Device Autonegotiation

An Ethernet process of autonegotiation allows mixed technologies to perform without interference when connected. The IEEE released the auto-negotiation method as a way for devices with different functionality to interact with one another successfully. With auto negotiating, two connected devices choose common transmission parameters, such as speed or duplex. The devices share information on their capabilities and then choose the transmission mode they can each support that provides optimal performance. In the OSI model, autonegotiation is implemented as part of the physical layer. The IEEE 802.3 standard defines autonegotiating for Ethernet over twisted pair cables. The autonegotiation protocol is mandatory for 1000BASE-T gigabit Ethernet over twisted pair technology.

802.3 Standard and Auto Negotiating

The 802.3 standard specifies an auto-negotiation algorithm, which was originally called NWay. The standard supports two devices on a 10 Mbps, 100 Mbps, or 1000 Mbps link as they choose between half or full duplex, with the highest priority configuration taking precedence. The 802.3-based autonegotiation standard lists mode priorities. It supports disruption-free network additions. If a higher speed network device is added, automatic negotiations will occur between two link ends.

Auto-negotiation Specification and Pulses

The auto-negotiation specification is based on pulses that detect device connections, and Ethernet devices can transmit these pulses. When one device learns the capabilities of another device, the two components can decide on the most favorable operational mode that they both support. The auto-negotiation specification also provides for backward compatibility with 10Base-T. Look to Comms Express for information on device functionality as network additions are planned.

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