Which type of QoS marking is applied to Ethernet frames?

In Ethernet frames, Class of Service (CoS) marking is used to prioritize traffic within a local area network. CoS is implemented in VLAN tagging, specifically in the IEEE 802.1Q standard, which includes a 3-bit priority field in the VLAN header. This prioritization allows network devices to manage traffic flow based on the needs of various types of data. For instance, voice and video traffic can be marked with a higher priority compared to best-effort data traffic, thus ensuring that time-sensitive applications receive the necessary bandwidth and low latency.

The use of CoS is essential in environments where Quality of Service (QoS) is significant, particularly in switched networks. This allows network administrators to enforce policies that differentiate traffic types and allocate bandwidth accordingly. CoS is particularly effective in Ethernet networks, making it the accurate choice for marking Ethernet frames.

In contrast, DSCP and IP Precedence are marking methods used at the IP layer for differentiating quality of service among packets traversing IP networks, while Weighted Random Early Detection (WRED) is a queue management technique used to control congestion in IP networks, rather than marking frames themselves.