Download the "LISS Development toolkit" - a simple Windows .exe program which acts as a LISS client, whereby RPC calls can be triggered at will using a sample dataset.
If you are a timetabling product then you will be wanting a LISS test server. There is no publicly available LISS test server, but you can contact admin systems e.g. Compass, Sentral or Millenium.
JSON is highly recommended over XML as it is far less verbose and more readable.