The tutorials explain how to set up the 3G/4G hats using PPP and QMI protocols, but which one is better? I’m using Quectel EC-25x modules and either the SixFab SIM or Verizon SIM. I’m currently using PPP, but wonder if I should switch. I have two applications: #1 is 500kbits/sec data only, the other is HD video (1280X960@30fps). BOTH ends are mobile. I use LogMeIn Hamachi to deal with the IP addressing issues. I need to be able to automatically reconnect if the cell signal “disappears” and later “re-appears”. I don’t know how much of that is handled by the various protocols, and how much I’ll have to do in a cron task. But if someone has some answers, I would like to know.
Hey @charles, you might want to take a look at this section of the docs.
Which one among PPP & QMI should I select?
PPP is a data layer communication protocol that is established through the serial port of the modem. These Serial port communication could be either the UART(/dev/ttyS0) or the serial exposed to USB(/dev/ttyUSB3). This serial is also used for both modem commands (AT commands) and responses. This connection is established by dial-up (ATD*99#).
PPP is easy to establish, widely used protocol, and flexible with the devices. PPP may show a drop of the connection while using the AT command set for other functionality of modem.
The LTE radio protocol has native support of TCP/IP and IPv6, so there is no need to actually wrap TCP/IP into PPP over the radio interface. The PPP protocol is just used between the computer and the modem to make the connection look like a legacy dial-up modem-based network connection.
To get rid of the legacy cruft, newer ways to present USB-connected LTE modems like QMI and MBIM have been developed.
Quectel modules offer QMI(Qualcomm MSM Interface) which is established as a real network interface, such as ethernet(typically shows as wwan0). The QMI is also counted among the non-AT protocols which are communicated over /dev/cdc-wdm0 port.
In order to establish a connection, proper qmi/gobinet proxy should be installed, which again depends on the chipset of the module/modem and the kernel of Linux, gets a bit complicated. The QMI offers a more accessible and faster connection compared to the PPP protocol.
We recommend QMI, if you are looking for a faster connection, and for a longer duration.
Speaking from experience, I have a Telit LE910-EU V2 that I use over PPP and was only able to get 8 to 10Mbps with the small antennas that SixFab has on their store.
I also have a Quectel EP06 that I got to try QMI but haven’t had the chance to test just yet…