Web Services Description Language (WSDL) is an XML schema for describing Web services and how they can be accessed by Web based applications. WSDL facilitates the creation and deployment of web based applications. For example, by using WSDL with many industry Web services development environments, a web services developer can access features provided by an implementation without knowing details of the network or underlying transport protocols.

ISO/IEC 18450:2013 specifies two WSDL documents: Computing Function WSDL and Switching Function WSDL, for ISO/IEC 18051, Services for Computer Supported Telecommunications Applications (CSTA) Phase III. All CSTA features (e.g., services and events) specified in ISO/IEC 18051 are specified in ISO/IEC 18450:2013. ISO/IEC 18450:2013 specifies pairs of port types, one from the Computing Function WSDL and one from the Switching Function WSDL, for all the profiles specified in ISO/IEC 18051.

A full WSDL document contains both abstract definitions (WSDL messages and port type elements) and concrete protocol specific definitions (WSDL bindings, ports, and service elements). This CSTA WSDL Standard specifies only the abstract definitions of a WSDL document. The concrete and protocol specific definitions are implementation specific and are outside the scope of ISO/IEC 18450:2013. Annex B illustrates an example SOAP over HTTP binding.

WSDL is defined in XML and XML Schemata. ISO/IEC 18450:2013 builds upon the XML data types and imports all message formats specified in ISO/IEC 18056.

Annex A specifies mechanisms to establish event channels based on WS-Eventing. The event channels allow the Switching Function and Computing Function to be both a Service Requester and a Service Provider.