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Glossary
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LAN
Local Area Network. An interconnection of devices in which data is
transferred without the use of public communications services.
Modbus Plus is an example of a LAN for controlling and monitoring
industrial processes.
layer
In the OSI Model, a portion of the structure of a device which
provides defined services for the transferring of information. See
Data Link Layer and Physical Layer.
LLC
Logical Link Control. The part of the device that performs the
protocols for identifying users of the network and for providing
reliable frame delivery. The LLC handles the framing and checking
of messages.
MAC
Medium (or Media) Access Control. The part of the device that
performs the protocols for sharing the network with other devices.
The MAC handles the queueing and transmission of outgoing LLC
level messages, address recognition for incoming messages, and
resolution of access contentions.
MAP
Manufacturing Automation Protocol. A network protocol that
allows devices or cells within an industrial environment to
communicate with each other.
master
A networked device which controls other devices to which it
connects. It initiates transactions, and schedules and transmits
tasks to a slave device. See slave.
medium
The entire cable system: the network cable, taps, connectors, and
terminators.
Modbus
An industrial networking system that uses RS232 serial
masterĆslave communications at data transfer rates of up to 19.2 k
baud.
Modbus Plus
An industrial networking system that uses tokenĆpassing
peerĆtoĆpeer communications at data transfer rates of one megabits
per second. The network medium is shielded twistedĆpair cable.