on incoming circuit.
.LP
    \(em
    If clear forward release guard sequence fails, inhibit the
repeat clear forward sequence. Resume the repeat clear forward sequence when
the transmission is restored limiting the number of simultaneous signals
to a value which will not overload the transmission system.
.LP
    \(em
    If clear forward release guard sequence is successful take
the circuit out of service to outgoing traffic.
.sp 1P
.LP
4.1.1.4
    \fIBLOCKED\fR
.sp 9p
.RT
.LP
    \(em
    No special action required.
.bp
.sp 2P
.LP
4.1.2
    \fIIncoming circuit failure\fR
.sp 1P
.RT
.sp 1P
.LP
4.1.2.1
    \fIIDLE STATE\fR
.sp 9p
.RT
.LP
    \(em
    No special action required, respond to incoming call as
normal.
.sp 1P
.LP
4.1.2.2
    \fIALL OTHER STATES\fR
.sp 9p
.RT
.LP
    \(em
    In answered state no special action to be taken, send all
signals as normal.
.LP
    \(em
    If answer signal has not been returned from called party,
start a time out device which after a certain interval clears the chain
beyond the faulty circuit.
.sp 2P
.LP
4.1.3
    \fIBothway circuit\fR
.sp 1P
.RT
.sp 1P
.LP
4.1.3.1
    \fIIDLE STATE\fR
.sp 9p
.RT
.LP
    \(em
     Take the circuit out of service to outgoing traffic, respond normally
to incoming signals.
.LP
    \(em
    Return to outgoing service when transmission is
restored.
.sp 1P
.LP
4.1.3.2
    \fIOUTGOING REGISTER STATE\fR
.sp 9p
.RT
.LP
    \(em
    See \(sc 4.1.1.2.
.sp 1P
.LP
4.1.3.3
    \fIOUTGOING AFTER REGISTER STATE\fR
.sp 9p
.RT
.LP
    \(em
    See \(sc 4.1.1.3.
.sp 1P
.LP
4.1.3.4
    \fIINCOMING ANY STATE\fR
.sp 9p
.RT
.LP
    \(em
    See \(sc 4.1.2.
.sp 1P
.LP
4.1.3.5
    \fIBLOCKED\fR
.sp 9p
.RT
.LP
    \(em
    See \(sc 4.1.1.4.
.sp 1P
.LP
4.2
    \fISignalling System No.\ 6 or Signalling System No.\ 7\fR
.sp 9p
.RT
.PP
The action taken per speech circuit is as follows.
.RT
.sp 2P
.LP
4.2.1
    \fIOutgoing circuit failure\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.1.1
    \fIIDLE STATE\fR
.sp 9p
.RT
.LP
    \(em
     Take the circuit out of service to outgoing traffic. Return to service
when the transmission is restored.
.sp 1P
.LP
4.2.1.2
    \fIREGISTER STATE\fR
.sp 9p
.RT
.PP
The register state is assumed to start with sending of Initial
Address Message and to end with the receipt of an address complete
message.
.RT
.LP
    \(em
    Send clear forward.
.LP
    \(em
    Send a call unsuccessful indication on incoming circuit or
possibly carry out a repeat attempt to set up the call on another circuit.
.LP
    \(em
     Following receipt of release guard signal, take the circuit out of service
to outgoing traffic. Return to service when transmission is
restored.
.LP
    \(em
    Inhibit any repeat continuity check which may be taking
place.
.sp 1P
.LP
4.2.1.3
    \fISEIZED BUT AFTER REGISTER STATE\fR
.sp 9p
.RT
.LP
    \(em
    If answer signal has not been received from called party,
send a call unsuccessful indication on incoming circuit.
.LP
    \(em
    If answer signal received, no special action required.
.LP
    \(em
     Take the circuit out of service when it becomes idle. Return to service
when the transmission is restored.
.bp
.sp 1P
.LP
4.2.1.4
    \fIBLOCKED\fR
.sp 9p
.RT
.LP
    \(em
    No special action required.
.sp 2P
.LP
4.2.2
    \fIIncoming circuit failure\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.2.1
    \fICIRCUIT IN ANY STATE\fR
.sp 9p
.RT
.LP
    \(em
    If answer signal has not been returned from called party,
start a time out device which after a certain interval clears the chain
beyond the faulty circuit.
.LP
    \(em
    If answer has been received no special action is required,
the transmission of blocking messages when end to end alarm continuity
is not provided should be for further study.
.sp 2P
.LP
4.2.3
    \fIBothway circuit failure\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.3.1
    \fIIDLE STATE\fR
.sp 9p
.RT
.LP
    \(em
    Take the circuit out of service to outgoing traffic, the
transmission of blocking messages when end to end alarm continuity is not
provided should be for further study.
.LP
    \(em
    Return to outgoing service when transmission is
restored.
.sp 1P
.LP
4.2.3.2
    \fIOUTGOING REGISTER STATE\fR
.sp 9p
.RT
.LP
    \(em
    See \(sc 4.2.1.2 above.
.sp 1P
.LP
4.2.3.3
    \fIOUTGOING AFTER REGISTER STATE\fR
.sp 9p
.RT
.LP
    \(em
    See \(sc 4.2.1.3 above.
.sp 1P
.LP
4.2.3.4
    \fIINCOMING CIRCUIT IN ANY STATE\fR
.sp 9p
.RT
.LP
    \(em
    See \(sc 4.2.2 above.
.sp 1P
.LP
4.2.3.5
    \fIBLOCKED\fR
.sp 9p
.RT
.LP
    \(em
    No special action required.
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation Q.33)
.sp 9p
.RT
.ce 0
.ce 1000
\fBCircuit supervision via TDMA/DSI satellite systems\fR
.sp 1P
.RT
.ce 0
.LP
A.1
    \fIGeneral\fR
.sp 1P
.RT
.PP
A.1.1
When satellite systems employ Time Division Multiple Access
(TDMA) transmission techniques with Digital Speech Interpolation (DSI)
equipment at an earth station, the integrity of multiplex transmission
systems, FDM as well as PCM, used for terrestrial access to the satellite
system cannot be maintained within the satellite system. For exemple, time
slots\ 0 and\ 16 of a 2048\ kbit/s PCM system of the group pilot of a FDM
system may not be
available between earth stations for the transfer of signalling or transmission
alarm information. The provision of equivalent facilities over the satellite
section therefore needs special consideration.
.sp 9p
.RT
.PP
A.1.2
Although not necessarily a fault condition, an increase in circuit
activity on a TDMA/DSI system may lead to an overload condition, e.g.\ \*Qbit
stealing\*U in the DSI equipment. Conveyance of overload indicators to the
associated ISC may be used to initiate appropriate network management actions
to reduce or eliminate the overload conditions on groups of circuits routed
on the TDMA/DSI systems.
.PP
Implementation of this capability is at the discretion of
individual Administrations.
.bp
.PP
A.1.3
In accordance with Recommendation Q.7, specified signalling
systems considered to be suitable for international application via TDMA/DSI
satellite systems are:
.LP
    \(em
    System R2, provided that the satellite system is designed to
be transparent to pulsed inter\(hyregister signals;
.LP
    \(em
    System No. 5;
.LP
    \(em
    Systems Nos. 6 and 7.
.sp 1P
.LP
A.2
    \fICircuit supervision\fR
.sp 9p
.RT
.PP
Possible methods of passing circuit supervision information for
these signalling systems via a TDMA/DSI satellite system are as follows:
.RT
.sp 1P
.LP
A.2.1
    \fISignalling System R2\fR \v'3p'
.sp 9p
.RT
.LP
A.2.1.1\ \ In the case of System R2, only the digital version of line
signalling (Recommendations\ Q.421\(hyQ.424) is specified for use on international
digital links.
.LP
A.2.1.2\ \ A satellite
Line Signalling Channel (LSC)
is
required to convey the System\ R2 digital line signalling code. Two signalling
bits, \*Qa\*U and \*Qb\*U are required in the LSC for each System\ R2 terrestrial
circuit accessing the satellite section. Under transmission failure conditions,
bits \*Qa\*U and \*Qb\*U are set to State\ 1, so that the line signalling
protocols of digital\ R2 will eventually block the circuit.
.PP
Appendix I shows a typical format and organization of the LSC for System\
R2 line signalling.
.LP
A.2.1.3\ \ Fault conditions detected at the earth station and the
consequent actions to be taken are given: in Tables\ A\(hy1/Q.33 and A\(hy2/Q.33
when terrestrial access is via a 2048 kbit/s PCM system or via an FDM system
with
signalling conversion employed at the earth station, respectively.
.PP
The application of actions given in these tables enables
appropriate end\(hyto\(hyend supervision to be provided on a per\(hycircuit
basis.
.sp 1P
.LP
A.2.2
    \fISignalling System No. 5\fR \v'3p'
.sp 9p
.RT
.LP
A.2.2.1\ \ It should be noted that on circuits employing System No.\ 5
signalling, some administrations utilize a repeat forward clear procedure
as a means of achieving clear down under failure conditions. This procedure,
which may involve periodic sending of forward clear signals synchronously
on a number of circuits, can result in severe periodic overloading of DSI
channels. In
order to avoid this possible overloading of DSI channels it is preferable to
limit the number of simultaneous forward clear signals on the circuits
involved.
.LP
A.2.2.2\ \ In order to convey circuit supervision information via the
satellite system, it will be necessary to provide a satellite signalling
channel.
.PP
The preferred method of conveying circuit supervision information by use
of a satellite digital non\(hyinterpolated (DNI) channel is
described in\ \(sc\ A.2.2.3.
.PP
If an LSC, as provided for in System R2, is available, then a second method
of passing circuit supervision information is as described
in\ \(sc\ A.2.2.4.
.RT
.sp 1P
.LP
A.2.2.3\ \ \fIUse of a\fR
\fIDNI supervision channel\fR
.sp 9p
.RT
.PP
When a DNI channel is utilized for circuit supervision purposes,
detection by an earth station of circuit failures on its terrestrial sector
will result in the setting of bits in the DNI channel to \*Q1\*U, in accordance
with the information contained in Appendix\ II.
.PP
Thus, if the failed circuits are digital, the detection of failure
conditions, such as loss of frame alignment, described in Table\ A\(hy3/Q.33
will result in the setting to \*Q1\*U of bits in the DNI channel associated
with the
affected circuits.
.PP
When the affected circuits are analogue, the failure will be detected at
the earth station, e.g. by the loss of pilot, or if appropriate, by receipt
of a pulsed bakward pilot. Fault conditions and consequent actions when
analogue access links are employed are given in Table\ A\(hy4/Q.33.
.PP
The alarm information passed over the DNI channel can be forwarded by the
receiving earth station to its associated ISC as described in
Recommendation\ Q.33.
.PP
An Administration may utilize the alarm information at its ISC to
block or busy affected circuits, or, for example, to inhibit the sending of
repeat forward clear signals.
.PP
Appendix II shows the format and organization of the DNI supervisory   channel.
.bp
.RT
.sp 1P
.LP
A.2.2.4\ \ \fIUse of System R2 LSC\fR
.sp 9p
.RT
.PP
In this case the \*Qa\*U and \*Qb\*U signalling bits in the LSC
corresponding to the Terrestrial Channels (TCs) for which supervision is
applied shall assume the following meaning:
.PP
Under normal conditions:
.RT
.LP
    b = 0 indicates that the relevant TC is in a normal condition.
The b\ =\ 0 state may be established either within the TDMA
terminal or at the ISC.
.PP
The \*Qa\*U signalling bit contained in the same slot shall be set, as
convenient, either to zero or\ \*Q1\*U.
.PP
Under abnormal conditions:
.RT
.LP
    a = b = 1 indicates that the relevant TC is in an abnormal
condition.
.PP
Thus, for effective application, the failure of a distant
terrestrial transmission system (FDM or PCM) in either direction between an
earth station and its associated ISC should result in the sending of a\
=\ b\ =\ 1 for each affected circuit backward over the satellite section.
The alarm
information passed via the LSC is transferred from the receiving earth
station to its associated ISC as follows:
.LP
    \(em
    when digital access circuits are provided, bits a and b, in
Time Slot\ 16 corresponding to the faulty circuits, are set
to\ \*Q1\*U;
.LP
    \(em
    when analogue access circuits are employed receipt by the
earth station of bits\ a\ =\ b\ =\ 1 for\ 6 or more circuits in an
analogue group should result in the removal of the group pilot
towards the ISC.
.PP
This method of using two signalling bits to convey circuit
supervision information for System\ No.\ 5 circuits is inefficient in the
utilization of satellite channel capacity. However, Administrations may need
to take into account the possible advantages of such utilization, for example,
a common terrestrial interface module for both System\ R2 and System\ No.\
5
circuits may be employed at the earth station.
.PP
Appendix I shows the format and organization of the LSC for System\ R2
line signalling. Where appropriate to such use of circuits employing
System\ No.\ 5 signalling, the fault conditions and consequent actions
given in Tables\ A\(hy1/Q.33 and A\(hy2/Q.33 also apply.
.RT
.sp 1P
.LP
A.2.3
    \fISignalling System No. 6 and No. 7\fR \v'3p'
.sp 9p
.RT
.LP
A.2.3.1\ \ These signalling systems employ a common signalling channel
which may be conveyed via the satellite system (for example, via a 64\ kbit/s
signalling channel) or via a terrestrial transmission path.
