Cellular Network Infrastructure » Core Network (CN) » OsmoMSC

I think it is just an error message that is safe to ignore, like those "transition to state FOO not permitted" errors that just show because we didn't bother to silence it, and then users are confused into thinking that it's really bad.

I'm not so familiar with SGs and 4G, but my guess is that simply, during the CSFB back to 2G to send the SMS from 4G, the messaging and code paths are quite different than a normal CM Service Request, so obviously there is no use count token for a normal CM Service Request. This error message probably comes from a time before SGs and is supposed to warn against unexpected situations, and it wasn't adjusted when SGs was added?

Does that sound about right, to the SGs / CSFB experts... dexter ?

On Thu, Oct 05, 2023 at 04:58:02PM +0000, neels wrote:

Does that sound about right, to the SGs / CSFB experts... dexter ?

I don't know the code in detail, but yes, that is likely the cause of this message. We still
should gracefully handle that situation, rather than printing bogus error messages that confuse
at least the users, but even some of our developers.

neels wrote in #note-2:

I'm not so familiar with SGs and 4G, but my guess is that simply, during the CSFB back to 2G to send the SMS from 4G,

I'm not sure about @dexter's test case here, but I'm also not convinced there's any CSFB going on. This is because the error message reported here is what I'm seeing with SMS attempts from a UE on 4G RAT. plus, it's worse, as the SMS fails, I'm about to make a ticket for that.