Adaptive Polling/Contention Protocol; Wlan Protocol - Psion Teklogix 9150 User Manual

Chapter 1: Introduction

Adaptive Polling/Contention Protocol

1.5.1 Adaptive Polling/Contention Protocol

The Adaptive Polling/Contention protocol is always used on Narrow Band radio
systems with baud rates of up to 19.2 kbps, and may also be used on Spread Spec-
trum systems at higher rates.
Terminals operating with this protocol do not transmit unless they receive polls from
the 9150. Terminals are generally polled en masse. Following each poll, groups of
terminals are assigned response windows in which they may respond to the poll.
If a "collision" occurs – more than one terminal attempts to respond in a particular
window – the 9150 that is polling divides and reassigns that group until the
colliding terminals can respond without a collision.
Adaptive features of this protocol allow the response windows to be adjusted to
accommodate high or low RF traffic conditions, and to prevent data from being
queued too long when a particular terminal has a burst of data to send or receive.
Systems using adaptive polling/contention can use the cellular option so that
terminal operators can roam the site, maintaining uninterrupted communication as
they pass between coverage areas.
If cellular base is not enabled, a "RESET: Press Enter" message appears on the
terminal screen each time an operator moves from one base station coverage area to
another. (Pressing <ENTER> restores communication, but some data may be lost.)

1.5.2 Wlan Protocol

The Wlan (Wireless LAN) protocol is used only on Spread Spectrum radio systems
at baud rates of 122 kbps and higher. The Wlan protocol allows base stations to be
added to a system without cable connections. A Wlan system consists of a minimum
of one wired base station and zero or more wireless base stations. It can operate on
either one channel – usually the case – or on multiple channels.
When a Wlan system is operating, base stations do not send out polls. Instead, both
wired and wireless base stations regularly broadcast routing information, indicating
the available routes back to the controller. Both terminals and wireless base stations
receive these broadcasts, determine the best communication route, and send their
messages. If a better route becomes available, the terminal or wireless base will
change communication paths.
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Teklogix 9150 Wireless Gateway User Manual