Information flow of status of SMS

i am still facing the issue that the status of sent sms is not shown correctly.
to sort out the root cause i want to know how the information flow is like when using smserver tools as sms gateway.

sms to be sent are written in folder x/outgoing by playsms. smsserver tools checks files in this folder for syntax correctness and moves the file to x/checked (or in x/failed, which is not needed here). after being sent by smsserver tools file is moved to x/sent.

how is playsms getting the status of the sms?

pending: file in x/checked
queued: ?
sent: ?