ePCO and LEGACY PCO considerations

[barbiz]

Hello,

we recently deployed a device in a network which does not support ePCO (we discovered this by trial and error).

As a consequence, we had to disable ePCO by setting the flag:

CONFIG_PDN_LEGACY_PCO = y

to make the device work correctly.

In general, we don't want to deploy dedicated builds, because they are very hard to mantain.

So the question is: what is the advantage of ePCO? Can't we just disable it on all devices? What would we lose?

Thanks,

Marco

[Didrik Rokhaug]

Hi,

Functionally, ePCO and PCO is the same. The difference is how the information sent to the device is encoded.

However, our experience is that ePCO and PCO are mutually exclusive in a network.

So a device that uses ePCO in a PCO only network will not work properly, and vice versa.

But, you can set a backup DNS server in the application, which should also solve the problem of not getting a DNS server from the network.

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.4.0/nrfxlib/nrf_modem/doc/api.html#c.nrf_setdnsaddr

Best regards,

Didrik

[barbiz]

I see. Thanks for the clarification,

We can set fallback DNS and this works. But which information are we also losing? I mean, if we set ePCO and the network only supports PCO, what other kind of information are we losing?

Thanks,

Marco

[Didrik Rokhaug]

I don't think you are loosing any other information.

Unfortunately, I am not able to test this myself.

To check, you can use the trace collector v2 or cellular monitor from nRF Connect for Desktop to capture a (pcap) modem trace, and then compare the PCO and ePCO parts. Look in the ESM message container in the Attach accept packet, and you should be able to find it. Remember that PCO is short for Protocol Configuration Options.