This group contains the default loopback attribute
values for all Vcc, Vpc and Vpt components. Note that these
attribute values can be overridden by setting different values in the
Vcd component of the provisioned Vcc or the Vpd component of the
provisioned Vpc or Vpt.
Certain loopback requests may not be possible on a given
connection. In such cases, the corresponding operational loopback
attribute in the AtmStatus group of the Vcc, Vpc, or Vpt component
is set to notApplicable and the requested loopback is not performed.