IDOC segment not populated any value after Mapping in PI

Hi,

I am working on File(FTP) to Idoc Scenario.When i put file on ftp server xi pick and Create Idoc. Idoc reach successfully to sap system.But Idoc not contain segment which i had mapped in Message Mapping in XI.For some field i pass constant Value those are populate in Idoc.

Why it's not populated any value after Mapping in PI ?

Thanks.