WCF:  Windows Communication Foundation
It includes a collection of .NET distributed technologies that have existed for long , but never got grouped under one name.
WCF can be considered as collection of the following technologies.

1. Web Services(ASMX)
2. NET Enterprise Services
3. MSMQ
4. .NET Remoting

Code written in WCF can interact across components, applications and systems.
WCF is in accordance with SOA (Service Oriented Architecture).

Following Sections provide the details of these ABCs.

Addresses

In WCF, every service has a unique address. The address provides two important elements
A)   Location of the service.
B)   Transport protocol or transport schema used to communicate with the service.

 The location indicates the name of the target machine, site, or network; a communication port, pipe, or queue; and an optional specific path or URI.
WCF supports the following transport schemas:
   A)   HTTP
   B)   TCP
   C)   Peer network
   D)   IPC (Inter-Process Communication over named pipes)
   E)   MSMQ

Addresses have the following format:
[base address]/[URI]
(Note: URI is optional and can be omitted, however when it is present it gets merged with the base address to provide the final address, where the service can be located).

 base address format:
[transport]:// [machine or domain][:optional port]

Following section is meant only to make you familiar with the various formats thatare used with specific type of transport protocol.
It can be skipped if desired.

Using different available address formats.

TCP Addresses

TCP addresses use net.tcp for the transport and generally uses a port:
net.tcp ://{ machine or domain}/ServiceName
e.g. Net.tcp//localhost/PService
(Note: If a port number is not specified, Port 808 is used as default)

HTTP Addresses

HTTP addresses use httpfor transport, and https can be used if secure transport is required.
e.g.http://localhost:8001
When the port number is not mentioned, it defaults to 80.

IPC Addresses

IPC addresses use net.pipe for transport.
Note: If a service uses this (i.e. named pipes, it can accept call only from thesame machine).
e.g. net.pipe://localhost/PrPipe

 MSMQ Addresses

MSMQ addresses use net.msmq for transport
When private queues are used, queue type needs to be mentioned and is  omittedfor public queues:
net.msmq://localhost/private/PService (using private queue)
net.msmq://localhost/PService             (usingPublic Queue)

Peer Network Address

Peer network addresses use net.p2p for transport peer network name, path and port needs to be specified.....

Bindings

The Standard Bindings Following 9 types of Bindings are defined for WCF:

Basic Binding

BasicHttpBinding class provides this type of binding.
It  exposes a WCF service as a legacy ASMX web service.
This binding is extremely useful when the intent is to design a WCF service that should provide backward compatibility with WebServices.

TCP binding

NetTcpBinding class provides this type of binding.
It uses TCP for cross-machine communication on the intranet.
It supports a variety of features, including reliability, transactions, andsecurity, and is optimized for WCF-to-WCF communication.
Restriction: It requires both the client and the service to use WCF.

Peer network binding

NetPeerTcpBinding class provides this type of binding and  uses peer networking as a transport. The peer network-enabled client and services all subscribe to the same grid and broadcast messages to it....

IPC binding

NetNamedPipeBinding class provides this type of binding and uses named pipes as a transport for same-machine communication. It is the most secure binding as it cannot accept calls from outside the machine and it supports a number of features similar to the TCP binding.

Web Service (WS) binding

WSHttpBinding class provides this type of binding, and  uses HTTP or HTTPS for transport....

Federated WS binding

WSFederationHttpBinding class provides this type of binding, this is a specializationof the WS binding, offering support for federated security......

Duplex WS binding

 WSDualHttpBinding class provides this type of binding. It is similar to the WS binding except it also supports bi-directional communication from the service to the client.

MSMQ binding

NetMsmqBinding class provides this type of binding and uses MSMQ for transport and is suitable for  disconnected queued calls...

MSMQ integration binding

MsmqIntegrationBinding class provides this type of binding and converts WCF messages to and from MSMQ messages. This is most suitable for usage when Service legacy MSMQ clients interoperability is critical.

Message Transfer Patterns
WCF use the following three messaging patterns:

1. Simplex,
2. Duplex
3. Request-Reply.

Simplex communication is commonly referred to as one-way communication. This approachis used when asynchronous write-only services are required. It simply means if onlyone directional (client to Service) communication is required, use this pattern.

     Duplex communication provides true asynchronous two-way communications. (using callback  operations).

     In simplex and duplex communication, the consumer is not locked into waiting for a reply.
     Request-Reply: General enough not to provide any details

Defining Bindings is one the most critical stages in WCF Service development. Service development.
Correct type of binding can save a lot of time and effort need to build an effective service.
As an effort to make you comfortable in Service development below is the checklist that needs to be referred before finalizing bindings for your service.

