User`s guide

DFE-650 Series Fast Ethernet PC Card User's Guide
Introduction
3
also offers 10Mbps Ethernet operation, in full-duplex and half-
duplex modes. Selection of the best operation mode in any given
installation is automatically governed by autonegotiation.
About Autonegotiation
The basic idea of autonegotiation can be understood by reflecting
for a moment on the familiar process of making a dialup connection
between two modems. You have probably heard some
gravelly
−
sounding exchanges between your local modem and a
modem at the other end of a telephone line. (These exchanges are
ordinarily played out through a speaker in your local modem). 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.
The preparatory work of the two modems during those few seconds
before you see the “connect” message is to
negotiate
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-650 Series PC Card and the hub
or switch through which it is connected into the LAN. (Switches
ordinarily provide autonegotiation functionality; hubs usually do