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The ElCo about peak-hour concentration
supports the pre-selection of the measurement
hour.
The study object in Helsinki local network
was the Sörnäinen AKE-transit
exchange with its 120 circuit-groups. The
fortnight measuring rounds lasted daily
from 8 a.m. to 10 p.m. in quarter-hours.
The measurements were carried out in
May 1988, totalling 110,000 quarterhours.
The complete study is published in
[7].
The peak loads outside the peak-hour
were classified as mild peaks, having an
intensity less than the peak-hour average
plus basic variations, and as higher
strong peaks. It was seen that
- 32 % of the circuit-groups had no outside
peaks
- mild peaks were found in 34 % and
strong peaks in the 44 % of circuitgroups
during at least one day
- due to the peak quarter-hours aside the
peak-hour, the peak-hours measured
on quarter-hour basis give on average
4.0 % higher intensity than on full
hour basis
- strong peaks were found in 20.3 % of
days on average in last-choice circuitgroups
but 1.5 % in first-choice and
8.25 % of single circuit-groups. This
might be caused more by the tightness
of the dimensioning than by the role of
the circuit-group, but this aspect has
not been studied
- the day’s outside peaks were primarily
not near the peak-hour, as the so-called
side-hour concept supposes. It might
work in that direction on the average
day, which might be the reason why it
is favoured when the peak-hour is
timed on quarter-hour basis on the
average day. It does, however, not help
much with the uselessness of the average
day.
Thus, the ElCo about peak-hour concentration
can be seen to be valid in every
third case only.
8 Comparison of some
measurement routines
Caused by the phenomena described
above, the choice of the measurement
routine influences the produced intensity
values. The measurement routines are
non-continuous, scheduled according to
the expected peak loads, or continuous,
the relevant information about peaks cho-
60 70 80 90 100 110 % TCBH
sen afterwards by data post-processing.
Scheduling concerns the year and/or the
day. The several e.g. fortnight measurement
rounds can be grouped in some way
over the seasons. The measurement periods
of the day define the scheduled routines.
The following measurement routines,
included in the ITU-T (late CCITT) recommendation
E.500, are compared by
their measured intensity values:
- The continuous post-selected peakhour
of the average day TCBH (Time-
Consistent Busy Hour) on quarter-hour
basis. (The name is misleading in
many ways; a better one were Peak-
Hour of the Average Day, PHAD)
- Average of continuously measured
post-selected peak-hours ADPH (Average
of Day’s Peak-Hours) on full hour
basis
- Pre-selected measurement hour FDMH
(Fixed Daily Measurement Hour), the
hour selected earlier by the TCBHroutine
- Peak-hour of the average day’s preselected
measurement hours FDMP
(Fixed Daily Measurement Period).
The study object in Helsinki local network
was the 115 circuit-groups in the
Sörnäinen AKE-transit exchange. The
measured fortnight rounds lasted daily
from 8 a.m. to 10 p.m., in quarter-hours.
The measurements were carried out in
August and November 1985, totalling
nearly 600 kEh per round. The complete
study is published in [6].
When the result of TCBH-routine is used
as reference (= 100 %), the other routines
give values as in Figure 12, describing
averages of the August and November
ADP H/Q
ADP H/F
indiv. FDMP 3h
" FDMH 1h
comm. FDMP 3h
" FDMH 1h
Figure 12 Intensity values, measured in different continuous and noncontinuous routines,
as percentages of the TCBH intensities -o-, with the confidence limits [6]. The
ADPH is presented in two versions, namely measured by quarter-hour /Q or by full
hour /F basis
measurements, and the typical variation
limits (until 2s or 100 %) are given. The
circuit-groups’ intensities are combined
without any weighting. The non-continuous
measurements were scheduled
according to the peak-hour of the earlier
measurement of each individual circuitgroup,
or for the exchange commonly.
The continuous TCBH- and ADPH-routines
give thus very similar results, and the
same dimensioning rules and tables have
been recommended for both of them [2].
But the TCBH is not usable if the day
profiles in the round differ remarkably, as
is the rule e.g. by weekend peaks and lastchoice
overflow circuit-groups. The
scheduled routines can occasionally give
results high enough, but mostly their average
is clearly below the real load, 10 to
20 %. The occasional underestimate can
be up to 20 or 40 %, or even more. There
is no means of identifying afterwards
which ones of the circuit-groups were
underestimated. – In this comparison the
circuit-groups having tight or loose
dimensioning were not distinguished; the
results present their total. Presumably a
loose dimensioning causes more differences
of the intensities, produced by different
routines, than a tight dimensioning.
9 Measurements of
overflow cluster for
optimising
A single circuit-group is dimensioned
according to its service goal. But in the
overflow clusters the aim has not only
service as its goal, but an optimum of the
total cost, covering investments and
usage of all first and last choice circuits
of the cluster. Compared with a radial
network structure, the direct route (e.g.
the first choice circuit-group) causes a
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