DiffServ is the correct scalable QoS architecture for classifying traffic according to business requirements and using DSCP values as the priority descriptor. Cisco QoS design distinguishes DiffServ from IntServ. IntServ uses per-flow signaling with RSVP and can reserve resources, but that model is not operationally scalable across large enterprise networks. DiffServ is class-based. Traffic is classified and marked at the network edge, then each device applies per-hop behavior to those classes using local QoS policy. DSCP provides a six-bit field in the IP header, which supports more than ten classification values and allows standardized treatment classes such as EF, AF, class selector, and default. Best effort provides no differentiated treatment, and RSVP is a signaling mechanism associated with IntServ rather than the requested scalable class-based architecture.
"Interserv" is not the correct Cisco QoS model term. Therefore, the engineer should design around DiffServ, with a clear trust boundary, marking policy, queuing model, and consistent treatment across WAN and campus boundaries. Reference topics: DiffServ, DSCP, per-hop behavior, class-based QoS, scalable QoS architecture.