Quality of service is a set of rules that prioritizes traffic on a network. Devices mark packets by class, and switches and routers queue the important ones first. It protects live video and alarm signals from being starved by downloads, backups or guests.
QoS decides who waits when a link is full. It is a scheduling decision, applied consistently or not at all.
Marking and queuing
Traffic is classified, marked and placed in queues that are served in priority order. Marking only helps if every device on the path honors it, so agree the scheme across switches, routers and the recorder.
What it cannot do
QoS cannot create capacity. If total demand exceeds the link, something still loses, so fix the bottleneck and reserve real headroom for video before relying on priority.
Related:Glossary: Network throughputGlossary: Network switch