SO_RAI_NO_DATA still does not cause RRC release

[Michal Mühlpachr]

Issue is related to  RE: NRF_SO_RAI_NO_DATA does not cause RRC release in SLM/nrf9160 without send 

Just after AT#XSOCKETOPT=1,50 modem should negotiate RRC Release, but it is not the case.

NCS v2.3 nrf9160_1.3.4

Serial LTE Modem, prj.conf changes:
CONFIG_SLM_START_SLEEP=y
CONFIG_SLM_WAKEUP_PIN=6
CONFIG_SLM_INDICATE_PIN=2
CONFIG_SLM_DATAMODE_URC=y
CONFIG_SLM_EXTERNAL_XTAL=y
CONFIG_NRF_MODEM_LIB_TRACE=y

Modem Trace: trace-2023-03-15T22-56-29.105Z.bin

AT dialogue and PPKII measurements:

[PPK2] DUT Powered, Measurement started
   0.13 <RESET> Wed Mar 15 23:56:33 2023
   1.01 [PPK2] 100k/s AVG   4.02 mA    Max  28.6  mA
   1.25 <INDICATE transition> -> High
   2.03 [PPK2] 100k/s AVG   2.21 mA    Max  29.8  mA
   3.01 [PPK2] 100k/s AVG   0.002mA    Max   0.009mA
   4.02 [PPK2] 100k/s AVG   0.002mA    Max   0.008mA
   4.26 <WAKEUP>
   5.02 [PPK2] 100k/s AVG   1.11 mA    Max  24.5  mA
   5.60     [RX] Ready
   5.60 [TX] AT
   5.61     [RX] OK
   5.61 [TX] AT+CFUN=0
   5.77     [RX] OK
   5.77 [TX] AT%MDMEV=1
   5.78     [RX] OK
   5.78 [TX] AT%XPOFWARN=1,30
   5.80     [RX] OK
   5.80 [TX] AT%XTEMPHIGHLVL=60
   5.81     [RX] OK
   5.81 [TX] AT%HWVERSION
   5.81     [RX] %HWVERSION: nRF9160 SICA BQA
   5.81     [RX] OK
   5.81 [TX] AT%SHORTSWVER
   5.83     [RX] %SHORTSWVER: nrf9160_1.3.4
   5.83     [RX] OK
   5.83 [TX] AT#XSLMVER
   5.83     [RX] #XSLMVER: "2.3.0","2.3.1-8622ee1c632e"
   5.83     [RX] OK
   5.83 [TX] AT%XSYSTEMMODE=0,1,0,0
   5.85     [RX] OK
   5.85 [TX] AT%REL14FEAT=1,1,1,1,0
   5.86     [RX] OK
   5.86 [TX] AT%RAI=1
   5.86     [RX] OK
   5.87 [TX] AT%REDMOB=1
   5.88     [RX] OK
   5.88 [TX] AT%XDATAPRFL=0
   5.89     [RX] OK
   5.89 [TX] AT+CEPPI=1
   5.90     [RX] OK
   5.90 [TX] AT%XNETTIME=1
   5.91     [RX] OK
   5.91 [TX] AT+CNEC=24
   5.92     [RX] OK
   5.92 [TX] AT+CMEE=1
   5.93     [RX] OK
   5.93 [TX] AT%XSIM=1
   5.94     [RX] OK
   5.94 [TX] AT+CEREG=5
   5.95     [RX] OK
   5.95 [TX] AT+CSCON=1
   5.97     [RX] OK
   5.97 [TX] AT+CGEREP=1
   5.97     [RX] OK
   5.97 [TX] AT%XTIME=1
   5.99     [RX] OK
   5.99 [TX] AT%XMODEMSLEEP=1,500,10240
   6.00     [RX] OK
   6.00 [TX] AT+CPSMS=1,,,"00111000","00000000"
   6.00     [RX] %XMODEMSLEEP: 4
   6.00     [RX] OK
   6.01 [TX] AT%XBANDLOCK=1,"0000000000000000000000000000000000000000000000000000000000001000000010000000100010011010"
   6.02 [PPK2] 100k/s AVG   4.64 mA    Max  37.1  mA
   6.02     [RX] OK
   6.03 [TX] AT+COPS=1,2,"23003"
   6.05     [RX] OK
   6.05 [TX] AT+CGDCONT=1,"IP","hardwario.com"
   6.05     [RX] OK
   6.05 [TX] AT+CFUN=1
   6.10     [RX] OK
   6.11     [RX] %XMODEMSLEEP: 4,0
   7.01 [PPK2] 100k/s AVG  27.2  mA    Max  48.0  mA
   7.02     [RX] %XSIM: 1
   7.02 [TX] AT+CGSN
   7.02     [RX] 352656106109476
   7.02     [RX] OK
   7.02 [TX] AT+CIMI
   7.03     [RX] 901288000012723
   7.03     [RX] OK
   8.01 [PPK2] 100k/s AVG  35.5  mA    Max  65.8  mA
   9.00 [PPK2] 100k/s AVG  39.3  mA    Max  66.5  mA
  10.01 [PPK2] 100k/s AVG  19.2  mA    Max  62.9  mA
  11.02 [PPK2] 100k/s AVG   1.89 mA    Max   2.53 mA
  12.03 [PPK2] 100k/s AVG   1.89 mA    Max   2.50 mA
  13.01 [PPK2] 100k/s AVG   1.89 mA    Max   2.51 mA
  13.46     [RX] +CEREG: 2,"AE38","000AC51F",9
