12. Which of the following is NOT a characteristic of the Media Access Control (MAC) sublayer of the data-link layer (Layer 2) of the OSI reference layered model? 13. Which OSI reference model layer is responsible for? (a) Setting up session (b) Maintaining a session (c) Tearing down a session 14. What layers of the OSI correspond to labels A and B? 15. John, the Network Administrator of XYZ Corporation, is interested in changing the format of text from American Standard Code for Information Interchange (ASCII) to Extended Binary Code Decimal Interchange Code (EBCDIC). In addition, his IT manager requested that all sensitive and confidential information on their servers should be protected by applying the appropriate encryption. What OSI reference model layer is responsible for data format such as encryption? 16. What is the purpose of a DNS server? 17. How fast can category 5e transfer data? 18. What is the purpose of a proxy server? 19. What is a virtual server? 20. What is the purpose of RTP in VoIP? 21. Which two types of media are twisted-pair cable?