Local area network technology (network technology terminology)

Twisted-pair cable

Twisted-pair cable (also known as twisted-pair cable) is the most common transmission medium. It is formed by twisting two insulated metal wires together. Several pairs of twisted pairs (2 pairs or 4 pairs) are bundled into a cable and wrapped in a tough sheath. Each pair of twisted pairs is used as a communication line to reduce the electromagnetic interference between the pairs of wires. Interference.

Twisted pair is divided into shielded twisted pair (STP) and unshielded twisted pair (UTP). There is a metal shielding protective film around the shielded twisted pair, which can reduce the electromagnetic interference generated during signal transmission, but it is relatively expensive.

Unshielded twisted-pair cable has no metal protective film, which is more sensitive to electromagnetic interference and has poor electrical characteristics. Its biggest advantage is that it is cheap, so it is widely used in telephone systems that transmit analog signals. However, the biggest disadvantage of this type of twisted pair is that the insulation performance is not good, the distributed capacitance parameter is large, and the signal attenuation is relatively severe. Therefore, in general, the transmission rate is not high, and the transmission distance is also very limited. On September 28, 1990, the IEEE recognized the 10BASET standard and promulgated it as an official standard. Since then, 10BASET has gradually been widely used in the LAN wiring of office buildings. Thanks to this standard, Ethernet, Token Ring and ARCnet networks can all directly use the already deployed telephone lines.

Coaxial cable

Coaxial cable (CoaxiaI Cable) is the most commonly used transmission medium in the network. It has four layers. The innermost layer is the central conductor. Insulation layer, conductor net and protective cover, divided according to bandwidth and purpose, coaxial cable can be divided into baseband (Baseband) and broadband (Broadband). The baseband coaxial cable transmits digital signals. In the transmission process, the signal will occupy the entire channel. The digital signal includes the highest frequency that the baseband coaxial cable can transmit from 0 to the baseband coaxial cable. Therefore, at the same time, the baseband coaxial cable Only one signal can be transmitted. Broadband coaxial cables transmit signals of different frequencies, and these signals need to be modulated to different sinusoidal carrier frequencies through modulation techniques. During transmission, frequency division multiplexing technology is used to divide into multiple channels for transmission, so that signals such as data, sound, and images can be transmitted in different channels at the same time. Broadband coaxial cable has better performance than baseband coaxial cable, but requires additional signal processing equipment and is difficult to install. It is suitable for long-distance telephone networks, cable television systems and broadband computer networks.

Optical fiber cable

Optical fiber cable is abbreviated as optical fiber cable or optical cable. As the requirements for data transmission speed continue to increase, the use of optical fiber cables is becoming more and more common. For computer networks, optical cables have unparalleled advantages.

The fiber optic cable consists of a fiber core. The cladding layer and the sheath layer are composed. The core is made of glass or plastic, the cladding is made of glass, and the sheath is made of plastic.

Optical fiber communication has many advantages. Firstly, the transmission rate is high, and the actual achievable transmission rate is tens to thousands of Mbit/s; secondly, it has strong anti-electromagnetic interference ability, light weight, small size, and toughness. Good, high security and confidentiality. It is mostly used as the backbone of a computer network. The biggest problem with optical fiber is that it is expensive compared to other transmission media. In addition, fiber connection and fiber branching are both difficult, and the signal energy loss is great when branching.

Fiber Distributed Data Interface (FDDI) is a network standard formulated by the American ANSIX3T9.5 committee in 1982. It is the only high-speed local area network with a unified standard with a data transmission rate of 100Mbit /s. FDDI is already a mature network technology, and many manufacturers in the world provide FDDI network products.

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