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1991-12-30
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Recommendation E.5101)
DETERMINATION OF THE NUMBER OF CIRCUITS
IN MANUAL OPERATION
1 The quality of an international manual demand service should be defined as the percentage of call requests which,
during the average busy hour (as defined later under
S 3) cannot be satisfied immediately because no circuit is free in
the relation considered.
By call requests satisfied immediately are meant those for
which the call is established by the same operator who
received the call, and within a period of two minutes from receipt
of that call, whether the operator (when she does not immediately
find a free circuit) continues observation of the group of
circuits, or whether she makes several attempts in the course of
this period.
Ultimately, it will be desirable to evolve a corresponding
definition based on the average speed of establishing calls in the
busy hour, i.e. the average time which elapses between the moment
when the operator has completed the recording of the call request
and the moment when the called subscriber is on the line, or the
caller receives the advice subscriber engaged, no reply, etc. But
for the moment, in the absence of information about the operating
time in the European international service, such a definition
cannot be established.
2 The number of circuits it is necessary to allocate to an
international relation, in order to obtain a given grade of
service, should be determined as a function of the total holding
time of the group in the busy hour.
The total holding time is the product of the number of calls
in the busy hour and a factor which is the sum of the average call
duration and the average operating time.
These durations will be obtained by means of a large number of
observations made during the busy hours, by agreement between the
Administrations concerned. If necessary, the particulars entered on
the tickets could also serve to determine the average duration of
the calls.
The average call duration will be obtained by dividing the
total number of minutes of conversation recorded by the recorded
number of effective calls.
The average operating time will be obtained by dividing the
total number of minutes given to operating (including ineffective
calls) by the number of effective calls recorded.
3 The number of calls in the busy hour will be determined from
the average of returns taken during the busy hours on a certain
number of busy days in the year.
Exceptionally busy days, such as those which occur around
certain holidays, etc., will be eliminated from these returns. The
Administrations concerned should plan, whenever possible, to put
additional circuits into service for these days.
In principle, these returns will be taken during the working
days of two consecutive weeks, or during ten consecutive working
days. If the monthly traffic curve shows only small variations,
they will be repeated twice a year only. They will be taken three
or four times a year or more if there are material seasonal
variations, so that the average established is in accordance with
all the characteristic periods of traffic flow.
4 The total occupied time thus determined should be increased by
a certain amount determined by agreement between the
Administrations concerned according to the statistics of traffic
1) This Recommendation dates from the XIIIth Plenary Assembly of the CCIF (London, 1946)
and has not been fundamentally revised since. It was studied under Question 13/II in
the Study Period 1968-1972 and was found to be still valid.
Fascicle II.3 - Rec. E.510 PAGE1
growth during earlier years, to take account of the probable growth
in traffic and the fact that putting new circuits into service
takes place some time after they are first found to be necessary.
5 The total holding time of the circuits thus obtained, in conjunction with a suitable table (see
Table 1/E.510), will enable the required number of circuits to be
ascertained.
6 In the international manual telephone service, the following
Tables A and B should be used as a basis of minimum allocation:
Table A corresponds to about 30% of calls failing at the first
attempt because of all circuits being engaged and to about 20% of
the calls being deferred.
Table B, corresponding to about 7% of calls deferred, will be
used whenever possible.
These tables do not take account of the fact that the
possibility of using secondary routes permits, particularly for
small groups, an increase in the permissible occupation time.
TABLE 1/E.510
Capacity of circuit groups
(See Supplement No. 2 at the end of this fascicle)
Table A Table B
Number of
circuits Percentage of Minutes of Percentage of Minutes of
circuit usage circuit usage circuit usage circuit usage
possible possible
in the busy hour in the busy hour
1 65.0 39 - -
2 76.7 92 46.6 56
3 83.3 150 56.7 102
4 86.7 208 63.3 152
5 88.6
PAGE1 Fascicle II.3 - Rec. E.510
266 68.3 205
6 90.0 324 72.0 259
7 91.0 382 74.5 313
8 91.7 440 76.5 367
9 92.2 498 78.0 421
10 92.6 556 79.2 475
11 93.0 614 80.1 529
Fascicle II.3 - Rec. E.510 PAGE1
12 93.4 672 81.0 583
13 93.6 730 81.7 637
14 93.9 788 82.3 691
15 94.1 846 82.8 745
16 94.2 904 83.2 799
17 94.3 962 83.6 853
18 94.4 1020
PAGE1 Fascicle II.3 - Rec. E.510
83.9 907
19 94.5 1078 84.2 961
20 94.6 1136 84.6 1015
Note - Tables A and B can be extended for groups comprising more than 20 circuits by using
the values given for 20 circuits.
Fascicle II.3 - Rec. E.510 PAGE1