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Which layer in TCP/IP model provides Quality of Service (QoS)? I am confused between Layer 2 and Layer 3?

sasuke_X220
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According to Computer Networks, by Andrew S. Tanenbaum, Quality of Service is provided by the Network Layer (Layer 3).

A stream of packets from a source to a destination is called a flow (Clark, 1988). A flow might be all the packets of a connection in a connection-oriented network, or all the packets sent from one process to another process in a connectionless network. The needs of each flow can be characterized by four primary parameters: bandwidth, delay, jitter, and loss. Together, these determine the QoS (Quality of Service) the flow requires.

Computer Networks - Andrew S. Tanenbaum, 5th Edition, Chapter 5 (The Network Layer), Section 5.4 (Quality of Service), p. 404

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Matheus Portela
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Any layer can distinguish between different qualities of service. Layers 2 & 3 offer "best effort" delivery, where QoS can influence relative amount of effort. There are many layer-2 technologies, but ethernet is certainly a popular one. Ether standards committees have published various QoS specs, including IEEE P802.1p. There have been many others. Sometimes queuing discipline (packet drop policy) is of interest, and sometimes a reservation of committed bit-rate is the goal.

A QoS field has been baked into layer-3 IP headers since the beginning -- see Type of Service in https://www.rfc-editor.org/rfc/rfc791#page-12

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J_H
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