Interoperability Level:
Make sure  if communication will only be in  a .NET to .NET scenario,or legacy ASMX service, or if it is to be used by a consumer that adheres to the WS* specifications.

Encoding:
    Select correct type of encoding, from among
    Text
    Message TransmissionOptimization Mechanism (MTOM) 
    Binary.

    Transport Protocols
           Select from  transport options TCP, HTTP, Named Pipe, and MSMQ.

    Messaging patterns : simplex, duplex, and request-reply.
    Security Considerations: WinTransactions and reliable sessions.

Contracts:
The contract is a platform-neutral and standard way of describing what the service does.
WCF defines four types of contracts.

Service contracts

Describe which operations the client can perform on the service.

Data contracts

Define which data types are passed to and from the service.

Fault contracts

Define which errors are raised by the service, and how the service hand Allow the service to interact directly with messages. Message contracts can be typed or untyped.

Service Type Support e.g. Message contract The following are the three types of services that can be written with WCF.

1. Typed Services: These services use exact parameterization(passingthe required parameters in the correct order, format and type) when calling a servicemethod and respond with a well-defined type(as expected by the caller).
2. Un-Typed Services: XML is the core of this type as it is used totransport the input parameters and the response output is also in XML. These servicesare the most flexible, but provide very little value back to the consumer.
3. Typed Message Services: A custom type is defined that will containthe required input parameters and one more type that will wrap up the output parameters.

This approach is generallyknown as Request Object / Response Object, since these are the types of objects that are result ofthese types of services.

This  tutorial is just meant as a base for understanding the nitty-gritties of WCF.
Next tutorial will cover the detailed implementation of the theoretical sections discussed here.

Till then, Happy Coding...

An interface contains only the signatures of methods,  events, indexers or properties. When a class or struct implements the interface then that class/struct must implement the members of the interface that are specified in the interface definition.

An interface cannot contain fields and members are automatically public in interface as well and an interface can inherit from one or more base interfaces. When a base type list contains a base class and interfaces, the base class must come first in the list.

A class that implements an interface can explicitly implement members of that interface. An explicitly implemented member cannot be accessed through a class instance, but only through an instance of the interface.

Interfaces can inherit other interfaces. It is possible for a class to inherit an interface multiple times, through base classes or interfaces it inherits. In this case, the class can only implement the interface one time, if it is declared as part of the new class. If the inherited interface is not declared as part of the new class, its implementation is provided by the base class that declared it. It is possible for a base class to implement interface members using virtual members; in that case, the class inheriting the interface can change the interface behavior by overriding the virtual members.

it was necessary to incorporate some other method so that the class can inherit the behavior of more than one class, avoiding the problem of name ambiguity that is found in C++. With name ambiguity, the object of a class does not know which method to call if the two base classes of that class object contain the same named method.

Interfaces Overview

An interface has the following properties:

•       An interface is like an abstract base class: any non-abstract type inheriting the interface must implement all its members.
•       An interface cannot be instantiated directly.
•       Interfaces can contain events, indexers, methods and properties.
•       Interfaces contain no implementation of methods.
•       Classes and structs can inherit from more than one interface.
•       An interface can itself inherit from multiple interfaces.

Both delegates and interfaces allow a class designer to separate type declarations and implementation. A given interface can be inherited and implemented by any class or struct; a delegate can created for a method on any class, as long as the method fits the method signature for the delegate. An interface reference or a delegate can be used by an object with no knowledge of the class that implements the interface or delegate method. Given these similarities, when should a class designer use a delegate and when should they use an interface?

Use a delegate when:

• An eventing design pattern is used.

• It is desirable to encapsulate a static method.

• The caller has no need access other properties, methods, or interfaces on the object implementing the method.

• Easy composition is desired.

• A class may need more than one implementation of the method.

Use an interface when:

• There are a group of related methods that may be called.

• A class only needs one implementation of the method.

• The class using the interface will want to cast that interface to other interface or class types.

• The method being implemented is linked to the type or identity of the class: for example, comparison methods.

One good example of using a single-method interface instead of a delegate is IComparable or IComparable. IComparable declares the CompareTo method, which returns an integer specifying a less than, equal to, or greater than relationship between two objects of the same type. IComparable can be used as the basis of a sort algorithm, and while using a delegate comparison method as the basis of a sort algorithm would be valid, it is not ideal. Because the ability to compare belongs to the class, and the comparison algorithm doesn’t change at run-time, a single-method interface is ideal.

Extracted from Microsoft Technet articles.