Impact weighted uptime in hierarchical LTE networks: Application and measurement

Abstract

The success of 4G LTE networks will depend upon the quality of new real-time high bandwidth applications like streaming video, on-line gaming, and Telepresence. These applications are very sensitive to short duration outages (SDOs) of network elements. The classical availability metric is not adequate for 4G LTE network evaluation because it is not sensitive enough to SDOs. We introduce a new metric: the Impact Weighted Network Uptime (IWNU), whereby uptime at each hierarchical level is weighted by the respective number of base stations affected as a result of that level failure. We illustrate its usefulness for segments of LTE networks having up to three levels of hierarchy. The reliability model of each hierarchical level is described by an absorbing Markov chain whose absorption states correspond to failures affecting base stations. We use the level uptime to compare different redundancy configurations at upper hierarchical levels and provide numerical results demonstrating that additional redundancy may not visibly increase the level uptime in the presence of silent failures which are not immediately detected. We propose also a new method for tracking the field reliability of the 4G LTE service by utilizing existing software features and protocols readily available within Cisco network elements. Service impacting hardware and software outages are registered by this method with an accuracy of one second. The outage data is then used for calculation of the downtime and the proposed IWNU metric which are not currently automated by any tool.