Communication over an Ethernet bridge
The data received on ETH channel are sent immediately to RFC. The packet received during RF
transmitting is discarded. The operating with the Repeater when the parameter NoR has a nonzero
value is a exception. The input buffer of depth 1 packet is used here. It allows accept the response
from ETH device connected in the short time after receiving the packet from RFC. The RFC transmitting
is suspended at that time, see the article Repeated packets.
The radio modem works as a standard Ethernet transparent bridge, i.e. received frames are filtered
and only frames for addresses behind the RF channel are transmitted to the RF channel. The only
exception are broadcast packets which are all transmitted to the RF channel.
More information on http://www.linux-foundation.org/en/Net:Bridge.
Example:
One RE400 is connected to a LAN1 segment, the second RE400 to a LAN2 segment. IP addresses
of both RE400 are not important for data transfer itself. They are used only for service purposes (setting
up parameters). It is FORBIDDEN, however, to set the IP address of any radio modem to the same
value of any equipment in either LAN1 or LAN2 segments.
The first RE400 connected to LAN1 processes frames as follows:
•
broadcast (arp req) and arp reply... — transmitted to RF channel
•
frame for destination addresses within LAN1 segment — discarded
•
frame for destination addresses within LAN2 segment — transmitted to RF channel
Repeater function
If station RE400 has the
Repeater
function switched ON then the received packet will again send an-
other packet to the RF channel. The packet received from the RF channel is also sent to SCC or to the
ETH port. In the radio network it is also possible to use more Repeaters without danger of cycling
packets. When switching on function Repeater it is necessary to enter the number of Repeaters in the
network into parameter
Number of repeaters
(NoR). Parameter NoR is set in the same way in all radio
modems of the network.
Repeated packets
Parameter
Number of repeaters
switches on protection mechanisms which prevent collisions with
packets sent by the repeater. After transmitting or receiving a packet from RFC further transmission is
blocked for the required period to prevent a collision with a packet sent by the Repeater. After transmitting
or receiving a packet from RFC recepit of its copy is checked and discarded.
These measures are not active when parameter NoR is zero, i.e. in a network without Repeaters.
Compression
There is built in compression on the RF channel. Its final efficiency depends on the data structure, of
course.
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© RACOM s.r.o. – Narrowband radio modem ECONOMY RE400
Description