1. (Single choice question) The transmission media used by 10Base-T in the IEEE 802.3 physical layer standard is (A).
- A. twisted pair
- B. Optical fiber
- C. Baseband thick coaxial cable
- D. Baseband thin coaxial cable
Analysis: The transmission medium used by 10Base-T in the IEEE 802.3 physical layer standard is twisted pair. Twisted pair is a transmission medium that is widely used in local area networks because of its low cost and easy installation, and its ability to meet the transmission rate requirement of 10 Mbps. Baseband thick coaxial cable and baseband thin coaxial cable were mainly used in early Ethernet and have now been gradually eliminated. Although optical fiber can also meet the transmission rate requirements of 10Base-T, it is expensive and complicated to install and maintain, so it is not used in 10Base-T. Therefore, option A "twisted pair" is the correct answer.
2. (Single choice question) For a 100Mbit/s Ethernet switch, when the output port has no queuing and forwards an Ethernet frame (excluding the preamble) in cut-through switching, the forwarding delay introduced is at least Yes(A).
- A. 0. 48us
- B. 5. 12us
- C. 121. 44us
- D.0us
Analysis:
For a 100Mbit/s Ethernet switch, when the output port has no queuing and forwards an Ethernet frame (excluding the preamble) in cut-through switching, the forwarding delay introduced is at least 0.48us. Cut-through switching is an efficient frame forwarding method that starts forwarding frames as soon as they arrive without waiting for the entire frame to be received. Therefore, the forwarding delay introduced by cut-through switching only includes the transmission time of the minimum frame length (64 bytes, excluding the preamble), that is:
64 * 8 / 100,000,000 ≈ 0.48us
Therefore, option A "0.48us" is the correct answer.
3. (Single choice question) Among the following protocols, the one that will not cause collision is (A).
- A. TDM
- B. CSMA
- C. LOVE
- D. CSMA/CD
4. (Single-choice question) For a 10Mbit/s switched Ethernet network connected by switches, if there are 10 users, the bandwidth that each user can occupy is (A).
- A. 10Mbit/s
- B. 100Mbit/S
- C. 2Mbit/s
- D. 1 Mbit/s
Analysis: For a 10Mbit/s switched Ethernet connected by a switch, if there are 10 users, the bandwidth each user can occupy is 10Mbit/s, because each user can use the 10Mbit/s bandwidth at the same time. So the answer is A.
5. (Single choice question) The minimum length of an Ethernet frame is (B) bytes.
- A. 128
- B. 64
- C. 256
- D. 32
6. (Single choice question) The functions provided by PPP are (B).
- A. Network Control Protocol (NCP)
- B. A, B and C are all
- C. Link Control Protocol (LCP)
- D. A framing method
7. (Single choice question) The main function implemented by the network card is (A)
- A. Functions of the physical layer and data link layer
- B. Functions of data link layer and network layer
- C. Functions of the physical layer and network layer
- D. Functions of the data link layer and application layer
Analysis: The main functions implemented by the network card are the functions of the physical layer and data link layer. The network card is the interface between the computer and the network. It is responsible for converting the data inside the computer into data frames that can be transmitted on the network, and receiving the data frames back from the network. In the OSI model, the physical layer is responsible for realizing the physical transmission of data, while the data link layer is responsible for grouping data into frames and adding control information such as frame headers and frame tails for transmission on the physical layer. Therefore, the network card needs to implement these two levels of functions, including encoding data into bit streams, decoding frames into data, and so on. Therefore, option A "Functions of the physical layer and data link layer" is the correct answer.
8. (Single choice question) The corresponding bit string after the HDLC protocol frames 01111100 01111110 is (C).
- A. 01111100 01111101 01111110
- B. 01111100 0111111001111101
- C. 01111100 0011111010
- D. 01111100011111010
Analysis: The HDLC protocol uses bit stuffing for frame delimitation. Therefore, escape characters need to be inserted into the data during framing to avoid conflict with the delimiter. In the HDLC protocol, the delimiter is 01111110 and the escape character is 01111101. If the delimiter or escape character appears in the data, you need to add the escape character 0x7D in front of them and replace the delimiter or escape character with The 6th bit of is inverted (that is, 1 becomes 0 and 0 becomes 1).
