The SAP application tier is based on the SAP proprietary ABAP code as well as Java. It runs on almost any platform, from Windows to Linux servers to mainframes. SAP application servers scale by separating functions into a Central Instance (CI) and Dialog Instance (DI). The CI is the message server and is responsible for queuing and locking, while the DIs perform the actual processing of the application. SAP increases capacity by adding more DIs, thus the need for load balancing.

Refer the document present in the following url for information on Server Load Balancing with SAP:

http://www.cisco.com/en/US/prod/collateral/modules/ps2706/ps6906/prod_white_paper0900aecd80653362.pdf