Specifications

10.2. Bridge mode

In Bridge mode, a packet is transmitted to the radio channel immediately, without any checking

whether the radio channel is occupied or not. If other radio was transmitting simultaneously, a collision

would occur and both packets would be lost. Consequently Bridge mode can be used only for applications

which never generate more than a single message at a time, e.g. master-slave polling applications.

Still appropriate measures have to be taken to avoid collisions in special situations.

10.2.1. Bridge mode with Repeaters

Repeaters can be used in the Bridge mode in order to extend the radio coverage. Considering the re-

peated packets, it is necessary to schedule the access to the radio channel to avoid systematic collisions.

In a polling-type network, there is a request packet from centre to remote, to which the remote responds

immediately. When a remote receives the request directly from the centre, its immediate response

would collide with the repeated request, so it would be never received by the centre – a perfect example

of a systematic collision.

Packet header contains information about the number of Repeaters on the route, i.e. how many times

the packet can be possibly repeated. This number is decremented when passing through each Repeater.

The remote radio modem which receives the packet must delay its own transmission for a period. This

delay is calculated from the number of the remaining repetitions, the packet length and the modulation

rate in the radio channel. Repeaters always transmit immediately, without any delay.

Example:

There are 4 radios in the network operated in the Bridge mode. Everyone can receive each other except

Radio 4, which is not able to receive Radio 1 and vice versa. Therefore, in the Radio 3 the Repeater

function is turned on, and it mediates the connection between 1 and 4.

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3REP

Channel access