Auto-Negotiation - D-Link DFE-530TX+ User Manual

Appendix A - Technology Basics

Auto-Negotiation

You have probably had the experience of making a dial-up connection through a modem, and have heard the sound exchange
between your modem and the modem at the other end of the telephone line. As unpleasant as those few seconds of noise may
be, they do let you know that your modem and the remote modem are on the job, preparing for your intended communication
with the remote computer.
When the two modems have tested the phone-line quality and settled on the combination of shared options and parameters
which will provide the best data communication over the connecting phone line, then you are given the "connect" message
which signals the end of the inter-modem negotiation and the beginning of your intended communication with the remote
computer.
Auto-negotiation between devices within an Ethernet Local Area Network (LAN) is similar in concept, but much briefer. The
two devices involved in the auto-negotiation will be the DFE-530TX+ Adapter serving your station (installed in your computer),
and the switch through which it is connected to the LAN. The options to be negotiated between the DFE-530TX+ and its
supporting switch includes Ethernet type (100BASE-TX Fast Ethernet or 10BASE-T Ethernet) and duplex mode (half-duplex,
being one-way-at-a-time, or full-duplex, being simultaneous transmit-and receive.)
Startup communication between the two devices occurs when both devices are powered up. Once the cable connection and
the Network Operating System software is satisfied, the preparatory process of auto-negotiation between the DFE-530TX+
and its supporting switch proceeds automatically. If the switch has auto-negotiation functionality, it and the DFE-530TX+
exchange a series of messages, each device signals its capabilities and listens for corresponding information about the other.
The auto-negotiation process requires only a few milliseconds, and the two devices select the best communication parameters
supported by both.
If the switch does not support auto-negotiation, the (single capability) message will be recognized by the DFE-530TX+ auto-
negotiation facility, which will switch to those settings of its own capabilities, which match that of the switch.
Auto-negotiation reoccurs any time the linkage is restored, making the line ready again for optimal data communications.
D-Link DFE-530TX+ User Manual 13