Which of the following statements aptly describes a network well designed for QoS?

A.
Packets are classified at each router, based on as many detail as possible, typically using extended IP ACLs to match the packets for classification.

B.
Packets are classified at each router, based on socket address only, typically using extended IP ACLs to match the packets for classification.

C.
Packets are classified and marked, close to the edge of the network. The packets are treated differently based on this marking at the routers in the middle of the network.

D.
Packets are classified based on different parameters, but close to the edge of the network. The packets are automatically characterized based on flow at the routers.

E.
Packets are classified based on socket address, at the router closest to the source of the traffic. The packets are automatically characterized based on flow at the routers.

Explanation:

To achieve the same level of quality in both directions the packets going to and coming from the customer network must first be classified and marked. Classification and marking packets going to the customer network is a more difficult task because:
1) Classifying and marking must be performed on all edge routers.
2) Classifying and marking requires the identification of the customer network. Using PBR, CAR, CB-Policing or CB-Marking does not scale because it involves the use of access lists (this is especially difficult if customer networks are dynamically learned via BGP).
Reference: Introduction to IP QoS (Course) p.2-35