Meaning of AT%XMONITOR reported PSM values?

[tedhavelka]

Hello Devzone,

I am building firmware for an nRF9160 based device, starting with an ncs 1.6.1 sample app and LTE modem firmware v1.3.1.  I'm in North America, and when testing LTE-M celular connection I can typically find -- or the modem finds -- two or three local celular network providers.

When I issue the AT command AT+CPSMS=1,,,"10101010","00110000", I find the modem remembers the values of this or my latest PSM settings request.  This is expected.  When I issue the querying command AT%XMONITOR, I see a report like either the first or second example here:

%XMONITOR: 5,"","","310260","352C",7,12,"014D3C15",87,5035,39,35,"","11100000","11100000","01001001"

%XMONITOR: 5,"AT&T","AT&T","310410","900C",7,12,"050B8210",391,5110,29,21,"","00110000","11100000","00110000"

In the first case, not one of my requested PSM values appears to be granted.  Am I reading this report correctly?  Are the three "one bits" in third from last and second from last quoted values the bit 8, 7 and 6 which are documented at Nordic Infocenter, command CPSMS and its 'set' syntax?

In the second report from %XMONITOR it appears that my requested active time value is granted by the network provider.  But what does it mean for active time to be granted, but Period-TAU value not to be granted?  How severely does this impact possible low power use of the nRF9160 in, for example, battery based devices?

- Ted

[Hakon]

tedhavelka said:

One new question however:  are eDRX and Active Time timers required to be turned on in order to enjoy the ultra low current power savings of PSM?

No, not as far as I know. But as I said, you can try measuring to make sure it's actually giving the desired power consumption.

[Achim Kraus]

Hi Ted,

I stumbled over similar questions here in Germany.

AFAIK, the answer is a complex mix of value the modem request, the network provider determines and the SIM-card provider preselects. Together with "roaming", that  makes it "very flexible" (selling people)  or "hardly deterministic" (making people). Sometimes I ask myself, if the mobile provider really wants to make business.

Hakon 

Thanks for the hint about the different units for the last value in %MONITOR. I was already struggling with 1h compared to 100h ("01001010").

Choosing different unit values then in CPSMS and the other fields of %MONITOR is in my opinion a not that good idea. Anyway, I guess, it's too late to fix it.