Introduction to Windows Communication Foundation (WCF)

The Windows Communication Foundation (WCF) presents a wide functionality of web services which enables to manage distributed computing, platform independent and interoperability, and also supports the service orientated architecture. The WCF works on layered architecture that simplifies the development of distributed applications using a new service oriented programming model. The service model for WCF web services is designed to enable the developers for developing the distributed applications easily. It also provides a capability to develop ASP.Net web services, enterprise services and .Net framework remoting. The serialization feature enables loose coupling and versioning that also provides integration and interoperability facilities with the existing .Net Framework technologies such as Message Queuing (MSMQ), COM+, and Web Services in ASP.Net, Enhancement Services and other functions.

Windows Communication Foundation Architecture

The WCF is composed of layered architecture. Let's discuss about its some of the major layers:

1. Contracts and Descriptions: The Contracts layer consists of data contract, message contract, service contract, policies and bindings. The data contract describes the parameters for the messages that a service can utilize. The message contract uses SOAP protocols which defines specific message parts. The service contract exposes the method signatures of the associated web service where policies and bindings define the security rules over the accessibility of web service.

2. Service Runtime: The service runtime layer holds the behaviors of the web service during its actual operations. The throttling behavior controls the number of messages processed. The error behavior represents the internal error thrown by the web service. The Metadata behavior determines a way to expose the metadata information globally. The Instance behavior specifies the limit for the number of instances of web services that can be run. The transaction behavior enables to rollback the transacted operations in case of failure. The dispatch behavior controls the way of processing a message by WCF. The concurrency behavior enables to control the concurrency of number of threads within a service instance and the parameter filtering enables to run the preset actions to occur based on the defined filters on the message headers.

3. Messaging Layer: The messaging layer consists of channels. A channel provides a way to process the messages like authentication of messages. The channels operate on messages and their headers. It is composed of two types of channels such as transport channels and protocol channels. The transport channels transmit the messages using a byte stream representation by the network. The examples of transports are HTTP, TCP, named pipes, and MSMQ. Some of the transport channels also use encoders to convert the messages using XML and optimized binary. The protocols channels apply message processing protocols by reading or writing additional message headers using WS-Security and WS-Reliability.

4. Hosting and Activation Layer: After the development of web service, the final version serves as a program. Services can also be run as independent executables (.exe). You can host it on the web server by providing a user interface using WPF or win forms which is also called self-hosted service. The Windows IIS web server provides a platform to host the web services easily. COM+ components can also be published as WCF service. The Windows Activation Service (WAS) enables to activate the WCF applications automatically when deployed on a system running WAS.