Connection keeps dropping, cannot keepalive

Connectivity LTE Cat-M1 & NB-IoT
1

Hi all,

I’ve raised this as a ‘ticket’ via support@hologram.io as the general help pages suggest I should do that - however, it feels like somebody in the community must have come across this too.

I am having trouble staying connected to the Hologram network, I initially thought this was a hardware problem – so have posted directly on the support forum of my manufacturers hardware (Thales Cinterion modules). The initial thread is here, which details the hardware, and the troubleshooting steps that I’ve taken so far.

I’ve followed the Hologram troubleshooting guide, and run the series of AT commands.

AT
OK
ATI
I
Cinterion
EXS62-W
REVISION 01.100
OK
AT+CGMI
+CGMI
Cinterion
OK
AT+CGMM
+CGMM
EXS62-W
OK
AT+GMM
+GMM
EXS62-W
OK
AT+CPIN?
+CPIN?
+CPIN: READY
OK
AT+CCID
+CCID
+CME ERROR: unknown
AT+CRSM=176,28539,0,0,12
+CRSM=176,28539,0,0,12
+CRSM: 144,0,“FFFFFFFFFFFFFFFFFFFFFFFF”
OK
AT+CFUN?
+CFUN?
+CFUN: 1
OK
AT+CSQ
+CSQ
+CSQ: 19,99
OK
AT+CREG?
+CREG?
+CREG: 0,5
OK
AT+CGREG?
+CGREG?
+CGREG: 0,5
OK
AT+CEREG?
+CEREG?
+CEREG: 0,5
OK
AT+CGDCONT?
+CGDCONT?
+CGDCONT: 1,“IP”,“hologram”,“0.0.0.0”,0,0
+CGDCONT: 2,“IPV4V6”,“attm2mglobal”,“0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0”,0,0
+CGDCONT: 3,“IPV4V6”,“m2m.com.attz”,“0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0”,0,0
OK
AT+CGACT?
+CGACT?
+CGACT: 1,1
+CGACT: 2,0
+CGACT: 3,0
OK
AT+COPS?
+COPS?
+COPS: 0,0,“O2 - UK”,7
OK
AT+COPS=?
+COPS=?
+COPS: (2,“O2 - UK”,“O2 - UK”,“23410”,7),(0,1,2,3,4),(0,1,2)
OK

It would appear AT+CCID is not supported by my device, but AT^SCID appears to return the ICCID from the SIM.

AT^SCID
^SCID
^SCID: 8944502210209402147
OK

Furthermore, AT+CEREG? Does not appear to return the information that the Hologram guide suggests.

I’ve tried configuring a 1, 2, 5, 10 and 15 second keepalives in an MQTT session too – and there seems to be no improvement, if anything – the disconnection seems to happen even faster with shorter keepalives.

The bit I really can’t get my head around, is needing to restart the device every time before I can make a new connection - almost as if my dynamically allocated IP has been ‘blacklisted’.

Hoping somebody in the community can help with this one!
All the best

2

So having reread the definition of a keepalive period in the MQTT spec, I see now such short times down in the 1, 5sec range are causing my session to be killed almost immediately.

I had interpreted the time spec as being time being keep alive handshakes.

However, setting the timer to 600s - whilst I can stay connected for around a minute or so, I still get disconnected.

And of course, if you ignore the MQTT session entirely - fundamentally my connection still gets dropped around the minute mark.

3

I have also tried reading the connection status with AT^SISI=1, which returns the following:

^SISI=1
^SISI: 1,4,0,0,0,0
OK

This is apparently an ‘UP’ (4) service status on profile 1. However, this same report is returned before, or after the loss of the MQTT session, and the ability to ping anything.

4

As a further experiment, I have just been able to keep a connection alive by automatically sending a ping every 1 second, for 10 minutes (albeit with some packet loss). Note, it didn’t fail at 10 minutes whilst sending 1 second interval pings, but rather I stopped sending these pings due to the high data consumption this test was causing.

