When write a service on ASMX you’re stuck serving up individual WSDL files. WCF fixes this.
Difference between WCF and ASMX web services
http://stackoverflow.com/a/2448568
Call WCF Services Synchronously and Asynchronously
http://www.codeproject.com/Articles/91528/How-to-Call-WCF-Services-Synchronously-and-Asynchr