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.