re the TCP/IP stack with the OSI reference model. Problem 6.15 Explain the principle of data flow in the layered protocol hierarchy from the application layer through the lower layers to the physical channel. Explain also what happens in the protocol stack of the receiving computer until the data arrive at the application software at the other end of the connection. Problem 6.16 List the most important Internet access technologies and compare their characteristics. Problem 6.17 Explain the purpose and basic operation of a voice-band modem. What addi- tional function does it provide in addition to actual data transmission? Problem 6.18 Explain how the frequency band of the subscriber loop is used by ADSL. How does it transmit data over the subscriber loop? What are its main characteristics? Problem 6.19 What are the main modifications needed in cable TV network when it is upgraded to provide Internet access to residential customers? Problem 6.20 Explain the basic structure, operation, and characteristics of LANs. Data Communications Problem 6.21 What does the LAN protocol CDMA/CD refer to, that is, how does it oper- ate in principle? Problem 6.22 Explain the Ethernet frame structure. Problem 6.23 How do DIX Ethernet and IEEE 803.2 frames differ? Problem 6.24 Explain how collision detection in Ethernet operates. Problem 6.25 Why is an Ethernet frame defined to be at least 64 bytes long? Why can't it be shorter? Problem 6.26 Assume that three workstations, A, B, and C, are connected to the same hub and they start to transmit simultaneously. How is this situation resolved SO that all frames will be successfully transmitted after a while? Problem 6.27 Assume that the only delay in a LAN is cable propagation delay. Signal speed in cable is 70% of the speed of light. What would be the maximum distance between computers in an Ethernet LAN connected to the same hubs in the same collision domain for a network data rate of (a) 10 Mbps, (b) 100 Mbps, and (c) 1 Gbps? The minimum frame length is 64 bytes. (Assume here that no 