Problem in receving SMS through Nokia phone

Hi All,
   I am having problem in receving SMS from Nokia phone...I am trying to
receive a multipart SMS...I receive UDHL as 0x05...I am receiving 21 bytes
extra at the start of the data...What are these extra 21 bytes?
The encoding used is GSM7 bit...What could be the problem?..I could not find
anything in the specs?

Thanks in Advance.
Shashikant Chowdhary