I see, thank you for your help. I suspect the blog.hu has a special field which is empty by default and the user must filll the correct value(s) by hand.
It is maybe due the tackback spam or intentional incompatibility to cramp other blogs to obtain attention.

This blog is here: http://japanblog.fisher.hu/

Here is a test entry: http://japanblog.fisher.hu/archives/189-tesztbejegyzes,-hagyd-figyelmen-kivuel,-bocsi.html

• Checking http://langologitarok.blog.hu/2010/06/14/rage_against_the_wall_london_calling_8 for possible trackbacks...
• Trackback failed ...

I understand where the trackback entry should be displayed. The serendipity found no trackback entry on any foreign blog page I have linked and I have no idea why and where to start look for a solution/debug.

If I understand everything well, then I only have to do the following:

- create a new blog entry in my serendipity installation
- put a link that points an another blog entry somewhere
- if the linked page contains the correct RDF line then my blog notifies the linked site
- the linked site can ...