(LTE-M) IP connectivity available only 3 seconds every 11 seconds

[Jesper Tiberg]

Hi,

Problem description

I wrote a program that initializes the modem (LTE-M) and goes on to send one UDP packet every second (is just the counter).

The server receives the first 2 or 3 packages, but then the next 10 or 11 are lost. This cycle repeats indefinately.

Does anyone know what's going on here?

PSM and eDRX is disabled (would this matter for outgoing data traffic?)

Cellular network is Telia @ Sweden.

SIM-card: iBasis or Telia LTE-M - same result

For a TCP connection (MQTT for example), this problem is slightly masked since (I guess) the lost packages during the 11 second downtime are resent during the 3 second uptime period - so looking at message logs it seems pretty fine unless you look at the time of arrival.

[Johan]

I have the same experience, but over TLS and TCP (with encryption) towards Amazon cloud.
I have sent traces to Nordic so far and they are investigating my case as well.
It doesn't happen in Norway according to Nordics tests.
Here in south Sweden with Telia it happens (Lund city).

[Jesper Tiberg]

Ok, I'm in Gothenburg area.

I found this issue when I was running a program acting as a "remote button" sending the events over MQTT from a Thingy:91 (both DK and Thingy has the issue).

Funny thing is that there was a day or two last week (when I happened to be traveling to Linköping) where I did not see the "lag" so I thought I had accidentally "fixed" the program during the last update.

Not sure if it was just a good day, if I was on another network, or if it was just due to me being on another cell though...

By the way, since you have the same issue:

Could you see if the problem still persists if you send data at least every 500 millis (see my reply above).

[Johan]

Sure I can test with 500ms between packets.

Do you also get a MQTT-ack ie data back (I use QOS_1, ie at least one response ACK) ? 

[Jesper Tiberg]

Yes, I was using QOS_1 as well.

The ack comes back after the "down" period of up to 10s.

I would guess the tcp packages are resent by the TCP/IP stack - but this is nothing I can see myself AFAIK. That's why I did verification and testing with udp packages instead.

[Johan]

Does the acks show up delayed even when you send every 500ms?

[Jesper Tiberg]

No, they are not delayed when sending every 500 millis.

For the udp tests I saw that at 600ms interval, the issue was present. At 500ms, it was not.

Using MQTT or even plain TCP might change this number a bit - I guess since several IP package is involved, both due to MQTT and TCP layers.