What is the structure of an italian sonnet?

An Italian sonnet, also known as Petrarchan sonnet is known to have a structure of fourteen lines in an iambic pentameter. However, there are also Italian sonnets that are tetrameter and hexameter, but only few. Italian sonnets are always divided into two parts, but of two different rhyming groups. The first part consists of the first eight lines known as octave and has a rhyming scheme of abbaabba. Then follows the remaining six lines known as sestet that can have two to three rhyming lines in a varied arrangement.