The purpose of QoS on an IP network is for:

FAX transmission uses store-and-forward signaling over circuit or IP paths and does not require the real-time packet prioritization that QoS provides.

Data representation refers to OSI Layer 6 (Presentation layer) encoding formats such as ASCII or JPEG and is unrelated to network traffic management.

Audio and voice traffic (VoIP) is the canonical driver for QoS because it requires end-to-end one-way latency under 150ms, minimal jitter, and very low packet loss to remain intelligible. QoS mechanisms such as DSCP marking and priority queuing ensure voice packets are forwarded ahead of less time-sensitive traffic. Without QoS, voice quality degrades severely on congested IP networks.

Streaming video relies on buffering to absorb network jitter, which significantly reduces its dependency on QoS compared to real-time audio.

Web-based services use TCP retransmission to recover from packet loss, making QoS less critical than it is for latency-sensitive, loss-intolerant audio streams.