Nortel Networks DCT1900 - Manual (Page 131)

Technical Product Manual - DCT1900
Configuration Directions, Traffic Capacity of the System
Config-DCT1900/R8/mw/ 5-1
© 2000-2005
C HAPTER 5
Traffic Capacity of the System
The traffic capacity of the DCT1900 system is mainly determined by the RE and in exceptional
cases also by the Base Stations. The RE can handle a maximum of 60 simultaneous calls, and a
single Base Station has a capacity of 8 simultaneous calls.
5.1 Traffic Capacity of the Radio Exchange
The traffic capacity of the RE is determined by:
z Total traffic (Erlang)
z The GOS accepted by the customer.
z The number of speech circuits available, with a limit of 60.
Erlang is a measurement of telphone traffic. One Erlang is equal to one full hour of use, or 60 x 60
= 3,600 seconds of phone conversation. You convert CCS (hundred call seconds) into Erlangs by
dividing by 36.
The GOS is the probability that a call cannot be made because of congestion in the system. The
customer has to indicate which GOS is acceptable. A GOS of 1%, or 0.01, means an average of 1
blocked call in every 100 calls.
SPU and SLU boards provide for 8 speech circuits. When a total of 8 SPU and SLU boards are
installed, then 64 circuits are available, of which only 60 can be used simultaneously, as the
DCT1900 system can handle only a maximum of 60 simultaneous 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. Table 5–1 below shows how these
parameters are related for certain values. This table is used to calculate from a given GOS and
Erlang value the number of SPUs/SLUs needed. The Erlang value is the total traffic generated by
all Portable Telephone users (including visiting Portable Telephone users) in the coverage area of
the system.
Table 5–1 Erlang Table–B values for given GOS and Number of Speech Circuits
GOS (GOS) Number of
SPUs/SLUs
Speech
circuits
2%
(1/50)
1%
(1/100)
0.5%
(1/200)
0.1%
(1/1000)
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 60 49.7 46.9 44.8 40.8