Identify a component of Intrusion Detection Systems (IDS).

• A. Transmission Line
• B. Firewall
• C. Encryption module
• D. Sensor node

Answer: (A)

In intrusion detection systems, data collection through sensors is a fundamental building block. A sensor node is placed on the network or on hosts to observe activity—such as network traffic, log entries, or system calls—and to collect the information the IDS analyzes to spot unusual or malicious behavior. This data flows to the analysis component, which looks for patterns, anomalies, or known signatures to generate alerts.

Why the other options aren’t components of an IDS: the transmission line is simply the physical medium that carries communications, not a part of the IDS structure. A firewall is a separate security device that blocks or allows traffic based on rules and is not an IDS component. An encryption module is used to protect data's confidentiality and integrity, not to detect intrusions.

So the best answer is the sensor node, as it directly provides the observability that an IDS relies on to detect threats.