What technique is primarily used to understand network performance and security?

Network Traffic Analysis is primarily used to understand network performance and security because it involves monitoring, capturing, and analyzing data packets as they traverse through the network. This technique provides insights into the behavior of network applications, identifies performance bottlenecks, and helps detect anomalies that may indicate security threats or breaches. By assessing metrics such as bandwidth usage, packet loss, and response times, this analysis enables network administrators to optimize performance and strengthen security measures.

In contrast, Deep Packet Inspection focuses more on examining the contents of data packets beyond just headers, which is beneficial for detailed inspection but is a subset of what network traffic analysis encompasses. Watermarking and Document Matching are unrelated to network performance or security; they concern information security and data integrity in digital content but do not address network monitoring or performance assessment. Therefore, Network Traffic Analysis is the most comprehensive technique for gaining an understanding of both network performance and security.