The ServerCall tag invokes an ITP/Server service. Depending on its attributes (see below) the ServerCall tag itself will get replaced by the value/result of this invocation.
A general invocation looks as follows:
<itp:ServerCall name="…" …>
<itp:ServerParameter>…</itp:ServerParameter>
…
<itp:ServerParameter>…</itp:ServerParameter>
</itp:ServerCall>
The JSP code above will invoke the service with the specified name, and pass the parameters in the order that they are listed. For details, see below.