Certified Information Systems Security Professional (CISSP) Practice Exam

The PSH (Push) flag in the Transmission Control Protocol (TCP) indicates that the sender has additional data that should be immediately delivered to the receiving application without waiting for the TCP buffer to fill up. When the PSH flag is set in a TCP segment, it signifies that the data is ready for processing and should be pushed up to the application layer as soon as possible. This is particularly important for applications that require real-time data or cannot afford delays, such as video streaming or online gaming.

In practice, setting the PSH flag is about ensuring timely delivery of data segments that the sender considers urgent, effectively prompting the receiving TCP stack to pass the data to the application layer immediately rather than buffering it for later delivery. This mechanism helps maintain the responsiveness and efficiency of network applications.

The other options pertain to different aspects of TCP operations, which do not accurately describe the function of the PSH flag. For example, the termination of a connection involves other flags, like FIN, while requesting additional data transmission typically uses acknowledgment signals rather than a specific flag. Prioritizing traffic is also not a function of the PSH flag; instead, this would generally be managed at other layers or through Quality of Service (QoS) policies.