14
Projecting the DECT network
The capacity must always be adjusted to the highest possible traffic volume if
capacity bottlenecks are to be excluded.
Traffic volume
The traffic volume is expressed in "erlangs (E)". One erlang corresponds to the continuous
full capacity utilisation of one connection channel in a specific period. Erlangs are usually
calculated over an observation period of one hour. Accordingly, the occupation of a con-
nection channel over one hour equals one erlang.
For example: if all eight connections of a base station are continuously occupied, this corre-
sponds to eight E. If a connection is occupied for 20 minutes, this corresponds to 1/3 E.
Examples:
Let us assume that 500 calls lasting 3 minutes each are made within one hour.
500 x 3 min/60 min = 25 E
Therefore, at least 25 connection channels, i.e., four base stations (in
),
would be necessary for this call volume.
However, this only applies if the grade of service is less than 4%. With a grade of service
of 4%, you need only three base stations, i.e., 24 connection channels. With a grade of
service of 4%, it is permissible for 20 calls from 500 not to be established. This means that
only 480 connections have to be achieved. The calculation is as follows:
480 x 3 min/60 min = 24 E
Since the traffic volume is not normally evenly distributed over the site to be covered, the
traffic volume must be calculated for each area (offices, reception, hotspots, stairwell, etc.)
in order to determine the relevant number of base stations that need to be installed.
Grade of
service
Calls at 3 min. per hour
The table contains some
sample values for the calcula-
tion of the traffic volume
depending on the grade of
service, call duration and
number of calls per hour.
Using the data you have
determined about the
telephony behaviour, you
can realistically estimate
your requirements.
10
50
100
500
0 %
0.5 E
2.5 E
5 E
25 E
2 %
0.49 E
2.45 E
4.9 E
24.5 E
4 %
0.48 E
2.4 E
4.8 E
24 E
Grade of
service
Calls at 15 min. per hour
10
50
100
500
0 %
2.5
E
12.5
E
25
E
125
E
2 %
2.45
E
12.25
E
24.5
E
122.5
E
4 %
2.4
E
12
E
24
E
120
E
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