What is an advantage of the IntServ QoS model？（）

A. It supports admission control that allows a network to reject or downgrade new RSVP sessions if one of the interfaces in the path has reached the limit （that is， all reservable bandwidth is booked）.
B. RSVP signals QoS requests per individual flow. In the request the authorized user （authorization object） and needed traffic policy （policy object） are sent. The network can then provide best-effort delivery to these individual flows.
C. RSVP streamlines communication by making it unnecessary to inform network devices of flow parameters （IP addresses and port numbers）.
D. Because of the stateful RSVP architecture， continuous signaling does not have to occur.
E. The flow-based approach is scalable to large implementations， such as the public Internet， because RSVP tracks each individual flow.