Marcel Langmaier

IoT evangelist & blockchain enthusiast :-P

How to use a Sierra Wireless MC8705 Modem with Direct-IP with Linux

Apr
23

When I plugged my MC8705 in, the kernel registered 4 USB devices (ttyUSB0-ttyUSB3) and 3 WWAN devices (wwan0-wwan2).

[ 5.959823] usb 1-4: Product: MC8705
[ 5.959884] usb 1-4: Manufacturer: Sierra Wireless, Incorporated
[ 5.959953] usb 1-4: SerialNumber: 35711504055xxxx
[ 6.056142] usbcore: registered new interface driver usbserial
[ 6.057052] usbcore: registered new interface driver usbserial_generic
[ 6.057188] usbserial: USB Serial support registered for generic
[ 6.166970] usbcore: registered new interface driver sierra
[ 6.167111] usbserial: USB Serial support registered for Sierra USB modem
[ 6.168048] sierra 1-4:1.0: Sierra USB modem converter detected
[ 6.168905] usb 1-4: Sierra USB modem converter now attached to ttyUSB0
[ 6.169046] sierra 1-4:1.1: Sierra USB modem converter detected
[ 6.169925] usb 1-4: Sierra USB modem converter now attached to ttyUSB1
[ 6.170134] sierra 1-4:1.2: Sierra USB modem converter detected
[ 6.171019] usb 1-4: Sierra USB modem converter now attached to ttyUSB2
[ 6.171172] sierra 1-4:1.3: Sierra USB modem converter detected
[ 6.171937] usb 1-4: Sierra USB modem converter now attached to ttyUSB3
[ 6.183628] sierra_net 1-4:1.7 wwan0: register 'sierra_net' at usb-0000:00:1a.7-4, Sierra Wireless USB-to-WWAN Modem, 7e:dd:cc:23:01:07
[ 6.195037] sierra_net 1-4:1.10 wwan1: register 'sierra_net' at usb-0000:00:1a.7-4, Sierra Wireless USB-to-WWAN Modem, 7e:dd:cc:23:02:0a
[ 6.198488] sierra_net 1-4:1.11 wwan2: register 'sierra_net' at usb-0000:00:1a.7-4, Sierra Wireless USB-to-WWAN Modem, 7e:dd:cc:23:03:0b
[ 6.199872] usbcore: registered new interface driver sierra_net

I found out that ttyUSB3 was the AT Interface. The other Interfaces were not responding to AT commands. I was able to connect to the Internet via ppp over this Interface. But I had no interface left to query status information. Another limitation of using ppp is that the maximum speed is about 20MB/s. To overcome these problems I decided to use Direct-IP. But how could this be accomplished?

  1. Switch the modem to another mode (5). Use minicom on the AT interface of the modem to issue the following commands:
    at!entercnd="A710"
    OK
    at!udusbcomp=5
    OK
    at!reset
    OK
    

    If you are using a different type of Sierra MC modem have a look at the available modes with at!udusbcomp=?.

  2. Now the modem registeres a cdc_ether device, for me it’s eth1
  3. Use minicom again to connect the modem to the internet:
    at+cpin="xxxx"
    OK
    at+cgdcont=1,"IP","web.yesss.at"
    OK
    at!scact=1,1
    OK
    at!scpaddr=1
    !SCPADDR: 1,"10.174.193.103"
    

    Of course you have to use your apn setting. If you need credentials for ppp issue the at$qcpdpp=1,1,”password”,”username” command after setting the apn.

  4. Exit minicom and issue the following commands:
    dhclient eth1
    ip route delete default
    ip route add dev eth1
    

That’s it. Now you are connected to the internet without using the linux ppp daemon.

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