Connexion Directory Server - python-ldap program

[Cdebard]

I'm testing the synology directory server application in order to be able to authenticate my users. I've creating a small python program which should connect the Synology Directory Server. This program can connect to an OpenLDAP server (installed on a VM) but it can't connect  to the Synology Directory Server. I've got this message
{'msgtype': 97, 'msgid': 1, 'result': 8, 'desc': 'Strong(er) authentication required', 'ctrls': [], 'info': 'BindSimple: Transport encryption required.'}

Any idea!! Thanks