Hi,

yes, the ajax frame is exactly needed to make XHR requests to the push server.
the problem in using the ajax frame for your case is that such file has to be downloaded from the server it will connect to, so after you've already chosen to which server to connect.
You can take a look to the ajax_frame.html file source, it's pretty simple and is not obfuscated (excluding calls to parent.LS* methods, but there are only three of those, LS_a is called to notify that the page is ready, LS_x is called on XHR errors and LS_h on onreadystatuschange events).
In any case if you're going to use the html approach you'll need to download two files, one per server
Unfortunately that is currently the only way to make a XHR request to the server. In the next release we're going to include support for cross-origin requests but that will not work on old browses anyway and will require extra code on modern IEs.

Another approach may be to deploy a js file like

in the Lightstreamer internal web server (see <web_server> in the server configuration) and then download it through <script> inclusion



Finally don't forget to keep into consideration the browser cache.

HTH