What are the media?

(1) working principle: twisted pair is the most common transmission medium at present, which consists of two mutually insulated copper wires with a typical diameter of1mm. Two wires are twisted together to prevent their electromagnetic induction from generating interference signals in adjacent pairs. Cover the outside with a new plastic sleeve.

(2) Classification:

Unshielded twisted pair: it has no shielding layer, and generally consists of four twisted pairs, with the longest length of 100 meter. It has good cost performance and wide application. Divided into 1, 2, 3, 4, 5, super 5 categories. Class 3 is used for 10MBPS transmission; 100MBPS or above.

Shielded twisted pair: It has a metal sheath and generally consists of two pairs of twisted pairs, the longest of which is more than ten kilometers. Good anti-interference, high performance, high cost and not widely used. Strong anti-electromagnetic interference ability, suitable for high-speed network protocol applications with large network traffic.

coaxial line

(1) concept: it consists of two coaxial inner and outer wires, the inner wire is a metal wire, the outer wire is a reticulated hollow cylindrical conductor, and each of the inner and outer wires has a layer of insulating material, and the outermost layer is a protective plastic sheath. The metal shielding layer can reflect the magnetic field back to the center conductor and protect the center conductor from external interference, so coaxial cable has higher bandwidth and better noise suppression characteristics than twisted pair cable.

(2) Classification:

50 Ω coaxial cable is used to transmit digital signals, that is, baseband coaxial cable.

Divided into: the maximum distance of thick cable is 2500 meters, and the price is high.

The maximum length of thin cable is185m.

The other is 75 Ω coaxial cable, which is used to transmit broadband analog signals, that is, broadband coaxial cable. However, it is difficult to install additional signals, which are suitable for long-distance telephone networks, television systems and broadband computer networks.

3) Disadvantages:

Because of poor physical reliability, it is easy to dry up, so twisted pair is used instead.

light guide

Optical fiber is a soft and thin transmission medium that uses the principle of total internal reflection to conduct light beams, which can be divided into single mode and multimode. Single-mode (mode, incident angle) optical fiber is mostly used in communication industry. Multimode optical fiber is mainly used in network wiring system.

Optical fiber is cylindrical and consists of three concentric parts: core, cladding and sheath. Each optical fiber includes two optical fibers, one for receiving and one for transmitting. Compared with coaxial cable, optical fiber can provide a wide frequency band, low power loss, long transmission distance (more than 2 kilometers), high transmission rate (up to thousands of Mbps) and strong anti-interference ability (not subject to electronic monitoring), so it is an ideal choice for building a secure network.