qualityofservice

Quality of Service (QoS) is a collection of techniques and policies used in computer networks and related systems to manage how different data flows access network resources. The overall goal is to provide predictable performance for high-priority applications by regulating bandwidth, latency, jitter, and packet loss, especially in networks with competing traffic and limited capacity.

Key methods include traffic classification and marking to label packets by priority; policing and shaping to enforce traffic profiles; queuing and scheduling to determine the order of packet transmission; and congestion management to prevent saturation and ensure smooth operation. QoS can be implemented within devices such as routers and switches, as well as across networks through coordinated policies.

Two principal architectural approaches are DiffServ and IntServ. DiffServ uses packet marking (DSCP) to assign per-hop behavior across a network, scaling to large deployments. IntServ provides explicit, per-flow resource reservations (often via RSVP), offering stronger guarantees at the cost of scalability. MPLS-based networks frequently employ traffic engineering to reserve resources along specific paths. Hybrid models combine these techniques.

Typical QoS use cases include real-time voice and video, interactive applications, critical data services, and multi-tenant data centers. Challenges include ensuring end-to-end guarantees across administrative boundaries, encryption that obscures traffic features, and the complexity of managing policies at scale.