Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 407)

Publication AG-UM008C-EN-P - February 2005
Glossary 3
Half-Duplex Protocol 1) A mode of operation for a point-to-point or multipoint
baseband link with two physical circuits in which messages or
transmission blocks can be sent in one direction or the other but
not both at the same time.
2) Contrasted with two-way simultaneous. The master
station-to-remote station communication uses a half-duplex
protocol.
Handshake A series of signals between a computer (DTE) and a peripheral
device (DCE; e.g., a modem) that establishes the parameters
required for passing data.
Integrated Service Unit
(ISU)
Data communication equipment for a digital data network, which
serves as the data transmitting and receiving device. An ISU is a
combination of a digital service unit (DSU) and a channel service
unit (CSU).
I/O Rack An I/O addressing unit that corresponds to 8 input image table
words and 8 output image table words.
Link A data channel established between two or more stations.
Master Station A device (programmable controller with I/O modules or a
workstation) that sends data to and collects data from devices
connected on a point-to-multipoint, half-duplex network.
Modem A device that modulates digital information from a programmable
controller or computer to an analog signal that is transported over
phone lines, radio waves, and satellite transmissions and
demodulates the analog data back into digital data at the
receiving site.
Modem Handshaking A signaling protocol used for transferring information between
devices in a synchronized manner at a rate acceptable to both
devices. It may be accomplished by hardware or software.
Multi-drop Link 1) A link that has more than 2 stations. 2) Contrasted with
point-to-point link.
NAK Negative Acknowledgment. An ASCII control character
transmitted by a receiver as a negative response to the sender.
Node A station on a network.
Octal Numbering System A numbering system that uses only the digits 0 through 7; also
called base-8.
Packet The transmission unit exchanged at the network layer.