Several terms in data transmission technology
Data information and data communication, channel and bandwidth, channel transmission rate and communication method, baseband transmission, broadband transmission, transmission frequency and transmission rate.
Twisted pair
Definition: Twist two mutually insulated copper wires clockwise or counterclockwise in a certain direction, the shape is like a twist, hence the name twisted pair.
Structure: The twisted pair is divided into 3 layers. The inner copper wire follows the AWG standard (American wire gauge size standard specifies the diameter of the conductor). The outer insulation layer is generally made of PVC (oxide of polyethylene compound) In addition, there is a plastic sheath on the outermost layer of the cable to protect the cable.
Classification of twisted pair
1. According to different classification of insulation
According to whether there is a metal shielding layer outside the insulation layer, the twisted pair can be divided into two categories: UTP (unshielded twisted pair) and STP (shielded twisted pair).
2. According to the different transmission rate classification
EIA / TIA defines 5 different quality models for twisted pair cables. Computer network integrated wiring uses categories 3, 4, and 5.
3. Classification by use
Article 800 of the National Electrical Code defines five grades of cables that can be used for LAN wiring and remote communications:
Ventilation channel use; shaft; general use; household use; under-carpet cable.
Performance parameters of twisted pair
Attenuation, capacitance, impedance and delay distortion, characteristic impedance, near-end crosstalk, background noise and signal to noise ratio, cable characteristics.
The purchase of category 5 twisted pair
Generally, when purchasing category 5 twisted pair, users should consider the following aspects.
1. Packed well 2. The logo is clear 3. Color clear 4. Stranding density 5. Good toughness 6. Flame retardant
Category 5 wiring system
Four advantages:
â— Provides a solid network foundation to facilitate the transfer and update of network technology.
â— Can meet the requirements of most applications, and meet the requirements of low deviation and low crosstalk.
â— Considered as a solution for future network applications.
â— Sufficient performance margin, easy installation and testing.
Category 6 twisted pair wiring system
Pay attention to the following elements when purchasing a real 6 type wiring system:
â‘´ The true Category 6 system should meet the performance requirements of Category 6 from connectors, cables to links and channels, including components such as modules, patch panels, jumpers and cables.
(2) The worst case model defined in the TIA / ISO standard must be used in the system test report submission, that is, a 90m link at 3 connection points or a 100m channel at 4 connection points.
(3) The manufacturer shall provide comprehensive test data of 6 types of products and systems in the 250MHz wideband, and can stand up to the comparison with the parameters and indicators required by the 6 types of ISO / TIA standards.
â‘· The manufacturer should also provide test certificates from some domestic and foreign third-party laboratories or official institutions.
⑸ The product is mature, has been commercialized, and has 6 types of system engineering applications.
⑹ The manufacturer can provide a full range of 6 types of products for users to choose from a variety of options, applicable to any user installation method and configuration requirements.
⑺ Users can also request the use of an on-site tester to perform on-site testing of links or channels submitted by manufacturers in accordance with the latest international standards to see if they can meet the 6 categories of indicators.
â‘» Manufacturers should provide integrators with training for the installation of Category 6 cabling systems, and relevant integrators can only participate in the installation and construction of Category 6 cabling system projects after this training (users can request the integrators to show this type of training Certificate).
Table 2.2 Common twisted pair wiring system
Performance mark | Industry Standards / Regulations | Performance parameter |
Category 5 wiring system | Description of initial industrial performance of Category 5 cabling system: | Bandwidth performance: 1 ~ 100MHz; |
Category 5 cabling system | Appendix to the draft TIA / EIA-568-A: "4 to 100 Ω additional category 5 transmission specifications" | Bandwidth performance: 1 ~ 100MHz |
Category 6 wiring system | 6 types of data cable product standards in China's communications industry (YD / T1019) | Broadband performance: 1 ~ 300MHz |
Category 7 wiring system | It was originally defined as Class E by EDIN 4431-5 (new-generation copper cable performance type established in Germany) | Broadband performance: 1 ~ 3600MHz |
Structure of coaxial cable
The coaxial cable is divided into four layers, which are composed of a central copper core, an insulating layer, a shielding layer and an outer sheath.
Classification of coaxial cable
There are currently two widely used coaxial cables.
⑴ 50Ω cable for digital transmission. Because it is mostly used for baseband transmission, it is also called baseband coaxial cable.
⑵ 75Ω cable, used for analog transmission, also called broadband coaxial cable.
Coaxial cable network wiring system
In the computer network wiring system, there are three different construction methods for the thick and thin cables of the coaxial cable, namely the thin cable structure, the thick cable structure and the thick / thin cable mixed structure.
optical fiber
Optical fiber is optical fiber, which is a thin and flexible medium that transmits light beam. Optical fiber cable is composed of a bundle of optical fibers, called optical cable.
Optical fiber is similar to coaxial cable, except that it does not have a mesh shield. Optical fiber is usually cylindrical and consists of three parts: fiber core, cladding (protective layer) and jacket.
Advantages of optical fiber as a transmission medium
â‘´ The frequency band is wider.
⑵ Good electromagnetic insulation performance.
⑶ Attenuation is small, it can be said that the signal is a constant in a long distance and range.
â‘· Long transmission distance can reduce the number of repeaters in the whole channel and reduce the cost.
Classification of optical fiber
There are three connection methods for optical fiber, which are mainly permanent connection, mechanical connection and active connection.
The optical fiber communication system is based on the light wave as the carrier and the optical fiber as the transmission medium. The light source, optical fiber, optical transmitter and optical receiver play a leading role.
Types of optical cables
According to the number of optical fibers in the optical cable: ⑴ single-core optical cable. ⑵ Double-core optical cable. ⑶ Multi-core optical cable.
2. According to the application classification of optical cable in wiring engineering: ⑴ Fiber optic jumper. ⑵ Indoor optical cable. ⑶ Outdoor optical cable.
Choice of wireless media and transmission media
The wireless network adopts the same working methods as the wired network. They establish a network through wireless transmission media according to PCs, servers, workstations, network operating systems, wireless adapters and access points.
1. Selection of media considerations
â‘´ Data transmission speed.
⑵ Use in a network topology.
⑶ Distance requirements.
â‘· Cost of cables and cable assemblies.
⑸ Other network equipment required.
⑹ Can prevent outside interference.
⑺ Flexibility and convenience of installation.
â‘» Upgrade option.
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