What information is tranferred when search engines are pinged?

[sericbiz1]

What information is provided to search enginges when they are pinged? Are they just notified that a new site map is generated and request the search engine to crawl the site again? Are search engines only notified if something changes?

Other than google and yahoo, what search engines are automatically pinged?

[XML-Sitemaps Support]

With ping generator provides a link to your sitemap so that search engines can read it.
Ping is sent every time sitemap is created.
Notified are: google, bing, yahoo, ask, moreover, [ External links are visible to logged in users only ].