Related Concepts and Terminology

In this section:

The following topics list and define specific terminology related to SAP ERP and SAP ERP event handling.


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Client and Server Programs

RFC (Remote Function Call) programs for non-SAP ERP systems can function as either the caller or the called program in an RFC communication. The two types of RFC programs are:

The RFC client is the instance that calls the RFC library to execute the function that is provided by an RFC server. The functions that can be executed remotely are called RFC functions, and the functions provided by the RFC API are called RFC calls.


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SAP ERP Gateway

The SAP ERP Gateway is a secure application server. No connections are accepted unless they were pre-registered previously from the SAP ERP presentation Client. A server connection presents itself to the Gateway and exposes a Program Identifier. If the Program Identifier is found in the list of registered Program IDs, the Gateway server then offers a connection to the server, which accepts a connection.

The Program ID then is linked with an RFC Destination within SAP ERP, which enables SAP ERP Function Modules and ALE documents (IDocs or BAPI IDocs) to be routed to the destination. The RFC Destination functions as a tag to mask the Program ID to SAP ERP users.

An RFC server program can be registered with the SAP ERP Gateway and wait for incoming RFC call requests. An RFC server program registers itself under a Program ID at an SAP ERP Gateway and not for a specific SAP ERP system.

In SAP GUI, the destination must be defined with transaction SM59, using connection type T and Register Mode. Moreover, this entry must contain information on the SAP ERP Gateway where the RFC server program is registered.


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Program IDs and Load Balancing

If the Gateway Server has a connection to a particular server instance and another server instance presents itself to the Gateway, the Gateway offers the connection and then begins functioning in Load Balancing mode. Using a proprietary algorithm, the Gateway sends different messages to each server depending on demand and total processing time. This could cause unpredictable results in a scenario where messages are validated by schema and application.

When configuring multiple events using a single SAP ERP program ID, SAP ERP load balances the event data. For example, if multiple remote function calls or BAPIs use the same program ID (for example, IWAYID) and multiple SAP ERP listeners are configured with this program ID, then SAP ERP sends one request to one listener and the next to another listener, and so on.

The SAP ERP Gateway Server includes a load balancing algorithm. This mechanism is proprietary to SAP ERP application development and may work by comparing total throughput of the connection, the number of times in wait state, and so on. This means connection 1 may receive nine messages and connection 2 may receive one message. If five of nine messages are rejected for schema validation and the message on the other ID is rejected for schema validation, the customer can very easily make a case of missing messages.


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