A PVC sub interface is intended to use an ATM PVC as an alternative serial connection, and to be allocated per PVC basis. A PVC sub interface looks as a point-to-point interface and is multicast capable, as opposed to the NBMA (NonBroadcast Multiple Access) model that requires a MARS server. A point-to-point interface is useful to run MBone or protocols requiring multicast, such as RSVP and IPv6, over a PVC WAN connection.
Note that a sub interface is not a full-fledged interface but just an indirect reference to the real interface.
The options are as follows: