libsmpp34 is a C-language library implementing the SMPP Protocol version 3.4 as specified by the SMPP Developers Forum.
The library was inherited from the c-open-smmp34 project, which unfortunately doesn't have any form of revision control
system and hence the Osmocom project has imported the v1.10 release into its git repository and performed subsequent improvements.
The library original homepage is at http://sourceforge.net/projects/c-open-smpp-34/
In OsmoNITB and OsmoMSC, we use libsmpp34 as a utility library for the built-in SMPP interface. See https://media.ccc.de/v/osmocon2018-64-external-sms-services-using-smpp for some details about how to use SMPP in Osmocom.