Which statement about QoS is true?

• A. QoS can control bandwidth.
• B. QoS can assign protocols dynamically.
• C. QoS can replace physical links.
• D. QoS can eliminate congestion completely.

Answer: (A)

Quality of Service focuses on how bandwidth is allocated among different traffic flows to meet performance needs. QoS can reserve, guarantee, or restrict the amount of bandwidth available to specific classes of traffic, using mechanisms like traffic shaping, policing, and various queuing/scheduling methods. This is why the statement about QoS that it can control bandwidth is the best choice: it directly reflects how QoS influences the actual capacity available to different traffic streams and enforces those limits or guarantees as traffic traverses a network.

QoS doesn't dynamically assign protocols; it classifies and treats traffic already using the network, but it doesn't switch or pick protocols on its own. It can't replace physical links or increase total network capacity. And even with QoS in place, congestion can't be eliminated entirely—what QoS does is manage it to reduce delays and packet loss for high-priority traffic, while lower-priority traffic may still experience slowdown when the network is congested.