WCF services are designed to be transport independent. Even when they are hosted inside ASP.NET applications, the decoupling of the relationship to the HTTP-flavored features is required so that users are not confused. Also most of those ASP.NET features have counterparts in WCF. Nevertheless, WCF provides a mechanism to support smooth migration from ASMX to WCF by introducing two different hosting modes for WCF services:
- Mixed Transports Mode
- ASP.NET compatibility mode
This is controlled by the application-level configuration flag “aspNetCompatibilityEnabled”:
This flag is false by default.
Details from Wenlong Dong’s Blog : ASP.NET Compatibility Mode