Which of the following provides a mechanism to prioritize traffic in DiffServ?

The correct choice is PHB, which stands for Per-Hop Behavior. In the Differentiated Services (DiffServ) architecture, PHB defines how packets are treated as they pass through each router in a network. This treatment allows for prioritization of various types of traffic based on their designated class of service.

PHBs are crucial because they provide a standardized way to handle packets, enabling devices on the network to implement different levels of service based on specific criteria, such as delay sensitivity or bandwidth requirements. For example, voice traffic can be assigned a higher priority over best-effort traffic, ensuring that time-sensitive data is transmitted with minimal delay.

While traffic classes, QoS (Quality of Service), and IPsec play roles in network traffic management and security, they do not directly define the mechanisms used for prioritizing traffic within the DiffServ framework. Traffic classes refer to the classification of data flows for treatment but don't dictate how those flows are managed at each router hop. QoS is a broader concept that encompasses various techniques and mechanisms to manage network resources but does not specifically refer to the behaviors at each hop. IPsec primarily deals with securing internet protocol communications rather than traffic prioritization.