TrackBacks, Pingbacks, and Backlinks, oh my

Back-links are the backbone of the blogosphere, allowing bidirectional linking that creates a web of conversation. Several standards exist, so how do they stack up?

TrackBack

is most commonly used by manually copying the TrackBack URL of an existing page and pasting it on a new page. Pages that support TrackBack include a TrackBack URL that can handle pings (e.g. http://somewhere.blog/trackback/demo-post). Supporting blog software includes a field in which to enter this URL, and will send an HTTP POST to the TrackBack URL when used. The post includes the source url as well as the following option parameters: title, excerpt, blog_name. The server responds with simple XML indicating success or failure. The spec also includes provisions for automatic discovery via RDF embedded in the target document. Typical exchange occurs as follows:

  1. Alice writes a blog entry that interests Bob.
  2. Bob writes a related blog entry, and manually copies and pastes the TrackBack URL in his blog software.
  3. Without interaction, Alice’s blog software receives the TrackBack, and adds a link and excerpt from Bob’s blog.

TrackBacks remain the most widely supported linking mechanism. Compared to Pingback, “the other open standard”, the TrackBack standard includes article titles and summaries, which are important for judging whether a link is worth reading. On the negative side, usage is effectively manual because the autodiscovery mechanism is not commonly supported. The standard doesn’t include provisions for well-known error codes, but this complaint is somewhat academic.

Pingback

also uses HTTP POST’s, but requests are submitted via XML-RPC. Autodiscovery is done via the X-Pingback HTTP header or an HTML link element (<link rel=”pingback” xhref=”” mce_href=”” >). The server responds with an arbitrary string indicating success, or any of several defined fault codes – nonexistent URI’s, already registered, access denied, etc. In short:

  1. Alice writes a blog entry that interests Bob.
  2. Bob writes a related blog entry that includes a link to Alice’s blog.
  3. Without interaction, Bob’s blog software uses the autodiscovery mechanism to send a Pingback to every URL in his entry, including Alice’s, that supports Pingback
  4. Without interaction, Alice’s blog receives the Pingback, and adds a link to Bob’s blog

Although less widely supported than TrackBack, Pingback has supported autodiscovery since it’s inception, so cut-and-paste is not necessary. The standards-based XML-RPC and error reporting mechanism are also arguably cleaner than TrackBack. Pingbacks are thus more transparent, and this transparency facilitates backlinking for incidental non-blog URL’s (e.g. news.com). Unfortunately, the spec doesn’t include provisions to relay a title or summary, which are important for judging relevance. Several implementations support these features, but it would be nice if the spec defined them.

Backlinks

are the proprietary mechanism used by Google’s Blogger.com. Back-links and exceprts are generated dynamically using google’s blog search engine blogsearch.google.com (alternately search.blogger.com). Blogs that notify an update service, such as rpc.pingomatic.com, should soon be indexed by blogsearch.google.com. The scenario occurs like this:

  1. Alice writes a blog entry that interests Bob.
  2. Bob writes a related blog entry that includes a link to Alice’s blog.
  3. Without interaction, Bob’s blog software updates several blog search engines using .
  4. blogsearch.google.com indexes Bob’s entry.
  5. Users who visit Alice’s entry see Bob’s entry by virtue of the fact that it includes a link to Alice’s entry.

Backlinks are implicitly supported by any blog indexed by blogserch.google.com. This is convenient because any indexed blog that refers to the Blogger.com page is automatically in the Backlink list. On the negative side, blogger.com generates the back-link list dynamically, and Alice receives no notification nor history.

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3 Responses to “TrackBacks, Pingbacks, and Backlinks, oh my”

  1. JonnyRo says:

    Wikipedia has a nice article on Trackbacks, which has this to say about trackback spam:

    Some individuals or companies have abused the TrackBack feature to insert spam links on some blogs (see sping). This is similar to comment spam but avoids some of the safeguards designed to stop the latter practice. As a result, TrackBack spam filters similar to those implemented against comment spam now exist in many weblog publishing systems. Many blogs have stopped using trackbacks because dealing with spam became too burdensome.

    Pretty much any standard that automatically displays content on a page has to have anti spam provisions from it’s inception or it’s doomed. Not all people are evil, not even most people, but the ones that are asshats have a disproportionate amount of effect on the activities of others.

  2. nathan says:

    Agreed. Speaking of spam protection, your comment went to moderation because it included more than one URL, per the WordPress default configuration. Several days ago I installed the Akismet plugin for WordPress, and I haven’t received any blogspam yet. Pingback implementations often check for the return link before they post an excerpt, which adds some protection as well. It’s become another cat and mouse game.

  3. […] Here is a good description of all the different methods for linking between blogs, such as Trackbacks, Pingbacks and Backlinks. […]

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