Ser2net

download and install
# sudo apt-get install ser2net

modify the config file
# sudo /etc/ser2net.conf

3001:telnet:0:/dev/ttyUSB0:9600 8DATABITS NONE 1STOPBIT banner
3002:telnet:0:/dev/ttyUSB1:9600 8DATABITS NONE 1STOPBIT banner
3003:telnet:0:/dev/ttyUSB2:9600 8DATABITS NONE 1STOPBIT banner
3004:telnet:0:/dev/ttyUSB3:9600 8DATABITS NONE 1STOPBIT banner
(looks like 2001:telnet:600  ….,  changed 0 so it won’t time out )

restart the ser2net:
# sudo /etc/init.d/ser2net restart

telnet localhost 3001 
telnet localhost 3002
telnet localhost 3003
telnet localhost 3004