An engineer must configure QoS for a VoIP network. Which option is the best QoS model for this task?

IntServ requires RSVP signaling to reserve resources per flow on every router in the path, which does not scale for large VoIP deployments.

DiffServ uses DSCP markings in the IP packet header to classify traffic at ingress and apply per-hop behaviors (PHBs) at each network node, requiring no per-flow state. For VoIP, voice RTP is marked with Expedited Forwarding (EF, DSCP 46) to guarantee low latency and jitter across the network. Its scalability and compatibility with standard IP infrastructure make it the preferred QoS model for enterprise and service provider VoIP.

MPLS is a packet forwarding and traffic engineering technology, not a standalone QoS model, and requires a separate QoS framework like DiffServ to prioritize traffic.

FIFO is the default queue discipline that processes packets in arrival order with no traffic classification or prioritization, making it unsuitable for QoS.