| Refback | Trackback | Pingback | Webmention |
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Trigger mechanism | Visitor to linking site clicks on the link, and their browser takes them to the linked site | Code on linking server examines added or updated documents, extracts links, and sends notification to linked server for each link found | Code on linking server examines added or updated documents, extracts links, and sends notification to linked server for each link found | Code on linking server examines added or updated documents, extracts links, and sends notification to linked server for each link found |
Notification medium | HTTP referrer value | HTTP POST | XML-RPC call | HTTP POST with source and target parameters |
Capture mechanism | Examination of incoming HTTP referrer values | Trackback capture script | XML-RPC function | Webmention capture script |
Information sent by linking server | None | - Linking site name (Optional)
- Linking post title (Optional)
- Linking post excerpt (Optional)
- Linking post URL
| - Linked post URL
- Linking post URL
| - Linked post URL (target)
- Linking post URL (source)
|
Additional information presented to linked server | HTTP referrer sent by a visitor's browser upon clicking the link | IP address of linking server | IP address of linking server | IP address of linking server |
Autodiscovery mechanism (how the linking server finds out how and where to send the notification) | None | LINK tag in the header of the linked page or trackback RDF documents | Special HTTP header or LINK tag on the linked page | HTTP Link header or link element on the linked page |
Action required when notification is received | - Extract referrer value from incoming HTTP headers
- Retrieve referring page
- Parse retrieved page for desired information
| - Gather desired information from
- Given parameters
- or retrieving and parsing the given URL
| - Retrieve page at "linking post URL"
- Parse retrieved page for desired information
| Verifying that linking page does indeed link to linked page is recommended, not explicitly required |
Advantages | Requires no special code on linking server (the link itself becomes the notification when someone clicks on it) | All the information desired by the linked server (Linking site name, post title, excerpt) is present in the notification itself | - Notification mechanism has a complete technical specification
- Less susceptible to spamming
| - Uses well-known parts of HTTP wherever possible (autodiscovery, encoding of data, response status)
- Reuses pingback's existing semantics
- Minimum amount of data transferred on-the-wire
|
Disadvantages | - No notification unless someone actually clicks on the link
- Relies upon visitors' browsers sending proper HTTP referrer information
- Linked site must retrieve and parse linking site's page to extract the information it wants
| - Notification requires positive action by linking server
- Notification mechanism has only a partial technical specification
- Autodiscovery information may prevent XHTML validation
| - Notification requires positive action by linking server
- Linked site must retrieve and parse linking site's page to extract the information it wants
- Can be abused for DDOS attacks
| - Notification requires positive action by linking server
- Linked site must retrieve and parse linking site's page to extract the information it wants
- Relatively new, so less widely implemented
|