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RFC 2474 uses the ToS byte for Differentiated Services Code Point:

   0   1   2   3   4   5   6   7
 |      DSCP field       |CU/ECN | 

Further, the DSCP field has more divisions:

  0   1   2   3   4   5   
|   Class   |  Drop | 0 |
|___________ ___________|
      DSCP field

My question is now, HOW is the 6. bit, the bit with the number 5, called? The only thing I know is that it is 0. But no name or anything for the 6. Bit. I'm reading the book 'Deploying QoS for cisco IP and Next-Generation-Networks' and there is where I found the table.

The same ToS Byte is also (and originally) used for IP Precedence (RFC 791), and there every bit is described and named:

  0 + 1 + 2     3         4          5             6  +  7
|Precedence | Delay |Throughput|Reliability|Reserved and unused |

I need this for further understanding of how QoS works and how the mapping from IP-Precedence-to-DSCP works.

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At a guess, I'd say that 6 doesn't have a name as it is CU, or Currently Unused.

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