Which QoS mechanism uses RSVP?

IntServ is a per-flow QoS model that uses RSVP (Resource Reservation Protocol) to explicitly reserve network resources such as bandwidth and buffer space along the entire path from source to destination, guaranteeing the required quality of service for individual application flows before they send data.

DiffServ is a scalable QoS model that classifies and marks packets using DSCP at the network edge and applies per-hop behaviors at each router based on those markings; it does not use RSVP and makes no end-to-end resource reservations.

CoS (Class of Service) refers to the 802.1p Layer 2 priority marking in Ethernet frames and is a traffic marking mechanism, not a QoS architecture, and it does not involve RSVP.

ToS (Type of Service) is the legacy IPv4 header field used for traffic marking and classification; it is not a QoS architecture and has no relationship to RSVP signaling.