nrf9160 NB-IoT DNS failure

[Thomas]

Hi, I am testing NB-IoT on the nrf9160 and it appears the DNS is failing.

I have two networks here and with an NB-IoT modem from a different manufacturer the DNS is resolved fine for both. 

I thought it could be my implementation but it is working fine on Cat-M1.

I am running modem firmware version 0.7.0-29.alpha.

Currently I am calling 

getaddrinfo("myserver.com", NULL, NULL, &myserver_addr) and it is returning error 22

[Jan Tore Guggedal]

Hi Thomas,

Some NB-IoT networks requires you to use PCO (Protocol Configuration Options) instead of the default ePCO in the modem. You can switch from ePCO to PCO by setting

CONFIG_LTE_LEGACY_PCO_MODE=y

in your prj.conf file.

That should hopefully help with the issues you're experiencing.

Best regards,

Jan Tore

[Thomas]

Thanks Jan,

It didn't work when I tried that however using the AT command XEPCO solved the issue.

Would it not be better to default to PCO if not all networks support the extended protocol? Or is the extended version not compatible, and its a case of networks supporting one or the other? 

[Jan Tore Guggedal]

Hi Thomas,

Glad to hear you were able to solve the issues. Support for ePCO is a mandatory part of the 3GPP standard for NB-IoT networks, but not all networks support the feature yet.

Could you elaborate more on this topic, Martin Lesund?

Kind regards,

Jan Tore

[Thomas]

Thanks Jan, Would you happen to know if they are required to support PCO as well?

[Jan Tore Guggedal]

Hi Thomas,

I got this info from an expert on the matter: ePCO is mandatory, and should be supported by the networks, but it depends on elements that in some networks have not been updated. PCO is not directly required for NB-IoT networks, but it's been in the networks since 2009, and it's supported by all NB-IoT networks and devices.

Jan Tore