You only require a connection to the System Landscape Directory (SLD) when you use the ABAP proxy generation or runtime.
Business systems with an Integration Engine require a connection to the SLD server to obtain their name from the SLD. The business system name is used in the header of the message sent to the Integration Server. The connection to the SLD is established by creating an RFC destination (as described below) and calling a registered server program (which is defined on the J2EE RFC engine of the Integration Server). The server program is called with the HTTP address as a parameter that is maintained with transaction SLDAPICUST.
For security reasons, you can also secure your SLD connection with HTTPS. For more information, see SAP Note 766215.
You have to use transaction SLDAPICUST in the business system to define the SLD access data. This data consists of the host and port of the SLD as well as a user and password (PIAPPLUSER, for example). You can use the entries that you maintained on your Integration Server.
The RFC destinations LCRSAPRFC and SAPSLDAPI are used for the SLD connection. They use the SLD access data maintained with transaction SLDAPICUST. The RFC destination LCRSAPRFC is used to read the exchange profile; SAPSLDAPI is used by the ABAP API.
The RFC destinations are also used to retrieve the information about where to find the Integration Builder required for the proxy generation. This information is located in the exchange profile.
You have to create both RFC destinations in your business system. They use the same registered server program, which is defined as part of the RFC engine settings of the J2EE Engine on the Integration Server host. This means that all business systems can use the same server program ID (SAPSLDAPI _UNICODE or SAPSLDAPI _NONUNICODE) for their RFC destinations LCRSAPRFC and SAPSLDAPI.
In the case of Unicode business systems (program ID SAPSLDAPI _UNICODE), the Unicode flag is set in the RFC engine settings.
In the case of non-Unicode business systems (program ID SAPSLDAPI_NONUNICODE), the Unicode flag is deactivated.