other possible causes
– Abis link is intermitent
– Someone resetted softwares in the BTS, from OMC, so all calls are dropped(= maintenance actions)
– There is some hardware issues with the combiner, TRX or clock/controller, leading to degraded calls handling.
– Mobile phone failure (but that won’t appear in statistics, because all mobile phones don’t just crash at the same time… but it can happen during the drive tests, your test mobile phone can crash / connection issues)