Set by the operator to indicate the protocol responsible
for establishing this VC. Value 'manual' is used in all
cases where no maintenance protocol (PW signaling) is used
to set-up the VC, i.e. require configuration of entries in
the VC tables including VC labels, etc. The value
'maintenanceProtocol' is used in case of standard
signaling of the VC for the specific PSN, for example LDP
for MPLS PSN as specified in <draft- draft-martini-
l2circuit-trans-mpls> or L2TP control protocol.
Value 'other' is used for other types of signaling.