Computer networks can be divided into three categories according to the transmission medium

Computer networks can be divided into wired networks, optical fiber networks, and wireless networks according to the transmission medium.

1.Wired network: refers to a computer network connected by twisted pairs.

2.Optical fiber network: optical fiber is used as the transmission medium.

3.Wireless network: A type of network that uses electromagnetic waves as a carrier to achieve data transmission.

According to the data exchange mode, it is divided into circuit switching network, message switching network, and packet switching network.

According to the mode of communication, it is divided into broadcast transmission network and point-to-point transmission network.

According to the coverage and scale of the network, it is divided into local area network, metropolitan area network and wide area network.

Extended Materials. Performance metrics for computer networks.

1) Rate. Speed in network technology refers to the rate at which a host connected to a computer network transmits data over a digital channel, and it is also known as data rate

rate) or bitrate (bit

rate）。Speed is one of the most important performance metrics in a computer network. The unit of rate is bits (bits per second) (i.e., bits

persecond）。

2) Bandwidth. The bandwidth of a signal refers to the range of frequencies occupied by the various frequency components that the signal contains.

3) Throughput.

Throughput refers to the amount of data that passes through a network (or channel, interface) per unit of time.

4) Latency. Latency refers to the time it takes for data (a packet or packet, or even a bit) to be transmitted from one end of the network (or link) to the other.

5) Delay bandwidth product.

Multiply the two measures of network performance discussed above—propagation delay and bandwidth—to get another useful measure: propagation delay bandwidth product, and instant delay bandwidth product = propagation delay bandwidth.

6) Round-trip time (RTT).

In computer networks, round-trip time is also an important performance indicator, representing the total amount of time elapsed from the time the sender sends the data to the time the sender receives an acknowledgment from the receiver (which is sent as soon as the receiver receives the data).

7) Utilization.

There are two types of utilization: channel utilization and network utilization. Channel utilization means that a channel is utilized (data passes through) a percentage of the time, and the utilization of a completely idle channel is zero. Network utilization is a weighted average of channel utilization across the network.

Divide from the transmission medium.

Wired network: The nodes of the network are connected by coaxial cables.

Twisted pairs, fiber optic cables, ** wires and other tangible lines connect the network.

Wireless network: Infrared light is passed between the nodes of the network.

Microwave, radio frequency (radio) and other invisible transmission media are connected to the network.

There are four types of transmission media in a computer network.

1. Twisted pair: STP (shielded twisted pair).

Unshielded twisted pair (UTP).

Features: It is easy to be interfered by external high-frequency electromagnetic waves, and has a high bit error rate, but because it is cheap and easy to install, it is suitable for point-to-point connection and can be used for multi-point connection, so it is still widely used.

2. Coaxial cable: 50 W coaxial cable 75 W coaxial cable.

Features: High bandwidth (up to 300 400Hz), low bit error rate, high performance** ratio, so used in LAN.

3. Characteristics of optical cable: small diameter and light weight;Large transmission frequency bandwidth and communication capacityAnti-lightning and electromagnetic interference performance, good bending and infiltration, no crosstalk interference, good confidentiality, and low bit error rate. But the optoelectronic interface is more expensive. Optical fiber is widely used in telecommunication systems to lay backbone lines.

4. Wireless transmission: short-wave communication, microwave satellite communication.

Features: high frequency, wide frequency range, large capacity of communication channel;The signal is less affected by industrial interference, the transmission quality is high, and the communication is relatively stableIt is not affected by the geographical environment, and the construction investment is small.

Commonly used transmission media are divided into two categories: wired transmission media and wireless transmission media.

The wired transmission medium mainly includes twisted pair, coaxial cable and optical fiber. Twisted pair and coaxial cables transmit electrical signals, and optical fibers transmit optical signals.

Wireless transmission medium According to the spectrum, it can be divided into radio waves, microwaves, infrared, lasers, etc., and the information is loaded on electromagnetic waves for transmission.

Answer]: a, b

According to the classification of network transmission media, computer networks can be divided into guided transmission networks and non-guided transmission networks.