Nortel Networks DCT1900 - Manual (Page 132)

Technical Product Manual - DCT1900
Configuration Directions, Traffic Capacity of the System
5-2 Config-DCT1900/R8/mw
© 2000-2005
As a RE can handle only as many simultaneous calls as the number of available speech circuits
while the number of Portable Telephones in the respective coverage area can be as many as 600,
a lack of speech circuits may occur in some occasions. To limit these occurrences, take into
account the number of regular (home) Portable Telephone users plus the maximum number of
visiting Portable Telephone users at a certain time while determining the required traffic capacity.
Table 5–2 shows what Erlang values mean in call–minutes for a Portable Telephone.
Table 5–2 Erlang Values Expressed in Call–Minutes
Example: A customer ordering a system that can handle 55 Portable Telephones (local users
and visiting users), generating 200 mE each in average, requires a system with a
traffic capacity of 11 E. With an accepted GOS of 0.5% the number of SPUs/SLUs is
found as follows:
The total traffic is 11 E. In the column of 0.5% GOS, the next higher value of 11 E is
14.2 E, resulting in 3 SPUs/SLUs.
So, the system should be equipped with 3 SPUs/SLUs, offering the client 14.2 E
instead of 11. This means that the system has an over–capacity 3.2 E, which allows
expansion of the system with 16 Portable Telephones without reducing the GOS or the
need of more SPUs or SLUs.
According to Table 5–1 60 circuits with an accepted GOS of 0.5% result in a maximum traffic
capacity of the system of 44.8 E. When each Portable Telephone generates 150 mE in average,
the system has a capacity of serving approximately 300 Portable Telephones.
5.2 Traffic Capacity of the Base Stations
The total traffic that is being generated by all Portable Telephones (visiting Portable Telephones
included) of the system should be in accordance with the capacity of the cordless network as well.
A Base Station, having 8 channels available, has an Erlang value of 2.7 with a GOS of 0.5%. This
value can be read from the Table 5-1. This means that each Base Station can serve 18 Portable
Telephones, assuming that Portable Telephones generate 150 mE each during busy hours (13.5
Portable Telephones if 200 mE each).
Example: Suppose that in the building of the customer in the example in paragraph 5.1, full
coverage can be achieved by 4 Base Stations. This means that all Portable
Telephones generate together 55 x 0.200 = 11 E, while the Base Stations traffic
capacity is only 4 x 2.7 = 10.8 Erlang. This is too little. This discrepancy can be solved
by adding another Base Station near the busiest part of the building.
From an average point of view, the total capacity offered by the cordless network is generally more
than sufficient. In certain places, traffic demands may vary such that locally the network is often
blocking, or has a lower GOS than required. For instance, a purchasing department may easily
generate 300 mE per Portable Telephone during a busy hour, with 6 persons giving a very high
mErlang Minutes per hour mErlang Minutes per hour
50
100
150
200
3
6
9
12
250
300
500
750 15
18
30
45