Which DSCP per-hop forwarding behavior is divided into subclasses based on drop probability?

Expedited Forwarding (EF) is a single, high-priority PHB designed for minimal delay and loss, and it is not divided into subclasses based on drop probability.

Default Forwarding (DF) represents best-effort traffic and does not have subclasses or differentiated drop probabilities.

Assured Forwarding (AF) is a DiffServ per-hop behavior (PHB) that is divided into four classes, with each class having three associated drop precedence levels (low, medium, high). This allows network devices to prioritize traffic within a class based on its drop probability during periods of congestion, offering differentiated forwarding treatment.

Class-Selector (CS) DSCP values are primarily for backward compatibility with IP Precedence and do not define subclasses based on drop probability in the same manner as Assured Forwarding.