Contents Telektronikk - Telenor

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Figure 8 The weights of hours, overlapping more or less with the average
day’s peak-hour [7]
8), the average day’s peak-hour overlaps
with the peak-hours of zero to nine
round’s days (1 to 8.25), averaging 4.86
(4.52) days. Thus it can be said that the
average day’s peak-hour represents two
of the round’s ten days’ peak-hours precisely,
a little for nearly three further
days, but not at all in the remaining over
five days.
The measurement round’s individual and
average days’ profiles are illustrated for
two different circuit-groups, Figures 9
and 10.
It is seen that in tightly dimensioned
first-choice circuit-group the daily variations
are limited by the number of circuits
(Figure 9), and the average day’s
peak-hour is not far from the individual
peaks. But the last-choice circuits, especially
if they are loosely dimensioned,
can have large daily variations, substantially
exceeding the average day’s peak
values (Figure 10). Then the days’ peaks
can hardly be expected by using the average
day. The averaging over the round’s
days just destroys the valuable information
about peak values. In such a case the
average day does not give any advice for
quality setting, dimensioning or optimising.
– Here is an example showing that
the dimensioning hour definition is more
important than the distributions during
that hour.
The validity of ElCo about average day is
quite weak, being an exception, not the
rule. In addition, the average day destroys
the most important dimensioning information.
Therefore, one may ask if there is
any real use of the average day concept.
One usage for the average day per
exchange was presumably in producing
the manual exchange operator’s working
hour schedules. The circuit-group’s average
day’s profile might be used in network
management to schedule daily
reroutings in those few cases only, where
all the week day profiles are similar. But
there is no use for the average day in normal
circuit-group dimensioning.
6 The ideality of traffic
during the peak-hour
The ElCo about peak-hour’s model is
that during the days peak-hour the offered
traffic is in a statistical equilibrium
and its distribution is ideal (Poissonian).
If the ElCo about peak-hour’s model is
valid, the simple mathematical models
about quality relations apply. The most
favoured model is the Erlang B-formula
with its derivatives in waiting and overflow
technologies.
The study object in Helsinki local network
was the Sörnäinen AKE-transit
exchange having 120 circuit-groups. The
fortnight measurement rounds in quarterhours
lasted daily from 8 a.m. to 10 p.m.
The measurements were carried out in
May 1988, totalling 110 000 quarterhours.
The complete study is published in
[7].
In order to have a reference level, a
“Class 1” Poisson distribution’s processdistinctive
natural “basic” variation D is
defined. The observed differences are
Υ
Erl
40
30
20
10
0
Υ
Erl
60
50
40
30
20
10
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8 10 12 14 16 18 20 t
8 10 12 14 16 18 20 t
Figures 9 and 10 A typical ten days’ three-top (A) or
two-top (B) average intensity profile -o- with its daily
variations, measured in May 1985. Peak-hours per
day are marked by x. Note the limited variations in
highly loaded 45 circuits first-choice circuit-group
(A), and the wide variations in the loosely dimensioned
90 circuits last-choice circuit-group [7]
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