This attribute specifies whether cell transfer delay calculation
should be performed on loopback cells for each SPVC and SPVP
connection under this interface.
Cell transfer delay is calculated as half of the measured segment
round trip delay of a loopback cell.
Cell transfer delay calculation is only supported when segment
switch side loopback is enabled on the source segment endpoint.
Cell transfer delay calculation is only performed on supported
connections when the accountCollection attribute of the AtmIf Uni
or AtmIf Iisp component has a non-empty reason. Cell transfer delay
calculation is not provided for connections under the Vpt.