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Configuring ATM Traffic Descriptors
About TDs
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/0512-7
When you choose the Forward (or Reverse) TD combination, select the combination 
that best describes the traffic characteristics. The UPC and NPC functions use the 
traffic parameters to determine the conforming cells of an ATM connection, based on 
the threshold values for PCR, SCR, and MBS as specified in the service contract. If a 
TD combination is not valid for the service class specified in the Forward (or Reverse) 
QoS class field, you cannot select it.
For more information on how each TD combination affects the cell streams under 
different traffic conditions, see Appendix B, āATM Traffic Descriptors.ā