socat を使う (シリアル-TCP変換, etc.) で紹介した socat を使用する場合、シリアルポートの設定(ビットレート、キャラクタバイト数など)を変更することはできません。
シリアルポートの設定変更に対応したプロトコルとして RFC-2217 - Telnet Com Port Control Option というものが策定されており、それに対応したアプリケーションが ser2net です。

/etc/ser2net.conf ファイルを作成・編集します。
サンプルファイルとして、/etc/ser2net.conf.example というファイルが入っていますので、それを変更して作成すると楽です。

ser2net.conf.example

#
# This is the configuration file for ser2net.  It has the following format:
#  <TCP port>:<state>:<timeout>:<device>:<options>
#     TCP port
#            Name   or  number of the TCP/IP port to accept con-
#            nections from for this device.  A port number may
#            be of the form [host,]port, such as 127.0.0.1,2000
#            or localhost,2000.  If this is specified, it will
#            only bind to the IP address specified. Otherwise
#            it will bind to all the ports on the machine.
#
#     state  Either raw or rawlp or telnet or off.  off disables
#            the  port  from  accepting  connections.  It can be
#            turned on later from the control port.  raw enables
#            the port and  transfers  all data as-is between the
#            port  and  the long.  rawlp  enables  the port  and
#            transfers  all input data to device, device is open
#            without  any  termios  setting.  It  allow  to  use
#            /dev/lpX  devices  and  printers connected to them.
#            telnet enables the port and runs the telnet  proto-
#            col  on the port to set up telnet parameters.  This
#            is most useful for using telnet.
#
#     timeout
#            The time (in seconds) before the port will be  dis-
#            connected  if  there  is no activity on it.  A zero
#            value disables this funciton.
#
#     device The  name  of  the  device   to  connect  to.  This
#            must be in the form of /dev/<device>.
#
#     options
#            Sets  operational  parameters  for the serial port.
#            Options 300, 1200, 2400, 4800, 9600, 19200, 38400,
#            57600, 115200 set the various baud rates.  EVEN,
#            ODD, NONE set the parity.  1STOPBIT, 2STOPBITS set
#            the number of stop bits.  7DATABITS, 8DATABITS set
#            the number of data bits.  [-]XONXOFF turns on (-
#            off) XON/XOFF support.  [-]RTSCTS turns on (- off)
#            hardware flow control, [-]LOCAL turns off (- on)
#            monitoring of the modem lines, and
#            [-]HANGUP_WHEN_DONE turns on (- off) lowering the
#            modem control lines when the connextion is done. 
#	     NOBREAK disables automatic setting of the break
#	     setting of the serial port.
#            The "remctl" option allow remote control (ala RFC
#            2217) of serial-port configuration.  A banner name
#            may also be specified, that banner will be printed
#            for the line.  If no banner is given, then no
#            banner is printed.
#
# or...
 
#  BANNER:<banner name>:banner
#    This will create a banner, if the banner name is given in the
#    options of a line, that banner will be printed.  This takes the
#    standard "C" \x characters (\r is carraige return, \n is newline,
#    etc.).  It also accepts \d, which prints the device name, \p,
#    which prints the TCP port number, and \s which prints the serial
#    parameters (eg 9600N81).  Banners can span lines if the last
#    character on a line is '\'.  Note that you *must* use \r\n to
#    start a new line.
#
# Note that the same device can be listed multiple times under different
# ports, this allows the same serial port to have both telnet and raw
# protocols.
 
# The original config file shipped with the upstream sources can be
# found in /usr/share/doc/ser2net/examples
 
BANNER:banner:\r\nser2net port \p device \d [\s] (Debian GNU/Linux)\r\n\r\n
 
2000:telnet:600:/dev/ttyS0:9600 8DATABITS NONE 1STOPBIT banner
2001:telnet:600:/dev/ttyS1:9600 8DATABITS NONE 1STOPBIT banner
3000:telnet:600:/dev/ttyS0:19200 8DATABITS NONE 1STOPBIT banner
3001:telnet:600:/dev/ttyS1:19200 8DATABITS NONE 1STOPBIT banner

Windows からアクセスするためのドライバもあります。

• HW VSP3 - Virtual Serial Port

• Free, unrestricted Virtual Serial Port driver for any TCP/IP devices
• Compatible with Windows 2000, XP (Win 98, NT), Windows 8 & even 32-bit or 64 bit.
• Runs as a standalone application, or as a NT service suitable for servers

• This software is FREEWARE, as long as you comply with the license terms and conditions

64bit にも対応しているという点がいいですね。

• http://com0com.sourceforge.net/