What is the 6-bit binary representation of DSCP value AF21?

The correct answer is E. 010010. AF21 maps to DSCP decimal value 18, calculated using the Assured Forwarding formula: DSCP = 8x + 2y, where x is the class (2) and y is the drop precedence (1) - giving 8(2) + 2(1) = 18. Converting 18 to 6-bit binary yields 010010, making E correct. The distractors each…

QoS Fundamentals

Question

Options

A010011
B100010
C010001
D001100
E010010

How the community answered

(41 responses)

A
2% (1)
B
2% (1)
C
5% (2)
E
90% (37)

Explanation

AF21 maps to DSCP decimal value 18, calculated using the Assured Forwarding formula: DSCP = 8x + 2y, where x is the class (2) and y is the drop precedence (1) - giving 8(2) + 2(1) = 18. Converting 18 to 6-bit binary yields 010010, making E correct.

The distractors each correspond to a different AF value: B (100010 = 34) is AF41, D (001100 = 12) is AF12, A (010011 = 19) and C (010001 = 17) are not standard DSCP AF values at all - making them easy to eliminate if you know the formula produces even numbers (2y is always even, 8x is always even, so all AF values are even; 19 and 17 are odd).

Memory tip: AF values are always even in decimal (the formula 8x + 2y guarantees this), so any odd binary number is automatically a wrong answer for any AFxy question.

Topics

#DSCP#Assured Forwarding#Binary Conversion#QoS Marking

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