RFC 2597 defines a group of DSCP settings called “Assured Forwarding” Per Hop Behavior (PHB) to be recognized by RFC compliant DSCP routers and switches called DS nodes. The Assured Forwarding PHB class is presented as AF(xy), where x=traffic class, and y=drop precedence. 4 traffic classes, and 3 drop precedences are defined. For example, AF21 = traffic class 2, drop precedence 1. The traffic class values (1-4) have escalating priority values where traffic marked as AF11 has a lower priority than AF41. Conversely, the drop precedence value (1-3) represents an escalating drop preference within the specified class, a descending priorty. For example, traffic marked as AF43 is more likely to be dropped than AF41.
March 22, 2006