WSDL VS MEX
MEX and WSDL are two different schemes to tell potential clients about the structure of your service. So you can choose to either make your service contracts public as (MEX) or WSDL.
A WSDL is generally exposed through http or https get urls that you can’t really configure (say for security limitations or for backward compatibility). MEX endpoints expose metadata over configurable endpoints, and can use different types of transports, such as TCP or HTTP, and different types of security mechanisms.
Developer Know How 