Without QoS, all packets compete equally for bandwidth. When congestion hits, packets drop randomly. This destroys real-time applications.
Real-time traffic is unforgiving:
- Voice calls become choppy with ms latency
- Video conferences freeze with % packet loss
- Trading systems lose money with ms delays
Elastic traffic is tolerant:
- Email delayed by seconds goes unnoticed
- File transfers retry dropped packets
- Web pages load slightly slower
QoS gives you control over which traffic suffers during congestion. You protect sensitive applications by making bulk transfers absorb the impact.