Chapter 5


1:

Complete this sentence: "Before sending end user data over an Ethernet LAN, the sender must _____________ the data in an Ethernet _____________."

A1:

Answer: "Before sending end user data over an Ethernet LAN, the sender must encapsulate the data in an Ethernet frame."

2:

Name the three general parts of an Ethernet frame.

A2:

Answer: An Ethernet frame has an Ethernet header, an Ethernet trailer, and the end user data.

3:

Imagine that PC1 has built an Ethernet frame, and it is ready to send the frame. What should PC1 do before sending the frame?

A3:

Answer: PC1 should listen to find out if someone else is sending a frame at that time. If so, PC1 should wait until the LAN is silent.

4:

What does the "CD" in CSMA/CD stand for?

A4:

Answer: CSMA/CD stands for carrier sense multiple access collision detect.

5:

Imagine that PC1 and PC2 send a frame at the same time, and the frames collide. Which one sends the jamming signal?

A5:

Answer: Both PCs send the jamming signal.

6:

Imagine that PC1 and PC2 send a frame at the same time, and the frames collide. How does the CSMA/CD algorithm minimize the chances that PC1 and PC2's frames might collide the next time they attempt to send the frames?

A6:

Answer: Both NICs generate a timer based on a random number. Often, one of their timers expires first, allowing that station to send its frame first.

7:

How many bytes are in a source Ethernet address? A destination Ethernet address?

A7:

Answer: Both the source and destination Ethernet addresses are 6 bytes long.

8:

Imagine that PC1 sends an Ethernet frame to PC2, but that PC3 and PC4 also get a copy, as a side effect of how a hub works. How does PC3 know to ignore the data in the frame?

A8:

Answer: All PCs, including PC3, look at the destination address. If that address does not match the PC3's NIC address, then PC3 discards the frame.

9:

List the IEEE committee that standardized Ethernet-specific details of Ethernet. Use both the numeric name and the three-word text name.

A9:

Answer: The IEEE 802.3 committee, also known as Media Access Control (MAC), defines the Ethernet-specific parts of Ethernet.

10:

List the IEEE committee that standardized Ethernet details that are in common with other types of LANS. Use both the numeric name and the three-word text name.

A10:

Answer: The IEEE 802.2 committee, also known as Logical Link Control (LLC), defines the parts of Ethernet that are shared with other types of LANs.

11:

If you were using a networking device from Cisco Systems, and you saw the output of a command that displayed a MAC address, how would it be formatted? Give an example, assuming that all digits in the actual MAC address are 1.

A11:

Answer: Cisco products show MAC addresses 4 hex digits at a time, with periods between them. For example, 1111.1111.1111 would be a sample Ethernet address.

12:

What does the acronym FCS stand for?

A12:

Answer: FCS stands for frame check sequence.

13:

Imagine that PC1 sends a frame to PC2, and PC2 notices that the FCS sent with the frame is different from the value calculated by PC2. What should PC2 do?

A13:

Answer: PC2 should discard the frame because the difference in values implies that bit errors occurred during the transmission of the frame.

14:

Explain the difference between error detection and error recovery. Which does Ethernet perform?

A14:

Answer: Error detection means that a device notices when frame errors occur, and when they do, the frame is discarded. Error recovery means that after the frame has been discarded, the receiver asks the sender to retransmit the data, and the sender obliges. Ethernet performs error detection.




Computer Networking first-step
Computer Networking First-Step
ISBN: 1587201011
EAN: 2147483647
Year: 2004
Pages: 173
Authors: Wendell Odom

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