Different applications have different requirements for bandwidth, delay, and jitter.
For example, voice applications have stringent delay requirements and can tolerate minimal packet loss. Alternatively, an FTP file transfer may be insensitive to delay but very sensitive to packet drops. QoS features provide the ability to manage traffic intelligently across the infrastructure. Voice and video traditionally ran over circuit-switched infrastructures. At the same time, LANs and LAN interconnects became far more reliable.