So as soon as I stop sending these pings - if I let the connection sit for even a few seconds - it drops. The data overhead to keep this connection live then is significant.

After this disconnection, I’m still experiencing the same issue where I am unable to reconnect to the internet without a power cycle, or software reset. Ping simply returns 100% packet loss.

With a 10 second ping interval, the connection remained up for only 90 seconds before all pings started returning 100% packet loss.

With a 5 second ping interval - same thing - only 90 seconds before disconnection again.

With a 1.5second ping interval - 7 min 38 sec before disconnection.

With a 2 second ping interval, 176 seconds before disconnection.

5

OK, this evening I switched to a second Hologram SIM, with a Maker Edition Flexible Data plan instead of the Pilot Plan - 1MB.

After activation, this card seemed to provide much better connectivity; I was able to keep a connection open with pings every 10 sec, for 10 minutes before the connection dropped. However, it seems to have ‘reverted’ to the same level of poor connectivity as the first card.

Also worth noting, during an MQTT session - after the connection drops, AT^SISI? returns a status code of UP (4) even though the connection clearly is not UP.

^SISI?
^SISI: 0,""
^SISI: 1,4,7,0,0,0
^SISI: 2,""
^SISI: 3,""
^SISI: 4,""
^SISI: 5,""
^SISI: 6,""
^SISI: 7,""
^SISI: 8,""
^SISI: 9,""
OK

6

Looks like progress this evening, I have configured the modem using AT^SXRAT=7 (Selection of Radio Access Technology), to force the modem into LTE CAT.M1 only mode, rather than LTE CAT.M1 / NB1 dual mode.

After doing this, I have held a connection open for 1 hour with 10 second interval pings (up from 90sec before).

I will attempt an overnight connection with a 60 second interval.

7

OK, we have been able to hold an active connection open for 24 hours, with pings only every 5 minutes., after forcing the module into LTE-M only mode. The connection wasn’t lost at 24 hours, we closed it ourselves at that point at it was evident we have a good connection. We have successfully transferred nearly 1MB of data via MQTT over this link too.

Forcing the module into NB-IoT mode only - we have been unable to establish a connection at all.

From what I can deduce from various web searches - the Hologram network is connecting us to O2 in the UK, whom seem only to provide LTE-M access, not NB-IoT. Is this correct?

Vodafone in the UK however seem to provide NB-IoT, but not LTE-M. Is this Hologram’s understanding? And if so - does Hologram therefore not provide NB-IoT access in the UK? This is critical for our application, as we would like to be using NB-IoT, not LTE-M, for the benefits of lower power consumption and increase signal penetration.

I really hope to hear back from your team at Hologram soon, as unfortunately I’ve heard nothing on these support forums, or a response to a support email in over a fortnight just yet.

8

Good evening, is there any progress on some feedback in relation to this issue? It has been over 30 days since posting this initially, and contacting your support team directly.

9

Hi, I can double check on coverage for you on Monday but we mostly don’t support NB with our partners yet as a lot of the roaming deals are still being worked out. What’s the reason for keeping the connection up all the time? Cat-M can be very efficient and get you more speed than NB if you power down the radio every so often

10

BTW as for keeping it open you may want to experiment with turning off some of the Cat-M power saving features like eDRX. They can cause the radio to disconnect more frequently. You’ll need to consult your modern docs about that

11

Hi Rueben,

Thanks for getting back to me - it would be great to understand the situation in the UK as it stands now in relation to NB-IoT availability on the Hologram network.

Ref keeping the link open though, I don’t have a requirement for continuous connection per se - only a few minutes at a time - the issue is that I simply can’t hold an NB-IoT connection open without continuous traffic (data or pings) without losing the connection at all.

Thanks for the tips ref eDRX, I’ll go investigate.

All the best.

12

Hi Reuben,

Is there any update on the status with UK carriers, as above?

Regards