Glossary of Terms

Some of the terms and abbreviations used on the website may be unfamiliar if you are new to digital radio systems. The following glossary explains these terms, which can be helpful in understanding the operation of many of our products.

Bit – is the smallest unit of digital data, computational quantity that can take on one of two values,
such as false and true or 0 and 1.

bps – bits per second. The unit in which data transfer rate is measured across a communication
channel in serial transmissions. 9600 bps indicates that 9600 bits are transmitted in one second.

Byte – is often eight bits and the smallest addressable unit of storage.

Channel bandwidth – in addition to the direction of transmission, a channel is characterized by its
bandwidth. In general, the greater the bandwidth of the assigned channels, the higher the possible
speed of transmission.

Data telemetry – transmission of the values of measured variables using telecommunication
techniques

Decibel (dB) – is a digital data telemetry measurement of the strength of a signal.

dBm – (Decibels below 1 Milliwatt) A measurement of power loss in decibels using 1 milliwatt as the
reference point.

DCE – Data Communication Equipment. The devices and connections of a data telemetry communications
network that connect the communication circuit between the data source and destination (the Data
Terminal Equipment or DTE). A modem is the most common kind of DCE.

DTE – Data Terminal Equipment. A device which acts as the source and/or destination of data and
which controls the communication channel. DTE includes terminals, computers, protocol converters,
and multiplexers.

Fade Margin – The greatest tolerable reduction in average received signal strength that will be
anticipated under most conditions. This measurement provides an allowance for reduced signal
strength due to multi-path, slight antenna movement or changing atmospheric losses. A fade margin
of 10…20 dB is usually sufficient in most systems.

Flow Control – The collection of techniques used in serial communications to stop the sender from
sending data until the receiver can accept it. This may be either software flow control or hardware
flow control. The receiver typically has a fixed buffer size into which received data is written as soon
as it is received. When the amount of buffered data exceeds a "high water mark", the receiver will
signal to the transmitter to stop transmitting until the process reading the data has read sufficient
data from the buffer that it has reached its "low water mark", at which point the receiver signals to
the transmitter to resume transmission.

FSK Frequency Shift Keying – The use of frequency modulation to transmit digital data, i.e. two
different modulation frequencies are used to represent zero and one. More than two frequencies
can be used to increase transmission rates.

Master – is the unique application entity within the distributed application which directly or indirectly
controls the entire activity for this atomic action.

Multiple RTU addressing – several RTU’s share the same radio unit; each RTU has its own
address in the radio unit network list.

Slave – is a unit, which is under the control of another unit (Master).
Packet switched – Describing a system whereby messages are broken down into smaller units
called packets, which are then individually addressed and routed through the network.

Parity – A one-bit quantity indicating whether the number of 1’s in a word is even or odd.

Peer-to-Peer – Peer-to-Peer is a communications model in which each party has the same
capabilities and either party can initiate a communication session. Other models with which it might
be compared to, include the client/server model and the master/slave model. In some cases, peer-to-
peer communications is implemented by giving each communication node both server and client
capabilities.

Point-to-multipoint – is one-way or two-way communications from a central point to a number of
subsidiary points, and vice versa.

Poll – is a method to check the status of an input line, sensor, or memory location to see if a
particular external event has been registered. The communications control procedure by which a
master station or computer systematically invites tributary stations on a multipoint circuit to transmit
data.

Repeater – is a device that will repeat serial communications on to the predetermined destination.
Routing of messages – is the selection of a path or channel for sending a message.

RTU – is a Remote Terminal Unit that is physically remote from a main station or computer but can
gain access through communication channels.
RSSI (Received Signal Strength Indication) – a parameter returned from a transceiver that gives a
measure of the RF signal strength between the mobile station and base transceiver station, either
as an uplink or downlink measurement.

SCADA – (Supervisory Control and Data Acquisition) is a system used in industry to monitor and
control equipment status and provide logging facilities.
Transceiver – A terminal unit which can both transmit and receive information from a data
transmission circuit.

Unsolicited system – In an unsolicited response system, the RTU’s generate all reporting
messages required, without being polled by the master. Typically, such messages report a change
of state or a fault, or simply pass data to the SCADA central host without being polled for the data.