Fundamental Windows Communication Foundation Concepts

WCF programming model consists of a runtime and a set of APIs and is used for creating systems that communicate (sends and receives messages) between clients and services.

Messaging and Endpoints

The main concept of WCF is Message–Based Communication. In the programming model anything that can can be modeled as a message (an HTTP request, a Message Queuing – MSMQ, etc), can be represented in a uniform way. This concept enables a unified API across contrasting transport mechanisms.

A client is an application which initiates a communication, while a service is an application which responds to the client's request. However, the client and the service may not be necessarily different applications, a single application may in fact act both as a client and a service (Duplex Services and Peer–to– Peer Networking).

As Endpoints are points or spots for message exchange, they define all the information required to facilitate message exchange. A WCF service can expose single or multiple endpoints (application endpoints or infrastructure endpoints or both). The client generated endpoint should be compatible with one of the service's endpoints.

Endpoints describe the address (location of the endpoint where the messages should be send), binding (how a client can communicate with the endpoint by sending messages), contracts (form of the message) and behaviors (local implementation details of the endpoint). This information can be exposed by the service as metadata, that can be processed to generate appropriate WCF clients and communication stacks.

Communication Protocols

The two elements required in the communication stack is given below:

• Transport protocol – Messages can be exchanged over the internet using common protocols such as HTTP and TCP. Protocols that support communication with Message Queuing applications and nodes on a Peer Networking mesh are also included.
• Encoding mechanisms – Encoding mechanisms specify the format of a message. Following encoding mechanisms are provided by WCF:
  a) Text encoding – this is an interoperable encoding.
  b) Message Transmission Optimization Mechanism (MTOM) encoding – this is an interoperable way for efficiently sending unstructured binary data to and from a service.
  c) Binary encoding – this is implemented for efficient transfer.

Note: Even more encoding mechanisms (for example, a compression encoding) can be added using the built-in extension points of WCF.

Message Patterns

Amongst the several messaging patterns supported by WCF, the most common Message Exchange Patterns include Request–Reply, One–Way, and Duplex. The variety of interactions supported by different protocols depends on the fact that they support different Message Exchange Patterns (MEX).

The messages exchanged in WCF is secure and reliable (a feature of WCF APIs and runtime).