I don't have a clear concept of backward compatibility.
Suppose that node A is DSCP capable and node B is IPprecedence capable only.
What happens if A sends frames to B, marking those using a specific DSCP value (ex. AF11)?
1) Node B maps AF11(001010) marked frames to IP-Precedence value equal to 1 or
2)Node B will consider the priority of the frames, only if A is marking using Class Selector (CS1 in this case )
3) Neither 1 or 2....(your explanation here ;))
I found the behaviour in the inverse direction (B to A) but nothing about a to B
Here's the behaviour of A to B:
Class selector DSCPs are values that are backward compatible with IP precedence. When converting between IP precedence and DSCP, match the three most significant bits. In other words:
IP Prec 5 (101) maps to IP DSCP 101 000