This attribute specifies the default cell delay variation tolerance
(CDVT) for all connections of the ABR service category. An
override to this default may be specified for a provisioned
connection under the Vcd Tm or Vpd Tm component, or signalled in
the SVC Traffic Descriptor Information Element.
This attribute is used by dynamic generic cell rate algorithm
(DGCRA) policer on ATM IP cards. On CQC-based ATM cards
ABR UPC is enforced using PCR and CDVT.