Modem Terminology Overview
Modem Terminology Overview - Page
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SPOT 14.4
SPOT 14.4 User's Guide
User's Guide
38GDE00001SCF - Issue 4 (11/96)
38GDE00001SCF - Issue 4 (11/96)
Half & Full Duplex
Half & Full Duplex
In half duplex mode, two-way communication is possible but only in one
direction at a time. This means that control signals must be passed
between the modems to make sure they understand when they are
expected to send or receive data. These are known as
handshaking
signals and include such things as XON/ XOFF (to prevent one station
from transmitting while the other is busy) and CTS/RTS (clear to send
and ready to send). You will need to set these parameters to their
relevant states when you configure the communications software before
making a call.
In full duplex mode, the modems can communicate with each other
simultaneously, just as two people can speak at the same time over the
telephone. If both computers send each other data simultaneously in a
full duplex mode, it would be impossible to differentiate between the
transmitted and the received data if both used the same audible tones.
This problem is overcome by assigning one pair of tones to the
originating DTE and a different pair of tones to the answering DTE. Thus
each can demodulate the tones transmitted by the other while ignoring
the tones it transmitted. For this operation to be successful, each modem
must know what tones are being used by the other; so standards have
been set.
Most of the world uses tone and transmission standards laid down by the
Consultative Committee on International Telegraphy and Telephony or
CCITT. This organisation is part of the International Telecommunications
Union or ITU. Its standards define the tones to be used by the Originating
and Answering DTE for different approved communication modes.
Echo
Echo
When configuring the SPOT, you can select Local or Remote echo when
working in a full duplex mode. This determines the way in which
characters appear on your terminal screen. With
local echo
, your screen
displays the characters you type on your keyboard. With
remote echo
your screen displays the characters sent to the remote computer and
then returned to your screen; thus you see exactly what was received by
the remote computer. If you find that nothing appears on your screen then
it is likely that the remote computer is not echoing your characters.
Selecting local echo should overcome this problem.
