Autonegotiation

Not to be confused with Automatic negotiation.

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 for twisted pair 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.

  1. ^ "Clause 28: Physical Layer link signaling for Auto-Negotiation on twisted pair", IEEE Standard for Ethernet, p. 278, doi:10.1109/IEEESTD.2018.8457469, ISBN 978-1-5044-5090-4[dead link]
  2. ^ Jayaswal, Kailash (2005). Administering Data Centers Servers, Storage, and Voice over IP. Hoboken: John Wiley & Sons. p. 168. ISBN 0471783358.
  3. ^ Schmidt, Daniel Minoli, Andrew (1998). Switched network services. New York: Wiley Computer Pub. p. 93. ISBN 0471190802.{{cite book}}: CS1 maint: multiple names: authors list (link)
  4. ^ IEEE. "Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method and Physical Layer specifications" (PDF). SECTION TWO: This section includes Clause21 through Clause 33 and Annex 22A through Annex 33E. Archived from the original (PDF) on November 26, 2013. Retrieved 2014-06-03.