The server manages
communications between the Ethernet network and the serial ports. A serial
server can also interface to a wireless (Wi-Fi) network. Many sources offer
serial-server modules.
Serial servers can use defined Internet protocols for network communications.
The specifications are available from www.rfc-editor.org.
Most serial servers communicate via TCP (specification STD0007), which
defines a way of establishing a connection to a device and exchanging data with
acknowledgements, sequence numbers, and other features that help ensure reliable
transfers. Each serial port uses a separate TCP connection. UDP
(STD0006) is an alternative for applications that don??™t require TCP??™s reliability.
Some serial servers use Telnet connections. The Telnet specification
(STD0008) defines a protocol for transmitting characters and control data over
a TCP connection.
Information specific to COM ports and modems can use protocols defined in
Telnet Com Port Control Option (RFC 2217). This document defines commands
for setting COM-port parameters and flow-control methods, reading
"#$
COM1 3F8h 4
COM2 2F8h 3
COM3 3E8h 4 or 11
COM4 2E8h 3 or 10
Chapter 3
38
RS-232 status signals, writing to RS-232 control signals, and reading error
information and other line-state data.
On a PC, COM-port redirector software can cause a serial server??™s serial ports to
appear as local COM ports.
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