Motivating examples Adoption of smart phones. Good:easy access to Internet,many cool apps,etc. Bad:expensive,absorbing too much time,.. ■ Once you start to use smart phones,it's hard to go back. There are not even many choices of traditional phones. Similar adoption:Religion,new idea,virus,.. This lecture focuses on progressive models: once a node becomes active,it stays active. There are also non-progressive models.Motivating examples ◼ Adoption of smart phones. ❑ Good: easy access to Internet, many cool apps, etc. ❑ Bad: expensive, absorbing too much time, … ◼ Once you start to use smart phones, it’s hard to go back. ❑ There are not even many choices of traditional phones. ◼ Similar adoption: Religion, new idea, virus, … ◼ This lecture focuses on progressive models: once a node becomes active, it stays active. ❑ There are also non-progressive models. 4