Quectel EC25 & AT&T connection Catch-22

[Bruce Johnson]

I have a question about using both QMI and the serial interface with ModemManager.

I had little difficulty getting ModemManager's SimpleModem to connect to T-Mobile (USA) using a Quectel EG25-G, but we found that modem wasn't compatible with AT&T and/or a private APN used by one of our customers. We were advised to use the Quectel EC25, and after engaging both Quectel and AT&T, we were told that we need to insert the APN into the modem using an AT command, AT+CGDCONT=1,"IPV4V6","mcm.com.attz". I had to tweak the kernel config and the ModemManager build.

Mods:

  *   I built ModemManager 1.18.4 with --with-at-command-via-dbus.
  *   In the kernel config, I added USB Serial Converter support -> USB driver for GSM and CDMA modems.

After I did this, the /dev/ttyUSB[1-4] files showed up, and I was able to issue AT commands using ModemManager, but while the modem would sort-of connect with SimpleModem's connect method -- I am getting a Bearer, and mmcli shows "connected" -- I receive no IP address information from the carrier. Port wwan0 is showing up as "ignored". (mmcli output below)

The Quectel docs also said to patch the kernel a certain way to allow use of serial and the QMI_WWAN driver, but wwan0 is still ignored.

Does anyone have any suggestions?

Thanks!

--
Bruce Johnson
Chantilly, Virginia
USA


  --------------------------------
  General  |                 path: /org/freedesktop/ModemManager1/Modem/0
           |            device id: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
  --------------------------------
  Hardware |         manufacturer: Quectel
           |                model: EC25
           |    firmware revision: EC25AFFAR07A14M4G
           |            supported: gsm-umts, lte
           |              current: gsm-umts, lte
           |         equipment id: 359401089771197
  --------------------------------
  System   |               device: /sys/devices/pci0000:00/0000:00:15.0/usb1/1-4
           |              drivers: option, qmi_wwan
           |               plugin: quectel
           |         primary port: ttyUSB3
           |                ports: ttyUSB2 (gps), ttyUSB3 (at), ttyUSB4 (at), wwan0 (ignored)
  --------------------------------
  Status   |       unlock retries: sim-pin (3), sim-puk (10), sim-pin2 (3), sim-puk2 (10)
           |                state: connected
           |          power state: on
           |          access tech: lte
           |       signal quality: 60% (recent)
  --------------------------------
  Modes    |            supported: allowed: 2g, 3g, 4g; preferred: none
           |              current: allowed: 2g, 3g, 4g; preferred: none
  --------------------------------
  IP       |            supported: ipv4, ipv6, ipv4v6
  --------------------------------
  3GPP     |                 imei: 3594010XXXXXXXX
           |          operator id: 310410
           |        operator name: AT&T
           |         registration: home
  --------------------------------
  3GPP EPS | ue mode of operation: csps-2
  --------------------------------
  SIM      |     primary sim path: /org/freedesktop/ModemManager1/SIM/0
  --------------------------------
  Bearer   |                paths: /org/freedesktop/ModemManager1/Bearer/0


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