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5.Proposed additions and revisions to Recommendation M.580
SETTING UP AND LINING UP OF AN
INTERNATIONAL CIRCUIT FOR PUBLIC TELEPHONY
Add the following text as a new sub-paragraph to 1 of M.580:
"As an alternative to the procedures given in 7 to 14 which require
testing personnel to be present at both ends of the circuit, 15 gives a
procedure involving the use of the CCITT Automatic Transmission Measuring and
Signalling Testing Equipment (ATME) No. 2 (Recommendation O.22) (with type a responding
equipment) which may be used subject to the agreement of the administrations
involved."
To 7 add a footnote to the heading of this paragraph consisting of the
following:
"The procedure given in 15 may be followed as an alternative to those
given in 7 to 14 if agreement has been reached with the distant administration
to use ATME No. 2 for lining up, measurement of circuit noise and functional
tests. It should be noted that this procedure does not include the tests in 12. The
administrations involved should consider scheduling such tests, if applicable,
when cooperative effort can be arranged."
Replace the existing note to Table 4/M.580 by the following one:
"Note - At the present time the section of a circuit provided by a satellite
employing FDM techniques with an earth station at its receiving end of INTELSAT
Standard A (Figure of merit 40.7 dB/k) or Standard C (Figure of merit 39.0 dB/k)
contributes approximately 10,000 pWOp (-50 dBmOp) of noise. The noise contributed by
earth stations with revised figures of merit are for further study. Therefore,
for the purpose of determining maintenance limits for noise measurements on
international public telephony circuits, the length of this section may be considered to
be equivalent to a terrestrial length of 2,500 km.
The section of a circuit provided by a satellite employing FDM techniques with
an earth station at its receiving end of INTELSAT Standard B contributes
approximately 80,000 pWOp (-41 dBmOp) of noise for FM companded circuits. The methods of
determining total distortion and/or noise objectives for such a circuit are given
in Recommendation M.590.
The contribution to noise of a circuit section provided by a satellite employing
TDM techniques remains a subject for further study."
Paragraph 8
Insert new sub-paragraph 8.1:
"8.1 Where a circuit is routed via a circuit multiplication system employing
digital speech interpolation techniques it may not be possible to make a reliable
noise test using the method described in this paragraph. In this case, a total
distortion measurement should be made instead, as described in 9.3."
All existing sub-paragraphs in 8 should be renumbered accordingly.
Insert a new 9 as follows:
"9. Measurement of total distortion
9.1 General
This measurement is required for composite (i.e. mixed analogue/digital)
circuits only. The measurement of total distortion should be made for both
directions of transmission.
The measuring equipment should be as specified in
Recommendation 0.132. [6].
The measuring equipment should be applied at the circuit access points.
A test frequency of 1 020 Hz should be used.
It is assumed that the measurements and adjustments outlined in 7.2.2
and 7.2.3 above have already been carried out.
9.2 Measurement of total distortion using a test signal level of -10 dBm0
9.2.1 The results of the total distortion measurement should be compared with
the total distortion objectives shown in Table 5/M.580 according to the number of
Quantizing Distortion Units (QDUs) in the circuit and the total length of the
analogue circuit sections.
9.2.2 If these objectives are exceeded by a circuit which has satisfied the
noise objectives described in 8, then a fault on a digital equipment causing
excessive quantizing distortion should be suspected.
9.3 Measurement of total distortion using a test signal level of -25 dBmo
9.3.1 On circuits routed via a circuit multiplication system employing digital
speech interpolation, this measurement may be regarded as a substitute for a
measurement of circuit noise. The results of the measurement should be compared with
the objectives shown in Table 6/M.580.
9.3.2 If the measured total distortion is higher by 5 dB or more than the
appropriate value from Table 6/M.580 or is higher than -37 dBm0p, whichever is the
more stringent requirement, on a circuit which has satisfied the test in 9.2
above, then a fault on an analogue circuit section causing excessive noise should be
suspected.
9.3.3 For maintenance purposes a measurement of total distortion using a
-25 dBm0 signal level can be useful on all composite circuits. In conjunction
with a measurement using a -10 dBm0 signal level it may be possible to identify
whether a fault lies in an analogue or digital circuit section from end-to-end
measurements using the same instrument.* If the circuit satisfies the objectives of
Table 5/M.580 but exceeds the objectives of Table 6/M.580, a faulty analogue circuit
section should be suspected. Conversely, if the objectives of Table 6/M.580 are
satisfied but those of Table 5/M.580 are not, faulty digital equipment is likely.
* Note - If the number of QDUs is 4 and the analogue noise level is -55 dBm0p,
this procedure will produce less accurate results. In this case, a -30 dBmO
test tone will be appropriate to check the analogue section, when a circuit is not
fitted with an echo-canceller or the echo canceller can be disabled."
Existing 9 to 11 should be renumbered 10 to 12. The note under
existing 9 should be deleted.
In 12.3 (old 11.3):
- replace the word "suppressors" with "control devices";
- add the following:
"In addition, a check of the echo control device with the
corresponding tester as specified in Recommendations O.22
and O.25 should be made if available."
Introduce the following new 13:
"13. Echo canceller test capability
When echo cancellers are fitted to a circuit, tests by other
administrations using test facilities specified in Recommendation O.22, can
successfully be carried out only if the canceller stages and echo path
delay characteristic are programmed into the test sequence. Therefore,
the administration placing echo cancellers in their international
switching centre should so apprise the other administration(s). This may be done
by a specific communication, for example a telex message, or by
including such information with the exchange of routine maintenance schedules
(Recommendation M.605)."
Renumber the existing 12 to 14, Record of results.
Add the following new paragraph after 14:
"15. Setting-up and lining-up an international circuit using ATME
15.1 The following procedure should be followed when it has been agreed
between the administrations concerned that ATME No. 2 can be used.
Generally, it is suitable only when there are no intermediate circuit sub-control
stations and for circuits which do not have particular measurement
requirements (see 9).
15.2 Setting-up the circuit
The circuit control and sub-control stations in conjunction with their
testing points should ensure that all associated signalling, switching and
other terminal equipment has been connected, is free from faults and is operating
satisfactorily. This should include the check of signalling level specified in
10. The sub-control station should advise the control station that these checks
have been made.
15.3 Lining-up the circuit
On receiving the advice from the sub-control station, the control
station should test the circuit using ATME No. 2. The time at which the tests are
performed should take into account the availability schedules of the ATME No. 2
responding equipments and the period of peak traffic at the distant terminal
exchange (see Recommendation M.150, 3). The ATME No. 2 should be programmed to
perform the full range of transmission measurements and signalling tests.
If the transmission level in the receive direction at the control
station is not within ± 1 dB of its nominal level, the level should be adjusted to
within ± 0.3 dB of its nominal level, and the circuit should then be retested.
If the transmission level in the receive direction at the sub-control
station distant end is not within ± 1 dB of its nominal level or if any of the
other limits specified in the Recommendation are not met in either direction of
transmission, then the procedures given in 7 to 12 should be followed.
When the ATME No. 2 tests have been successfully completed, the control
station informs the sub-control station of the results.
15.4 Recording of results
The control station should record all results given by ATME No. 2 for
both directions of transmission."
Include the following two new Tables 5/M.580 and 6/M.580 in the
Recommendation and renumber existing Tables 5/M.580 to Table 7/M.580. Existing
references should be amended.
15.5 Other tests
When the line-up procedure, as described above, has been completed, a
check should be made of the functioning of the compandors, where appropriate, in
accordance with Recommendation M.590. This should be followed by a speaking test
including a check of the satisfactory operation of echo suppressors and echo
cancellers.