About Autonegotiation - D-Link DFE-650TXD User Manual

About Autonegotiation

The basic idea of auto-negotiation is similar to the familiar process
of making a dialup connection between two modems. When you
attempt a connection you have probably heard some gravelly-
sounding exchanges between your local modem and a modem at
the other end of a telephone line. These annoying sounds let you
know that your modem and the remote modem are preparing for
your intended communication with the remote computer.
During those few seconds before you see the "connect" message
the modems are negotiating the best data communication scheme
which is supported by both modems, and which is suitable for the
quality of the telephone-line connection between them. The
parameters to be settled between the two modems include best
baud rate, compression method, and error correction method.
When the two modems have tested the phone-line quality and
have switched to the combination of parameters which will provide
the best data communication, 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.
Autonegotiation between devices within an Ethernet LAN is similar
in concept, but much briefer. The two devices involved in the
autonegotiation will be your DFE-650TXD and the switch or hub
through which it is connected into the LAN. (Switches ordinarily
provide for autonegotiation; traditional hubs do not.)
The parameters to be negotiated between the DFE-650TXD
and its supporting switch or hub include speed (100Mbps = Fast
Ethernet, or 10Mbps = traditional Ethernet) and duplex mode (half-
duplex or full-duplex.)
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