1. The main features of the network card
1. Basic knowledge
Network Interface Card (NIC), also known as network adapter, is a device that connects a computer to a local area network. Whether it is an ordinary computer or a high-end server, as long as it is connected to a local area network, you need to install a network card. If necessary, a computer can also install two or more network cards at the same time.
When computers communicate with each other, data is transmitted not in streams but in frames. We can regard the frame as a kind of data packet. The data packet not only contains data information, but also contains the data sending and receiving information and data verification information.
A network card includes two layers of the OSI model-the physical layer and the data link layer.
a-Physical layer
Defines the electrical and optical signals, line status, clock reference, data encoding and circuits required for data transmission and reception, and provides standard interfaces for data link layer equipment.
b-Data link layer
Provides functions such as addressing mechanism, data frame construction, data error checking, transmission control, and standard data interface to the network layer.
2. The function of the
network card There are two main functions of the network card:
one is to encapsulate the data of the computer into a frame, and to send the data to the network through a network cable (electromagnetic waves for wireless networks); the
other is to receive transmissions from other devices on the network. The incoming frames are recombined into data and sent to the computer where they are.
The network card can receive all the signals transmitted on the network, but under normal circumstances it only accepts frames and broadcast frames sent to the computer, and discards the remaining frames. Then, it is sent to the system CPU for further processing. When the computer sends data, the network card waits for the appropriate time to insert the packet into the data stream. The receiving system informs the computer whether the message has arrived completely, and if there is a problem, it will ask the other party to resend it.
2. Graphical network card
Take the most common PCI interface network card as an example. A network card is mainly composed of PCB circuit board, main chip, data mercury, gold finger (bus slot interface), BOOTROM, EEPROM, crystal oscillator, RJ45 interface, indicator light, Fixed pieces, etc., as well as some diodes, resistors and capacitors. Let's take a look at the main components separately.
1. The main chip
The main control chip of the network card is the core component of the network card. The performance and function of a network card mainly depend on the quality of the chip. Take the common RTL8139C and RTL8139D introduced by Realtek as an example. First of all, the two are slightly different in packaging. The former is 128pin QFP/LQFP and the latter is 100pin. Secondly, on the matched EEPROM, 8139C has more pairs of 93c56 than the latter. Support, while 8139D is 93C46. But in terms of function, 8139D is stronger, it provides support for PCI Multi-function and PCI-bridge I/F, PCI Multi-function allows RTL8139D chip and other functional chips (such as hardware modem chip) Designed to work together on the same PCB board to make different types of multi-function cards, the role of 8139 is to distinguish between LAN signals and PCI bus signals; 8139D also enhances the power management function.
If divided by the speed of the main chip of the network card, the common 10/100M adaptive network card chips are Realtek 8139 series/810X series, VIA VT610 series, Intel 82550PM/82559 series, Broadcom 44xx series, 3COM 3C920 series, Davicom DM9102, Mxic MX98715 and many more.
Common 10/100/1000M adaptive network card chips include Intel’s 8254 series, Broadcom’s BCM57** series, Marvell’s 88E8001/88E8053/88E806 series, Realtek’s RTL8169S-32/64, RTL8110S-32/64 (LOM), RTL8169SB, RTL8110SB (LOM), RTL8168 (PCI Express), RTL8111 (LOM, PCI Express) series, VIA's VT612 series and so on.
Marvell's 88E8001 gigabit chip. It
should be noted that the network card chip also has "soft and hard" points, especially for the motherboard onboard (LOM) network card chip. What is going on?
a-Protocol layer It is implemented by a single module called MAC (Media Access Layer) controller.
b-The physical layer consists of two parts, namely the PHY (Physical Layer) and the transmitter.
Common network card chips integrate MAC and PHY into one chip, but the South Bridge chips of many motherboards currently include Ethernet MAC control functions, but they do not provide physical layer interfaces. Therefore, an external PHY chip is required to provide Ethernet. Access channel. This type of PHY network chip is commonly known as "soft network card chip". Common PHY function chips include RTL8201BL, VT6103, and so on.
The "soft network card" generally transfers the computing part of the network control chip to the processor or the south bridge chip to simplify the circuit design and reduce the cost, but it will take up more system resources.
