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Chapter 3. Communication Patterns
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## Chapter 3. Communication Patterns

## 3.1. One-Way Communication

In the context of this document, one-way communication refers to the communication pattern in which only one of the communicating parties, the service provider (a.k.a. the server), has an addressable endpoint and the ability to receive and process incoming Web Services messages; and the other parties, the service consumer (a.k.a. the client), can send Web Services requests and receive their response in one HTTP cycle, but does not have an addressable endpoint to receive incoming messages initiated by another party. In this communication pattern, messages always originate from the client to the server.

### 3.1.1. One-Way Synchronous Communication

The client uses ProcessMessage to achieve synchronous communication and receive a response immediately as shown in ProcessMessage sequence diagram earlier. Upon receiving the request, the server starts processing it while holding the connection with the client open until a response (or an error) is ready to be returned to the client on the open connection.

### 3.1.2. One-Way Asynchronous Communication

The client can also use PutMessage and PullMessage together to achieve asynchronous communication as shown in the figure below. In this pattern, the client must send a PullMessage request to receive contents queued at the server side. The client can either implement a polling service to periodically request contents from the server or send the requests only when contents are expected to be available for download, for example, through an event notification model, the details of which is out of the scope of this document.

Figure 3.1. One-way Asynchronous Communication

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