In many practical cases, this definition needs to be further expanded with a number of detailed specifications describing which calls exactly are counted as successfully set up and which not.
The call setup success rate in conventional (so-called land-line) networks is extremely high and is significantly above 99.9%.
In mobile communication systems using radio channels the call setup success rate is lower and may range for commercial networks between 90% and 98% or higher.
The call setup success rate is usually included, together with other technical parameters of the network, in a key performance indicator known as service accessibility.
The operators of telecommunication networks aim at increasing the call setup success rate as much as practical and affordable.