Message state in DELIVER_SM operation

Hello,
     I am looking for a little clarification with respect to the message
delivery status
in smpp. While browsing through the source file (gw/smsc/smsc_smpp.c) in
handle_pdu()
function , in case:deliver_sm , we call the function handle_dlr and the last

argument which is passed is pdu->u.deliver_sm.message_state. I am not able
to
understand from where we get the message_state as there is no such parameter
specified in the SMPP 3.4 specification for DELIVER_SM message.

can someone correct me in the understanding the logic behind this part ?

Regards,
Basileis