.LP
A.2.3.2\ \ The provision of transmission alarm information for circuit
supervision purposes is necessary because:
.LP
    a)
    Although a speech path continuity check, where used, will
remove faulty circuits from service, a faster method is required if
severe operational problems at the ISC are to be avoided when
a large number of circuits are affected by a transmission
system failure.
.LP
    b)
     In the case of circuits employing System No.\ 7, end\(hyto\(hyend circuit
supervision is required in accordance with
Recommendation\ Q.724.
.LP
    c)
    It is not mandatory for an ISC recognizing a transmission
system failure to send a blocking signal for each affected circuit.
.LP
A.2.3.3\ \ If the common signalling channel and associated circuits are
routed via the same satellite system, methods of conveying circuit supervision
information are identical to those described for System No.\ 5. This will
require a DNI satellite channel to carry circuit supervision information in
addition to the common signalling channel. Digital terrestrial access systems
will also require a time slot for circuit supervision purposes besides
that
required for common channel signalling.
.LP
A.2.3.4\ \ Methods of utilizing the common signalling channel in lieu of
the DNI channel for the purpose of conveying information on the status
of the transmission path of the speech circuits require further study.
.LP
A.2.3.5\ \ Fault conditions and consequent actions to be taken at earth
stations when system No.\ 6 or No.\ 7 is employed, via digital and analogue
access links, are given in Tables\ A\(hy3/Q.33 and\ A\(hy4/Q.33, respectively.
.bp
.ce
\fBH.T. [1T1.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
TABLE\ A\(hy1/Q.33
.T&
cw(342p) .
 {
\fBFault conditions and consequent actions at earth stations\fR
\fBwith 2048 kbit/s digital access links for System R2 circuits\fR
 }
.TE
.TS
cw(72p) | cw(27p) sw(21p) sw(21p) sw(21p) | lw(27p) | lw(21p) sw(21p) sw(21p) sw(27p) sw(21p) sw(21p) sw(21p) , ^  | c | c | l | l ^  | | l | l | l | l | l | l | l.
 {
Digital earth station
equipment
(digital access links)
Fault conditions
 }     {
Terrestrial link to own CT
Remote backward alarm indication
(bit 3, TS 0, even frames)
Backward alarm indication
(bit 6, TS 16, frame 0)
a = b = 1
in TS 16 for all circuits concerned
AIS in non\(hyinterp\(hy
olated
channels
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hy
interpolated channels
a = b = 1
in satellite signalling channel for circuits
concerned
Block switched circuits concerned
Backward alarm indication concerning satellite
signalling channel
 }
_
.T&
lw(12p) | lw(60p) | cw(27p) | cw(21p) | cw(21p) | cw(21p) | cw(27p) | lw(21p) | cw(21p) | cw(21p) | cw(27p) | lw(21p) | cw(21p) | lw(21p) , ^  | c | c | c | c | c | l | c | c | c | l | l | l | l
^  | l | l | l | l | l | l | l | l | l | l | l | l | l
^  | l | l | l | l | l | l | l | l | l | l | l | l | l
^  | l | l | l | l | l | l | l | l | l | l | l | l | l.
     {
Loss of frame alignment, BER exceeded or loss of incoming signal
 }    Yes    Yes  Note 1    Yes    Yes    Yes    Loss of multiframe alignment    Yes    Yes  Note 1    Yes     {
Alarm indication from CT
(bit 3 TS\ 0 even frame,
bit 6
TS 16 frame 0)
 }    Yes     {
Power supply failure \(em TDMA/DSI
 }
    Yes if possible    Yes    Yes if possible    Yes if possible    Yes if possible     {
Power supply failure \(em satellite signalling equipment
 }    Yes if possible    Yes    Yes if possible
_
.T&
lw(12p) | cw(60p) | cw(27p) | cw(21p) | cw(21p) | lw(21p) | cw(27p) | cw(21p) | cw(21p) | cw(21p) | lw(27p) | cw(21p) | cw(21p) | lw(21p) .
Loss of reference timing    Yes    Yes    Yes    Yes     {
BER exceeded in satellite path
 }    Yes    Yes    Yes    Yes     {
Backward alarm indication from remote ES concerning
BER in satellite path
 }    Yes    Yes  Note 2    Loss of data unique word
_
.T&
cw(12p) | cw(60p) | cw(27p) | cw(21p) | cw(21p) | lw(21p) | cw(27p) | cw(21p) | cw(21p) | cw(21p) | lw(27p) | cw(21p) | cw(21p) | lw(21p) .
Yes    Yes    Yes    Yes
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy1/Q.33 [1T1.33], p.  \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [2T1.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
 {
TABLE\ A\(hy1/Q.33\ \fI(cont.)\fR
 }
.TE
.TS
cw(72p) | cw(27p) sw(21p) sw(21p) sw(21p) | lw(27p) | lw(21p) sw(21p) sw(21p) sw(27p) sw(21p) sw(21p) sw(21p) , ^  | c | c | l | l ^  | | l | l | l | l | l | l | l.
 {
Digital earth station
equipment
(digital access links)
Fault conditions
 }     {
Terrestrial link to own CT
Remote backward alarm indication
(bit 3, TS\ 0,
even frames)
Backward alarm indication
(bit 6, TS 16, frame 0)
a = b = 1
in TS 16 for all circuits concerned
AIS in non\(hyinterp\(hy
olated
channels
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hy
interpolated channels
a = b = 1
in satellite signalling channel for circuits
concerned
Block switched circuits concerned
Backward alarm indication concerning satellite
signalling channel
 }
_
.T&
lw(12p) | cw(60p) | cw(27p) | cw(21p) | lw(21p) | cw(21p) | cw(27p) | cw(21p) | lw(21p) | cw(21p) | cw(27p) | lw(21p) | cw(21p) | cw(21p) .
 {
Backward alarm indication from remote ES concerning
data unique word
 }    Yes    Yes Note 2    Yes Note 3     {
Loss of alignment or BER exceeded in satellite
signalling channel
 }    Yes    Yes    Yes     {
Backward alarm indication from remote ES concerning satellite
signalling channel
 }    Yes    Yes  Note 2     {
Power supply failure \(em TDMA/DSI
 }    Yes if possible    Yes if possible
_
.T&
cw(12p) | cw(60p) | lw(27p) | cw(21p) | cw(21p) | cw(21p) | cw(27p) | cw(21p) | lw(21p) | cw(21p) | cw(27p) | lw(21p) | cw(21p) | cw(21p) .
Yes    Yes if possible     {
Power supply failure \(em satellite signalling equipment
 }    Yes if possible    Yes    Yes if possible
.TE
.LP
\fINote\ 1\fR
\ \(em\ Prompt maintenance alarm is inhibited if AIS is present.
.LP
\fINote\ 2\fR
\ \(em\ Prompt maintenance alarm shall be inhibited if the backward
alarm is received from only one origin if the interface concerned is
working to more than one destination. It is not inhibited when working to a
single destination.
.LP
\fINote\ 3\fR
\ \(em\ If prompt maintenance alarm according to Note 2 is not inhibited.
.LP
\fBPOUR MONTAGE:\fR
.LP
Consequent actions\ \ \ \ Transmitting part\ \ \ \ Receiving part
.LP
Consequent actions\ \ \ \ Transmitting part\ \ \ \ Receiving part
.nr PS 9
.RT
.ad r
\fBTable A\(hy1/Q.33 (cont.) [2T1.33], p.  \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [1T2.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
TABLE\ A\(hy2/Q.33
.T&
cw(342p) .
 {
\fBFault conditions and consequent actions at earth stations with\fR
\fBanalogue access links for System R2 circuits\fR
\fBand signalling conversion at the earth station\fR
 }
.TE
.TS
cw(72p) | cw(30p) sw(24p) | lw(30p) | lw(24p) sw(30p) sw(24p) sw(30p) sw(24p) sw(30p) sw(24p) , ^  | c | c ^  | | l | l | l | l | l | l | l.
 {
Digital earth station
equipment
(analogue access links)
Fault conditions
 }     {
Terrestrial link to own CT
Relevant blocking signal (Note 1)
a = b = 1 at the input of the converter
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hy
interpolated channels
a = b = 1 in satellite signalling channel for circuits
concerned
Block switched circuits concerned
Backward alarm indication concerning satellite signalling
channel
 }
_
.T&
lw(12p) | lw(60p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | lw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) , ^  | c | l | c | c | c | l | l | l | l | l | l
^  | l | l | l | l | l | l | l | l | l | l | l.
     {
Loss of forward signal (Group pilot failure)
 }    Yes    Yes    Yes    Note 4    Yes     {
Power supply failure from trans. equip.
 }    Yes  if possible    Yes    Yes  if possible    Note 4
    Yes  if possible     {
Failure of line signal converter
 }    Yes    Yes    Note 5
_
.T&
lw(12p) | lw(60p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | lw(30p) | lw(24p) , ^  | c ^  | | l | l | l | l | l | l | l | l | l.
 {
Power supply failure \(em TDMA/DSI
 }     {
Power supply failure \(em satellite signalling equipment
 }    Yes  if possible    Yes    Yes  if possible    Yes  if possible    Yes  if possible    Yes  if possible    Yes    Yes  if possible
    Note 6
_
.T&
lw(12p) | cw(60p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) .
Loss of reference timing    Yes    Yes    Yes     {
BER exceeded in satellite path
 }    Yes    Yes    Yes     {
Backward alarm indication from remote ES concerning BER in
satellite path
 }    Note 6    Yes    Yes  Note 2
_
.T&
lw(12p) | cw(60p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) .
Loss of data unique word    Yes    Yes    Yes
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy2/Q.33 [1T2.33], p.   \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [2T2.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
 {
TABLE\ A\(hy2/Q.33\ \fI(cont.)\fR
 }
.TE
.TS
cw(72p) | cw(30p) sw(24p) | lw(30p) | lw(24p) sw(30p) sw(24p) sw(30p) sw(24p) sw(30p) sw(24p) , ^  | c | c ^  | | l | l | l | l | l | l | l.
 {
Digital earth station
equipment
(analogue access links)
Fault conditions
 }     {
Terrestrial link to own CT
Relevant blocking signal (Note 1)
a = b = 1 at the input of the converter
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hy
interpolated channels
a = b = 1 in satellite signalling channel for circuits
concerned
Block switched circuits concerned
Backward alarm indication concerning satellite signalling
channel
 }
_
.T&
lw(12p) | cw(60p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) .
 {
Backward alarm indication from remote ES concerning data
unique word
 }    Yes    Yes  Note 2    Yes  Note 3     {
Loss of alignment or BER exceeded in satellite signalling
channel
 }    Yes    Yes    Yes     {
Backward alarm indication from remote ES concerning satellite
signalling channel
 }    Note 6    Yes    Yes Note 2
_
.T&
lw(12p) | cw(60p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) | lw(30p) | cw(24p) | cw(30p) | cw(24p) .
 {
Power supply failure \(em TDMA/DSI
 }    Yes  if possible    Yes    Yes  if possible     {
Power supply failure \(em satellite signalling equipment
 }    Yes  if possible    Yes    Yes if possible
.TE
.LP
\fINote\ 1\fR
\ \(em\ The \*Qrelevant blocking signal\*U is that signal which the
Recommendation for analogue\ R.2 line signalling calls for in the event of
interruption control or it may be the defined blocking condition resulting
from busying equipment (Orange Book, Recommendation\ Q.416 and\ Q.424).
.LP
\fINote\ 2\fR
\ \(em\ Prompt maintenance alarm shall be inhibited if the backward alarm is received from only one origin if the interface concerned is working to more
than one destination. It is not inhibited when working to a single
destination.
.LP
\fINote\ 3\fR
\ \(em\ If prompt maintenance alarm according to Note\ 2 is not inhibited.
.LP
\fINote\ 4\fR
\ \(em\ In this case the line signalling converter shall apply this
condition. It is assumed that power supply failure on FDM transmission
equipment will result in a group pilot failure.
.LP
\fINote\ 5\fR
\ \(em\ The line signalling converter should comply with the principles
described in Recommendation\ Q.422.
.LP
\fINote\ 6\fR
\ \(em\ A relevant blocking signal will be generated by the converter in the analogue part.
.LP
\fBPour Montage\fR
.LP
Receiving part\ \ \ \ Transmitting part\ \ \ \ Consequent actions
.LP
Receiving part\ \ \ \ Transmitting part\ \ \ \ Consequent actions
.nr PS 9
.RT
.ad r
\fBTable A\(hy2/Q.33 (cont.) [2T2.33], p.  \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [1T3.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
TABLE\ A\(hy3/Q.33
.T&
cw(342p) .
 {
\fBFault conditions and consequent actions at earth stations using\fR
\fBDNI supervision channel for circuits using in\(hyband\fR
\fBand common channel signalling with digital\fR
\fBaccess links\fR
 }
.TE
.TS
cw(78p) | cw(24p) sw(24p) sw(24p) sw(24p) | lw(24p) | lw(24p) sw(24p) sw(24p) sw(24p) sw(24p) sw(24p) , ^  | c | c | l | l ^  | | l | l | l | l | l | l.
