1. The ISO Reference Model defines seven protocol layers, each of which is responsible for a specific range of functions. By considering this model, explain the main functions performed by a protocol operating at: 1.1 The Physical layer [3] 1.2 The Transport layer [3] 2. Explain how a network connection is established between a user and a server over the Internet using the TCP protocol. [5] 3. Both the TCP and UDP protocols use port numbers. What are these port numbers used for and what is meant by the term well-known port? Give an example of a well-known port. [6] 4. For each of the following three applications, state whether you would use TCP or UDP. [2x3= 6 marks] 4.2 File transfer 4.3Video streaming 4.4 An audio conference