The acknowledgement pattern is a simple method of flow-control for methods that would otherwise be one way calls. Rather than leaving the method as a one way call, it is instead turned into the a two way call with an absent response, colloquially known as an ack. The ack's only reason for existence is to inform the sended that the message has been received, which the sender can use to make decisions about how to proceed.

The cost of this acknowledgement is added chatter over the channel. This pattern can also result in degraded performance if the client waits for the acknowledgement before proceeding with the next call.

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