US Robotics COURIER HST User'smanual page 116

Cyclic Redun-
dancy Checking
(CRC)
Data
Communications
DCE
DTE
Dedicated
Line
Default
Digital Signals
Duplex
Equalization
COURIER HST
characters per second (cps). Some protocols, such as USR-
HST and MNP-Service Class 3, employ advanced tech-
niques to increase cps. When the Courier HST is set for
maximum throughput, as described in Chapter 3, 140 char-
acters in addition to the standard 960 can be transmitted for
a total of 1100 cps.
An error-detection technique consisting of a cyclic algorithm
performed on each block or frame of data by both sending
and receiving modems. The sending modem inserts the re-
sults of its computation in each data block in the form of a
CRC code. The receiving modem compares its results with
the received CRC code and responds with either a positive
or negative acknowledgment. In the ARQ protocol imple-
mented in the Courier HST, the receiving modem accepts
no more data until a defective block is received correctly.
A type of communications in which computers and terminals
are able to exchange data over an electronic medium.
Data Communication (or Circuit-Terminating) Equipment. In
this manual, the dial-up modems that establish and control
the data link via the telephone network.
Data Terminal (or Terminating) Equipment. The device,
such as a personal computer, terminal, or mainframe, that
generates or is the final destination of data.
Often used to describe a user-installed phone line, or one
leased from the telephone company, that provides a con-
tinuous point-to-point connection between two modems,
hence "dedicated" to those two devices. The line is "non-
switched' ': the connection does not require dialing into
the phone company's central switching equipment.
Any setting assumed, at startup or reset, by the computer's
software and attached devices, and operational until changed
by the user.
Discrete, uniform signals. In this manual, the term refers to
the binary digits 0 and I .
Indicates a communications channel capable of carrying sig-
nals in both directions.
~ See Half Duplex, Full Duplex.
A compensation circuit designed into modems to counteract
certain distortions introduced by the telephone channel. Two
types are used: fixed (compromise) equalizers and those that
adapt to channel conditions.
G-3