TCP/IP layers application - Quiz Explanation

The answers you selected are indicated below, along with text that explains the correct answers.
 
1. What is the function of the link layer?
Please select the best answer.
  A. Routing data between machines that do not have a direct physical connection
  B. Directing information between processes running on a single host, rather than between hosts
  C. Establishing communication between machines that have a direct physical connection
  D. Providing a universal language for clients and servers to use to communicate with each other
  The correct answer is C.
The function of the link layer is to establish communication between machines that have a direct physical connection. The link-layer protocols are usually concerned only with the local network.

2. What does the network layer do?
Please select the best answer.
  A. Routes data between machines that do not necessarily have a direct physical connection
  B. Directs information between processes running on a single host, rather than between hosts
  C. Establishes communication between machines that have a direct physical connection
  D. Provides a universal language for clients and servers to use to communicate with each other
  The correct answer is A.
The network routes data between machines that do not necessarily have a direct physical connection. The key capability of this layer is routing.

3. Which of the following is a characteristic of the transport layer?
Please select the best answer.
  A. To serve as a universal language that network clients and servers use to communicate with each other
  B. To establish communication between machines at the physical-connection level
  C. To move data between machines across the boundaries of physical networks
  D. To enable addressing of specific processes on a host machine
  The correct answer is D.
The transport layer enables addressing of specific processes on a host machine. The TCP transport-layer protocol adds reliability to the process-level addressing capabilities it shares with UDP.

4. What is the function of the application layer?
Please select the best answer.
  A. To direct information between processes, rather than just between machines
  B. To move data between machines across the boundaries of physical networks
  C. To provide a structured command language between client and server processes on the network
  D. To establish communication between machines at the physical-connection level
  The correct answer is C.
The application layer provides a structured command language between client and server processes on the network.
The familiar Internet services
  1. FTP,
  2. HTTP, and
  3. telnet
are examples of application-layer protocols.