ASMX web service and WCF web service

WCF web service provides a complete solution for the WS* specification. asmx does not.

WCF vs. ASMX

Protocols Support

WCF

HTTP
TCP
Named pipes
MSMQ
Custom
UDP
ASMX

HTTP only
Hosting

ASMX

Can be hosted only with HttpRuntime on IIS.
WCF

A WCF component can be hosted in any kind of environment in .NET 3.0, such as a console application, Windows application, or IIS.
WCF services are known as services as opposed to web services because you can host services without a web server.
Self-hosting the services gives you the flexibility to use transports other than HTTP.
WCF Backwards Compatibility

The purpose of WCF is to provide a unified programming model for distributed applications.
Backwards compatibility
WCF takes all the capabilities of the existing technology stacks while not relying upon any of them.
Applications built with these earlier technologies will continue to work unchanged on systems with WCF installed.
Existing applications are able to upgrade with WCF
New WCF transacted application will work with existing transaction application built on System.Transactions
WCF & ASMX Integration

WCF can use WS-* or HTTP bindings to communicate with ASMX pages
Limitations of ASMX:

An ASMX page doesnt tell you how to deliver it over the transports and to use a specific type of security. This is something that WCF enhances quite significantly.

ASMX has a tight coupling with the HTTP runtime and the dependence on IIS to host it. WCF can be hosted by any Windows process that is able to host the .NET Framework 3.0.

ASMX service is instantiated on a per-call basis, while WCF gives you flexibility by providing various instancing options such as Singleton, private session, per call.

ASMX provides the way for interoperability but it does not provide or guarantee end-to-end security or reliable communication.

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