Kyle is an IT consultant working on a contract for a large energy company in Houston. Kyle was hired on to do contract work three weeks ago so the company could prepare for an external IT security audit. With suggestions from upper management, Kyle has installed a network-based IDS system. This system checks for abnormal behavior and patterns found in network traffic that appear to be dissimilar from the traffic normally recorded by the IDS. What type of detection is this network-based IDS system using?