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ODEM
DCE . Data Communications Equipment. The local and/or remote
modem. A DCE is usually connected to a DTE.
DTE . Data Terminal Equipment. The computer or terminal, either
local (yours), or the remote (the one you’re communicating with). A
DTE is usually connected to a DCE.
DTR . Data Terminal Ready. The computer issues this signal to the
attached modem indicating that it is ready to receive data.
data compression . A technique that examines transmitted data for
redundancy and replaces strings (groups) of characters with special
codes which the receiving modem interprets and restores to its
original form. Transmission of compressed data results in shorter
connect times and hence cost savings for connect charges. Data
compression is sometimes called “source encoding”.
data mode . The modem is in data mode when a connection has been
established with a remote modem and sends a CONNECT response
confirming the connection. User data may then be transmitted or
received.
dial modifier . Dial modifiers are special characters appended to the
ATD command which instruct the modem how to place a call.
digital signa l. A discrete signal which can only take on one of several
(usually only two) discrete levels in contrast to analog signals which
can take a continuous range of levels.
E
error detection and correction
. The transmitting modem attaches a
special pattern (called a frame check sequence) calculated according
to a prescribed algorithm from user-defined data to the end of a block
of data. The receiving modem performs the same algorithm and
compares it to the one with the transmitted data. If these match, then
the block of data has been received correctly. If not, the block of data
is re-transmitted until no errors are detected.
escape sequence . Also referred to as the escape command. This
special command is entered as three plus symbols (+++) and places
the modem in command mode and interrupts user data transmission,
but does not terminate the data connection. This allows the entering
of commands while the connection is maintained.
HOMEOFF.PM6 5/9/97, 9:15 AM 64