 {
Digital earth station
equipment
(digital access links)
Fault conditions
 }     {
Terrestrial link to own CT
Remote backward alarm indication
Backward alarm indication
Circuit supervision signal for all circuits
concerned
AIS in non\(hy
interpolated channels
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hy
interpolated channels
Indication of fault in affected channels via circuit
supervision channel
Block switched circuits concerned
 }
_
.T&
lw(12p) | cw(66p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | lw(24p) , ^  | c | c | c | c | c | l | c | c | c | l | l | l
^  | l | l | l | l | l | l | l | l | l | l | l | l
^  | l | l | l | l | l | l | l | l | l | l | l | l.
 {
Loss of frame alignment. BER exceeded or loss of incoming
signal
 }    Yes Note 4    Yes  Note 1    Yes    Yes    Yes    Loss of multiframe alignment    Yes    Yes  Note 1    Yes    Alarm indication from CT    Yes     {
Power supply failure \(em TDMA/DSI
 }
    Yes if possible    Yes    Yes if possible    Yes if possible    Yes if possible     {
Power supply failure \(em service supervision signalling equipment
 }    Yes if possible    Yes    Yes if possible
_
.T&
lw(12p) | cw(66p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) .
 {
Loss of reference timing or burst
 }    Yes    Yes    Yes    Yes     {
BER exceeded in satellite path
 }    Yes    Yes    Yes    Yes     {
Backward alarm indication from remote ES concerning BER
in satellite path
 }    Yes    Yes Note 2
_
.T&
lw(12p) | cw(66p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) .
Loss of data unique word    Yes    Yes    Yes    Yes
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy3/Q.33 [1T3.33], p.   \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [2T3.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
 {
TABLE\ A\(hy3/Q.33\ \fI(cont.)\fR
 }
.TE
.TS
cw(78p) | cw(24p) sw(24p) sw(24p) sw(24p) | lw(24p) | lw(24p) sw(24p) sw(24p) sw(24p) sw(24p) sw(24p) , ^  | c | c | l | l ^  | | l | l | l | l | l | l.
 {
Digital earth station
equipment
(digital access links)
Fault conditions
 }     {
Terrestrial link to own CT
Remote backward alarm indication
Backward alarm indication
Circuit supervision signal for all circuits
concerned
AIS in non\(hy
interpolated channels
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hy
interpolated channels
Indication of fault in affected channels via circuit
supervision channel
Block switched circuits concerned
 }
_
.T&
lw(12p) | cw(66p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) .
 {
Backward alarm indication from remote ES concerning data unique
word
 }    Yes    Yes Note 2    Yes Note 3    Loss of TDMA frame alignment    Yes    Yes     {
Power supply failure \(em TDMA/DSI
 }    Yes if possible    Yes if possible    Yes    Yes if possible     {
Power supply failure \(em service supervision signalling equipment
 }
_
.T&
cw(12p) | cw(66p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | lw(24p) .
Yes  if possible    Yes    Yes  if possible     {
Indication of remote end transmission failure via circuit supervision
channel
 }    Yes
.TE
.LP
\fINote\ 1\fR
\ \(em\ Prompt maintenance alarm is inhibited if AIS is present.
.LP
\fINote\ 2\fR
\ \(em\ Prompt maintenance alarm shall be inhibited if the backward alarm is received from only one origin. If the interface concerned is working to more
than one destination. It is not inhibited when working to a single
destination.
.LP
\fINote\ 3\fR
\ \(em\ If prompt maintenance alarm according to Note 2 is not
inhibited.
.LP
\fINote\ 4\fR
\ \(em\ For a 2048\ kbit/s digital access, bit\ 3 (TS\ 0, even frames)
could be used for this indication. For a 1544\ kbit/s digital access,
fault indication as described in G.733, \(sc\ 4.2.4 could be used for
this indication.
.LP
\fBPour Montage\fR
.LP
Consequent actions\ \ \ \ Receiving part\ \ \ \ Transmitting part
.LP
Consequent actions\ \ \ \ Receiving part\ \ \ \ Transmitting part
.nr PS 9
.RT
.ad r
\fBTable A\(hy3/Q.33 (cont.) [2T3.33], p.  \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [1T4.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
TABLE\ A\(hy4/Q.33
.T&
cw(342p) .
 {
\fBFault conditions and consequent actions at earth stations using\fR
\fBDNI supervision channel for circuits using in\(hyband\fR
\fBand common channel signalling with analogue\fR
\fBaccess links\fR
 }
.TE
.TS
cw(84p) | cw(28p) sw(28p) | lw(28p) | lw(34p) sw(28p) sw(28p) sw(28p) sw(28p) sw(28p) , ^  | c | c ^  | | l | l | l | l | l | l.
 {
Digital earth station
equipment
(analogue access links)
Note 3
Fault conditions
 }     {
Terrestrial link to own CT
Removal of group pilot or supergroup pilot
.
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hyinterpolated channels
Indication of fault in affected channels via circuit
supervision channel
Block switched circuits concerned
 }
_
.T&
lw(12p) | cw(72p) | cw(28p) | cw(28p) | cw(28p) | lw(34p) | cw(28p) | cw(28p) | cw(28p) | cw(28p) | lw(28p) .
 {
Loss of forward signal (group pilot failure) or supergroup
 }    Yes    Yes    Yes    Yes     {
Power supply failure from trans. equip.
 }    Yes    Yes  if possible    Yes    Yes  if possible     {
Power supply failure \(em TDMA/DSI
 }
_
.T&
cw(12p) | cw(72p) | cw(28p) | cw(28p) | lw(28p) | cw(34p) | cw(28p) | cw(28p) | cw(28p) | cw(28p) | lw(28p) .
Yes    Yes  if possible    Yes  if possible    Yes  if possible     {
Power supply failure \(em service supervision signalling equipment
 }    Yes    Yes  if possible
_
.T&
lw(12p) | cw(72p) | cw(28p) | cw(28p) | lw(28p) | cw(34p) | cw(28p) | cw(28p) | lw(28p) | cw(28p) | cw(28p) .
 {
Loss of reference timing or burst
 }    Yes    Yes    Yes     {
BER exceeded in satellite path
 }    Yes    Yes    Yes     {
Backward alarm indication from remote ES concerning BER in
satellite path
 }    Yes    Yes  Note 1
_
.T&
lw(12p) | cw(72p) | cw(28p) | cw(28p) | lw(28p) | cw(34p) | cw(28p) | cw(28p) | lw(28p) | cw(28p) | cw(28p) .
Loss of data unique word    Yes    Yes    Yes
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy4/Q.33 [1T4.33], p.   \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [2T4.33]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
 {
TABLE\ A\(hy4/Q.33\ \fI(cont.)\fR
 }
.TE
.TS
cw(84p) | cw(28p) sw(28p) | lw(28p) | lw(34p) sw(28p) sw(28p) sw(28p) sw(28p) sw(28p) , ^  | c | c ^  | | l | l | l | l | l | l.
 {
Digital earth station
equipment
(analogue access links)
Note 3
Fault conditions
 }     {
Terrestrial link to own CT
Removal of group pilot or supergroup pilot
.
 }
    Prompt maintenance alarm     {
Satellite link
Action to prevent overlap of bursts in a TDMA frame
Backward alarm indication concerning satellite path
Backward alarm indication concerning data unique word
AIS in non\(hyinterpolated channels
Indication of fault in affected channels via circuit
supervision channel
Block switched circuits concerned
 }
_
.T&
lw(12p) | cw(72p) | cw(28p) | cw(28p) | lw(28p) | cw(34p) | cw(28p) | lw(28p) | cw(28p) | cw(28p) | cw(28p) .
 {
Backward alarm indication from remote ES concerning data unique
word
 }    Yes    Yes  Note 1    Yes  Note 2    Loss of TDMA frame alignment    Yes    Yes     {
Power supply failure \(em TDMA/DSI
 }    Yes    Yes    Yes if possible
_
.T&
lw(12p) | cw(72p) | cw(28p) | cw(28p) | lw(28p) | cw(34p) | cw(28p) | lw(28p) | cw(28p) | cw(28p) | cw(28p) .
 {
Power supply failure \(em service supervision signalling equipment
 }    Yes    Yes    Yes  if possible     {
Indication of remote end transmission failure via circuit supervision
channel
 }    Yes Note 4
.TE
.LP
\fINote\ 1\fR
\ \(em\ Prompt maintenance alarm shall be inhibited if the backward alarm is received from only one origin if the interface concerned is working to more
than one destination. It is not inhibited when working to a single
destination.
.LP
\fINote\ 2\fR
\ \(em\ If prompt maintenance alarm according to Note 1 is not inhibited.
.LP
\fINote\ 3\fR
\ \(em\ Apart from the requirements concerning the loss of group or
supergroup pilots and indication of remote and transmission failure, all other fault conditions and subsequent actions are optional.
.LP
\fINote\ 4\fR
\ \(em\ An Administration's decision to remove group or supergroup pilot is dependent on the number of failed circuits in the group or supergroup.
.LP
\fBPour Montage\fR
.LP
Consequent actions\ \ \ \ Receiving part\ \ \ \ Transmitting part
.LP
Consequent actions\ \ \ \ Receiving part\ \ \ \ Transmitting part
.nr PS 9
.RT
.ad r
\fBTable A\(hy4/Q.33 (cont.) [2T4.33], p.   \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce 1000
APPENDIX\ I
.ce 0
.ce 1000
(to Annex A of Recommendation Q.33)
.sp 9p
.RT
.ce 0
.ce 1000
\fBFormat of each 64 kbit/s unit forming\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBa satellite line signalling channel (LSC)\fR
.ce 0
.ce 1000
\fBfor System R2 line signalling\fR
.ce 0
.LP
.sp 2
.ce
\fBH.T. [T5.33]\fR
.ce

.ce
\fBvide\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(36p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Symbol N    1    2    3    4    5    6    7    63    64
_
.T&
lw(36p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
P channel    0    1    Y 1    Y 3    a \dx+1 \u    a \dx+2 \u    a \dx+3 \u    a \dx+59 \u    a \dx+60 \u
_
.T&
lw(36p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
Q channel    1    0    Y 2    Y 4    b \dx+1 \u    b \dx+2 \u    b \dx+3 \u    b \dx+59 \u    b \dx+60
.TE
.LP
\u
Symbols 1 and 2 carry the fixed pattern shown.
.LP
Symbols 3 and 4 carry Backward Alarm Indications related to the satellite
system.
.LP
a
n and b
n are the signalling bits relating to the terrestrial channel
connected to International Circuit (IC) number\ n.
.LP
Indicated by the subscript, where:
.LP
x = \ \ 0 in the first 64 kbit/s unit,
.LP
x = \ 60 in the second 64 kbit/s unit,
.LP
x = 120 in the third 64 kbit/s unit,
.LP
x = 180 in the fourth 64 kbit/s unit.
.nr PS 9
.RT
.ad r
\fBTableau I\(hyA/Q.33 [T5.33], p. 9\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 22
.bp
.ce 1000
APPENDIX\ II
.ce 0
.ce 1000
(to Annex A of Recommendation Q.33)
.sp 9p
.RT
.ce 0
.ce 1000
\fBEnd\(hyto\(hyend circuit supervision\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBfor in\(hyband and common channel\fR
.ce 0
.ce 1000
\fBsignalling systems\fR
.ce 0
.PP
End\(hyto\(hyend circuit supervision between corresponding
Administrations may be provided using a pre\(hyassigned digital non\(hyinterpolated
(DNI) supervisory channel allocated for the purpose.
.sp 1P
.RT
.PP
A recommended method of providing such supervision, which uses the binary
information content of the DNI supervisory channel, is shown below. It
should be noted that multi\(hydestination operation requires a DNI supervisory
channel from each destination.
.ce
\fBH.T. [T6.33]\fR
.ce
\fBFormat of satellite circuit supervision channel\fR
.ce
\fB(non\(hyinterpolated)\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(36p) | cw(20p) | cw(20p) | cw(20p) | cw(20p) | cw(20p) | cw(14p) | cw(20p) | cw(20p) | cw(22p) | cw(16p) .
Symbol No.    1    2    3    4    5    6    7    \(em    63    64
_
.T&
lw(36p) | cw(20p) | cw(20p) | cw(20p) | cw(20p) | cw(20p) | cw(14p) | cw(20p) | cw(20p) | cw(22p) | cw(16p) .
P Channel    0    1    1    0    a 1    a 3    a 5    \(em    a \d117 \u    a \d119 \u
_
.T&
lw(36p) | cw(20p) | cw(20p) | cw(20p) | cw(20p) | cw(20p) | cw(14p) | cw(20p) | cw(20p) | cw(22p) | cw(16p) .
Q Channel    1    0    1    0    a 2    a 4    a 6    \(em    a \d118 \u    a \d120
.TE
.LP
\u
Symbols 1, 2, 3 and 4 are not used and carry the fixed sequence shown.
.LP
Symbols 5 to 64 represent supervision conditions, with bit a
n being used
for supervision of the Terrestrial Channels (TCs) 2n and (2n\(em1), connected to international circuits.
