Cisco Certified Network Associate (CCNA) Practice Mode

Community Discussion

Written by other learners. Comments can disagree with the marked answer — check the official documentation when in doubt.

• Chose C1

  The purpose of the preamble is to allow devices to synchronize their receiver clocks, to make sure that they are ready to receive the rest of the frame and the data inside. It helps the receiving device to recognize the start of a frame and synchronize its clock with the sender's clock. i.e, It tells the receiver that a valid frame is about to start. When the sender transmits an Ethernet frame, it starts with the preamble. The repeating pattern of 10101010 is sent over the physical medium. Start Frame Delimiter (SFD) on the other hand, marks the end of the preamble and signals the beginning of the actual Ethernet frame. It has a pattern of 10101011, which indicates to the receiver that the next byte is the start of the frame.

• 12

  Imagine you have a special code that you want to send to your friend using a walkie-talkie. Before you start talking in your code, you want to make sure your friend is listening and ready to hear your message. So, you and your friend decide on a special clapping pattern that you'll do before you start talking. In the same way, in a computer network, before sending important information, devices use a special pattern of signals called a "preamble." This preamble works like the clapping pattern. It helps the devices get ready to listen to the upcoming message and understand it correctly. It's like a little signal that says, "Hey, get ready, some important stuff is about to come!"

• 1

  C. Preamble The preamble is a sequence of alternating ones and zeros that serves as a synchronization signal at the beginning of an Ethernet frame. It notifies a host that traffic is coming and helps the receiving device synchronize its clock with the sender's clock. This synchronization is essential for correctly interpreting the subsequent data in the frame.