Therefore, for the data 01111100 01111110, it needs to be escaped when framing, and we get:
01111100 01111101 00111110
Among them, 01111101 00111110 is the result of escaping the delimiter 01111110 in the data. You need to add the escape character 0x7D in front and invert the 6th bit to get 0011111010.
Therefore, option C "01111100 0011111010" is the correct answer.
9. (Single choice question) Among the following multiplexing technologies, (A) has the function of dynamically allocating time slots.
- A. Statistical time division multiplexing
- B. Synchronous Time Division Multiplexing
- C. Frequency division multiplexing
- D. Code division multiplexing
10. (Single choice question) Among the following media access control methods, which one may conflict is (C).
- A. CDMA
- B. FDMA
- C. CSMA
- D. TDMA
11. (Single choice question) Two devices on the same LAN have the same static MAC address (B)
- A. Both devices can communicate normally
- B. Neither device can communicate
- C. The device booted for the first time uses this address, and the second device cannot communicate.
- D. The last booted device uses this address, and the first device cannot communicate.
Analysis: When two devices on the same LAN have the same static MAC address, neither device can communicate normally. Because MAC addresses are unique, if two devices have the same MAC address, the network will not be able to identify which device should receive the incoming data frame, causing communication errors.
12. (Single choice question) Ethernet switches forward according to (B).
- A.IP address
- B. MAC address
- C. Port number
- D. Agreement type
13. (Single choice question) Which of the following statements about the PPP agreement is correct (C)
- A. Network layer protocols
- B. Bit-oriented
- C. Data link layer protocol
- D. Byte-oriented
14. (Single choice question) According to the working principle of the CSMA/CD protocol, the minimum frame length needs to be increased (D).
- A. The network transmission rate remains unchanged and the maximum distance of the collision domain becomes shorter.
- B. The probability of upper layer protocols using TCP increases
- C. Reduce the number of repeaters on the line while keeping the collision domain unchanged
- D. The maximum distance of the collision domain remains unchanged, and the network transmission rate increases
Analysis: According to the working principle of the CSMA/CD protocol, what needs to be increased is option D: the maximum distance of the collision domain remains unchanged, and the network transmission rate is increased. The shortest frame length refers to the minimum frame length. If the frame length is too short, conflicts may not be detected due to the delay of the conflict detection algorithm during signal transmission, which may lead to collisions and ultimately reduce network performance. Therefore, increasing the minimum frame length is to avoid this situation and ensure network performance.
15. (Single choice question) The function of the "padding" field in the Ethernet frame structure is (C)
- A. Used for piggyback responses
- B. Carrying optional routing information
- C. Keep the minimum frame length
- D. Send urgent data
16. (Single choice question) Transparent transmission is the basic function of the data link layer. The so-called transparency refers to (A).
- A. There are no restrictions on the content, format and encoding of transmitted data.
- B. The direction of data transmission is transparent
- C. The method of transmitting data is transparent
- D. There are restrictions on the content, format and encoding of transmitted data.
17. (Single-choice question) The characteristics of full-duplex Ethernet transmission technology are: (B)
a. Can send and receive frames at the same time
b. Not subject to CSMA/CD restrictions
c. Cannot send and receive frames at the same time
d. Subject to CSMA/CD CD restrictions
- A.a sum c
- B. a and b
- C. c and d
- D. b and c
18. (Single choice question) The main function of a multiplexer is (B).
- A. Reduce the communication processing intensity of the host
- B. Combine transmissions from multiple lines
- C. Perform digital/analog conversion
- D. Perform serial/parallel conversion
21. (Single choice question) In the data link layer, network interconnection is represented by (C).
- A. Connecting networks of different architectures
- B. Forwarding messages between networks
- C. Forward data frames between network segments
- D. Copy bitstream between cable segments