An engineer has an implemented a QOS architecture that requires a signaling protocol to tell routers which flows of packets require special treatment. Which two mechanisms are important to establish…

Classification identifies and categorizes packets but is a DiffServ mechanism that does not involve per-flow signaling or reservation.

Tagging marks packets with a DSCP or CoS value for downstream treatment, which is also a DiffServ mechanism unrelated to signaling or resource reservation.

Packet scheduling (e.g., WFQ, CBWFQ) manages how packets are dequeued and transmitted, but it does not involve a signaling protocol or the establishment of per-flow resource reservations.

Admission control is the process by which a router determines whether sufficient resources exist to accept a new flow requesting special treatment; without it, routers would accept unlimited reservations and defeat the purpose of the signaling protocol.

Resource reservation, implemented via RSVP, is the actual signaling mechanism that communicates per-flow bandwidth and delay requirements hop-by-hop along the path, causing each router to allocate and hold resources for the duration of the flow.