Gigaset N870 IP Pro Site Planning And Measurement Manual page 20

Projecting the DECT network
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Grade of Service, GoS
The grade of service determines the number of connections that may not be achieved due
to the system being at full capacity, i.e., the line is engaged. A grade of service of 1% means
that out of 100 calls, one cannot be connected for capacity reasons.
The capacity required can be determined using these two factors and the traffic volume expected.
Please note that the volume of traffic can vary during the course of the day.
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 connection channel
over one hour equals one erlang.
For example: If all 8 connections of a base station are continuously occupied, this corresponds
to eight E. If a connection is occupied for 20 minutes, this corresponds to 1/3 E.
Example calculation
Calculation details:
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It is a multi-cell system with only one DECT manager. The DECT manager system includes no
base station, i.e. it is provided as a separate Gigaset N870 IP PRO device. All other devices only
include one base station.
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Narrowband connections with codec G.711 or G.729 are permitted, i.e. the base stations each
have 8 connection channels.
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The overall system makes available a maximum of 60 connection channels.
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1000 calls (of 3 minutes each) are accepted in 1 hour.
Other connection requirements are also taken into account here.
Calculation: 1000 x 3 min/60 min = 50 E
So for the volume of traffic accepted, at least 50 connection channels would be necessary
(i.e. 7 (6.25) base stations).
However, this only applies if the grade of service is less than 4%. With a grade of service of 4%,
you only need 48 connection channels, i.e. 6 base stations. With a grade of service of 4%, it is
permissible for 4% of 1000 calls (40 connections) not to be established. This means that only
960 connections have to be achieved.
The calculation is as follows: 1120 x 3 min/60 min = 48 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.
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