High Latency in NB-IoT communication using Telefonica DE

RE: High Latency in NB-IoT communication using Telefonica DE

lobaro-theo — Mon, 03 Jul 2023 10:11:32 GMT

Hi,

thank you.

Over other channels I got also the information that this issue has been fixed in the O2/Telefonica network for 1/2 basestation vendors. So it might be solved in the future once they update also the 2nd vendor of base stations.

Thank you for your reply and ruling out a malfunction of the modem.

RE: High Latency in NB-IoT communication using Telefonica DE

Didrik Rokhaug — Fri, 30 Jun 2023 13:58:36 GMT

Hi, and sorry for the delay.

Due to summer vacations, it is harder than usual to find someone who can study the traces.

However, I got an answer in the end.

In NB-IoT, the network can automatically allocate uplink (UL) resources for a device (UE, short for User Equipment, in LTE-spec-speach) to send data or UE can request UL resources with RACH procedure. logicalChannelSR-ProhibitTimer (~16 s) is started when data becomes available and timer expiry will trigger RACH procedure if NW has not allocated UL resources before that. After each UL allocation retxBSR-Timer is started (~16s) and timer expiry will also trigger RACH procedure if there is data waiting for transmission.

In this case, one UL allocation is received after successful PDN activation. There is no data available for transmission yet and padding is sent instead, and the retxBSR timer is started. After that socket is opened and data is sent, but the network does not send new UL allocations, so no data is sent before the retxBSR timer expires and the UE requests UL resources.

The modem team means that the device works as expected. To reach fluent data flow with this NW configuration NW should allocate UL resources more frequently. After a successful PDN activation only one UL allocation is received.

RE: High Latency in NB-IoT communication using Telefonica DE

lobaro-theo — Wed, 21 Jun 2023 13:36:36 GMT

Yes it has been tested 1.3.5 also with same behavior, since the trace collector v2 (preview) app does not have support for it (yet) we used the 1.3.4.

RE: High Latency in NB-IoT communication using Telefonica DE

Didrik Rokhaug — Wed, 21 Jun 2023 13:32:03 GMT

Hi, I'll give the traces to the modem team so they can analyse them.

In the mean time, could you check if you see the same behaviour happens with modem FW v1.3.5?

I expect it to be something caused by the network, and not the modem FW, but it would be nice to have it confirmed.

Best regards,

Didrik