The OVPN providing system can have some available OCs,
which can be used to interconnect PE devices taking part in an
OVPN. These OCs are leased from optical channel providing
systems [6]. Choosing an OC depends on the characteristics
(such as bandwidth, QoS, etc.) of both ACs at the end of the
OC, on the set of VCs to multiplex, and on the available OCs
of optical channel providing systems. In the last case, it is
possible that many OCs are leased between OVPN
components and they must be concatenated together to support
VCs.