.LP
The meaning of each bit a
n is shown below:
.LP
a
n = 0 Indicates that both of the relevant TCs are in a normal
condition.
.LP
a
n = 1 Indicates that either or both of the relevant TCs are in
an abnormal or fault condition.
.nr PS 9
.RT
.ad r
\fBTableau II\(hyA/Q.33 [T6.33], p. 10\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fICharacteristics of primary PCM multiplex\fR
\fIequipment operating at 2048 kbit/s\fR , Vol.\ III, Rec.\ G.732.
.LP
[2]
    CCITT Recommendation \fICharacteristics of primary PCM multiplex\fR
\fIequipment operating at 1544\ kbit/s\fR , Vol.\ III, Rec.\ G.733.
.LP
.rs
.sp 11P
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 5
.ce 0
.sp 1P
.ce 1000
\fBTONES\ FOR\ USE\ IN\ NATIONAL\ SIGNALLING\ SYSTEMS\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.35\fR
.FS
This Recommendation is also included in the Series E Recommendations under
the number E.180 (Fascicle\ II.2)
.FE
.RT
.sp 2P
.ce 1000
\fBTECHNICAL\ CHARACTERISTICS\ OF\ TONES\fR
.FS
See [1] for
particular values of tone cadences and frequencies in actual use.
.FE
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.35''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.35    %'
.ce 0
.sp 1P
.ce 1000
\fBFOR\ THE\ TELEPHONE\ SERVICE\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
Administrations are reminded of the advantages of standardizing
audible tones
as far as possible so that subscribers and operators may quickly recognize
any tone transmitted of whatever
origin
.FS
Recommendation E.181 [3] specifies the information which could be
given to users to facilitate recognition of foreign tones.
.FE
.
.PP
Guidance on the application of tones and recorded announcements in
various situations is given in Recommendation\ E.182\ [2].
.PP
In considering the degree of standardization, the CCITT took
account of the nature of the various tones already in use. It was also
considered that Administrations introducing new tones would find it helpful
to know the preferred limits of cadence frequency and level.
.PP
Limits for
tone cadences and frequencies
are set forth below,  all working tolerances being included in the limits.
.PP
Besides the limits applying to specifications, limits have been laid down
for application to existing exchanges.
.PP
These latter limits are herein called \fIaccepted\fR limits, while those
for new equipment are called \fIrecommended\fR limits.
.PP
The present Recommendation covers the case where audible tones are
applied within the network. However, the same frequencies and cadences
are to be applied if, in the ISDN, the audible tones are generated at the
terminal
equipment.
.RT
.sp 2P
.LP
\fB2\fR     \fBElectrical levels for tones\fR
.sp 1P
.RT
.PP
For international purposes, the levels of the
ringing tone
,
the
busy tone
, the
congestion tone
, the
special information
tone
and the
warning
tone
have to be defined at a
zero relative level point
at the
incoming (in the traffic direction) end of the international circuit.
.PP
The level of tones so defined must have a nominal value of \(em10\ dBm0.
The recommended limits should be not more than \(em5\ dBm0 nor less than
\(em15\ dBm0 measured with continuous tone.
.bp
.PP
For the special information tone, a difference in level of 3\ dB is
tolerable between any two of the three frequencies which make up the tone.
.PP
For the power level of the
dial tone
the point of reference is the local exchange, where the subscriber line
is connected. In the existing
networks the absolute power at the 2\(hywire access in the direction towards
the subscriber station is normally in the range of \(em10\ dBm \(+- | \
dB. However, with
respect to interference with
multifrequency pushbutton (MFPB)
receivers
dial tone levels higher than \(em10\ dBm should be avoided.
.PP
\fINote\fR \ \(em\ The relative level of local exchanges in an analogue
network is not fixed. For digital local exchanges the relative levels are
given in
Recommendation\ Q.552\ [4]. A preferred level range of digital tone generators
is \(em8\ dBm0 to \(em3\ dBm0 corresponding with the above level range
at the output of
local exchanges.
.RT
.sp 2P
.LP
\fB3\fR     \fBAcoustical levels for tones\fR
.sp 1P
.RT
.PP
When tones are generated by a source within a network, e.g.\ by a
telephone exchange, the power level as perceived by the user will be influenced
by the characteristics of the subscriber's line and the equipment between
the source and the user's ear.
.PP
Furthermore, tones can be generated within the user's equipment,
triggered by signals from the exchange. In these circumstances it is necessary
to define the tone level in terms of the preferred range of sound pressure
levels as heard by the listener.
.PP
Research has shown that the preferred listening level for information tones
is substantially independent of room noise, circuit noise and tone
cadence, but does vary over a range of tone frequencies. Figure\ 1/Q.35
shows the recommended sound pressure levels, with upper and lower limits
of the recommended range, over a range of tone frequencies, based on these
experiments.
.RT
.LP
.rs
.sp 26P
.ad r
\fBFigure 1/Q.35, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
It is emphasized that there is no one\(hyto\(hyone relationship between
electrical and
acoustical power levels
. What acoustic level will result from a given electrical level is dependent
on various parameters such as the
characteristics of the user's equipment.
.PP
It should be noted that the recommended sound pressure levels apply
only to the most common situation of a user listening via a telephone handset,
held reasonably close to the ear so that normal \*Qear coupling loss\*U
values
apply.
.PP
When using a loudspeaking telephone or a headset, the preferred sound pressure
level is generally lower than the recommended levels.
.RT
.sp 2P
.LP
\fB4\fR     \fBDial tone\fR
.sp 1P
.RT
.PP
4.1
It is recommended that dial tone should be a continuous tone.
.sp 9p
.RT
.PP
4.2
It is recommended that dial tone should be:
.LP
    \(em
    \fIeither\fR  | a single frequency tone in the range 400\(hy450 Hz,
.LP
    \(em
    \fIor\fR  | a combined tone composed of up to three frequencies,
with at least one frequency in each of the ranges 340\(hy425\ Hz and
400\(hy450\ Hz. The difference between any two frequencies should
be at least 25\ Hz.
.PP
4.3
Recognizing the local nature of \*Qnormal\*U use of dial tone, as well as
the technical and economic consequences and consequences on customer habits
of changes in dial tone, the full range of existing dial tones, including
non\(hycontinuous tones as in Supplement No.\ 2 at the end of Fascicle\
II.2\ [1],
are considered acceptable. However, when adopting a new single frequency
dial tone, Administrations are recommended to use 425\ Hz.
.PP
4.4
Where digital tone generation is applied, the frequencies for
dial tone should be the same as those recommended for analogue generated
tones (see Annex\ A).
.PP
4.5
In order to prevent interference of harmonics or spurious
components of the dial tone with the frequencies recommended for pushbutton
telephone sets in Recommendation\ Q.23 and the MFPB signal reception specified
in Recommendation\ Q.24, the maximum permissible power level of harmonics
or
quantizing noise of the dial tone has to be limited in a suitable way,
depending on the specific characteristics of the implementations of the dial
tone generator and the MFPB receivers within the same exchange. Examples of
such limitations for the dial tone generator are given in Annex\ B.
.PP
\fINote\fR \ \(em\ In cases of digital generation of the dial tone, the
quantizing noise is composed of a number of spectral lines which depend
on the number of samples in the generating pattern. In order to reduce
the amplitude of the quantizing components, the number of samples should
be chosen
sufficiently high, thus spreading the quantizing distortion power more
evenly over the whole spectrum.
.sp 2P
.LP
\fB5\fR     \fBRinging tone\fR
.sp 1P
.RT
.PP
5.1
Ringing tone is a slow period tone, in which the tone period is shorter
than the silent period.
.sp 9p
.RT
.PP
The \fIrecommended\fR  | limits for the tone period (including
tolerances) are from 0.67 to 1.5 seconds. For existing exchanges, the
\fIaccepted\fR upper limit for the tone period is 2.5\ seconds.
.PP
The \fIrecommended\fR  | limits for the silent period separating two tone
periods are 3\ to 5\ seconds. For existing exchanges, the \fIaccepted\fR
upper limit is 6\ seconds.
.PP
The first tone period should start as soon as possible after the
called subscriber's line has been found.
.PP
Figure 2/Q.35 shows the recommended and accepted limits for the
ringing tone periods.
.bp
.RT
.LP
.rs
.sp 25P
.ad r
\fBFigure 2/Q.35, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
5.2
The ringing tone cadence should be similar to the cadence used for
applying ringing current to the called subscriber's telephone set, but
these two cadences need not be synchronized. The electrical parameters
of the ringing current must be evaluated by the Administration concerned to
prevent shock hazard.
.PP
5.3
The recommended frequency for the ringing tone is between 400 and
450\ Hz. The accepted frequency should be not less than 340\ Hz, nor more than
500\ Hz. Frequencies between 450 and 500\ Hz in the accepted frequency range
should, however, be avoided. Administrations adopting a new single frequency
ringing tone are recommended to use\ 425\ Hz.
.PP
The ringing tone frequency may be modulated by a frequency
between 16\ and 100\ Hz, but such modulation is not recommended for new
equipment. If the accepted frequency is more than 475\ Hz, no modulation by a
lower frequency is allowed.
.PP
5.4
Where digital tone generation is applied, the frequency for
ringing tone should be the same as that recommended for analogue generated
tones (see Annex\ A).
.sp 2P
.LP
\fB6\fR     \fBBusy tone\fR \fBand\fR
\fBcongestion tone\fR
.sp 1P
.RT
.PP
6.1
The (subscriber) busy tone and the (equipment or circuit group) congestion
tone are \fIquick\fR period tones in which the
tone period
is
theoretically equal to the
silent period
. The total duration of a
complete cycle (tone period\ \fIE\fR \ + silent period\ \fIS\fR ) should
be between
300 and 1100\ milliseconds.
.sp 9p
.RT
.PP
The ratio \fIE\fR /\fIS\fR of the tone period to the silent period should
be between 0.67 and 1.5 (\fIrecommended\fR values).
.PP
For existing exchanges, or for tones to be used in a special way, it is
\fIaccepted\fR that the tone period may be up to 500\ milliseconds shorter
than the silent period (\fIE\fR \ \(>="\ \fIS\fR \ \(em\ 500\ milliseconds).
In no circumstances should
the tone period be shorter than 100\ milliseconds.
.bp
.PP
Figure 3/Q.35 shows the recommended and the accepted areas for
the busy tone and the congestion tone periods.
.RT
.LP
.rs
.sp 32P
.ad r
\fBFigure 3/Q.35, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
6.2
The busy tone (of the called subscriber) and the congestion
tone (of switching equipment or circuit groups) can be identical or almost
identical, providing that this does not create any serious problems for the
network and does not cause the subscriber to become confused. However, a
distinction between these two tones is desirable:
.LP
    \(em
    to allow Administrations to assess the quality of service,
.LP
    \(em
    for the convenience of experienced subscribers.
.PP
6.3
Where a distinct congestion tone is used, it is recommended
that:
.LP
    a)
     the same \fIfrequency\fR  | should be used for the busy tone and the
congestion tone;
.LP
    b)
     the busy tone should have a slower cadence than the congestion tone,
but both cadences should be within the limits mentioned in
\(sc\ 5.1 above.
.PP
6.4
The \fIrecommended\fR  | frequency for the busy tone and for the
congestion tone must be between\ 400 and 450\ Hz. The \fIaccepted\fR frequency
must not be less than 340 nor more than 500\ Hz. Frequencies between 450
and 500\ Hz in the accepted frequency range should, however, be avoided.
Administrations
adopting a new single frequency for busy and congestion tones are recommended
to use 425\ Hz.
.bp
.PP
6.5
Where digital tone generation is applied, the frequency for busy
and congestion tones should be the same as that recommended for analogue
generated tones (see Annex\ A).
.sp 2P
.LP
\fB7\fR     \fBSpecial information tone\fR
.sp 1P
.RT
.PP
7.1
The special information tone is provided for all cases in which
neither the busy nor the congestion tone can give the required information
to the calling subscriber in the case of call failure. There are three
ways in
which it may be used:
.sp 9p
.RT
.LP
    a)
    when in special cases no provision is made for recourse either
to a recorded announcement or to an operator, the equipment at the
point which the calls have reached must:
.LP
    1)
    \fIeither\fR  | connect the special information tone to the call,
.LP
    2)
    \fIor\fR  | preferably, if technically available,
send an appropriate backward signal such that connection to
the special information tone will be made by equipment which
is nearer to the caller;
.LP
    b)
     when the call is connected to a recorded voice machine; the tone is then
given during the silent intervals between transmissions of the
announcement;
.LP
    c)
    under arrangements made at manual positions serving lines
which have been abnormally routed so that by operating a key the operators
may send the special information signal when, for example, the calling
subscriber fails to understand the operator.
.PP
When the special information tone is applied with or without a
recorded announcement, it should be recognized that customers may refer
to an operator if they fail to understand the meaning of the recorded announcement
and/or the special information tone.
.PP
7.2
The special information tone has a tone period theoretically
equal in length to the silent period.
.PP
\fITone period\fR \ \(em\ The tone period consists of three successive
tone signals, each lasting for 330\ \(+-\ 70\ milli
seconds. Between these tone signals there may be a gap of up to 30\ milliseconds.
