In order to communicate with other applications as LDAP Server the system should support the LDAPv3 control attribute. Since with the attribute in a ldap search the pbx does not deliver any results.

As query example:

ldapsearch -v -x -D 'ot-ldap' -W -H ldap://x.x.x.x/ -b 'cn=pbx0' -s sub -a allways -M guid cn objectClass email