The qRFC (queued Remote Function Call) is an extension of the tRFC. It allows you to serialize tRFC calls using a queue.
The tRFC call is preceded by function module TRFC_SET_QUEUE_NAME, which starts the serialization. The calls are then actually dispatched by a tRFC call.
The qRFC can be made with an outbound queue (serialization at the calling application) and also an inbound queue (serialization at the called application).
This results in the following scenarios for transactional data transfer:
Scenario 1: tRFC
This scenario is appropriate is the data being sent is independent of each other. A calling application (client) in system 1 uses a tRFC connection to a called application (r server) in system 2. In this scenario, data is transferred by tRFC, meaning that each function module sent to the target system is guaranteed to be executed once only. You cannot define the sequence in which the function modules are executed, nor the time of execution. If an error occurs during the transfer, a batch job is scheduled, which sends the function module again after 15 minutes.
Scenario 2: qRFC with Outbound Queue
In this scenario, the sending system uses an outbound queue to serialize the data being sent. This means that mutually dependent function modules are placed in the outbound queue of the sending system. When the data is sent, the exact order is kept to, and the calls are sent to the target system exactly once in order. Exactly Once In Order).
The server system coding does not need to be changed in order to process qRFC calls. However, it must be tRFC enabled.
Scenario 3: qRFC with Inbound Queue (& Outbound Queue)
In this scenario, as well as an outbound queue in the sender system (client), there is also an inbound queue in the target system (server). If a qRFC with inbound queue exists, this always means that an outbound queue exists in the sender system.
The inbound queue only processes as many function modules as the system resources in the target system (server) at that time allow. This prevents a server being blocked by a client. A scenario with just one inbound queue in the server system is not possible, since the outbound queue is needed in the client system in order to set the order and to prevent individual applications from blocking all work processes in the client system.
You can find detailed information about qRFC in: