D-Link DFE-538TX — понимание авто-торговли в Ethernet сетях [7/64]

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About Auto-Negotiation

You have probably had the experience of making a dialup 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 irritating 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 intermodem negotiation and the beginning of

your intended communication with the remote computer.

Auto-negotiation between devices within an Ethernet LAN is similar in concept, but

much briefer. The two devices involved in the auto-negotiation will be the DFE-

538TX 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-538TX 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-538TX and its supporting switch proceeds automatically. If

the switch has auto-negotiation functionality, it and the DFE-538TX 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.