User guide

TD 92422GB
18 February 2010 / Ver. E
System Planning
Ascom IP-DECT System
6
5 Traffic Capacity of the System
The traffic capacity of the Ascom IP-DECT system is mainly determined by the number of
base stations and in exceptional cases also by the LAN bandwidth. A single base station
has a capacity of 8 simultaneous calls and a single gateway has a capacity of 40
simultaneous calls.
The traffic capacity of the Ascom IP-DECT system is determined by:
• Grade Of Service (GOS) accepted by the customer.
• Number of speech circuits available - 8 per IPBS/RFP, 40 per IPBL.
The grade of service is the probability that a call cannot be made because of congestion in
the system. The customer has to indicate which grade of service is acceptable. A grade of
service of 1%, or 0.01, means an average of 1 lost call in every 100 calls.
The two parameters mentioned above (GOS and number of speech circuits) and the total
amount of traffic (erlang) that is required, are related to each other. The table below
shows an except of these relations. Practically, this table is used to calculate from a given
GOS and erlang value the number of base stations needed. The erlang value is the total
traffic generated by all cordless phone users.
A base station provide for 8 speech circuits. The IPBL handle a maximum of 40.
Figure 2. .
The table below shows what erlang values practically mean in call-minutes for a cordless
phone.
Figure 3.
Number
of base
stations
Speech
circuits
Grade Of Service (GOS)
2% 1% 0.5% 0.1%
1 8 3.6 3.2 2.7 2.1
2 16 9.8 8.9 8.1 6.7
3 24 16.6 15.3 14.2 12.2
4 32 23.8 22.1 20.6 18.2
5 40 31.0 29.0 27.3 24.5
6 48 38.4 36.1 34.2 30.9
7 56 45.9 43.3 41.2 37.5
8 64 53.4 50.6 48.3 44.2
mE Minutes per hour mE Minutes per hour
50
100
150
200
3
6
9
12
250
300
500
750
15
18
30
45