"Chapter 4:Installing eTrust DSI" of the CA LDAP Getting Started Guide documents installing DSI (Distributed Security Integration).
Is DSI required to run CA LDAP Server?
DSI (Distributed Security Integration) is unnecessary to run CA LDAP Server stand alone.
In a multi z/OS environment, DSI can be used to route LDAP commands between z/OS environments.
DSI is necessary, if you will be (re)routing LDAP commands :
This allows one occurrence of CA LDAP running and the other z/OS environments running just DSI.
Please see the CA LDAP Getting Started Guide for further details.