PHB, contd.

• bit pattern in TOS byte (DS filed)

  DS control point (DSPCP)
  

• use table mapping of DSCP code to PHB

  no guarantee of specific behavior for specific code
  
  defaults provided

• unknown DSCP should use default forwarding

  must not crash
  

• xxx000 set of DSCPs defined

  backward compatibility with current practice in use of Precedence field
  
  old use of TOS & DIR bits not supported

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