Tiered link building boosts your site's authority by creating two link levels....

https://www.4shared.com/office/BIObF2h6fa/pdf-72309-44204.html

Tiered link building boosts your site's authority by creating two link levels. Tier 1 links point directly to your site, gaining search engines’ trust. Tier 2 links support those Tier 1 links, making them stronger and more effective