Page 191 - CISSO_Prep_ Guide

Polling

Polling is used by networks that require high integrity
communications. To ensure that all devices are online and able
to respond, a master device manages all communications and
sends a note to each device on the network, in turn, asking if
they have data to transmit. A device will respond, thereby
validating that it is online and providing any information it has
to send. Still, it will only communicate when it is polled by the
master device. This form of communication is frequently used in
networks that handle alarm circuits and video lottery terminals
or other areas requiring carefully controlled communications.

Token Passing
Token ring networks operate on a deterministic communications
process and use a token to control data communications. The
token circulates around the ring at a fixed speed, and a device is
only able to speak when it has possession of an unused token.
Since the token circulates at a fixed speed, each device knows
that it will have the ability to communicate at regular intervals.

Network Devices
Many types of devices make up networks of today. Several
devices have faded away and no longer in common use.

To transmit long distances, it is often necessary to install devices
such as repeaters that will compensate for the attenuation of the
signal.