.PP
\fISilent period\fR \ \(em\ This lasts for 1000\ \(+-\ 250\ milliseconds.
.RT
.PP
7.3
The frequencies used for the three tone signals are:
950\ \(+-\ 50\ Hz; 1400\ \(+-\ 50\ Hz; 1800\ \(+-\ 50\ Hz, sent in that order.
.sp 2P
.LP
\fB8\fR     \fBWarning tone to indicate that a conversation is being\fR
\fBrecorded\fR
.sp 1P
.RT
.PP
Where a conversation is being recorded at a subscriber's station, it is
recommended that the Administration require the use of a warning tone to
indicate that the conversation is being recorded. When such a tone is applied,
it is recommended that:
.RT
.LP
    a)
    it consists of a 350\(hy500 ms pulse every 15\ \(+-\ 3 seconds of
recording time, and
.LP
    b)
    the frequency of the tone should be 1400 Hz\ \(+-\ 1.5%.
.sp 2P
.LP
\fB9\fR     \fBPayphone recognition tone\fR
.sp 1P
.RT
.PP
9.1
Where Administrations see the necessity of application of a
payphone recognition tone in order to allow operators to recognize that
a call originates at a payphone station or that the called number belongs
to a
payphone station it is recommended to use a payphone recognition tone.
.sp 9p
.RT
.PP
The application of the tone will depend on the operational
requirements of individual Administrations, e.g.\ in some cases the tone will
only be required on an incoming call to the payphone, whilst in others there
may be a requirement for the tone to be present on originating calls and
throughout the period of the call.
.PP
9.2
The tone is a combination of two frequencies \fIf\fR\d1\uand
\fIf\fR\d2\uin the range:
.sp 9p
.RT
.LP
    \fIf\fR\d1\u:\ 1100\(hy1750 Hz
.LP
    \fIf\fR\d2\u:\ \ 750\(hy1450 Hz
.LP
with the ratio: \fIf\fR\d1\u/\fIf\fR\d2\u= 1.2 to 1.5 and with a cadence
(frequency
sequence) as follows:
.LP
     \fIf\fR\d1\uon 200 ms, silence 200 ms, \fIf\fR\d2\uon 200 ms, silence
2\ s (one
cycle is therefore 2.6.\ s).
.bp
.sp 2P
.LP
9.3
    \fIDuration and level\fR
.sp 1P
.RT
.PP
9.3.1
A principal purpose of the payphone recognition tone in
international telephony is to identify a called station as a payphone where
the possibility exists of attempted fraud on a collect call. For this purpose
the tone must be produced as soon as a payphone answers a call, it must
be clearly audible to an operator, and it must cease before it can seriously
interfere
with conversation.
.sp 9p
.RT
.PP
When the tone is used on an incoming call to a payphone, it should have,
in addition to those characteristics defined in \(sc\ 9.2, a duration of
5\ complete cycles (13\ s).
.PP
9.3.2
If the tone is used to identify payphones which are originating
calls, its duration is not specified.
.sp 9p
.RT
.PP
9.3.3
The specification in \(sc 9.3.1 applies only to the first five cycles of
the tone when the payphone is the receiving station.
.PP
For use throughout a call or during conversation, the level and
duration of the tone have to meet two contradictory requirements:
.LP
    \(em
    the public exchange operator should be able to detect and
recognize the tone in the presence of the highest expected
levels of speech;
.LP
    \(em
    the tone should not interfere unduly with normal
conversation.
.PP
Experience of customer reaction to the tone requires that the time during
which the tone is applied should be as short as possible, subject to
operational requirements. Similarly the level of the tone should be as
low as possible and significantly lower than the recommended levels for
other tones
(e.g.\ \(em20\ dBm at the payphone output). The duration of the tone and
the level at which it is applied are interdependent factors, the shorter
the duration the higher the level and vice versa. (Further studies on the
recommended levels and duration will be carried out.)
.sp 2P
.LP
\fB10\fR     \fBCall waiting tone\fR
.sp 1P
.RT
.PP
10.1
The call waiting tone is used to advise a subscriber who is
engaged on a call that another subscriber is attempting to call.
.sp 9p
.RT
.PP
10.2
The tone is intended to be sufficiently alerting to succeed in its purpose
without interfering with existing conversation.
.PP
10.3
The \fIrecommended\fR  | specification of the tone is one or more cycles
defined by a frequency \fIf\fR in the range:
.LP
    \fIf\fR : 400 to 450 Hz
.LP
and with a cadence (frequency sequence) as follows:
.LP
    a)
    \fIf\fR on 300 to 500 ms, silence 8 to 10s; (
\fIf\fR = 300 ms is preferable to the longer tone since the ongoing conversation
would be interrupted for a briefer interval), or
.LP
    b)
    \fIf\fR on 100 to 200 ms, silence 100 to 200 ms, \fIf\fR on 100\ to
200\ ms (the total to be no more than 500\ ms); 8\ to 10\ s
silence.
.PP
Other tones may be \fIacceptable\fR
.PP
10.4
The second and subsequent cycles may be at a lower level than the initial
tone.
.sp 9p
.RT
.PP
10.5
Where the tone continues for more than one cycle, it should
preferably cease when it is no longer possible to accept the waiting call.
.sp 2P
.LP
\fB11\fR     \fBCaller waiting tone\fR
.sp 1P
.RT
.PP
11.1
This tone advises a caller that a called station, though busy, has a call
waiting service active.
.sp 9p
.RT
.PP
11.2
It is intended that, if this tone is not correctly interpreted by subscribers,
it be misinterpreted as the ringing tone.
.PP
11.3
To dissuade a caller from waiting indefinitely, the tone may cease 30\ seconds
.FS
The specification of this time needs further study.
.FE
after it starts and may be replaced by busy tone, or an Administration
may decide to disconnect the calling station.
.bp
.PP
11.4
The caller waiting tone consists of a ringing tone followed after a silent
interval of 0\ to 200\ ms, by one of the following:
.LP
    (a)
    the tone defined in \(sc\ 10.3\ a),
.LP
    (b)
    the pair of tones defined in \(sc\ 10.3\ b), or
.LP
    (c)
    another call waiting tone in use by an Administration,
provided that it can be appended to each sounded part of the ringing
tone.
.PP
11.5
The caller waiting tone, as defined in \(sc\ 11.4, should be
distinguishably different from the ringing tone when directly compared with
it.
.sp 9p
.RT
.sp 2P
.LP
\fB12\fR     \fBMachine recognition of tones\fR
.sp 1P
.RT
.PP
The CCITT appreciates the value of machine recognition of tones for the
purpose of service observations, maintenance, testing or for the collection
of statistics where equivalent electrical signals do not exist. However,
the
CCITT considered, at Mar del Plata in 1968, that such machine recognition
should not be a substitute for electrical signals. Where machine recognition
of audible tones is to be introduced, the tone frequencies and cadences
must be
within close limits of precision.
.PP
For dial tone, ringing tone, busy and congestion tones a working
frequency tolerance of \(+- | % should be met.
.PP
\fINote\fR \ \(em\ The figure of 1% is taken as a compromise out of several
national specifications which vary between \(+- | .5% and \(+- | .5%. (See also
Supplement No.\ 3 in Fascicle\ II.2.)
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation Q.35)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDigital generation of tones\fR
.sp 1P
.RT
.ce 0
.PP
The practice of several Administrations and equipment designers for digital
generation of tones is known to deviate largely:
.sp 1P
.RT
.LP
    \(em
    in the frequency chosen within the recommended range;
.LP
    \(em
    in the power level which varies with the national
application;
.LP
    \(em
    in the mechanism of generation of tones and signal
frequencies where, in part, the same equipment is used.
.PP
Therefore, it was found difficult to standardize on a fixed number of samples
with a coded bit\(hystream, which represents one frequency with one
distinct power level.
.PP
On the other hand there is no necessity for standardizing digital
generated tones in a more stringent way than analogue generated tones for
the following reasons:
.RT
.LP
    \(em
    It is to the interest of Administrations that subscribers
should not be confused by hearing different tones for the same
purpose within their national networks. Consequently
the practice already in use for analogue generated tones should
be maintained for reasons associated with the human factor.
.LP
    \(em
    The advantages that can be achieved by standardizing the code
words for the tones in order to allow automatic recognition of
tones by monitoring the bit stream seem to be so small that they
do not justify a stringent restriction on all possible methods
for digital generation of any frequency allocated with any
level.
.LP
    \(em
    For a long period of time a mixture of analogue and digital
networks will exist. Thus, machine recognition of tones will
have to be performed also with analogue receivers.
.PP
However, when Administrations have full freedom to make new
decisions about tones in future networks, especially with respect to an
all\(hydigital network, they may consider a preferred solution for the digital
generation of dial tone, busy tone, congestion tone and ringing tone having
a uniform frequency of 425\ Hz, as recommended by CCITT.
.bp
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation Q.35)
.sp 9p
.RT
.ce 0
.ce 1000
\fBExamples for\fR
\fBlimitation of spurious components of the dial\fR
\fBtone\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBwith respect to interference with the frequencies\fR
\fBrecommended\fR
.ce 0
.ce 1000
\fBfor\fR
\fBpushbutton telephone sets\fR \fBin\fR \fBRecommendation Q.23\fR
.ce 0
.LP
B.1
    \fIMethod A\fR  | (used by ATT)
.sp 1P
.RT
.PP
The total distortion power should be at least 33\ dB less than the dial
tone power, and the distortion power in any 100\ Hz band above 500\ Hz
should be at least 40\ dB less than the dial tone power.
.RT
.sp 1P
.LP
B.2
    \fIMethod B\fR  | (used by the Federal Republic of Germany)
.sp 9p
.RT
.PP
In the frequency range from 500 to 2000\ Hz [i.e.\ the range of
multifrequency pushbutton (MFPB) frequencies] the distortion power in any
100\ Hz band should be at least 40\ dB below the dial tone power. In addition,
in the frequency range above 2000\ Hz up to 4000\ Hz the total distortion
power
should be at least 25\ dB below the dial tone power.
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    \fIVarious tones used in national networks\fR ,
Vol.\ II, Supplement\ No.\ 2.
.LP
[2]
    CCITT Recommendation \fIApplication of tones and recorded announcements\fR
\fIin telephone services\fR , Vol.\ II, Rec.\ E.182.
.LP
[3]
    CCITT Recommendation \fICustomer recognition of foreing tones\fR ,
Vol.\ II, Rec.\ E.181.
.LP
[4]
    CCITT Recommendation \fITransmission characteristics at 2\(hywire analogue\fR
\fIinterfaces of a digital exchange\fR , Vol.\ VI, fascicle\ VI.5,
Rec.\ Q.552.
\v'1P'
.sp 2P
.LP
\fBRecommendation\ Q.36\fR
.FS
This Recommendation is also included in the Series\ E Recommendations under
the number\ E.181.
.FE
.RT
.sp 2P
.sp 1P
.ce 1000
\fBCUSTOMER\ RECOGNITION\ OF\ FOREIGN\ TONES\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.36''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.36    %'
.ce 0
.sp 1P
.PP
\fB1\fR
In order to facilitate recognition of foreign ringing and
busy tones by a subscriber dialling an automatic international call,
the information given to subscribers should:
.sp 1P
.RT
.LP
    1)
    emphasize that a slow repetition rate of the tone
means \*Qringing\*U whereas a rapid repetition rate means \*Qbusy\*U;
.LP
    2)
    indicate that in some countries the ringing tone may
be heard as a sequence of two short tones, pause, two more short
tones, pause, and so on.
.PP
In addition, it may be useful for the purpose of educating
subscribers:
.LP
    \(em
     to provide auditory samples of such tones by tape recording or other
means, or
.LP
    \(em
    to include detailed descriptions of tones in
directories.
.LP
.sp 6
.bp
.PP
\fB2\fR Modern international signalling systems are capable of exchanging
signals corresponding to indications normally given to subscribers by means
of audible tones (busy, congestion, ringing,\ etc.). Administrations
are encouraged to arrange their networks so that these information signals
can be sent between countries in order that they can be recognized and
converted
into tones or announcements as near to the calling subscriber as practical.
This procedure could significantly reduce the language problems arising from
the growing use of recorded announcements.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ This Recommendation is complementary to
Recommendation\ E.180 on the standardization of tones in the international
telephone network. Whilst standardization is of primary importance, telephone
users need information to assist them in recognizing foreign tones until
such time as standardization is complete.
.PP
This is the purpose of \(sc\ 1 of the present Recommendation which,
as extensive human factor experiments show, should greatly reduce subscriber
confusion.
.PP
The measure mentioned in \(sc\ 2 does not eliminate the need for
tone standardization as well, but can reduce customer difficulties in cases
where standardization may be impractical for a long period but sophisticated
exchanges arrangements are available.
.RT
.LP
.rs
.sp 39P
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 6
.ce 0
.sp 1P
.ce 1000
\fBGENERAL\ CHARACTERISTICS\ FOR\ INTERNATIONAL\ TELEPHONE\fR
.ce 0
.sp 1P
.ce 1000
\fBCONNECTIONS\ AND\ INTERNATIONAL\ TELEPHONE\ CIRCUITS\fR
.ce 0
.sp 1P
.IP
\fB6.0\fR     \fBGeneral\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.40\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTHE\ TRANSMISSION\ PLAN\fR
.FS
This Recommendation is an extract of Recommendation\ G.101\ [3]. The suspensive
points show where a passage in Recommendation\ G.101 has not been reproduced
under\ Q.40.
.FE
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.40''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.40    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBPrinciples\fR
.sp 1P
.RT
.PP
The transmission plan of the CCITT established in 1964 was drawn up with
the object of making use, in the international service, of the advantages
offered by 4\(hywire switching. It is referred to in the Recommendations
appearing in Part\ I, Section\ 1 of the Series\ G Recommendations. However,
the
recommendations in the plan are to be considered as met if the use of technical
means other than those described below gives an equivalent performance
at the international exchange.
.PP
Recommendations G.121\ [1] and G.122\ [2] describe the conditions to be
fulfilled by a national network for this transmission plan to be put into
effect.
.PP
\fINote\ 1\fR \ \(em\ From the point of view of the transmission plan, no
distinction is made between intercontinental circuits and other international
circuits.
.PP
\fINote\ 2\fR \ \(em\ Short trans\(hyfrontier circuits are not covered
by this plan and should be the subject of agreement between the Administrations
concerned.
.RT
.sp 1P
.LP
.
.sp 9p
.RT
.sp 2P
.LP
\fB2\fR     \fBDefinition of the constituent parts of a connection\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIThe international chain of circuits and the national systems\fR
.sp 9p
.RT
.PP
A complete \fBinternational telephone connection\fR consists of
three parts, as shown in Figure\ 1/Q.40. The division between these parts is
determined by the \fIvirtual analogue switching points\fR in the
originating/terminating international switching centres (ISCs). These are
theoretical points with specified relative levels (see Figure\ 2/Q.40 and
\(sc\(sc\ 5.1 and 5.2 of Recommendation\ G.101).
.RT
.LP
.sp 5
.bp
.PP
The three parts of the connection are:
.RT
.LP
    \(em
     Two national systems, one at each end. These may comprise one or more
4\(hywire national trunk circuits with 4\(hywire interconnection,
as well as circuits with 2\(hywire connection up to the local
exchanges and the subscribers sets with their subscriber lines.
.LP
    \(em
    An international chain made up of one or more 4\(hywire
international circuits. These are interconnected on a 4\(hywire
basis in the international centres which provide for transit traffic
and are also connected on a 4\(hywire basis to national systems in the
international centres.
.LP
    \(em
     An international 4\(hywire circuit is delimited by its virtual analogue
switching points in an international switching centre.
.PP
\fINote\ 1\fR \ \(em\ In principle the choice of values of the relative
levels
at the virtual analogue switching points on the side of a national system
is a national matter. In practice, several countries have chosen \(em3.5\
dBr for
receiving as well as for sending. These are theoretical values; they need
not actually occur at any specific equipment item; however they serve to
determine the relative levels at other points in the national network.
If, for instance, the loss \*Q\fIt\fR \(hy\fIb\fR \*U or \*Q\fIa\fR \(hy\fIt\fR
\*U is 3.5\ dB (as is the case in several countries, see Table\ A\(hy1/G.121),
then it follows that the relative levels at point \fIt\fR are 0\ dBr (input)
and \(em7\ dBr (output).
.PP
\fINote\ 2\fR \ \(em\ The virtual analogue switching points may not be
the same as the points at which the circuit terminates physically in the
switching
equipment. These latter points are known as the \fIcircuit terminals\fR
; the exact position of these terminals is decided in each case by the
Administration
concerned.
.RT
.LP
.rs
.sp 14P
.ad r
\fBFIGURE 1/Q.40 p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2
    \fINational extension circuits: 4\(hywire chain\fR
.sp 9p
.RT
.PP
When the maximum distance between an international exchange and a subscriber
who can be reached from it does not exceed about 1000\ km or,
exceptionally, 1500\ km, the country concerned is considered as of average
size. In such countries, in most cases, not more than three national circuits
are
interconnected on a 4\(hywire basis between each other and to international
circuits. These circuits should comply with the Recommendations of
Subsection\ 1.2\ [4] of Volume\ III, Fascicle\ III.1 (Recs.\ G.120, G.121,
G.122,
G.123 and\ G.125).
.PP
In a large country, a fourth and possibly a fifth national circuit may
be included in the 4\(hywire chain, provided it has the nominal transmission
loss and the characteristics recommended for international circuits used
in a 4\(hywire chain (see Recommendation\ G.141, \(sc\ 1, \(sc\ 4 of this
Recommendation and the
Recommendations in Subsection\ 1.5 of Volume\ III, Fascicle\ III.1,
Recs.\ G.151\ [5], G.152\ [6] and\ G.153\ [7]).
.PP
\fINote\fR \ \(em\ The abbreviation \*Qa \fB4\(hywire chain\fR \*U (see
Figure\ 3/Q.40)
signifies the chain composed of the international chain and the national
extension circuits connected to it, either by 4\(hywire switching or by some
equivalent procedure (as understood in \(sc\ 1 above).
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFIGURE 2/Q.40, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 22P
.ad r
\fBFigure 3/Q.40 p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB3\fR     \fBNumber of circuits in a connection\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fINational circuits\fR
.sp 9p
.RT
.PP
It seems reasonable to assume that in most countries any \fIlocal\fR \fIexchange\fR
 | can be connected to the international network by means of a chain of
four (or less) national circuits. Five national circuits may be needed
in
some countries, but it is unlikely that any country may need to use more
than five circuits. Hence the CCITT has reached the conclusion that four
circuits is a representative figure to assume for the great majority of
international
connections.
.PP
In most modern national networks, the four circuits will probably
include three 4\(hywire amplified circuits (usually set up on FDM carrier
systems) and one 2\(hywire circuit, probably unamplified. However, cases
in which local
exchanges are reached by four amplified circuits, among them usually at
least one PCM circuit, are becoming more and more frequent. All these circuits
may be 4\(hywire circuits.
.RT
.LP
.sp 1P
.LP
3.2
    \fIInternational circuits\fR
.sp 9p
.RT
.PP
According to the International Telephone Routing Plan
(Recommendation\ E.171), the number of international circuits is restricted
to four.
.RT
.sp 1P
.LP
3.3
    \fIHypothetical reference connections\fR
.sp 9p
.RT
.PP
(See Recommendation G.103\ [9].)
.RT
.sp 1P
.LP
.
.sp 9p
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fILoudness ratings (LRs) of national systems\fR ,
Vol.\ III, Rec.\ G.121.
.LP
[2]
    CCITT Recommendation \fIInfluence of national systems on stability,\fR
\fItalker echo, and listener echo in international connections\fR , Vol.\ III,
Rec.\ G.122.
.bp
.LP
[3]
    CCITT Recommendation \fIThe transmission plan\fR , Vol.\ III, Rec.\ G.101.
.LP
[4]
    CCITT Recommendations G.120, G.121, G.122, G.123 and G.124;
Subsection\ 1.2: \fIGeneral characteristics of national systems forming
part\fR
\fIof international connections\fR of Volume\ III.
.LP
[5]
     CCITT Recommendation \fIGeneral performance objectives applicable to
all\fR \fImodern international circuits and national extension circuits\fR
, Vol.\ III,
Rec.\ G.151.
.LP
[6]
    CCITT Recommendation \fICharacteristics appropriate to long\(hydistance\fR
\fIcircuits of a length not exceeding 2500\ km\fR , Vol.\ III, Rec.\ G.152.
.LP
[7]
    CCITT Recommendation \fICharacteristics appropriate to international\fR
\fIcircuits more than 2500\ km in length\fR , Vol.\ III, Rec.\ G.153.
.LP
[8]
     CCITT Recommendation \fIPulse code modulation (PCM) of voice frequencies\fR
, Vol.\ III, Rec.\ G.711.
.LP
[9]
    CCITT Recommendation \fIHypothetical reference connections\fR , Vol.\ III,
Rec.\ G.103.
.IP
\fB6.1\fR     \fBGeneral recommendations on the transmission quality for an\fR
\fBentire international telephone connection\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.41\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBMEAN\ ONE\(hyWAY\ PROPAGATION\ TIME\fR
.FS
This Recommendation is an extract of Recommendation\ G.114 [1]. The suspensive
points show where a passage
in Recommendation\ G.114 has not been reproduced under\ Q.41.
.FE
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.41''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.41    %'
.ce 0
.sp 1P
.PP
The times in this Recommendation are the means of the propagation times
in the two directions of transmission in a connection. When opposite
directions of transmission are provided by different media (e.g.\ a satellite
channel in one direction and a terrestrial channel in the other) the two
times contributing to the mean may differ considerably.
.sp 1P
.RT
.sp 2P
.LP
\fB1\fR     \fBLimits for a connection\fR
.sp 1P
.RT
.PP
It is necessary in an international telephone connection to limit the propagation
time between two subscribers. As the propagation time is
increased, subscriber difficulties increase, and the rate of increase of
difficulty rises, see b) below. Relevant evidence is given in the
bibliography of Recommendation\ G.114\ [1].
.PP
As a network performance objective, CCITT therefore \fIrecommends\fR
the following limitations on mean one\(hyway propagation times when echo
sources exist and appropriate echo control devices, such as echo suppressors
and echo cancellers, are used:
.RT
.LP
    a)
    0 to 150\ ms, acceptable.
.LP
     \fINote\fR \ \(em\ Echo suppressors specified in Reference [2] may be
used for delays not exceeding 50\ ms (see Reference\ [3]).
.LP
    b)
    150 to\ 400\ ms, acceptable, provided that increasing care is
exercised on connections as the mean one\(hyway propagation time
exceeds about 300\ ms, and provided that echo control devices,
such as echo suppressors and echo cancellers, designed for long
delay circuits are used.
.LP
    c)
    Above 400\ ms, unacceptable. Connections with these delays
should not be used except under the most exceptional
circumstances.
.sp 1P
.LP
.
.bp
.sp 9p
.RT
.sp 2P
.LP
\fB2\fR     \fBValues for circuits\fR
.sp 1P
.RT
.PP
In the establishment of the general interconnection plan within the limits
in \(sc\ 1 the one\(hyway propagation time of both the national extension
circuits and the international circuits must be taken into account. The
propagation time of circuits and connections is the aggregate of several
components; e.g.\ group delay in cables and in filters encountered in FDM
modems of different types. Digital transmission and switching also contribute
delays. The conventional planning values given in \(sc\ 2.1 may be used
to estimate
the total propagation time of specified assemblies which may form circuits
or connections.
.RT
.sp 1P
.LP
2.1
    \fIConventional planning values of propagation time\fR
.sp 9p
.RT
.PP
Provisionally, the conventional planning values of propagation
time in Table\ 1/Q.41 may be used.
.RT
.sp 1P
.LP
2.2
    \fINational extension circuits\fR
.sp 9p
.RT
.PP
The main arteries of the national network should consist of
high\(hyvelocity propagation lines. In these conditions, the propagation time
between the international centre and the subscriber farthest away from it in
the national network will probably not exceed:
.RT
.LP
    a)
    In purely analogue networks
.sp 1P
.ce 1000
12\ +\ (0.004\ \(mu\ distance in kilometres) ms.
.ce 0
.sp 1P
.LP
    Here the factor 0.004 is based on the assumption that national
trunk circuits will be routed over high\(hyvelocity plant (250\ km/ms).
The 12\ ms constant term makes allowance for terminal equipment and for
the probable
presence in the national network of a certain quantity of loaded cables
(e.g.\ three pairs of channel translating equipments plus about 160\ km of
H\ 88/36 loaded cables). For an average\(hysized country (see Figure\ 2/G.103)
the one\(hyway propagation time will be less than 18\ ms.
.LP
    b)
     In mixed analogue/digital networks the propagation time can generally
be estimated by the equation given for purely analogue networks.
However, under certain unfavourable conditions increased delay may
occur compared with the purely analogue case. This occurs in particular when
digital exchanges are connected with analogue transmission systems through
PCM/FDM equipments in tandem, or transmultiplexers. With the growing degree
of digitisation the propagation time will gradually approach the condition
of
purely digital networks.
.LP
    c)
     In purely digital networks between exchanges (e.g.\ an IDN) the propagation
time as defined above will probably not exceed:
.sp 1P
.ce 1000
3\ +\ (0.004\ \(mu\ distance in kilometres) ms.
.ce 0
.sp 1P
.LP
    The 3 ms constant term makes allowance for one PCM coder or
decoder and five digitally switched exchanges.
.LP
     \fINote\fR \ \(em\ The value 0.004 is a mean value for coaxial cable
systems and
radio\(hyrelay systems; for optical fibre systems 0.005 is to be used.
.LP
    d)
    In purely digital networks between subscribers (e.g.\ an
ISDN) the delay of c) above has to be increased by up to 3.6\ ms
if burst\(hymode (time compression multiplexing) transmission is
used on 2\(hyW local subscriber lines.
.sp 1P
.LP
2.3
    \fIInternational circuits\fR
.sp 9p
.RT
.PP
International circuits
.FS
For short nearby links,
telecommunications cables operated at voice frequencies may also be used
in the conditions set out in the introduction to Sub\(hysection\ 5.4 of
Fascicle\ III.2.
