Where two or more repeaters are used, collisions resulting from simultaneous reception of a repeated
packet must be eliminated. Collisions happen because repeaters repeat packets immediately after re-
ception, i.e. if two repeaters receive a packet from the centre, they both relay it at the same time. If
there is a radiomodem which is within the range of both repeaters, it receives both repeated packets
at the same time rendering them unreadable.
Examples:
1. Repeaters connected serially
A packet is transmitted and repeated
in steps 1, 2, 3.
Centre
RPT1
RPT2 Remote
1
2
3
In improperly designed networks collisions happen
if a remote radio modem lies in the range of two
X
COLLISION!
1
1
2
2
WRONG
CEN RPT1
RPT2 REM
repeaters (see the image): the packet sent from
the centre (1) is received by both repeaters. It is
repeated by them both (2) causing a collision at
the remote. In other words – there should not be
more than one repeater where the centre and re-
motes' coverage areas overlap.
Solution 1.
Adjust signal coverage so that RPT2 is out of range
of the centre and RPT1 is out of the range of the
GOOD
Coverage area
1
2
3
CEN RPT1
RPT2 REM
remote radio modem. This can be achieved for
example by reducing the output power or using a
unidirectional antenna.
Solution 2.
Use a single repeater. (Whenever network layout
allows that.)
1
2
Good
CEN
RPT1
REM
RipEX Radio modem & Router – © RACOM s.r.o.
16
RipEX in detail
