Complex sentence: According to Cisco, the Zettabyte Era first came about when global IP traffic exceeded that of one zettabyte, in 2016 this milestone was reached when global IP traffic reached that of 1.2 ZB (or an average of 96 exabytes (EB) a month).
Split into simpler sentences: According to Cisco, the Zettabyte Era first came about when global IP traffic exceeded that of one zettabyte. In 2016 this milestone was reached when global IP traffic was estimated to have reached that of 1.2 ZB (or an average of 96 exabytes (EB) a month).