Default - ASP.NET Compatibility Mode

In general WCF service hosting AppDomain can run in two different mode

• Mixed Transports Mode(Default): In this mode does not participate in ASP.NET HTTP pipeline and it behaves consistently independent of hosting environment and transport.
• ASP.Net Compatibility Mode: In this mode, service will participate in ASP.Net HTTP pipeline and it is similar to old web service (.asmx). ASP.NET features such as File Authorization, UrlAuthorization, and HTTP Session State are applicable to services running in this mode

In WCF 4.5 default aspNetCompatibilityEnabled attribute to true in web.config

WCF 4.5 Configuration Settings 

WCF 4.0 Configuration file

Configuration tool tips

In WCF 4.5, tooltips are provided for configuration file, this makes the developers job simple

XmlDictionaryReaderQuotas

XmlDictionaryReaderQuotas contains configurable quota values for XML dictionary readers which limit the amount of memory utilized by an encoder while creating a message. While these quotas are configurable, the default values have changed to lessen the possibility that a developer will need to set them explicitly

MaxArrayLength	Int32.MaxValue
MaxBytesPerRead	Int32.MaxValue
MaxDepth	128 nodes deep
MaxNameTableCharCount	Int32.MaxValue
MaxStringContentLength	Int32.MaxValue