Last Updated on August 7, 2021 by Admin 3
Which of the following DSCP values has a binary value of 101110? (Select the best answer.)
The Differentiated Services Code Point (DSCP) value EF has a binary value of 101110, which is equal to a decimal value of 46. DSCP values are sixbit header values that identify the Quality of Service (QoS) traffic class that is assigned to the packet. The Expedited Forwarding (EF) per-hop behavior (PHB), which is defined in Request for Comments (RFC) 2598, indicates a high-priority packet that should be given queuing priority over other packets but should not be allowed to completely monopolize the interface. Voice over IP (VoIP) traffic is often assigned a DSCP value of EF.
DSCP values beginning with CS are called Class Selector (CS) PHBs, which are defined in RFC 2475. CS values are backward compatible with three-bit IP precedence values; the first three bits of the DSCP value correspond to the IP precedence value, and the last three bits of the DSCP value are set to 0. Packets with higher CS values are given queuing priority over packets with lower CS values. The following table displays the CS values with their binary values, decimal values, and IP precedence category names:
DSCP values beginning with AF are called Assured Forwarding (AF) PHBs, which are defined in RFC 2597. AF separates packets into four queue classes and three drop priorities. The AF values are specified in the format AFxy, where x is the queue class and y is the drop priority. The following table displays the AF values with their queue classes and drop rates:
The first three DSCP bits correspond to the queue class, the fourth and fifth DSCP bits correspond to the drop priority, and the sixth bit is always set to 0. To quickly convert AF values to decimal values, you should use the formula 8x + 2y. For example, AF42 converts to a decimal value of 36, because (8 x 4) + (2 x 2) = 32 + 4 = 36.
Packets with higher AF values are not necessarily given preference over packets with lower AF values. Packets with a higher queue class value are given queuing priority over packets with a lower queue class, but packets with a higher drop rate value are dropped more often than packets with a lower drop rate value.