To use internet over Serial, you can create dial-up ppp connection from linux to RV50.
You can refer this document to setup a ppp connection on linux https://source.sierrawireless.com/resources/airprime/application_notes_and_code_samples/airprime_-ppp_using_linux-_application_note/#sthash.Vd3XlTcy.dpbs
Below is some notes that you can setup quickly a ppp connection with None authentication:
On RV50, Go to ACE manager -> Serial -> RS232 configuration ->General -> Enable RS232, Startup mode =“Normal”, DB9 Serial Echo field to Disable.
PPP tab -> Enter device IP, host IP ( default is 192.168.15.x) -> Select authentication (None)
On Linux host, create “gsm” and “gsm_chat” file under /etc/ppp/peers (update correct USB com port on your linux), I attached the example here peers.7z (818 Bytes)
Execute command: pppd file gsm
No driver is required on linux host
Hope it can help.