Product manual
Configuration directions, Traffic capacity of the system
Technical Product Manual - DCT1800-GAP
TD 92093 (1/LZBNB 103 108 R4D) / 2006-03-09/ Ver.C
© 2006
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Example:
A customer ordering a system with 55 cordless phones, 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
SPU-Ss/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 SPU-Ss/SLUs.
So, the system shall be equipped with 3 SPU-Ss/SLUs, offering the client 14.4 E in stead of 11.
This means that the system has an over-capacity 3.2 E, which allows expansion of the system
with 16 cordless phones without reducing the grade of service or the need of more SPU-Ss or
SLUs.
According to table 5, 60 circuits with an accepted GOS of 0.5% result in a maximum traffic capacity
of the system of 44.8 E. When each cordless phone generates 150 mE in average, the system
has a capacity of serving approximately 300 cordless phones.
6.2 Traffic capacity of the base stations
The total traffic that is being generated by all cordless phones of the systems 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 table
5. This means that each
base station can serve 18 cordless phones, assuming that cordless phones generate 150 mE each
during busy hour, (13.5 cordless phones if 200 mE each).
Example:
Suppose that in the building of the customer in the example of paragraph 6.1, full coverage can
be achieved by 4 base stations. This means that all cordless phones 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 nearby the busiest part of the company.
Practically, the total capacity offered by the cordless network is generally more than sufficient,
but this is from an average point of view. On certain places, traffic demands may vary such that
locally the network is often blocking, or has a lower GOS than required. For instance a purchase
department may easily generate 300 mE per cordless phone during busy hour, thus, when e.g.
with 6 persons giving a very high load on the base station close by. It may be necessary to add
a base station in this area to have enough capacity for others to call as well. Also think of e.g.
canteens during lunch time etc.
6.3 Traffic capacity of the system
Above the traffic capacity limitations of both the radio exchange and the cordless network are
discussed. A user making calls will first face a blocking chance by the cordless network and then face
another blocking chance by the system. These two parameters are statistically independent and should
therefore be summed to find the overall blocking probability of the system.
Practically this means that when an overall GOS is 0.5% is required, the system must be configured
such that the GOS of the radio exchange summed with the GOS of the network together result in a
GOS of 0.5%. For example, the radio exchange has a GOS of 0.25% and the network as well.