Data Connections start to fail on 7455

IoT Modules
1

I have problem with data connections (PDP / PDN) starting to fail using Twilio SIMs (ie TMO) in Canada.
The module works fine initially but the suddenly gets in a state where the PDP won’t activity. Because the Attach works, the module sits there unable to get a data connection.

ati

Manufacturer: Sierra Wireless, Incorporated

Model: EM7455

Revision: SWI9X30C_02.30.01.01 r7792 CARMD-EV-FRMWR2 2018/07/13 02:24:52

MEID: 35907306133302

ESN: 12802254084, 80226504

IMEI: 359073061333021

IMEI SV: 16

FSN: LF830284750410

+GCAP: +CGSM,+DS,+ES

:at!gstatus?

at!gstatus?

!GSTATUS:

Current Time: 271 Temperature: 45

Reset Counter: 7 Mode: ONLINE

System mode: WCDMA PS state: Attached

WCDMA band: WCDMA 850

WCDMA channel: 4412

MM (CS) state: IDLE NORMAL SERVICE

WCDMA L1 state:L1M_PCH_SLEEP LAC: 2937 (10551)

RRC state: DISCONNECTED UTRAN Cell ID: 0DC2A7C1 (230860737)

RxM RSSI C0: -79 RxD RSSI C0: —

RxM RSSI C1: — RxD RSSI C1: —

OK

:at+cops?

at+cops?

+cops: 0,0,“TELUS”,2

OK

:at+cgact?

at+cgact?

+CGACT: 1,0

OK

:at+cgact=1,1

at+cgact=1,1

+CME ERROR: unknown

:at+cgdcont?

at+cgdcont?

+CGDCONT: 1,“IP”,“wireless.twilio.com”,“0.0.0.0”,0,0,0,0

Using the AT+CGACT=1,1 seems to return very quickly. It is as though the PDP Request was not sent to the network.
We debugged with TMO and they could see the Attach from the device but no data connection attempt.
Putting another SIM in the module seems to allow the condition to clear. We have hundreds of 7455 in field so swapping SIMs is not a real fix.
Do the 7455 have an internal state where it will block PDP attempts for a particular APN? Is there an AT command that could clear this condition?

Thanks.

2

From your description, the module works perfectly with the other SIM so the root cause might be not from the module. Can you verify that whether the original SIM is in data service (out of data)?
Thanks

3

Hi,
I am not sure what you mean by “In data service”. The SIM is active and paid for.
As I mentioned, original SIM is initially working before it gets in this “blocked PDP context” state. Once its in this state, if you take the original SIM out of the 7455 and put it in a phone, it is able to get data service. This points it being the module blocking the PDP activation.

4

Hi @fraser.gibbs .

I saw that the module selects Telus provider but the APN is configured [wireless.twilio.com]. Are you using the twilio SIM for roaming?

5

Yes. Twilio uses TMO-US. And we deploy a lot in Canada so Twilio is roaming in Canada.

6

Hi @fraser.gibbs,
I am thinking of the APN configured as the command below. Basically, When the module uses roaming SIM, it should be set APN to operator roaming (Telus). Can you double check it
Please share if you have any concerns
Thanks

7

Thanks for your replys. The instructions from TMO and Twilio are to use the twilio APN. As I mentioned, this set up has worked well for us most of the time but we occasionally have modules get in this state where the PDP won’t activate.
My suspision is that the module gets a spurious PDP reject from the network and the module blacklists the APN. Is that something that the 7455 does?

8

Hi @fraser.gibbs ,
There’s no option to block the APN on the module. As you share, the module works well most of the time and it occasionally loses connection. It means the issue is not from the configuration perspective. I doubt that the signal is not stable. Could you please check the antenna, and the other physical connections to make sure the module gets a good environment. Enable registration state notifications AT+CEREG=2. Can you check AT+CSQ when the module is attached but connected?

9

We are are confident this is not a signal related issue. We see this problem in multiple locations across the country. As I mentioned, initially the module is working fine, then without a physical change, it gets into this state. The CSQ is generally good. The module is able to Attach to the network just fine. It is just the PDP that is failing. Thus far evidence is that the module is blocking the PDP context attempt.
Thanks.

10

Hi @fraser.gibbs ,
To understand to issue, please help enable package domain event reporting by command AT+CGEREP=2. This might show the root cause. Please re-start the connection, monitor and share the event when the module goes to disconnected state
Thanks

11

Thanks. Following the AT+CGEREP commmand are the events reported over the AT channel? Or through another channel?

12

Hi @fraser.gibbs
The events of AT+CGEREP command are reported over the AT channel.
Thanks