Hi,
I believe the interface requirement is to pick up a file from a FTP server using PI & post the data to GTS system. To achieve this, ESR content for GTS has to be imported.
Exact GTS related content to be loaded in GTS is "XI Content SLL-LEG". Latest content for this is available in SAP Service Market Place under Software Downloads (https://websmp204.sap-ag.de/~form/handler?_APP=00200682500000001943&_EVENT=SWDC_ALIAS&TMPL=INTRO_SWDC&V=INST&SWDCQL=swdc…)
The guide How to import SAP content into the PI ESR - Process Integration - SCN Wiki
will help in importing the SLL-LEG content into SAP PI.
A SAP note (875420) explains the complete scenario creation for feeder system (ERP or CRM) to GTS. If your feeder system is not ERP or CRM then sections related to them on this note are not applicable. Configuration for SAP PI & GTS system in this note is still holds valid.
PI connects with GTS system by Proxy protocol. For which RFC Destination of type HTTP connection to ABAP System needs to be created in PI system for the GTS System. In GTS system ABAP Proxy program has to be activated to receive the message.
Hope this information helps.
Regards
Prem A