Cisco Certified Network Associate (CCNA) Practice Exam

Which of the following statements correctly describe steps in the OSI data encapsulation process?

1. The data link layer adds physical source and destination addresses and an FCS to the segment.

2. The transport layer divides a data stream into segments and adds reliability and flow control information.

3. The presentation layer translates bits into voltages for transmission across the physical link.

4. Packets are created when the network layer adds Layer 3 addresses and control information to a segment.

The correct answer is: The transport layer divides a data stream into segments and adds reliability and flow control information.

The correct answer highlights the role of the transport layer in the OSI model, which is crucial for ensuring reliable communication between devices. The transport layer takes a continuous stream of data from the session layer and breaks it into manageable segments. This layer is responsible for adding crucial information such as sequence numbers, acknowledgment numbers, and other mechanisms that facilitate reliability and flow control, ensuring that data is transmitted in the correct order and without errors. By understanding this part of the OSI model, one recognizes the critical function the transport layer plays in preparing data for reliable delivery over the network. This encapsulation step is vital before data is passed down to the session layer and eventually transmitted over the physical layer. The other statements misattribute functions to the wrong layers or describe inaccurate processes within the OSI model. For instance, the data link layer is responsible for creating frames, which involves adding physical addresses and a Frame Check Sequence (FCS) but does not work directly with segments; the presentation layer deals with data format conversions rather than translating bits into voltages; and packets are formed at the network layer, where logical addressing occurs, not directly from the segment itself. Understanding these distinctions is key to mastering the OSI model's encapsulation process.