How Pingback work

First = receptor
Second = originator<br><br />Pingback:
-> First blog exposes a ping back server
X-Pingback header or,
<link rel="pingback" href="([^"]+)" ?/?>

-> Second blog put a <a href> to First blog
-> Second pingback client will discover First pingback server from HTTP header or <link>
-> Second pingback client sends a xml-rpc request to First server with:
 method: pingback.ping
 param: sourceURI, targetURI

-> First pingback server now can do anything
 . check whether targetURI exits?
 . check whether srouceURI exits and has the link
 . record the pingback
 . change model so site page contains a link to source URI

Refback:
Nothing special required at Second end.
When browser loads url from First blog URL, it sends 'Referer' header with value Second blog URL

Trackback:
-> Trackback URI is RESTful .

-> service discovery with RDF xml