At the most basic level, all serial to
Ethernet transmissions consist of packets of data represented by voltage
changes in an electrical signal. However, different applications require
different higher level structure. For example, some applications may
require that the serial device initiates the transmission, with the
application program on a PC waiting passively for incoming data.
For other applications the situation could be reversed.
In other instances, engineers may want to modify an existing serial device
application - in which the serial device is connected directly to the
computer - to an application for which the serial device is connected
"over the network" with the help of a serial terminal
server.
In general, the mode name describes the behavior of a
serial terminal server in relation to one or more
network hosts. The operation modes supported by
serial terminal server are divided into two classes - Socket and Real
COM.
Socket Mode - TCP Server
When the serial terminal server is configured
for TCP Server mode, the serial terminal server
acts like a server. That is, the serial terminal
server establishes a unique IP:Port address on the TCP/IP network, and
then waits passively to be contacted by a host (the host plays the role of
Client). Once a connection has been established, the host computer can
receive and transmit data to and from the serial device.
TCP Server mode supports up to 4 simultaneous connections, allowing
multiple hosts to communicate with the same serial device, at the same
time.
Benefits
- OS-independent
- Hosts can poll serial devices over a TCP/IP network
- Supports up to 4 simultaneous connections
Socket Mode - TCP Client
When the serial terminal server is configured
for TCP Client mode, the serial terminal server
acts like a client. That is, the serial terminal
server establishes a unique IP:Port address on the TCP/IP network, and
then actively contacts one or more hosts (the hosts play the role of
Server). Once a connection has been established, the hosts can receive and
transmit data to and from the serial device.
TCP Client mode supports up to 4 simultaneous connections, allowing
multiple hosts to communicate with the same serial device, at the same
time.
Benefits
- OS-independent
- Event handing over TCP/IP
- Supports up to 4 simultaneous connections
Socket Mode - UDP
Compared to TCP communication, UDP is faster and more efficient. In UDP
mode, you can unicast or multicast data from the serial device to one or
multiple host computers, and the serial device can also receive data from
one or multiple host computers, making this mode ideal for message display
applications.
TCP Client mode supports up to 4 simultaneous connections, allowing
multiple hosts to communicate with the same serial device, at the same
time.
Benefits
- OS-independent
- Multicasting over TCP/IP
Virtual COM Mode (COM Port Redirection)
Serial terminal server manufacturers should
provide COM drivers that work with Windows 95/98/ME, NT/2000, and XP/2003
systems, and also TTY drivers for Linux systems. The driver establishes a
transparent connection between host and serial device by mapping the
IP:Port of the serial terminal server's serial
port to a local COM/TTY port on the host
computer.
Benefits
- Upgrade COM/TTY applications to Ethernet without modifying your
application source code
