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White Paper
SOA with .Net
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Introduction
SOA, a rich technology foundation designed for building distributed service-oriented applications for the enterprise and the web that are secure, reliable, transactional and scalable.
A Platform for SOA
The evolution of component-oriented programming makes it possible to encapsulate, reuse and distribute business functionality with the added benefit of interoperability across technology platforms.
Unified Programming Model
WCF supports Enterprise Services/COM+, .NET Remoting, System.Messaging, ASP.NET Web Services and Web Services Enhancements (WSE) thus the developer experience is consistent for service design, configuration and deployment.
Flexible Hosting Model
Services can be hosted in any managed Windows process including Internet Information Services (IIS), Windows Activation Service (WAS), Windows NT Services, and Windows Forms or WPF client applications.
SOA Architecture - WCF
The WCF architecture is based on the design principles of service-oriented architecture (SOA).
The SOA-based WCF architecture contains four layers – Contracts, Service Runtime, Messaging, and Hosting.
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Contracts
The Contracts layer describes the WCF message system. This is described in terms of
A Service Contract describes the method signatures of a service. It’s defined using programming languages, such as Visual Basic and Visual C# and is distributed as an interface.
A Data Contract enables .NET types to be expressed in XML. The data contract describes every parameter that makes up every message that a service can create or consume. The message parameters are defined by XML Schema definition language (XSD) documents, enabling any system that understands XML to process the documents.
Message Contracts define the structure of SOAP messages exchanged between a service and a client, and they allow you to view or modify messages and allows finergrained control over parts of the message.
Policies and Bindings: Policies and Bindings stipulate the conditions required to communicate with a service. They define the configuration, such as security levels, required by clients to communicate with a service.HexaCorp
Service Runtime
It describes the runtime behaviors of the service.
Throttling controls how many messages are processed, which can be varied if the demand for the service grows to a preset limit.
Error behavior decides the sequence of events when an occurs in service. This prevents the display of too much of error information to outside entities.
Metadata behavior governs how and whether metadata is made available to the outside world.
Message inspection is the facility to inspect parts of a message.
Instance behavior specifies how many instances of the service can be run (for example, a singleton specifies only one instance to process all messages).
Transaction behavior enables the rollback of transacted operations if a failure occurs.
Dispatch behavior is the control of how a message is processed by the WCF infrastructure.HexaCorp
Messaging
The Messaging layer contains channels that process messages and operate on messages and message headers.A channel is a component that processes a message in some way, for example, by authenticating a message. A set of channels is also known as a channel stack. Channels operate on messages and message headers.
There are two types of channels: Transport channels and Protocol channels.
Transport channels read and write messages from the network, and protocol channels implement message processing protocols.Some transports use an encoder to convert messages (which are represented as XML Infosets) to and from the byte stream representation used by the network. Examples of transports are HTTP, named pipes, TCP, and MSMQ. Examples of encodings are XML and optimized binary.
Protocol channels implement message processing protocols, often by reading or writing additional headers to the message. Examples of such protocols include WS-Security and WS-Reliability.
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WS-Security is an implementation of the WS-Security specification enabling security at the message layer.
The WS-Reliable Messaging channel enables the guarantee of message delivery.
The encoders present a variety of encodings that can be used to suit the needs of the message.
The HTTP channel specifies that the HyperText Transport Protocol is used for message delivery.
The TCP channel similarly specifies the TCP protocol.
The Transaction Flow channel governs transacted message patterns.
The Named Pipe channel enables interprocess communication.HexaCorp
Hosting Environment
WCF services that are part of a client-server deployment can be hosted in a Windows NT Service for Windows Server 2003 machines, or in WAS for Windows Server 2008 machines. Both of these hosting environments can host services over named pipes, TCP and MSMQ and Windows NT Services can also support HTTP protocol if IIS hosting is not desirable.
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The relationship between client and services when TCP sockets
are
used for communication
WCF services hosted over TCP behind the firewall have similar hosting implications for secure sessions and reliable sessions – clients must be directed back to the same server machine where the TCP socket was created. Software load balancers and network load balancing devices can be configured for sticky IP to address this.
