Computer Networking Basics
When a web page's data is sent, what happens on the sending side each time the data is passed from an upper layer to a lower layer?
- AEach layer wraps it with its own control information (a header), and the receiver removes the headers starting from the lowest layer
- BEach layer compresses the data, so the lower the layer, the smaller the data to send
- CThe upper layer's header is removed and replaced with that layer's header
Show answer and explanation
Answer: A. Each layer wraps it with its own control information (a header), and the receiver removes the headers starting from the lowest layer
This mechanism is called encapsulation. Application data gets a TCP header to become a segment, an IP header to become a packet, and an Ethernet header plus an error-detecting code (FCS) to become a frame. The receiver reads and removes the headers starting from the lowest layer, and each layer processes the data using only its own header. Because no layer needs to know the contents of the others, you can, for example, replace wired LAN with wireless LAN and keep the upper layers unchanged. The cost is that the headers make the bits on the line more than the application data.
- A. Correct. This is called encapsulation.
- B. Headers are added, so the data grows at lower layers. Compression is generally not done.
- C. The upper layer's header is kept and wrapped from outside; the receiver's upper layer needs it.