Which best describes real-time-based IDS?

Real-time-based Intrusion Detection Systems (IDS) are designed to actively monitor and analyze network traffic as it occurs. This means that they assess data streams continuously rather than at fixed intervals or based on a schedule. By operating in real-time, these systems can identify and respond to potential threats immediately, making them crucial for detecting and mitigating attacks as they happen. This capability allows organizations to maintain a proactive security posture rather than reacting to events after they have occurred.

In contrast, the other options describe systems or processes that do not embody the characteristics of real-time monitoring. Fixed schedules indicate a lack of immediacy in response, while periodic data processing suggests that there could be delays in detection. Alerts for historically known attacks imply a reactive rather than proactive approach, which does not align with the essential function of real-time monitoring in effective cybersecurity strategies.