Specifications

Page C–2
FOCUS System Manual
or local Central Office.
Channel In communications , a path for transmis-
sion (usually both ways) between two or more
points.
CODEC A contraction of Code/Decode. A device
that converts analog signals to a digital form for
transmission over a digital medium (typically
voice to 64 Kbps digital) and back to analog after
transmission.
Common Equipment Refers to the portion of a
chassis that is common to all channel units and
required to support overall operation (i.e.,
Maintenance Module, framer Module, Power
Supply, and a Transceiver Module).
Compander (Compressor/Expander) A device
placed on a telephone circuit to compress the
volume range at one point and expand it at another
point in order to improve the signal-to-noise ratio.
Compression The application of any of several
techniques that reduce the number of bits required
to represent information on data transmission or
storage, therefore, conserving bandwidth and/or
memory.
Conference of European Postal and
Telecommunications (CEPT) A European
administrative body that makes recommendations
for telecommunications practices within Europe.
Connection The logical connection between two
terminals (origin port and destination port) over a
network route that enables the exchange of data.
Consultative Committee International for
Telegraphy and Telephony (CCITT) A
European advisory committee established by the
United Nations to recommend worldwide
standards of transmission within the International
Telecommunications Union (ITU).
Critical Angle The minimum angle at which total
reflection of the incident ray first occurs.
Cross-talk Unwanted transfer of energy from one
circuit to another (typically adjacent).
CTS (Clear-To-Send) A control signal sent from
the DCE to the DTE in response to RTS (Request-
To-Send) from the DTE, used to tell the DTE that
the DCE is ready to transmit data.
D-A Converter A device that converts a digital
input signal to an analog output signal repre-
senting equivalent information.
Data Digital representation of facts, concepts, or
instructions.
DCE (Data Circuit-termination Equipment) A
device that maintains and terminates a connection
between the data terminal equipment and the
transmission facility (i.e., a modem).
Digital Transmission of discontinuous signals
where information is encoded in binary form (e.g.,
binary ‘l’s or ‘0’s).
Direction The path of transmission to the next
terminal.
Distortion The amount by which an output
waveform or pulse differs from the input. It may
be expressed as the change in amplitude,
frequency, composition, phase, shape, or other
attribute.
Drop and Insert Refers to the capability to drop
off specific DS0 channels at a chassis and insert
DS0 channels into vacated time slots.
DSR (Data Set Ready) An EIA RS-232 control
signal sent from a DCE to a DTE, used to tell the
DTE that the DCE is ready for normal operation.
DS0 (Digital Signal Level 0) A telephony term
for a 64 Kbps standard digital telecommunications
signal or channel.
DS1 (Digital Signal Level 1) The 1.544 Mbps
signal, in the Bell hierarchy, that is transmitted
over an T1/E1 aggregate link (two-twisted pair) at
a rate of 1.544 Mbps.
DTE (Data Terminal Equipment) Terminals,
printers, or computers which generate or receive
information over the communications network.
DTMF (Dual Tone Multi-Frequency) The basis
for operation of push-button telephone sets. A
method of signaling in which a matrix combina-
tion of two frequencies, each from a group of four,
are used to transmit numerical address informa-
tion.
D4 Frame A frame format that consists of twelve
frames (193 bits per frame). It provides synchro-