  14.01 [PPK2] 100k/s AVG   4.55 mA    Max  55.8  mA
  14.16     [RX] +CSCON: 1
  15.02 [PPK2] 100k/s AVG  33.2  mA    Max 290mA
  16.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.3  mA
  17.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.3  mA
  18.02 [PPK2] 100k/s AVG  33.6  mA    Max  46.1  mA
  19.01 [PPK2] 100k/s AVG  33.1  mA    Max  47.8  mA
  20.01 [PPK2] 100k/s AVG  33.2  mA    Max  46.5  mA
  21.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.3  mA
  22.02 [PPK2] 100k/s AVG  33.6  mA    Max  46.2  mA
  23.02 [PPK2] 100k/s AVG  33.6  mA    Max  46.3  mA
  24.02 [PPK2] 100k/s AVG  33.3  mA    Max  46.1  mA
  24.43     [RX] +CGEV: ME PDN ACT 0,0
  24.43     [RX] +CNEC_ESM: 50,0
  24.43     [RX] %MDMEV: SEARCH STATUS 2
  24.44     [RX] +CEREG: 5,"AE38","000AC51F",9,,,"00000000","00111000"
  24.44 [TX] AT+COPS?
  24.45     [RX] +COPS: 1,2,"23003",9
  24.45     [RX] OK
  24.45 [TX] AT%XCBAND
  24.46     [RX] %XCBAND: 20
  24.46     [RX] OK
  24.46 [TX] AT+CEINFO?
  24.46     [RX] +CEINFO: 0,1,C,8,1,-87,18
  24.46     [RX] OK
  24.46 [TX] AT+CGDCONT?
  24.47     [RX] +CGDCONT: 0,"IP","hardwario.com","10.0.0.157",0,0
  24.48     [RX] +CGDCONT: 1,"IP","hardwario.com","",0,0
  24.48     [RX] OK
  24.48 [TX] AT#XDATACTRL=40
  24.48     [RX] %XTIME: ,"32305122655540",
  24.49     [RX] OK
  24.49 [TX] AT#XSOCKET=1,2,0
  24.49     [RX] #XSOCKET: 0,2,17
  24.50     [RX] OK
  24.50 [TX] AT%CONEVAL
  24.51     [RX] %CONEVAL: 0,1,7,54,24,42,"000AC51F","23003",493,6447,20,0,0,16,2,1,114
  24.51     [RX] OK
  25.00 [PPK2] 100k/s AVG  33.0  mA    Max 148mA
  25.65 [PPK2] ====== SUM: ATTACH   0.157uA/h during  25.6  s ======
  26.73 [TX] AT#XCONNECT="192.168.168.1",20000
  26.73     [RX] #XCONNECT: 1
  26.73     [RX] OK
  26.73 [TX] AT#XSOCKETOPT=1,50
  26.74     [RX] OK
  27.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.2  mA
  28.02 [PPK2] 100k/s AVG  33.6  mA    Max  46.3  mA
  29.00 [PPK2] 100k/s AVG  33.4  mA    Max  46.3  mA
  30.01 [PPK2] 100k/s AVG  33.0  mA    Max  46.2  mA
  31.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.3  mA
  32.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.1  mA
  33.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.1  mA
  34.01 [PPK2] 100k/s AVG  33.5  mA    Max  46.4  mA
  35.02 [PPK2] 100k/s AVG  32.8  mA    Max  46.3  mA
  36.00 [PPK2] 100k/s AVG  33.6  mA    Max  46.2  mA
  37.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.2  mA
  38.02 [PPK2] 100k/s AVG  33.6  mA    Max  46.1  mA
  39.01 [PPK2] 100k/s AVG  33.6  mA    Max  46.5  mA
  40.00 [PPK2] 100k/s AVG  32.6  mA    Max  46.0  mA
  41.01 [PPK2] 100k/s AVG  33.7  mA    Max  46.1  mA
  42.02 [PPK2] 100k/s AVG  33.6  mA    Max  46.2  mA
  43.02 [PPK2] 100k/s AVG  33.6  mA    Max  46.6  mA
  44.02 [PPK2] 100k/s AVG  33.7  mA    Max  48.2  mA
  45.02 [PPK2] 100k/s AVG  32.7  mA    Max  45.9  mA
  45.49     [RX] +CSCON: 0
  45.49     [RX] %XMODEMSLEEP: 1,86399999
  45.49 [TX] AT#XSLEEP=2
  45.49     [RX] OK
  46.00 [PPK2] 100k/s AVG  16.5  mA    Max 194mA
  47.02 [PPK2] 100k/s AVG   0.017mA    Max   0.023mA
  48.01 [PPK2] 100k/s AVG   0.017mA    Max   0.023mA
  49.03 [PPK2] 100k/s AVG   0.017mA    Max   0.023mA
  50.02 [PPK2] 100k/s AVG   0.017mA    Max   0.023mA

