Failures and changes in cellular access networks; A study of field data.

The operator diversity of different wireless and cellular networks integrated by IP-based networks does not imply independencies in the respective access networks. We have used incident and change records covering more than 1000 days from a GSM/UMTS network operator. Service failures vs. population density and time periodicity of failures have been studied. Our results indicate higher failure intensity in rural areas than in the urban areas and higher failure intensity during working hours. Leased services and power give major contributions to the failure intensity. This indicates dependencies between network operators. The operator staff's logged common root causes for failures show that the restoration times for the affected BTS/Node B are not identical. The number of changes in the network is significant compared to the number of failures. Our analysis does not indicate correlations between logged network changes and failures.