Router - Flexible, Detail Description; Router - Flexible, Functionality Example - RACOM RipEX User Manual

RipEX in detail

2.3.1. Router - Flexible, Detail description

Router mode with Flexible protocol is suitable for Multipoint networks of all topologies with unlimited
number of repeaters on the way, and all types of network traffic where Multi-master applications and
any combination of simultaneous polling and/or report-by-exception protocols can be used
Each RipEX can access the Radio channel spontaneously using sophisticated algorithms to prevent
collisions when transmitting to the Radio channel. Radio channel access is a proprietary combination
of CSMA and TDMA; the Radio channel is deemed to be free when there is no noise, no interfering
signals and no frames being transmitted by other RipEX stations. In this situation, a random selection
of time slots follows and a frame is then transmitted on the Radio channel.
Frame acknowledgement, retransmissions and CRC check, guarantee data delivery and integrity even
under harsh interference conditions on the Radio channel.

2.3.2. Router - Flexible, Functionality example

In the following example, there are two independent SCADA devices connected to RipEX's two COM
ports. One is designated RTU (Remote Telemetry Unit) and is assumed to be polled from the centre
by the FEP (Front End Processor). The other is labelled PLC (Programmable Logic Controller) and is
assumed to communicate spontaneously with arbitrary chosen peer PLCs.
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Step 1
FEP sends a request packet for RTU1 through COM2 to
its connected RipEX.
Simultaneously PLC2 sends a packet for PLC1 to RipEX2
through COM1.
Step 2
FEP's RipEX transmits an addressed packet for RTU1 on
Radio channel.
RipEX1 receives this packet, checks data integrity and
transmits the acknowledgement.
At the same time packet is sent to RTU1 through COM2.
RipEX3 receives this packet too. It doesn't react, because
this packet is directed to RipEX1 only.
Step 3
RipEX2 waits till previous transaction on Radio channel is
finished (anti-collision mechanism).
Then RipEX2 transmits on Radio channel the addressed
packet for PLC1.
RipEX1 receives this packet, checks data integrity and
transmits acknowledgement.
At the same time packet is sent to PLC1 through COM1.
Simultaneously the reply packet from RTU1 for FEP is re-
ceived on COM2.
RipEX Radio modem & Router – © RACOM s.r.o.