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Voice and video are the use cases QoS exists for. Latency and jitter budgets, DSCP markings, IP phone trust, LLQ configuration, codec bandwidth math, and wireless voice via WMM.

LLQ, CBWFQ, policing, and shaping each do something different. The three primitives, when to use which, hierarchical shaping for sub-rate WAN handoffs, and the production patterns.

Classification and marking at the trust boundary are the foundation of every QoS deployment. The patterns (untrusted access ports, conditional trust for IP phones, explicit MQC marking) and the discipline that makes them work.

The Cisco MQC three-construct model (class-map, policy-map, service-policy) covers every QoS feature on IOS, IOS XE, and IOS XR. The grammar, common actions, hierarchical policies, and verification.

DSCP is the 6-bit Layer 3 marking that drives modern QoS. The byte format, the standardized PHBs (CS, AF, EF), Cisco's DSCP-to-CoS-to-MPLS-EXP mapping, and trust boundary discipline.

SD-WAN provides encryption and segmentation but creates an inspection gap. SASE fills that gap with cloud-delivered SWG, CASB, FWaaS, ZTNA, and DLP. The 2026 vendor landscape compared.