The sonnet form is a "prescribed" form made by fixing the length and character of this stanza form. Of the 125 poems surviving from Frederick's court, 35 are sonnets, 25 by one lawyer, Giacomo da Lentino. These are 14 lines of 11-syllables with an octave always rhyming abababab, 24 with 2 new rhymes after the turn into the sestet, and 24 dealing with Love.
The form made its way north in the hands of Guittone d'Arezzo (1230-1294), who wrote 246 sonnets on any topic imaginable, and into the hands of the circle of stilnovisti from which Dante Alighieri (1265-1321) emerged--like Guido Cavalcanti (1255-1300). Their Lady is more idealized. In form, they prefer the "crossed rhymes" of the ABBAABBA octave to the linked rhyme pattern. Instead of an argument throughout, they often use the octave for description/presentation and the sestet for comment. Sonnets are the dominant form in Dante's Vita Nuova, his account of his love for Beatrice.
Dante's heir was Francis Petrarch (1304-1374), another Florentine exile. His collected vernacular Canzoniere (or Rime) are mostly sonnets, 317 of them, mostly to Laura, a merchant's wife in Avignon whom he loved from his first sight of her and past her death 21 years later. Petrarch prefered the crossed rhyme octave; his sestets are most often CDECDE or CDCDCD. Petrarch influenced all European love poetry in the next century.
Early English sonnets are often adaptations of Petrarch. They also adapted contemporary continental poets. Spenser, for example, has sonnets which are taken from the Italian Torquato Tasso and the French poet Desportes.