[dejans]

Hi,

Michal Mühlpachr said:

Do I understand well, that ONE_RESP with R14 AS-RAI is not useful at all for power consumption optimization?

This is correct. This is the reason for the recommendation that NO_DATA should be used after receiving the response.

Best regards,
Dejan

[Michal Mühlpachr]

dejans said:

UDP is non-reliable protocol. Therefore, the information that UDP message left the modem would not guarantee anything or give any additional information. Typically, the assumption could be made that single UL UDP has left the modem when modem switches to RRC_IDLE.

Yes, UDP is non-reliable as any datagram, but available information for data transfer timings has to be passed to the application.
Assumption can not be made on RRC_IDLE, because in such case link speed could not be utilized, i.e. such an approach wastes energy.

For good energy management, it is essential to know whether packet dropping occurs/does not occur in the device, as this information is inherently available to the device.
Another possibility is a statistical estimation, which needs to be based on the current line rate, which is known by the modem but not by the application, which needs to do the transmission timing, so the modem has to pass the information about the current line rate.

How does the application know that the packet is not dropped in the modem?

How does the application know what the current line rate is?

[Achim Kraus]

> UDP is non-reliable protocol. 

UDP is the MOST reliable base for an upper protocol running over cellular modems using NB-IoT! The most serious upper protocols based on UDP do a much better job with NB-IoT and are much more reliable than TCP when running over NB-IoT.

TCP handles "congestion control" and "message drops" internally, but that depends a lot on additional messages and the timings. The generally assumed times are far away from the times of NB-IoT and that causes then a lot of retransmissions. So the only thing you get reliable using TCP over NB-IoT is a lot more data ;-)

> Typically, the assumption could be made that single UL UDP has left the modem when modem switches to RRC_IDLE.

For a useful congestion control of the radio layer, the event, that a message is sent by the radio layer helps a lot. Other modems offer that.

Using the RRC Idle event doesn't really help in that case. RRC IDLE is reached, if no more data is to be exchanged. That's either indicated by RAI (therefore all this discussion) or when the network's RRC Active Timer expires. It's not usable for the mentioned bulk transfer.

I guess, if you ask the modem developers, there is a number of messages, which are queued and send one after the other. But the exact implementation is not documented. And for many applications it's better to have a feedback, how fast actually the messages are sent in order to do the queuing in a more specific way in the application. Maybe using POSIX poll with POLLOUT works, but AFAIK, that is missing in the documentation.