What protocol is commonly used for managing network traffic effectively?

Quality of Service (QoS) is the correct protocol used for managing network traffic effectively. QoS refers to the set of technologies and standards that prioritize network traffic and guarantee a certain level of performance for critical applications. This is particularly important in scenarios where bandwidth is limited or when multiple types of traffic are competing for the same network resources.

QoS mechanisms can differentiate between various types of data streams, managing aspects such as bandwidth allocation, latency, jitter, and packet loss. By ensuring that high-priority traffic, such as voice over IP (VoIP) or video streaming, receives the bandwidth it needs, QoS helps maintain the quality of those services while also allowing other types of traffic to function effectively.

The other protocols listed serve different functions and, while they are essential for specific tasks (like transferring files or handling email), they do not directly manage traffic flow in a way that optimizes performance based on varying network conditions and demands. Therefore, understanding the role and functionality of QoS is key for effective network management and ensuring smooth operation of critical applications.