IP920 Operating Manual: Appendix F Glossary 61
F. Glossary
Terminology Used in the IP920 Operating Manual
Asynchronous communications A method of
telecommunications in which units of single bytes
of data are sent separately and at an arbitrary time
(not periodically or referenced to a clock). Bytes
are “padded” with start and stop bits to distinguish
each as a unit for the receiving end, which need
not be synchronized with the sending terminal.
Attenuation The loss of signal power through
equipment, lines/cables, or other transmission
devices. Measured in decibels (dB).
Bandwidth The information-carrying capacity of a
data transmission medium or device, usually
expressed in bits/second (bps).
Baud Unit of signaling speed equivalent to the
number of discrete conditions or events per
second. If each signal event represents only one
bit condition, then baud rate equals bits per
second (bps) – this is generally true of the serial
data port, so baud and bps have been used
interchangeably in this manual when referring to
the serial port; this is not always the case during
the DCE-to-DCE communications, where a
number of modulation techniques are used to
increase the bps rate over the baud rate.
Bit The smallest unit of information in a binary
system, represented by either a 1 or 0.
Abbreviated “b”.
Bits per second (b/s or bps) A measure of data
transmission rate in serial communications. Also
see baud.
Byte A group of bits, generally 8 bits in length. A
byte typically represents a character of data.
Abbreviated “B”.
Characters per second (cps) A measure of data
transmission rate for common exchanges of data.
A character is usually represented by 10 bits: an
8-bit byte plus two additional bits for marking the
start and stop. Thus, in most cases (but not
always), cps is related to bits per second (bps) by
a 1:10 ratio.
CRC (Cyclic Redundancy Check) An error-
detection scheme for transmitted data. Performed
by using a polynomial algorithm on data, and
appending a checksum to the end of the packet.
At the receiving end, a similar algorithm is
performed and checked against the transmitted
checksum.
Crossover cable (Also known as rollover, null-
modem, or modem-eliminator cable) A cable
which allows direct DTE-to-DTE connection
without intermediate DCEs typically used to
bridge the two communicating devices. Can also
be used to make cabled DCE-to-DCE con-
nections. The name is derived from “crossing” or
“rolling” several lines, including the TX and RX
lines so that transmitted data from one DTE is
received on the RX pin of the other DTE and
vice-versa.
Data Communications Equipment (DCE, also
referred to as Data Circuit-Terminating
Equipment, Data Set) A device which facilitates a
communications connection between Data
Terminal Equipment (DTEs). Often, two or more
compatible DCE devices are used to “bridge”
DTEs which need to exchange data. A DCE
performs signal encoding, decoding, and
conversion of data sent/received by the DTE, and
transmits/receives data with another DCE.
Common example is a modem.
Data Terminal Equipment (DTE) An end-
device which sends/receives data to/from a DCE,
often providing a user-interface for information
exchange. Common examples are computers,
terminals, and printers.
dBm Stands for “Decibels referenced to one
milliwatt (1 mW)”. A standard unit of power
level commonly used in RF and communications
work. n dBm is equal to 10
(n/10)
milliwatt, so
0dBm = 1mW, -10dBm = 0.1mW, -20dBm =
0.01mW, etc.
DCE See Data Communications Equipment.
DTE See Data Terminal Equipment.
Flow Control A method of moderating the
transmission of data so that all devices within the
communications link (DTEs and DCEs) transmit
and receive only as much data as they can handle
at once. This prevents devices from sending data
which cannot be received at the other end due to
conditions such as a full buffer or hardware not in
a ready state. This is ideally handled by hardware
using flow-control and handshaking signals, but
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