Auto-Negotiation Process Overview

As defined by the IEEE 802.3 Working Group, Auto-Negotiation is the process that Ethernet Devices use to identify and resolve the highest possible link between two devices. In simplified terms, Auto-Negotiation aids a user in finding the highest and most efficient operating speed for their system. 

Featured between the Physical and Data Link layers on an OSI Model, Auto-Negotiation is responsible for finding the link speed between two link partners. In order to do so, the system transmits a “link pulse” which then forms a “link codeword.” Each link partner has their own codeword that is exchanged between systems. This process acknowledges the unique codewords, processes supported abilities, and transmits appropriate signals. 

Auto-Negotiation is present in multiple clauses and technologies, specifically in the networking industry under Twisted Pair ANEG, Fiber ANEG, Backplane ANEG, and Single Pair Ethernet. In each case, codewords are utilized differently within their advertised abilities. 

For Backplane and Single Plane Ethernet, Differential Manchester Encoding (DME) characterizes the link keywords and contains 48 data bits that can be used for negotiating an operating mode. Fiber uses “/C/” ordered sets, which contain 16 data bits, and Twisted Pair uses Base Pages, which also contain 16 data bits. 

Looking to the future, Auto-Negotiation will continue to be a required process whenever any networking media must support at varied speeds, duplexes, or operating modes. For a more in-depth explanation on the Auto-Negotiation Process and specifically Twisted Pair ANEG as outlined by IEEE in the 803.3 standard, refer to UNH-IOL’s Spencer Janelle’s report. Spencer is a senior Computer Science major at the University of New Hampshire and has worked in the Lab since 2018.