If the operation being invoked is one way, there's no fault or out terminals because these can only exist for two-way operations (see Figure 6).

A service invocation is almost always a two-way operation, meaning that a request is sent from the consumer to the provider and a response is sent back in the other direction.

The process contains a receive activity followed by an invoke activity, and a reply activity that is needed only if the operation offered by the process is a two-way operation.