.FE
will use high\(hyvelocity transmission systems,
e.g.\ terrestrial cable or radio\(hyrelay systems, submarine systems or
satellite systems. The planning values of \(sc\ 2.1 may be used.
.PP
The magnitude of the mean one\(hyway propagation time for circuits on
high altitude communication satellite systems makes it desirable to impose
some routing restrictions on their use. Details of these restrictions are
given in Recommendation\ Q.13. (See also Annex\ A to Recommendation\ G.114.)
.RT
.sp 1P
.LP
.
.bp
.sp 9p
.RT
.ce
\fBH.T. [T1.41]\fR
.ce
TABLE\ 1/Q.41
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(84p) | cw(60p) | cw(84p) .
Transmission medium     {
Contribution to one\(hyway
propagation time
 }    Remarks
_
.T&
lw(84p) | cw(60p) | lw(84p) .
 {
Terrestrial coaxial cable or radio relay system;
FDM and digital transmission
 }    4 \(*ms/km     {
Allows for delay in repeaters and regenerators
 }
_
.T&
lw(84p) | cw(60p) | lw(84p) .
 {
Optical fibre cable system;
digital transmission
 }    5 \(*ms/km     {
Allows for delay in repeaters and regenerators
 }
_
.T&
lw(84p) | cw(60p) | lw(84p) .
 {
Submarine coaxial cable system
 }    6 \(*ms/km
_
.T&
lw(84p) | cw(60p) | lw(84p) .
Satellite system
.T&
lw(84p) | cw(60p) | lw(84p) .
 {
\(em\ 14 | 00 km altitude
\(em\ 36 | 00 km altitude
 }    110 ms 260 ms    Between earth stations only
_
.T&
lw(84p) | cw(60p) | lw(84p) , l | c | ^ , l | c | ^ , l | c | ^ , l | c | ^ , l | c | ^ , l | c | ^ , l | c | ^ , l | c | ^ , l | c | ^ .
 {
FDM channel modulator or demodulator
 }    0.75 ms | ua\d\u)\d     {
Half the sum of propagation times in both directions of
transmission
 }
.TE
.LP
\ua\d\u)\d
These values allow for group\(hydelay distortion around frequencies
of peak speech energy and for delay of intermediate higher order
multiplex and through\(hyconnecting equipment.
.LP
\ub\d\u)\d
This value refers to FDM equipments designed to be used with a
compandor and special filters.
.LP
\uc\d\u)\d
For satellite digital communications where the transmultiplexer
is located at the earth station, this value may be increased to
3.3\ ms.
.LP
\ud\d\u)\d
These are mean values; depending on traffic loading, higher
values can be encountered, e.g.\ 0.75\ ms (1.950\ ms,
1.350\ ms or 1.250\ ms respectively
with 0.95\ probability of not exceeding). (For details see
Recommendation\ Q.551).
.LP
\ue\d\u)\d
Echo cancellers, when placed in service, will add a one\(hyway
propagation time of up to 1\ ms in the send path of each echo
canceller. This delay excludes the delay through any codec
in the echo canceller. No significant delay should be incurred
in the receive path of the echo canceller.
 }    0.5\  ms | ub\d\u)\d
PCM coder or decoder    0.3\  ms | ua\d\u)\d
PCM/ADPCM/PCM transcoding    0.5\  ms  | ua\d\u)\d
Transmultiplexer    1.5\  ms | uc\d\u)\d
 {
Digital transit exchange, digital\(hydigital
 }    0.45 ms | ud\d\u)\d
 {
Digital local exchange, analogue\(hyanalogue
 }    1.5\  ms | ud\d\u)\d
 {
Digital local exchange, analogue subscriber line\(hydigital junction
 }    0.975 ms | ud\d\u)\d
 {
Digital local exchange, digital subscriber line\(hydigital junction
 }    0.825 ms | ud\d\u)\d
Echo cancellers    1 |  \  ms | ue\d\u)\d
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/Q.41 [T1.41] p. (\*`a traiter comme tableau MEP)\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIMean one\(hyway propagation time\fR , Vol.\ III,
Rec.\ G.114.
.LP
[2]
    CCITT Recommendation \fIDefinitions relating to echo suppressors and\fR
\fIcharacteristics of a far\(hyend operated, differential, half\(hyecho
suppressor\fR ,
Blue Book, Vol.\ III, Rec.\ G.161, ITU, Geneva, 1965.
.LP
[3]
    CCITT Recommendation \fIStability and echo\fR , Vol.\ III,
Rec.\ G.131, \(sc\ 2.2.
.IP
\fB6.2\fR     \fBGeneral characteristics of national systems forming part\fR
\fBof international connections\fR
.sp 1P
.RT
.PP
    (See Recommendations\ G.120 to\ G.125, Fascicle III.1.)
\v'6p'
.RT
.IP
\fB6.3\fR \fBGeneral characteristics of the \*Q4\(hywire chain\*U formed
by the\fR
\fBinternational circuits and national extension circuits\fR
.sp 1P
.RT
.PP
    (Overall characteristics for the 4\(hywire chain are defined in
Recommendation\ Q.40, \(sc\ 2.)
.RT
.sp 2P
.LP
\fBRecommendation\ Q.42\fR
.RT
.sp 2P
.LP
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.42''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.42    %'
.sp 1P
.ce 1000
\fBSTABILITY\ AND\ ECHO\ (ECHO\ SUPPRESSORS)\fR
.ce 0
.sp 1P
.ce 1000
(See Recommendation G.131 in Fascicle III.1 and
Recommendation Q.115)
.sp 9p
.RT
.ce 0
.sp 1P
.IP
\fB6.4\fR \fBGeneral characteristics of the 4\(hywire chain of international\fR
\fBcircuits; international transit\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.43\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTRANSMISSION\ LOSSES,\ RELATIVE\ LEVELS\fR
.FS
This
Recommendation is an extract of Recommendation G.101
[1]. The suspensive points show where a passage in Recommendation\ G.101 has
not been reproduced under\ Q.43.
.FE
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.43''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.43    %'
.ce 0
.sp 1P
.LP
.
.sp 1P
.RT
.sp 2P
.LP
5.3
    \fIDefinitions\fR
.sp 1P
.RT
.sp 1P
.LP
5.3.1
    \fBtransmission reference point\fR
.sp 9p
.RT
.LP
    \fIF:\ point de r\*'ef\*'erence pour la transmission\fR
.LP
    \fIS:\ punto de referencia para la transmisi\*'on\fR
.PP
A hypothetical point used as the zero relative level point in the computation
of nominal relative levels. At those points in a telephone circuit the
nominal mean power level (\(em15\ dBm) defined in the Recommendation\ G.223\
[2] shall be applied when checking whether the transmission system conforms
to the noise objectives defined in Recommendation\ G.222\ [3].
.PP
\fINote\fR \ \(em\ For certain systems, e.g. submarine cable systems
(Recommendation\ G.371\ [4]), other values apply.
.PP
Such a point exists at the sending end of each channel of a 4\(hywire
switched circuit preceding the virtual switching point; on an international
circuit it is defined as having a signal level of +3.5\ dB above that of the
virtual switching point.
.PP
In frequency division multiplex equipment, a hypothetical point of
flat zero relative level (i.e.\ where all channels have the same relative
level) is defined as a point where the multiplex signal, as far as the
effect of
intermodulation is concerned,
.bp
.PP
can be represented by a uniform spectrum random
noise signal with a mean power level as defined in the Recommendation cited
in\ [5]. The nominal mean power level in each telephone channel is \(em15\
dBm as
defined in the Recommendation cited in\ [2].
.RT
.sp 1P
.LP
5.3.2
    \fBrelative (power) level\fR
.sp 9p
.RT
.LP
    \fIF:\ niveau relatif de puissance\fR
.LP
    \fIS:\ nivel relativo (de potencia)\fR
.sp 1P
.LP
5.3.2.1
    \fIBasic significance of relative level in FDM systems\fR
.sp 9p
.RT
.PP
The relative level at a point in a transmission system
characterizes the signal power handling capacity at this point with respect
to the conventional power level at a zero relative level point
.FS
Taking into
account such aspects as (basic) noise, intermodulation noise, peak power,
etc. (see Recommendation\ G.223).
.FE
.
.PP
If, for example, at a particular point in an FDM system designed for a
large number of channels the mean power handling capacity per telephone
channel corresponds to an absolute power level of \fIS\fR \ dBm, the relative
level
associated
with this point is (\fIS\fR \ +\ 15)\ dBr. In particular, at a 0\ dBr point,
the
conventional mean power level referred to one telephone channel is
\(em15\ dBm.
.RT
.sp 1P
.LP
5.3.2.2
    \fIDefinition of relative level, generally applicable to all\fR
\fIsystems\fR
.sp 9p
.RT
.PP
The relative level at a point on a circuit is given by the
expression 10\ log\d1\\d0\u(\fIP\fR /\fIP\fR\d0\u)\ dBr, where \fIP\fR
represents the power of a sinusoidal test signal at the point concerned
and \fIP\fR\d0\uto the power of
that signal at the transmission reference point. This is numerically equal
to the composite gain (definition in \fIYellow Book\fR , Fascicle\ X.1)
between the
transmission reference point and the point concerned, for a nominal frequency
of 1000\ Hz. For example, if a reference signal of 0\ dBm at 1000\ Hz is
injected at the transmission reference point, the level at a point of \fIx\fR
\ dBr will be
\fIx\fR \ dBm (apparent power \fIP\fR\d\fIx\fR\u\ =\ 10\fI\fI
\u\fIx\fR\d\u/\d\u1\d\u0\dmW). In addition,
application of a digital reference sequence (DRS, \(sc\ 5.3.3) will give
a level of \fIx\fR \ dBm at a point of \fIx\fR \ dBr. The voltage of 0\
dBm0 tone at any voiceband frequency at a point of \fIx\fR \ dBr is given
by the expression:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIV\fR =
@ sqrt { 10~\u\fIx\fR~/10~\d~\(mu~1~W~\(mu~10~\u\(em3~\d left | fIZ~\dR\u\fR right | ~\d~1000~\u } @  volts
.ce 0
.sp 1P
.LP
.sp 1
where
@ left | fIZ~\dR\u\fR right | @
\d
1000
\u is the modulus of the nominal
impedance of the point at a nominal frequency of 1000\ Hz.
.LP
.PP
\fINote\ 1\fR \ \(em\ The nominal reference frequency of 1000\ Hz is in
accordance with Recommendation\ G.712, \(sc\ 16. For existing (analogue)
transmission systems, one may continue to use a reference frequency of 800\ Hz.
.PP
\fINote\ 2\fR \ \(em\ The relative levels at particular points in a transmission
system (e.g.\ input and output of distribution frames or of equipment like
channel translators) are fixed by convention, usually by agreement between
manufacturers and users.
.RT
.LP
The Recommendations of the CCITT are elaborated in such a way that the
absolute power level of any testing signal to be applied at the input of a
particular transmission system, to check whether it conforms to these
recommendations, is clearly defined as soon as the relative level at this
point is fixed.
.PP
\fINote\ 3\fR \ \(em\ The impedance \fIZ\fR\d\fIR\fR\umay be resistive
or complex; in
the latter case the power \fIP\fR\d\fIx\fR\uis an apparent power.
.PP
\fINote\ 4\fR \ \(em\ It is assumed that between the virtual analogue switching
points of a circuit, established over international transmission systems,
only points of equal relative level are interconnected in those systems,
so that the transmission loss of the circuit will be equal to the difference
in relative
levels at the virtual analogue switching points (see \(sc\ 5.2 of this
Recommendation).
.RT
.sp 1P
.LP
5.3.2.3
    \fIRelation between corrected send reference equivalents,\fR
\fIloudness ratings and relative levels\fR
.sp 9p
.RT
.PP
The relationship between the 0\ dBr point and the level of
\fIT\fR\dm\\da\\dx\uin PCM encoding/decoding processes standardized by
the CCITT
is set forth in Recommendation\ G.711\ [6]. In particular, if the minimum
nominal corrected send reference equivalent (CSRE) of local systems referred
to a
point of 0\ dBr of a PCM encoder is not less than 3.5\ dB, or the minimum
nominal send loudness rating (SLR) under the same conditions is not less
than
\(em1.5\ dB, and the value of \fIT\fR\dm\\da\\dx\uof the process is set
at +3\ dBm0
(more accurately 3.14\ dBm0 for A\(hylaw and 3.17 for \(*m\(hylaw), then in
accordance with \(sc\ 3 of Recommendation\ G.121\ [7], the peak power of
the speech will be suitably controlled.
.bp
.RT
.sp 1P
.LP
5.3.2.4
    \fICompatibility of relative levels of analogue and digital\fR
\fIsystems\fR
.sp 9p
.RT
.PP
When the signal load is controlled as outlined in \(sc\ 5.3.2.3, points
of equal relative levels of FDM and PCM circuits may be directly connected
together and each will respect the other's design criteria. This is of
particular importance when points in the two multiplex hierarchies are
connected together by means of transmultiplexers, codecs or modems.
.RT
.sp 1P
.LP
5.3.2.5
    \fIDetermination of relative level\fR
.sp 9p
.RT
.PP
Figure 1/Q.43 illustrates the principle of how the relative level at the
input and output analogue points of a \*Qreal\*U codec can be
determined.
.RT
.LP
.rs
.sp 17P
.ad r
\fBFigure 1/Q.43, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
When using Figure 1/Q.43 to determine the relative levels of a
\*Qreal\*U codec with non\(hyresistive impedances at the analogue input
and output
ports, the following precautions must be observed:
.LP
    i)
    the test frequency should be 1000\ Hz with a suitable
offset;
.LP
    ii)
    the power at points \fIs\fR and \fIr\fR is expressed as
apparent power
, i.e.:
\v'6p'
.sp 1P
.ce 1000
Apparent power level = 10 log
\d10
\u
@ left [ { Voltage~at~point) \u2\d~\(mu~10~\u3\d } over { Modulus~of~nominal~impedance~at~1000\~Hz) (1~W) }  right ] @
dBm
.ce 0
.sp 1P
.LP
.sp 1
.LP
    iii)
    point r is terminated with the nominal design impedance
of the decoder to avoid significant impedance mismatch errors.
.PP
\fINote\fR \ \(em\ Precautions ii), iii) above are, of course equally
applicable to the case of resistive input and output impedances and would
generally be observed by conventional test procedures. Standardizing the
reference frequency as in\ i) above is, however, essential for complex
impedances because of the variation of nominal impedance with the test
frequency.
.LP
.sp 1P
.LP
5.3.2.6
    \fIRelative level of a point in a digital link\fR
.sp 9p
.RT
.PP
The relative level to be associated with a point in a digital path carrying
a digital bit stream generated by a coder lined\(hyup in accordance with
the principles of \(sc\ 5.3.2.3 above is determined by the value of the
digital
loss or gain between the output of the coder and the point considered.
If there is no such loss or gain the relative level at the point considered
is, by
convention, said to be 0\ dBr.
.PP
The equivalent absolute power level of a digital link may be
established as in Figure\ 2/Q.43 by using an
ideal decoder
. The relative level at a point\ X in the bit stream can then be assigned
by comparing the
power at the output of the ideal decoder with that at the analogue zero
relative level point originating the digital signal.
.bp
.RT
.LP
.rs
.sp 21P
.ad r
\fBFigure 2/Q.43, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
5.3.3
    \fBPCM digital reference sequence (DRS)\fR
.sp 9p
.RT
.LP
    \fIF:\ s\*'equence num\*'erique de r\*'ef\*'erence MIC\fR
.LP
    \fIS:\ secuencia de referencia digital MIC (SRD)\fR
.PP
5.3.3.1
A PCM digital reference sequence is one of the set of possible
PCM code sequences that, when decoded by an ideal decoder, produces an
analogue sinusoidal signal at the agreed test reference frequency (i.e.\
a nominal 800 or 1000\ Hz signal suitably offset) at a level of 0\ dBm0.
.PP
Conversely, an analogue sinusoidal signal at 0\ dBm0 at the test
reference frequency applied to the input of an ideal coder will generate
a PCM digital reference sequence.
.PP
Some particular PCM digital reference sequences are defined in
Recommendation\ G.711\ [6] in respect to A\(hylaw and \(*m\(hylaw codecs.
.RT
.LP
.PP
5.3.3.2
In studying circuits and connections in mixed analogue/digital
networks, use of the digital reference sequence can be helpful. For example,
Figure\ 3/Q.43 shows the various level relationships that one obtains
(conceptually) on a Type\ 2 international circuit where one end terminates
at a digital exchange and the other end at an analogue exchange. In the
example of Figure\ 3/Q.43, the analogue portion is assumed to require a
loss of 0.5\ dB and that provision for this loss is made by introducing
a 1.0\ dB pad (0.5\ dB for
each direction of transmission) in the receive direction at the analogue
exchange. This has been deliberately chosen to illustrate the utility of the
concept of a digital reference sequence.
.PP
Figure 3/Q.43 gives an example where all the analogue loss is
introduced in the output direction at the analogue exchange. In this case
the relative levels at the various codecs can be derived from either the
DRS or the transmission reference point at the input of the international
circuit with no ambiguity.
.PP
If, however, in Figure\ 3/Q.43 the analogue circuit section is lined up
so as to give an overall loss in the direction \fIb\fR\d1\u\(hy\fIa\fR\d2\u,
care must be
taken in the use of the DRS. In this case the 0\ dBm0 sinusoidal reference
signal and DRS may result in different levels at the point \fIa\fR\d2\u.
Account
should be taken of this effect when designing lining\(hyup procedures for mixed
analogue/digital circuits.
.PP
As a general principle, the relative levels on a mixed
analogue/digital circuit should be referred to the transmission reference
point at the input of the circuit.
.RT
.sp 1P
.LP
5.3.4
    \fBcircuit test access point\fR
.sp 9p
.RT
.PP
The CCITT has defined circuit test access points as being \*Q4\(hywire
test\(hyaccess points so located that as much as possible of the international
circuit is included between corresponding pairs of these access points
at the two centres concerned\*U. These points, and their relative
.bp
.PP
level (with   reference
to the transmission reference point), are determined in each case by the
Administration concerned. They are used in practice as points of known
relative level to which other transmission measurements will be related.
In other words, for measurement and lining\(hyup purposes, the relative
level at the appropriate circuit test access point is the relative level
with respect to which other
levels are adjusted.
.RT
.sp 1P
.LP
5.3.5
    \fIMeasurement frequency\fR
.sp 9p
.RT
.PP
For all international circuits 800 Hz is the recommended frequency  for
single\(hyfrequency maintenance measurements
. However, by agreement
between the Administrations concerned, 1000\ Hz may be used for such
measurements.
.PP
A frequency of 1000 Hz is in fact now widely used for single\(hyfrequency
measurements on some international circuits.
.PP
Multifrequency measurements made to determine the loss/frequency
characteristic will include a measurement at 800\ Hz and the frequency of the
reference measurement signal for such characteristics can still be 800\ Hz.
.PP
\fINote\ 1\fR \ \(em\ Definitions of \(sc\(sc\ 5.3.1 and 5.3.2 are used
in the work of Study Group\ XII. Definitions of \(sc\(sc\ 5.3.4 and\ 5.3.5,
taken from
Recommendations\ M.565\ [10] and\ M.580\ [11], are included for information.
.PP
\fINote\ 2\fR \ \(em\ In order to take account of PCM circuits and circuit
sections, the nominal frequencies 800\ Hz and 1000\ Hz are in fact offset by
appropriate amounts to avoid interaction with the sampling frequency. Details
can be found in Supplement No.\ 3.5 to Volume\ IV\ [12].
.RT
.LP
.rs
.sp 32P
.ad r
\fBFigure 3/Q.43, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
5.4
    \fIInterconnection of international circuits in a transit centre\fR
.sp 9p
.RT
.PP
In a transit centre, the virtual analogue switching points of the two international
circuits to be interconnected are considered to be connected
together directly without any additional loss or gain. In this way a chain
of international circuits has a nominal transmission loss in transit equal
to the sum of the individual circuit losses.
.RT
.LP
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIThe transmission plan\fR , Vol. III, Rec.\ G.101.
.LP
[2]
    CCITT Recommendation \fIAssumptions for the calculation of noise on\fR
\fIhypothetical reference circuits for telephony\fR , Vol.\ III, Rec.\
G.223, \(sc\ 1.
.LP
[3]
     CCITT Recommendation \fINoise objectives for design of\fR \fIcarrier\(hytransmission
systems of 2500\ km\fR , Vol.\ III, Rec.\ G.222.
.LP
[4]
    CCITT Recommendation \fIFDM carrier systems for submarine cable\fR ,
Vol.\ III, Rec.\ G.371.
.LP
[5]
    CCITT Recommendation \fIAssumptions for the calculation of noise on\fR
\fIhypothetical reference circuits for telephony\fR , Vol.\ III, Rec.\
G.223, \(sc\ 2.
.LP
[6]
    CCITT Recommendation \fIPulse code modulation (PCM) of voice\fR
\fIfrequencies\fR , Vol.\ III, Rec.\ G.711.
.LP
[7]
     CCITT Recommendation \fILoudness ratings (LRs) of\fR \fInational systems\fR
, Vol.\ III,
Rec.\ G.121,\ \(sc\ 3.
.LP
[8]
    CCITT Recommendation \fI12\(hychannel terminal equipments\fR , Vol.\ III,
Rec.\ G.232, \(sc\ 11.
.LP
[9]
    CCITT Recommendation \fIThe transmission plan\fR , Vol.\ III,
Rec.\ G.101, Figure\ 5/G.101.
.LP
[10]
    CCITT Recommendation \fIAccess points for international telephone\fR
\fIcircuits\fR , Vol.\ IV, Rec.\ M.565.
.LP
[11]
    CCITT Recommendation \fISetting up and lining up an international\fR
\fIcircuit for public telephony\fR , Vol.\ IV, Rec.\ M.580.
.LP
[12]
    \fITest frequencies on circuit routed over PCM systems\fR , Vol.\ IV,
Supplement\ No. 3.5.
.sp 2P
.LP
\fBRecommendation\ Q.44\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBATTENUATION\ DISTORTION\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.44''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.44    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBAttenuation distortion\fR
.sp 1P
.RT
.sp 1P
.LP
1.1
    \fIAll\(hyanalogue conditions\fR
.sp 9p
.RT
.PP
The design objectives recommended for carrier terminal
equipment by the Recommendation cited in\ [3] are such that for a chain
of six circuits, each equipped with a single pair of channel translating
equipments in accordance with that Recommendation, the network performance
objective for the attenuation distortion given by Figure\ 1/G.132\ [2]
will in most cases be met. The distortion contributed by the seven international
centres is thereby
included.
.PP
\fINote\fR \ \(em\ To assess the attenuation distortion of the international
chain, the limits indicated for international circuits in Recommendation\
G.151, \(sc\ 1\ [4] must not be added to the limits for international centres
mentioned in Recommendation\ Q.45. In fact, on the one hand, some exchange
equipment would be counted twice if this addition were made; on the other,
the specification
limits of Recommendation\ Q.45 apply to the worst possible connection through
an international exchange, while the maintenance limits of Recommendation\
G.151, \(sc\ 1 apply to the poorest international circuit. The specifications
of the
various equipments are such that the mean performance will be appreciably
better than could be estimated by the above\(hymentioned addition.
.RT
.sp 1P
.LP
1.2
    \fIMixed analogue/digital conditions\fR
.sp 9p
.RT
.PP
In the mixed analogue/digital period, it is expected that the
attenuation/frequency characteristics of the analogue carrier terminal
equipment that is to be used in international telephone connections will
continue to be governed by existing Recommendations that are relevant to
this type of circuit.
.bp
.PP
Where unintegrated PCM digital processes are to be included in
international telephone connections, it is recommended that the
attenuation/frequency characteristic of the bandpass filters associated with
such processes should comply with the more stringent version of
Figure\ 1/G.712\ [5]. The latter Recommendation applies specifically to cases
where integrated PCM digital processes are associated with trunk junctions
(toll connecting trunks), trunk circuits (intertoll trunks), and international
circuits.
.PP
With regard to the incoporation of unintegrated PCM digital processes in
local telephone networks, the required attenuation/frequency characteristics
of the bandpass filters involved are still under study.
.RT
.LP
.PP
\fB2\fR
The network performance objectives for the variation with
frequency of transmission loss in terminal condition of a worldwide 4\(hywire
chain of 12\ circuits (international plus national extensions), each one
routed over a single group link, are shown in Figure\ 1/Q.44 which assumes
that no use is made of high\(hyfrequency radio circuits or 3\(hykHz channel
equipment.
.sp 9p
.RT
.LP
.rs
.sp 18P
.ad r
\fBFigure 1/Q.44 p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fITransmission losses, relative levels and\fR
\fIattenuation distortion\fR , Vol.\ III, Rec.\ G.141.
.LP
[2]
    CCITT Recommendation \fIAttenuation distortion\fR , Vol.\ III,
Rec.\ G.132.
.LP
[3]
    CCITT Recommendation \fI12\(hychannel terminal equipments\fR , Vol.\ III,
Rec.\ G.232, \(sc\ 1.
.LP
[4]
     CCITT Recommendation \fIGeneral performance objectives applicable to
all\fR \fImodern international circuits and national extension circuits\fR
, Vol.\ III,
Rec.\ G.151, \(sc\ 1.
.LP
[5]
    CCITT Recommendation \fIPerformance characteristics of the PCM\fR
\fImultiplex at audio frequencies\fR , Vol.\ III, Rec.\ G.712.
.sp 2P
.LP
\fBRecommendation\ Q.45\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTRANSMISSION\ CHARACTERISTICS\ OF\ AN\ ANALOGUE\ INTERNATIONAL\ EXCHANGE\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.45''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.45    %'
.ce 0
.sp 1P
.PP
A new Recommendation Q.45 | fIbis\fR is published in the \fIBlue Book\fR
with terminology and structure consistent with Recommendations\ Q.551\(hyQ.554.
There are no changes of technical substance. Recommendation\ Q.45 in the
\fIRed\fR \fIBook\fR is adequate for existing references to Q.45.
.sp 1P
.RT
.LP
.bp