User`s guide

Repeater Mode
This mode of operation is determined by the configuration command keyword
rptmode being set to ON or ALL. Repeater mode takes precedence over the setting
of ptpmode. Note that the RMX232-151/173 only supports a maximum of 1 repeater
hop.
In repeater mode the radio modem becomes a dedicated packet repeater node. Using
a number of repeater nodes effectively enables a network to be extended beyond the
operating range of an individual radio modem pair. The following diagram illustrates an
example radio modem and repeater configuration required for a point-to-point link with
one repeater hop. Also shown is the return data acknowledgement path.
Radio
Modem
A
Radio
Modem
B
Repeater
(HopCnt – 1)
(Hop = 1) (Hop = 0)
Config:
unit = 1
site = 0
hop = 1
Config:
site 0
rptmode on
Config:
unit = 1
site = 0
hop = 1
Data from A Data from A
ACK from B ACK from B
(Hop = 1) (Hop = 0)
Point-to-point link showing data and return ACK path with
their respective hop counts for traversing the repeater.
Each data packet contains a 2 bit field called the hop count. Upon a packet being
transmitted from a radio modem, the hop count field is set with the units hop count
setting. The hop count field is decremented every time a network repeater retransmits
the packet. Upon this hop count reaching zero, a repeater will not retransmit the
packet, thus preventing it from bouncing around the network indefinitely.
Repeater
Repeater
Repeater
hop=3 hop=0
Hop
count 3
hop-1
hop-1
Hop
count 2
Hop
count 1
Hop
count 0
hop-1
Transmitting
Unit
Receiving
Unit
Up to 3 repeaters can be used
in a network to extend the
effective operating range.
Traversing 3 repeaters requires an initial hop count setting of 3.
With rptmode being set to ON, the repeater will retransmit all packets with the
specified site address but regardless of unit address, provided the hop count for that
packet is greater than or equal to 1. If a data packet is received by a repeater node
with a hop count of zero, it is not retransmitted as it is considered to be at the end of
its network life.
User’s Guide Modem Operation Explained 4-9