Specifications

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

Data checking

Before sending to the radio channel the checksum is calculated. After data is received from RFC it is

checked. If the CRC does not match the packet is discarded.

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.

Description