Which three characteristics are drawbacks to the use of a best-effort with over-provisioning backbone design? (Choose three.)

A.
The design costs more to implement than a DiffServ backbone.

B.
Denial of Service attacks on one service can affect all network traffic.

C.
The design uses a different over-provisioning ratio for the different traffic classes.

D.
It requires complex QoS mechanisms at the network edge.

E.
It requires complex QoS mechanisms at the network core.

F.
Unplanned network failures can cause unexpected congestion in the network.