问题：

[单选] 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.