Network basics required course series graphic network card hardware-accessories 2

Network basics required course series graphic network card hardware-accessories 2

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● Data Mercury

Figure 10 Data Mercury

Data mercury is a device on the consumption-level PCI Nic. Data mercury is also called a Network Transformer or a network isolation transformer. It plays two main roles in one network card. One is to transmit data. It filters the difference signal sent by the PHY using the difference mode coupled coil to enhance the signal, in addition, the electromagnetic field is switched to the other end of the connected network cable at different levels. The first is to isolate different levels of different network devices connected by the network cable, so as to prevent different voltages from being transmitted through the network cable to damage the device. In addition, data mercury can also protect the equipment against lightning.

● Crystal Oscillator

Crystal oscillator is short for Z oscillator, and its English name is Crystal. It is the most important component in the clock circuit, and its function is to provide the reference frequency to each part of the video card, Nic, motherboard and other accessories, it is like a ruler. unstable operating frequency may cause unstable operation frequency of related equipment, which is naturally prone to problems. As the manufacturing process continues to improve, the frequency deviation, temperature stability, aging rate, sealing and other important technical indicators of the crystal oscillator are very good, and it is no longer prone to faults, however, you can still pay attention to the quality of the Crystal Oscillator when selecting it.

For example, the clock circuit of a network card uses a high-precision sko25 MHz crystal oscillator, which ensures accurate synchronization of data transmission and greatly reduces the possibility of packet loss, in addition, the design of the line is as close as possible to the main chip, which greatly shortens the signal line length and further increases the reliability. However, if a poor crystal oscillator is used, this can reduce the cost of the NIC. However, due to the accuracy of the frequency, it is easy to cause data packet loss during transmission.

● Network cable Interface

In the desktop consumption level network interface interfaces are common interfaces BNC interface and RJ-45 interface (similar to the phone interface), there are two interfaces are dual interface. The choice of the interface is related to the network wiring form, in the small shared LAN, BNC port Nic directly connected to other computers and servers through coaxial cable; RJ-45 port Nic connected to the hub through twisted pair wire (hub) or vswitch, and then connect to other computers and servers through a hub or vswitch.

Currently, interfaces such as BNC interfaces are rarely seen. This is mainly because the number of networks using a fine coaxial cable as the transmission medium is relatively small and there are many problems related to the networking mode. RJ-45 is 8-core line, while the telephone line interface is 4-core, usually only 2-core line (ISDN telephone line connected to 4-core line); but you can take a closer look, in fact, 10 m network card RJ-45 plug also used only 1, 2, 3, 6 Four needles, and m or M network card is eight needles are all, this is also a way to distinguish between 10 M and M NICs (see figure 8 ).

● Transmission media type

Speaking of NICs, let's talk about the twisted pair wires connected to NICs.

Figure 12

Twisted Pair wires are a data transmission line consisting of many pairs of cables in an Insulating Coat. They are characterized by low prices. Currently, most network adapters use twisted pair wires as transmission cables. Twisted pair wire is generally used for star network cabling, the two ends of the installation of a RJ-45 (crystal head), the connection network card and the hub, the maximum length of the network cable is about 100.

Twisted Pair wires are STP (shielded twisted pair wires) and UTP (unshielded twisted pair wires. STP twisted pair wires have a metal isolation film, which can reduce electromagnetic interference during data transmission, so it has high stability. UTP does not have this layer of metal film, so it has poor stability, but its advantage is that it is cheaper. Among them, STP (shielded twisted pair wires) is mainly divided into 3 categories and 5 categories, UTP (unshielded twisted pair wires) it is mainly divided into 3 categories/4 categories/5 categories/super 5 categories/6 categories. Generally, the network mainly uses 5 categories of twisted pair wires and 5 categories of twisted pair wires with thick outer protection rubber, mark "cat5" on the rubber cover. Category 5 twisted pair wires are unshielded twisted pair wires. Compared with common category 5 twisted pair wires, Category 5 twisted pair wires have lower attenuation and stronger anti-interference capabilities during signal transmission. In a m network, the interference level of user devices is only 1/4 of that of common category 5 lines, which is also the mainstream application.