User guide

TD 92422GB
18 February 2010 / Ver. E
System Planning
Ascom IP-DECT System
7
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 base stations 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 base stations. The system shall be equipped with 3 base stations, offering
the client 14.4 E instead 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 base stations.
5.1 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 the table above. 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 in 5 Traffic Capacity of the
System, 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.