2.4.2. The DS CodePoints

[RFC2474]The DSCP field within the DS field is capable of conveying 64 distinct codepoints.  The codepoint space is divided into three pools for the purpose of codepoint assignment and management: a pool of 32 Recommended codepoints (Pool 1) to be assigned, a pool of 16 codepoints (Pool 2) to be reserved for experimental or Local Use (EXP/LU) , and a pool of 16 codepoints (Pool 3) which are initially available for experimental or local use, but which should be preferentially utilized for standardized assignments if Pool 1 is ever exhausted.

The pools are defined in the following table (where 'x' refers to either '0' or '1'):
Codepoint space
Assignment Policy 
Standards Action 
EXP/LU (*) 
(*) may be utilized for future Standards Action allocations as necessary .

These codepoints must be mapped, not to specific PHBs, but to PHBs that meet "at least" the requirements set forth to provide a minimal level of backwards compatibility.