Ethernet flow control

Ethernet flow control is a mechanism for temporarily stopping the transmission of data on Ethernet family computer networks. The first flow control mechanism, the pause frame, was defined by the IEEE 802.3x standard.

The follow-on priority-based flow control, as defined in the IEEE 802.1Qbb standard, provides a link-level flow control mechanism that can be controlled independently for each Class of Service (CoS), as defined by IEEE P802.1p. The goal of this mechanism is to ensure zero loss under congestion in data center bridging (DCB) networks.

Ethernet is a popular family of computer network . Flow control can be implemented at the data link layer. A sending station (computer or network switch) may be transmitting data faster than the other end of the link can accept it.

The first flow control mechanism, the pause frame, was defined by the Institute of Electrical and Electronics Engineers (IEEE) task force that defined full duplex Ethernet link segments. The IEEE standard 802.3x was issued in 1997.

An overwhelmed network node can send a pause frame, which halts the transmission of the sender for a specified period of time. A media access control (MAC) frame is used to carry the pause command, with the Control opcode set to 0x0001 (hexadecimal). Only stations configured for full-duplex operation may send PAUSE frames. When a station wishes to pause the other end of a link, it sends a pause frame to either the unique 48-bit destination address of this link or to the 48-bit reserved multicast address of 01-80-C2-00-00-01. The use of a well-known address makes it unnecessary for a station to discover and store the address of the station at the other end of the link.

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