Using TCP/IP allows data to be sent as packets, instead of a byte stream as per serial. The advantage is that this prevents mis-interpreting messages sent, when bytes are dropped, or the definition of the message is different.
Suppose we have:
Computer1 -> USB-Serial Converter -> Serial Cable -> Serial->USB Converter -> Computer 2
On computer 1 we type :
pppd /dev/ttyUSB0 115200 lock nodetach noauth debug 18.104.22.168:22.214.171.124
On computer 2 we type:
pppd /dev/ttyUSB0 115200 lock nodetach noauth debug
And watch it connect!
You should see a new device (usually ppp0) when you type:
See full pppd documentation here: http://linux.die.net/man/8/pppd
Increasing Connection Re-tries
Should you need the pppd to keep trying to connect, you can add the following flag at the back of your command – lcp-max-configure
pppd /dev/ttyUSB0 115200 lock nodetach noauth debug lcp-max-configure 1000000 126.96.36.199:188.8.131.52
where 1000000 is number of times pppd tries to connect to the other party.