Proxima ASA 7911 - Manual (Page 16)

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In Figure 3 above, Serial Adapters 1 and 2 can communicate
with each other, as can Serial Adapters 3 and 4. Even though all
four units may be in range of one another and may “hear” the
others’ messages, each unit will filter out messages not intended
for it. Since this topology establishes a one-to-one, Master-
Station relationship between two Serial Adapters, it acts as a
wireless substitute for an RS-232 cable in a wide variety of
applications.
Using the TCP/IP protocol as the transport mechanism for
information, a Serial Adapter that receives a message from its
serial port will turn the message into a data packet that includes
the transmitting unit’s IP address and the destination unit’s IP
address.
The transmitting Serial Adapter will then “listen” on the radio
frequency to ensure that the other Serial Adapter is not transmit-
ting a packet. If free, the unit will transmit the packet. It will
wait for an acknowledgment from the receiving Serial Adapter
that the packet was received without error. If it does not receive
such an acknowledgment and it has not exceeded its maximum
retry count, the unit will retransmit the packet.
A receiving Serial Adapter will filter packets based on the
packet’s destination IP address. Only the unit with the correct IP
address will save the packet and send an acknowledgment back
to the source unit. Upon receiving a packet, the unit will also
extract the original message out of the packet and send it out
over the serial port. If there is an error in the packet, the unit
will ignore it. This guarantees the delivery of only error-free
transmissions.