The ABC of Windows Communication Foundation

“ABC” is the WCF mantra. “ABC” is the key to understanding how a WCF service endpoint is composed. Think Ernie, Bert, Cookie Monster or Big Bird. Remember “ABC”.

• “A” stands for Address: Where is the service?
• “B” stands for Binding: How do I talk to the service?
• “C” stands for Contract: What can the service do for me?

Web services zealots who read Web Service Description Language (WSDL) descriptions at the breakfast table will easily recognize these three concepts as the three levels of abstraction expressed in WSDL. So if you live in a world full of angle brackets, you can look at it this way:

• “A” stands for Address—as expressed in the wsdl:service section and links wsdl:binding to a concrete service endpoint address.
• “B” stands for Binding—as expressed in the wsdl:binding section and binds a wsdl:portType contract description to a concrete transport, an envelope format and associated policies.
• “C” stands for Contract—as expressed in the wsdl:portType, wsdl:message and wsdl:type sections and describes types, messages, message exchange patterns and operations.

“ABC” means that writing (and configuring) a WCF service is always a three-step process:

• You define a contract and implement it on a service
• You choose or define a service binding that selects a transport along with quality of service, security and other options
• You deploy an endpoint for the contract by binding it (using the binding definition, hence the name) to a network address.

Bindings are nothing but the transport protocols that are used for the communication with the client application. WCF provides a wide range of transport protocols that can be used as in the requirements.

A binding has the following characteristics:

• Transport: Defines the base protocol to be used, like HTTP, Named Pipes, TCP and MSMQ are some of the protocols.
• Encoding (Optional): Three types of encodings are available, they are:

1. Text Encoding
2. Binary Encoding
3. Message Transmission Optimization Mechanism (MTOM)

• Protocol (Optional): Defines the information to be used in the binding such as Security, transaction or reliable messaging capability.

Some predefined bindings are :

• It is suitable for communicating with ASP.NET Web services (ASMX)-based services that comfort with WS-Basic Profile conformant Web services.
• This binding uses HTTP as the transport and text/XML as the default message encoding.
• Security is disabled by default
• This binding does not support WS-* functionalities like WS- Addressing, WS-Security, WS-ReliableMessaging
• It is fairly weak on interoperability.

• Defines a secure, reliable, interoperable binding suitable for non-duplex service contracts.
• It offers lot more functionality in the area of interoperability.
• It supports WS-* functionality and distributed transactions with reliable and secure sessions using SOAP security.
• It uses HTTP and HTTPS transport for communication.
• Reliable sessions are disabled by default.

This binding is same as that of WSHttpBinding, except it supports duplex service. Duplex service is a service which uses duplex message pattern, which allows service to communicate with client via callback.

In WSDualHttpBinding reliable sessions are enabled by default. It also supports communication via SOAP intermediaries.

This binding support federated security. It helps implementing federation which is the ability to flow and share identities across multiple enterprises or trust domains for authentication and authorization. It supports WS-Federation protocol. NetTcpBinding

This binding provides secure and reliable binding environment for .Net to .Net cross machine communication. By default it creates communication stack using WS-ReliableMessaging protocol for reliability, TCP for message delivery and windows security for message and authentication at run time. It uses TCP protocol and provides support for security, transaction and reliability.

This binding provides secure and reliable binding environment for on-machine cross process communication. It uses NamedPipe protocol and provides full support for SOAP security, transaction and reliability. By default it creates communication stack with WS-ReliableMessaging for reliability, transport security for transfer security, named pipes for message delivery and binary encoding.

• This binding provides secure and reliable queued communication for cross-machine environment.
• Queuing is provided by using MSMQ as transport.
• It enables for disconnected operations, failure isolation and load leveling

• This binding provides secure binding for peer-to-peer environment and network applications.
• It uses TCP protocol for communication
• It provides full support for SOAP security, transaction and reliability.

Endpoints provide clients with access to the functionality a Windows Communication Foundation (WCF) service offers. You can define one or more endpoints for a service by using a combination of relative and absolute endpoint addresses, or if you do not define any service endpoints, the runtime provides some by default for you.

• Take the calculator Web service (with and add and sub between two value)
• Define two endpoints : one with basicHttpBinding and wsHttpBinding (two standard bindings for SOAP based web services)
• What are the differences between both services now ?
• To test them write a console or a graphical client that propose add and sub operations on the two endpoints.