I'm using a u-blox LARA R211 modem on a private cellular network (PCN). When sending a cell broadcast message on the PCN I am able to receive it on any other phone (iPhone + Samsung) that is connected to that network, but not on the LARA modem. On the LARA I am able to verify my connection to the network, and even ping outside hosts like Google.
On the PCN I am able to set the explicit message ID for the message, and the encoding scheme is the default 7bit 3GPP standard. After sending the message there is no information showing in the AT command interface, nor do the message buffers increment.
I'm using the following AT commands for the cell broadcast setup:
at+cpms="BM","ME","ME"
at+cmgf=1
at+cnmi=2,1,2,1,0
at+cscb=0,"4356",""
AT command documentation if it helps.
Turns out the issue I was experiencing was due to the message formatting scheme. The private network we were using was setup to only use CMAS messaging format, where the cellular modem was expecting ETWS formatting on that specific message ID. It is possible to send CMAS messages on any message ID, but the modems that are receiving have to understand the structure to properly receive it.
Changing settings on the network end resolved the issue, and using message IDs that are specific to CMAS such as the presidential alert also worked successfully.