Network card-1
The communication medium is used for computer network and the connection between the signal transmission, and realize the media.
The communication medium can be divided into two categories: cable medium and wireless medium. Cable transmission medium is using of cable or optical fiber cable conductor transmission interface as the transmission quality, such as twisted pair, coaxial cable and optical fiber cable; Wireless transmission medium is using of electric wave or light transmission of media as a conductor, such as radio waves, microwave, and infrared and satellite communication, etc.
Transmission medium to the performance of the network has a bigger impact. Measure the transmission medium of the main technical performance indicators are: the transmission distance, transmission bandwidth, anti-interference ability, connecting method and price.
(a) twisted pair
Twisted pair is currently the most widely used medium Ethernet. The popularity of the twisted pair with the success of the hub and switches and realize. Telephone cable is twisted pair.
The basic principle of twisted pair is stick with insulating copper wires for the use of for a (stranding machine) according to certain specification intertwined with each other.
In a twisted pair speaking, when the outside electromagnetic signal in PA3399U-2BAS battery the two wires produce dry interference signals equal and opposite phase, jamming signal will offset each other.
Used in network of twisted pair, there are eight line, every two root twisted together.
Twisted pair has two kinds: the shielded twisted-pair cable and shielded twisted-pair cable. Shielded twisted-pair cables external package has a metal nets, used to shield the external interference. You put the phone with metal teacup cover up immediately, you can’t hear anything, it is this principle.
But the most popular are shielded twisted-pair cable, because the shielding twisted pair of the effect is not obvious, and the cost to high. Shielded twisted-pair cable at present general used only for industrial control field. About the standard of Ethernet have different versions, each version required cable specification and the transmission distance is different. Basically, use twisted-pair cable connection, dozens of meters to more than one hundred meters between the is reasonable.
(2) coaxial cable
Coaxial cables are the most widely cable TV network, but the computer network, the coaxial cable and network with the specification is not the same.
The interior of the coaxial cable has a copper-core as conductor, filled with middle of the insulation material layer is plastic, plastic layer is shielded network, and external as another wire, the cable from PVC or teflon material to cover the sheath.
At present more commonly used have two kinds of coaxial cable: a 50 cable, used for several words transmission, also known as “baseband coaxial cable”; Another for 75 cable, used to model the transmission, to is also referred to as a “broadband coaxial cable”.
Coaxial cable has very good anti-interference characteristics, the signal attenuation is less than twisted pair, can further distance transmission. In the etheric network have used two kind of coaxial cable, one kind is thick cable, and the other is the fine cable, thick cable is more good transmission characteristic.
Coaxial cable in the local area network applications with twisted pair and the popularity of the optical fiber has been eliminated.
(3) fiber
Optical fiber is the most promising transmission media outlets that almost all of the new network trunk are using optical fiber technology. Optical fiber to the desktop refers to use fiber instead of twisted pair computer connected to the Internet.
Optical fiber is in the form of a light pulse signal transmission, and the material is glass or plastic fiber d. Cable including fiber core, the packet level and protection to three.
Optical fiber can be divided into single-mode optical fiber and multimode fiber. Single-mode optical fiber provide only a light path, processing complex, but has the greater communication capacity and further to the transmission distance. Multimode fiber DuoTiao use light path through the same signal transmission, the refraction of light to control the transmission speed.
And cable, optical cable compared with many of the advantages:
Transmission communication capacity, can achieve very high transmission rate;
The light signal transmission loss of far smaller than the electrical signals, can further distance transmission, suitable for long distance transmission;
The light signal almost from external interference of electromagnetic signal, and has a strong dv3000 battery resistance to ray electricity and anti-electromagnetism interference ability;
The light signal transmission in the fiber, almost nonexistent signal of the leak, good secrecy, information is not easy to be eavesdropping or intercept;
Fiber optic light weight, wiring easily;
The light signal transmission process is very low, ber transmission high reliability.
And cable, fiber optic cable connection at different ends of the need for electrical signals and light signal converter photoelectric conversion.
(4) wireless medium
Wireless media communication medium is a very important categories. Human beings use wireless as the communication medium of very long history, from the invention of the telegraph it started.
Wireless medium the biggest advantage is not to need to use a cable connection on both ends of the equipment, mobile flexible.
(5) infrared
Infrared almost is the earliest of the wireless medium into the computer. Infrared interface is a new generation of mobile phones with standard, it support cell phone and computer and other digital equipment according to the number communication. Infrared communication has low cost, easy to use and convenient connection, the characteristics of the structure tight gather together, so in small mobile equipment has been widely used. Through the red outside, all kinds of mobile equipment can interface free exchange data. Infrared wavelength is in 750 nm-1 the electromagnetic wave, it between nm the frequency of microwave and higher than the lower than visible light, and is a kind of the eyes of the one you can’t see the light. Due to the infrared wavelength is short, the obstacles to the diffraction ability is poor thing, so the more suitable for application in short-range wireless communication occasions need, point-to-point linear data transmission. Infrared data association will infrared data communication with the team, the range of wavelengths of light within 850 nm-within 900 nm. Equipped with infrared interface mobile phones wireless Internet access is very simple, need not connecting cables and PC CARD, as long as all Dell D630 battery set up infrared connection agreement can directly over the Internet. Infrared interface is orders in the world before range widely used a wireless connection technology, by many hardware and software platforms support; Through the data electrical impulses and infrared pulse the interaction between the turn in the wireless data transceiver to realize. Infrared interface features:
Used to replace point-to-point cable connection; New communication standard compatible early communication standard; Small Angle (30 degrees within the cone Angle), short, peer-to-peer linear data privacy is strong; the lose,
The transmission rate is higher, at present 4 M of the rate of FIR technology has been widely used, the rate of 16 M VFIR technology has been release. The main advantage of the infrared technology: make handset and computer can wireless transmission between data; Can also have the infrared interface in the exchange of information between devices; Infrared interface can save download or other information exchange the expenses; Due to the need for docking to transmit information, safety is stronger. Infrared technology faults:
