Issue with EM7431/EM7565 and SoftBank SIM in Japan – Communication Stops Unexpectedly

IoT Modules
1

We are using the Sierra Wireless EM7431 and EM7565 modules in Japan. However, when using a SoftBank SIM card, communication stops partway through and the module becomes unusable.

Here are the connection settings:

  • APN: m2m4biz.js
  • IP setting: IPv4

Interestingly, when we switch the firmware from SOFTBANK to GENERIC, the module works without any problems.

We reached out to SoftBank for support, but they mentioned they are not familiar with the module itself.

Additionally, we found that light data usage (such as simple Google searches) sometimes works, but when trying to access heavier sites like Amazon, the communication stops completely.

Has anyone experienced a similar issue or found a solution? Any advice would be appreciated.

2

i checked from the internet, the APN of local SoftBank SIM card should be “plus.4g”.
Are you using roaming SIM card?
Why can’t you use GENERIC PRI ?

3

Thank you for your response.

We are using a local SoftBank M2M SIM, not a roaming SIM.
The APN we are using — m2m4biz.js — was provided directly by our SoftBank account representative at the time of purchase.
From what we understand, plus.4g is typically used for consumer or smartphone SIMs, whereas m2m4biz.js is specific to M2M applications.

Regarding the use of the GENERIC PRI, yes, it works without any issues.
However, SoftBank has specifically instructed us to use the SOFTBANK carrier firmware/PRI for proper compatibility with their M2M services and network certification.

4

what is the return of AT!GSTATUS? and aT+CGREG? when you were using GENERIC PRI?

BTW, are you using the latest FW already?
https://source.sierrawireless.com/resources/airprime/minicard/74xx/em_mc74x1-approved-fw-packages/#sthash.mtfHJ971.nswKOQYi.dpbs

When you first load the SOFTBANK firmware to module, what is the default APN in AT+CGDCONT?
Is it already using “plus.4g”?

5
  1. Regarding GENERIC PRI operation:
    When using the GENERIC PRI, the module connects normally and functions without issues.
    Here are the responses from the relevant AT commands:
  • AT!GSTATUS?:
    • Mode: ONLINE
    • System mode: LTE
    • PS state: Attached
    • RRC state: RRC Connected
    • EMM state: Registered
    • SINR: 4.2 dB
      (Full output available if needed.)
  • AT+CGREG?:
    • Response: +CGREG: 0,1 (registered, home network)
  1. Firmware version:
    We initially used an older firmware version, but the issue persisted even after updating to the latest version from Sierra Wireless.
    Here’s the result of AT!IMPREF?:
!IMPREF:  
 preferred fw version:    00.00.00.00  
 preferred carrier name:  AUTO-SIM  
 preferred config name:   AUTO-SIM_000.000_000  
 preferred subpri index:  000  
 current fw version:      01.14.25.01
 current carrier name:    SOFTBANK
 current config name:     SOFTBANK_002.051_000
 current subpri index:    000'
  1. APN settings and behavior:
    After flashing the SOFTBANK firmware, the default APN shown in AT+CGDCONT? was:
+CGDCONT: 1,"IPV4V6","plus.4g","0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0",0,0,0,0'

We configure the APN using mmcli, with the following setting:

+CGDCONT: 1,"IP","m2m4biz.js","0.0.0.0",0,0,0,0
6

probably the SOFTBANK firmware is for SIM with APN “plus.4g”

BTW, why don’t you just use GENERIC firmware which is working fine now?
is it breaking some regulation?

7

We did some further testing and found that reducing the MTU to 1200 allows communication to work, even when using the SOFTBANK firmware with the “m2m4biz.js” APN.

It seems the issue was related to packet size — larger payloads were likely getting dropped or blocked.

We are currently contacting SoftBank to confirm whether 1200 is an appropriate value and to ask if they recommend an official MTU setting for their M2M SIMs.

So far, setting MTU to 1200 is a working solution.