Computer Network (Third Edition) Hu Liang Answers to Chapter 3 of After-Class Exercises

Computer Network (Third Edition) Hu Liang Answers to Chapter 3 of After-Class Exercises

1. What are the two types of twisted pair cables?

Unshielded twisted pair (UTP) and shielded twisted pair (STP)

2. How many categories is UTP divided into?

UTP safety electrical performance is divided into 8 types: Category 1, Category 2, Category 3, Category 4, Category 5, Category 5e, Category 6 and Category 6e

3. What layers does a coaxial cable consist of?

Composed of four layers:

1. The innermost is a bare copper or aluminum wire;
2. The second layer is an insulator;
3. The third layer (shielding layer) is a metal foil film or metal mesh, which acts as a shield and protects the bare wires from electromagnetic interference;
4. The fourth layer is the protective plastic skin.

4. What is multi-mode propagation of light? What are the two types of multimode propagation?

Multimode propagation: Multiple light beams propagate through different paths in the core material. Divided into two types:

1. Multi-mode transition light: The density is from the center to the edge. The light propagates straightly in the core material and is reflected back when it encounters the boundary.
2. Multi-mode graded optical fiber: The core density is the largest at the center, gradually becomes smaller outward, and is the smallest at the boundary. Only horizontal rays travel straight through the center of constant density. , the others bend into a curve, with low density propagating quickly and high density propagating slowly. The angle of incidence is different, and the distance traveled is different, but the time taken is basically the same.

5. What is single-mode propagation of light?

Single-mode propagation: The emitted light is limited to a small range that is very close to the level. Generally, step materials and highly concentrated light sources are used to make the propagated light basically horizontal.

6. What are the main problems that the physical layer needs to solve?

1. Line configuration
2. Data communication mode
3. Topology
4. Signal
5. coding
6. interface
7. media

7. What is DTE? What is DCE?

DTE (data terminal equipment) is a device with data processing capabilities and the ability to send and receive data information

DCE (Data Circuit Terminating Equipment) is a device capable of sending and receiving analog or digital signal data over a network.

8. Explain the wiring standards of 568A and 568B.

568A standard: color sequence: green and white, green, orange and white, blue, blue and white, orange, brown and white, brown

568B standard: Color sequence: orange-white, orange, green-white, blue, blue-white, green, brown-white, brown

9. What does the mechanical specification of EIA-232 define?

One end of the interface is a DB-25 pin connector, and the other end is a 25-wire cable with a DB-25 hole connector. The cable length does not exceed 25 meters.

10. What does the electrical specification of EIA-232 define?

1. It is stipulated that all data must be transmitted in the form of logical 0 and 1
2. The encoding uses non-return-to-zero level encoding (NRZ-L), with 0 corresponding to positive level and 1 corresponding to negative level.
3. Specified voltage range: positive voltage area 3V ~ 15V, negative voltage -3V ~ -15V

11. What is the mechanical function definition of EIA-232?

Defines the function of each pin

12. Explain the procedural characteristics of EIA-232.

Communication using the main communication channel: five steps from preparation to clearing

13. What are the physical layer devices?

Physical layer equipment includes: network interface cards, cables, cables, repeaters, hubs, fiber optics, satellites, radio transmitters/receivers, multimedia circuit switches, and other equipment that transmits information through physical media.