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5
Establishing a (virtual) RS232 connection over Ethernet
Using an Ethernet Converter box it is possible to establish a virtual RS232 connection over Ethernet to transmit
and receive serial data to and from a remote location as if you're using a very long serial cable.
5.1
Supported protocols
To transmit serial data over the Ethernet two different protocols can be used: UDP and TCP. They both have
advantages and disadvantages depending on reliability and maximum throughput.
TCP: uses TCP/IP handshaking, so any lost or incorrectly received packets will be retransmitted. However,
because of the handshaking the maximum throughput over the Ethernet is variable, which makes it possible to
overflow the serial buffers if too much data is transmitted at once. Therefore when transmitting large blocks of
serial data over a TCP connection it is strongly recommended to listen to the CTS signal of the Ethernet box,
which indicates whether or the Ethernet box is ready to receive more data or not. Opticon barcode readers
support listening to the CTS signal by enabling the 'Modem handshaking' protocol (Menu option: 'P2') which
can be found in chapter 2.1.3 of the universal menu book, including a description on how RTS/CTS signals are
used for handshaking.
UDP: UDP uses no handshaking protocol, so data can be lost due to packet loss, since there are no
retransmissions using UDP. It is possible to add an extra protocol like Xmodem or NetO to fix this problem of
loosing packets. When no additional serial protocol is used it is recommended to use the TCP protocol for a
reliable transfer of serial data. The advantage of UDP is that maximum throughput will be higher than with TCP.
This means that if you use the virtual RS232 connection for:
Transmitting / receiving of small data packages (i.e. barcodes)
-> TCP is more reliable.
Transmitting / receiving large quantities of data
-> TCP in combination with modem handshaking is recommended (when no serial protocol is used)
-> UDP is recommended when using an additional serial protocol and a higher throughput is needed.
5.2
Finding remote Ethernet Converters
To find other Ethernet Converter boxes the following AT-command is available:
AT+DISCOVERY
Also an application like 'ECB Viewer' can be used to listen for power-up event of Ethernet boxes. This program
can passively listen to, but also actively discover using UDP port 30303 to retrieve IP-addresses of Ethernet
boxes that are located on the same LAN. (See chapter 2.2.3)
More information on how to discover Ethernet boxes using your own application can be found
in chapter 2.4.4.2.2.
Returns IP and MAC addresses of all Ethernet boxes that are connected on
the same local Ethernet.
Example of the search result:
Searching...
192.168.0.2 00-12-6A-00-12-34 OSE_ETHERNETBOX
192.168.0.14 00-12-6A-00-00-12 OSE_ETHERNETBOX2
Done
Opticon Ethernet Converter
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