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. This Standard specifies two WSDL documents: Computing Function WSDL and Switching Function WSDL@ for ECMA-269@ Services for Computer Supported Telecommunications Applications (CSTA) Phase III. All CSTA features (e.g.@ services and events) specified in ECMA-269 are specified in this Standard. This Standard specifies pairs of port types@ one from the Computing Function WSDL and one from the Switching Function WSDL@ for all the profiles specified in ECMA-269. 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 this Standard. Annex B illustrates an example SOAP over HTTP binding. WSDL is defined in XML and XML Schemata. This Standard builds upon the XML data types and imports all message formats specified in ECMA-323. 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.