Class of Service (CoS) operates at Layer 2, utilizing the 3-bit Priority Code Point (PCP) field within the 802.1Q Ethernet header to define 8 priority levels (0–7). Differentiated Services (DiffServ) functions at Layer 3. It re-purposes the ToS byte in the IPv4 header (or Traffic Class in IPv6) to use the 6-bit Differentiated Services Code Point (DSCP), allowing for 2^6 = 64 distinct traffic classifications. Best Effort Service is the default behavior where no QoS mechanisms are applied. Network devices forward packets in the order they arrive (First-In, First-Out) without guarantees for bandwidth or latency.

WMM (Wi-Fi Multimedia) is a subset of the IEEE 802.11e standard adapted by the Wi-Fi Alliance. It prioritizes wireless traffic into four Access Categories (AC): Voice, Video, Best Effort, and Background.

RFC 2474, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers," Internet Engineering Task Force (IETF), December 1998. (Defines Layer 3 DiffServ and the 6-bit DSCP field).

IEEE Std 802.1Q-2018, "IEEE Standard for Local and Metropolitan Area Networks—Bridges and Bridged Networks," IEEE Computer Society, Section 6.9.3 "Priority Code Point (PCP) encoding". (Defines Layer 2 classification using the 3-bit field for 8 priority levels).

Cisco Systems, "Quality of Service (QoS) Configuration Guide, Cisco IOS XE 17.x," Chapter: "QoS Overview," Section: "QoS Models." (Details Best Effort, IntServ, and DiffServ models).

Wi-Fi Alliance, "WMM (Wi-Fi Multimedia) Specification," Version 1.2.0. (Defines the implementation of IEEE 802.11e QoS and Access Categories).

Aruba (HPE), "ArubaOS 8.6.0.0 User Guide," Chapter: "Quality of Service," Section: "Wi-Fi Multimedia." (Explains WMM and its relation to 802.11e Access Categories).