Signaling mechanism used by Ethernet by which devices choose common transmission parameters / From Wikipedia, the free encyclopedia

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Autonegotiation is a signaling mechanism and procedure used by Ethernet over twisted pair by which two connected devices choose common transmission parameters, such as speed, duplex mode, and flow control. In this process, the connected devices first share their capabilities regarding these parameters and then choose the highest performance transmission mode they both support.

Autonegotiation is defined in clause 28 of IEEE 802.3.[1] and was originally an optional component in the Fast Ethernet standard.[2] It is backwards compatible with the normal link pulses (NLP) used by 10BASE-T.[3] The protocol was significantly extended in the Gigabit Ethernet standard, and is mandatory for 1000BASE-T gigabit Ethernet over twisted pair.[4]

In the OSI model, autonegotiation resides in the physical layer.