4. Smartphones and tablets are typically wirelessly connected to the Internet via cellular or Wi-Fi network. The challenges posed by wireless networking are different from traditional wired computer networks. Considering wireless and mobile network, answer the following: (a) A wireless link differs from a wired link. Briefly describe the characteristics and challenges of wireless links. (8 marks) (b) Briefly explain the difference between the two terms infrastructure and ad-hoc when used to describe the operational modes of a Wi-Fi access point. And in what circumstances is it appropriate to use the ad-hoc mode? (6 marks) (c) Give a brief description of the 3G cellular network architecture. Also, which enhancements does the 4G-LTE network have over the 3G network? (6 marks)