AWS IoT Core - mqtt_helper connection was unexpectedly closed - Telstra/Simbase

[Craig12]

We have an nRF9160 based product with firmware based on your AWS IoT Core example.

Our devices are connected to the Telstra CAT-M1 Network in Australia (50501) using Modem Firmware1.3.6.

When using a global SIM card from Simbase, we frequently get data sessions that appear to result in no data flow after approximately 20 minutes. This may repeat a couple of times, and then stay connected for a longer period, i.e. days.

On the console, we get:

00> [00:20:17.619,140] <inf> lte: RRC mode: Connected
00> [00:20:17.619,812] <inf> lte: RSRP: -103dBm (37)
00> [00:20:18.563,262] <err> mqtt_helper: Socket error: POLLERR
00> [00:20:18.563,262] <err> mqtt_helper: Connection was unexpectedly closed
00> [00:20:18.563,995] <inf> aws: AWS_IOT_EVT_DISCONNECTED

Using wireshark to look at the modem trace, every 4.5 minutes there appears to be a TCP packet sent from the modem to AWS.

At 1216 seconds (20 minutes), the device starts to perform a DNS lookup and there appears to be no response. I suspect no dataflow.

We only have this problem with Simbase (roaming). We have tried a Hologram SIM (roaming) on Telstra and a SIM homed on the Telstra Network - they both appear to operate fine with long session times. I have contacted Simbase, but they provide a response that they have lots of devices connected using their SIMs to Telstra with no issues.

I note another ticket on DevZone with something similar. When looking at the AT commands, they just happen to be using Simbase on the Telstra Network (50501)
devzone.nordicsemi.com/.../438479

Would you be able to indicate if the modem trace shows anything that could be useful in narrowing down this problem? Or if the problem is upstream of the Telstra RAN.

trace-2024-08-15T12-26-25.945Z.zip

[Øyvind]

Hello, 

From the initial look at the modem trace it appears that the device is disconnected i.e. connection reset, afterwards the device will timout. 

Are there any special Packet Data Networks (PDN) settings that are needed to connect to the network? 

I note another ticket on DevZone with something similar. When looking at the AT commands, they just happen to be using Simbase on the Telstra Network (50501)

It does look similar but I'm not able to tell from my initial look. The DevZone case you referred to does receive ESM 50 - 

Cause #50 – PDN type IPv4 only allowed This ESM cause is used by the network to indicate that only PDN type IPv4 is allowed for the requested PDN connectivity.

There could be an issue with IPv6 vs IPv4. Could you please try setting the following settings in your prj.conf

CONFIG_NET_IPV4=y

CONFIG_NET_IPV6=n

Also, could you please collect a modem trace from the Hologram SIM and/or Telstra home SiM?

Thanks!

Kind regards,
Øyvind