Hello Chris

If you take a look at the full DS field, you will see that it is 8 bits in length. As shown below, it is separated into two portions, the DSCP and the CU:

CU stands for “Currently Unused” so those two bits are always set to 0. More about the DS field can be found in this lesson.

Now, if the value of DSCP is EF (46) in binary is 101110. That’s 46 in binary, and it’s 6 bits because the DSCP portion of the DS field is 6 bits… However, for the purposes of generating a ping with a ToS value, we must put in the decimal value of the whole DS field, which is 8 bits. So you must add the two zeros at the end that correspond to the CU. This results in **10111000**. If you convert that to decimal you get a value of 184.

Let’s take a look at CS3 (24) in the lesson as well. The value of the DSCP is 24 which in binary is 011000. We add the two zeros of the CU portion and we get 01100000 as the value of the full ToS 8 bit field, which is a value of 96, which is what appears in the lesson. Does that make sense?

I hope this has been helpful!

Laz