HTTP Status 204 (No Content) indicates that the server has successfully fulfilled the request and that there is no content to send in the response payload body.

RSSI, or "Received Signal Strength Indicator," is a measurement of how well your device can hear a signal from an access point or router. It's a value that is useful for determining if you have enough signal to get a good wireless connection.
This value is measured in decibels (dBm) from 0 (zero) to -120 (minus 120). The closer to 0 (zero) the stronger the signal is which means it's better, typically voice networks require a -65db or better signal level while a data network needs -80db or better.

Cisco Stealthwatch is a comprehensive, network telemetry-based, security monitoring and analytics solution that streamlines incident response through behavioral analysis; detecting denial of service attacks, anomalous behaviour, malicious activity and insider threats. Based on a scalable enterprise architecture, Stealthwatch provides near real-time situational awareness of all users and devices on the network.
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Note: Although answer A seems to be correct but in fact, Stealthwatch does not provide real-time protection for DDoS attack. It just helps detect DDoS attack only.
Stealthwatch aggregates observed network activity and performs behavioral and policy driven analytics against what it sees in order to surface problematic activities. While we don't position our self as a DDOS solution, we're going to leverage our analytical capabilities to identify a DDoS attack against an internal host using the WebUI.