There is 3 levels of indexer service,
The indexer #1 is a complex process that insure that all of backlinks have been crawled by google spiders, it is including some techniques such as: shorten your links, ping each single link, create rss feeds, create xml sitemaps... etc.
The indexer #2 will include all processes in the indexer #1 more than 1 time + some extra tactics to get high indexer rate not only crawled by Google.
The indexer #3 have all processes in the indexer #2 plus submitting each backlink to 1k - 2k of authority filter sites like whois, redirect, stats... etc.
The indexer #3 gives the maximum indexer rate