Failure to receive IP address since 12-Sep-2018


#1

Abruptly yesterday our devices using SIMCOM 7000E and uBlox SARA-G350 cellular modems started having issues receiving IP addresses from the UK 2G cell networks. We can see them connecting to a network, but sometimes not being allocated an IP address.

This was a non-issue for us up until yesterday, but since the 12th it is happening to multiple devices, but not all of them. Is anyone else seeing similar issues?


#2

Hey @iainwoolley,

Can you please email success@hologram.io with the SIM numbers of the devices that are giving you issues.

I want to check our back-end to see if there is anything we can spot.

Cheers,
Maiky


#3

To close this thread off, we now strongly suspect we know what was happening:

Whilst Hologram have roaming agreements with a lot of operators, the SIM does not roam on all networks. Additionally the info on the Hologram dashboard lags the real world by a period of time.

So both of our modems were connecting to a network that Hologram does not roam onto. The modem was able to connect, but was refused an IP address. Looking on the dashboard the info we were seeing was the last connection to a supported network, not the current network.

Our fix has been to code the list of supported networks into our firmware, and then lock the modem to one of the Hologram supported networks using AT+COPS.

Pedantically this might not be a SIM issue, but a modem issue. But it does imply that simply powering up the modem, connecting to any old network and asking for an IP address may not always work.


#4

Hi @iainwoolley,

Thanks for reaching out and sorry to hear you are experiencing trouble. A device cannot connect to a tower operated by a network that a selected plan does not have access to, so your suspicion is incorrect as your device would not be allowed to attach to the tower in that scenario long before a PDP context could be attempted to be created (which is when the device attempts to access an APN and obtain an IP address).

During the operator scan, when a device solicits attaching to a tower, that request is sent back to our network where our network approves or denies the request. Once approved, a device is then allowed to attach to the tower, and after it is attached then a device must set the APN configuration appropriately and create a PDP context to enable a data session. If a particular operator is not accessible via Hologram, the attach would not succeed and the module will continue its operator scan to find another suitable operator in range.

The situation you described, where a device attaches to a tower but does not obtain an IP address, can occur only for one of the following reasons:

  • Device does not have the hologram APN set correctly (you can check this with the AT+CGDCONT? command if supported by your hardware)
  • A problem with the local visiting network (very rare)

If you have not already done so, please reach out to success@hologram.io so we can diagnose the issue you’re experiencing, and we’d be happy to help track down the fault.

Best,
PFW


#5

Hi @HologramPat, thanks for responding. I’ve passed your comments on to the team, and we’ll investigate your points.

Iain