Here are the 10 important differences between WCF Services and ASP.NET Web Services:

10 Differences Between WCF and ASP.NET Web Services

Windows Communication Foundation (WCF) is a framework for building service-oriented applications. Using WCF, you can send data as asynchronous messages from one service endpoint to another. A service endpoint can be part of a continuously available service hosted by IIS, or it can be a service hosted in an application. An endpoint can be a client of a service that requests data from a service endpoint. The messages can be as simple as a single character or word sent as XML, or as complex as a stream of binary data. A few sample scenarios include: A secure service to process business transactions. A service that supplies current data to others, such as a traffic report or other monitoring service. A chat service that allows two people to communicate or exchange data in real time. A dashboard application that polls one or more services for data and presents it in a logical presentation. Exposing a workflow implemented using Windows Workflow Foundation as a WCF service. A Silverlight application to poll a service for the latest data feeds.

Features of WCF

WCF includes the following set of features. For more information, see WCF Feature Details.

• Service Orientation
  
  One consequence of using WS standards is that WCF enables you to create service oriented applications. Service-oriented architecture (SOA) is the reliance on Web services to send and receive data. The services have the general advantage of being loosely-coupled instead of hard-coded from one application to another. A loosely-coupled relationship implies that any client created on any platform can connect to any service as long as the essential contracts are met.
• Interoperability
  
  WCF implements modern industry standards for Web service interoperability. For more information about the supported standards, see Interoperability and Integration.
• Multiple Message Patterns
  
  Messages are exchanged in one of several patterns. The most common pattern is the request/reply pattern, where one endpoint requests data from a second endpoint. The second endpoint replies. There are other patterns such as a one-way message in which a single endpoint sends a message without any expectation of a reply. A more complex pattern is the duplex exchange pattern where two endpoints establish a connection and send data back and forth, similar to an instant messaging program. For more information about how to implement different message exchange patterns using WCF see Contracts.
• Service Metadata
  
  WCF supports publishing service metadata using formats specified in industry standards such as WSDL, XML Schema and WS-Policy. This metadata can be used to automatically generate and configure clients for accessing WCF services. Metadata can be published over HTTP and HTTPS or using the Web Service Metadata Exchange standard. For more information, see Metadata.
• Data Contracts
  
  Because WCF is built using the .NET Framework, it also includes code-friendly methods of supplying the contracts you want to enforce. One of the universal types of contracts is the data contract. In essence, as you code your service using Visual C# or Visual Basic, the easiest way to handle data is by creating classes that represent a data entity with properties that belong to the data entity. WCF includes a comprehensive system for working with data in this easy manner. Once you have created the classes that represent data, your service automatically generates the metadata that allows clients to comply with the data types you have designed. For more information, see Using Data Contracts
• Security
  
  Messages can be encrypted to protect privacy and you can require users to authenticate themselves before being allowed to receive messages. Security can be implemented using well-known standards such as SSL or WS-SecureConversation. For more information, see Windows Communication Foundation Security.
• Multiple Transports and Encodings
  
  Messages can be sent on any of several built-in transport protocols and encodings. The most common protocol and encoding is to send text encoded SOAP messages using is the HyperText Transfer Protocol (HTTP) for use on the World Wide Web. Alternatively, WCF allows you to send messages over TCP, named pipes, or MSMQ. These messages can be encoded as text or using an optimized binary format. Binary data can be sent efficiently using the MTOM standard. If none of the provided transports or encodings suit your needs you can create your own custom transport or encoding. For more information about transports and encodings supported by WCF see Transports in Windows Communication Foundation.
• Reliable and Queued Messages
  
  WCF supports reliable message exchange using reliable sessions implemented over WS-Reliable Messaging and using MSMQ. For more information about reliable and queued messaging support in WCF see Queues and Reliable Sessions.
• Durable Messages
  
  A durable message is one that is never lost due to a disruption in the communication. The messages in a durable message pattern are always saved to a database. If a disruption occurs, the database allows you to resume the message exchange when the connection is restored. You can also create a durable message using the Windows Workflow Foundation (WF). For more information, see Workflow Services.
• Transactions
  
  WCF also supports transactions using one of three transaction models: WS-AtomicTtransactions, the APIs in the System.Transactions namespace, and Microsoft Distributed Transaction Coordinator. For more information about transaction support in WCF see Transactions.
• AJAX and REST Support
  
  REST is an example of an evolving Web 2.0 technology. WCF can be configured to process "plain" XML data that is not wrapped in a SOAP envelope. WCF can also be extended to support specific XML formats, such as ATOM (a popular RSS standard), and even non-XML formats, such as JavaScript Object Notation (JSON).
• Extensibility
  
  The WCF architecture has a number of extensibility points. If extra capability is required, there are a number of entry points that allow you to customize the behavior of a service. For more information about available extensibility points see Extending WCF.

 Below figures shows the different technology combined to form WCF.

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  Advantage

  1. WCF is interoperable with other services when compared to .Net Remoting,where the client and service have to be .Net.
  2. WCF services provide better reliability and security in compared to ASMX web services.
  3. In WCF, there is no need to make much change in code for implementing the security model and changing the binding. Small changes in the configuration will make your requirements.
  4. WCF has integrated logging mechanism, changing the configuration file settings will provide this functionality. In other technology developer has to write the code.

  Disadvantage

  Making right design for your requirement is little bit difficult. I will try to help you on solving these difficulties in the following article.