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Chapter 9
| 1: | Which of the seven layers in the OSI reference model does UDP occupy? |
| A1: | Answer: UDP occupies Layer 4, the transport layer of the OSI reference model. |
| 2: | What is the relationship between TCP and UDP? |
| A2: | Answer: UDP and TCP are peers. They are both transport layer protocols designed specifically to work with the Internet Protocol (IP). |
| 3: | What is meant by the term best effort? |
| A3: | Answer: UDP's best effort is to make one attempt at delivering data. There are no guarantees nor any complicated mechanisms needed to fulfill any guarantees. The result is a spartan but fast and efficient transport protocol ideally suited to the needs of real-time applications. |
| 4: | What is meant by the term connectionless? |
| A4: | Answer: The term connectionless describes the loose, unstructured communications that occurs between a source and destination machine when using UDP. Unlike TCP, UDP does not establish a session, nor does it try to identify the sequential relationship between different packets of data sent.In TCP, that was done using sequence numbers and the establishment of a session. With UDP, each datagram sent is essentially a standalone piece of data that does not require correlation with any other data. |
| 5: | What is the difference between TCP port numbers and UDP port numbers? |
| A5: | Answer: TCP and UDP port numbers are identical in size, shape, and function. Their only difference is that they are two separate lists of applications. Those two lists might have a lot of applications in common (to avoid confusion), but they remain separate lists. |
| 6: | Identify the functions performed by UDP on a source machine. |
| A6: | Answer: UDP on a source machine accepts data from an application, wraps a header around that data, and populates that field with pertinent information, including application port numbers. Next, UDP performs a mathematical process on the contents of the datagram it has just created and stores the resulting value in the UDP header's checksum field. Lastly, UDP passes that datagram onto IP for further processing. |
| 7: | Identify the functions performed by UDP on a destination machine. |
| A7: | Answer: On a destination machine, UDP gets involved after IP has received the incoming data from the local-area network (LAN). Its first task is to verify that the data contained inside the datagram is the same as when it left the source machine. It does so by performing the same mathematical process on the datagram and compares the results it received with the results stored in the UDP header's checksum field.If the values match, UDP is satisfied with the integrity of the data. If the values don't match, the packet is discarded. The header is checked to identify the destination application (as indicated by the destination port address). That header is then removed and the data embedded within the datagram handed off to its destination application. |
