TDV is the server

Using NTLM to authenticate clients requesting a published web service through Studio. After receiving a client request, TDV replies with the NTLM challenge, to which the client must respond with an authentication message. After TDV is satisfied with the response, it returns the results to the client.

TDV is the client

Introspecting or consuming a WSDL or XML/HTTP data source through a Web service such as Microsoft SharePoint. To retrieve the data, TDV makes a request to which the Web service replies with the NTLM challenge. TDV must then respond with the correct authentication message. After the challenge is resolved, TDV gets the results from the Web services.