Which two are characteristics of RSVP?（）

• A、RSVP itself provides bandwidth and delay guarantees.
• B、For RSVP to be end-to-end, all devices must support RSVP.
• C、RSVP reservations are maintained by a centralized reservations server.
• D、An RSVP compatible QoS mechanism must be used to implement guarantees according to RSVP reservations.