2. BOOTROM The
BOOTROM socket is also commonly referred to as the diskless boot ROM interface, which is used to construct a diskless workstation through the remote boot service. Remote boot service (Remoteboot, usually also called RPL) makes it possible to boot a workstation on a network by using the software on the server hard disk instead of the workstation hard disk. A RPL (Remote Program Load) ROM chip must be installed on the network card to realize diskless boot. Each RPL ROM chip is made for a specific type of network interface card, and they cannot be interchanged. . The network interface card with RPL sends out broadcasts of boot record requests, and the server automatically establishes a connection to respond to it, and loads the MS-DOS startup file into the memory of the workstation.
In addition, there is generally a 93C46, 93LC46 or 93c56 EEPROM chip in the center of the BOOTROM slot (93C56 is a 128 16-bit EEPROM, and 93C46 is a 64 16-bit EEPROM), which is equivalent to the BIOS of the network card, which records the supply of the network card chip Vendor ID, subsystem supplier ID, MAC address of the network card, some configuration of the network card, such as the address of the PHY on the bus, the capacity of the BOOTROM, whether to enable the BOOTROM to boot the system, etc. The EEPROM information of the onboard network card of the motherboard is generally integrated in the motherboard BIOS.
3. LED indicator light
Generally speaking, each network card has more than one LED (Light Emitting Diode) indicator, which is used to indicate the different working status of the network card, so that we can check whether the network card is working properly. Typical LED indicators are Link/Act, Full, Power, etc. Link/Act means connection activity status, Full means full duplex (Full Duplex), and Power means power indicator (mainly used on USB or PCMCIA network card) and so on.
4. Wake-on-LAN interface
There is a special 3-pin socket Wake-on-LAN (WOL) interface (PCI2.1 standard network card) on the early network card. Wake On LAN (Wake-on-LAN) provides the function of remotely waking up the computer. A result of the Advanced Manageability Alliance established by Intel in October 1996, it allows administrators to remotely wake up computers during non-working hours and enable them to automatically complete some management services, such as software updates or Virus scanning. It is also part of the basic specification of Wired for Management. The working principle of Wake-on-LAN is that a management software package sends out a wake-up frame based on the Magic Packet standard. After receiving the wake-up frame, the network card that supports Wake-on-LAN analyzes it and determines whether the frame contains the MAC address of the network card. If the MAC address of this network card is included, the computer system will automatically enter the boot state.
At present, mainstream independent network cards or motherboard onboard network cards are in compliance with PCI2.2 and above specifications, so this interface is no longer needed. To enable the wake-on-LAN function, you only need to enable the "Wake on PCI Card" function in the motherboard BIOS.
5. Data Mercury
Data Mercury is a device available on consumer-level PCI network cards. Data Mercury is also called a network transformer or a network isolation transformer. There are two main functions it plays on a network card. One is to transmit data. It uses differential mode coupling coils to filter the differential signal sent by the PHY to enhance the signal, and couples to different levels through the conversion of electromagnetic fields. Connect the other end of the network cable; one is to isolate the different levels of different network devices connected by the network cable to prevent the transmission of different voltages through the network cable from damaging the equipment. In addition, data mercury can also play a role in lightning protection for equipment.
6. Crystal
Oscillator Crystal oscillator is the abbreviation of Quartz Oscillator, and its English name is Crystal. It is the most important component in the clock circuit. Its function is to provide reference frequencies to various parts of the graphics card, network card, motherboard and other accessories. , The unstable working frequency will cause the working frequency of the related equipment to be unstable, which is naturally prone to problems. Due to the continuous improvement of the manufacturing process, the important technical indicators such as frequency deviation, temperature stability, aging rate, and tightness of the crystal oscillator are now very good, and it is not prone to failure, but 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 SKO25MHz crystal oscillator, which can ensure the precise synchronization of data transmission and greatly reduce the possibility of packet loss. In addition, the circuit design is as close to the main chip as possible to make the signal routing The length is greatly shortened, and the reliability is further increased. And if you use a low-quality crystal oscillator, although this can reduce the cost of the network card a little, but because of the accuracy of the frequency, it is very easy to cause data packet loss during the transmission process.
7. Network cable interface
Common network card interfaces in desktop consumer-level network cards include BNC interface and RJ-45 interface (similar to a telephone interface), and there are also dual-port network cards that have both interfaces. The choice of interface is related to the form of network wiring. In a small shared LAN, the BNC port network card is directly connected to other computers and servers through a coaxial cable; the RJ-45 port network card is connected to a hub (HUB) or switch through a twisted pair, and then through Hubs or switches connect other computers and servers.
At present, the network card with this interface type of BNC interface is rare, mainly because there are fewer networks using thin coaxial cables as the transmission medium and there are more problems in the networking mode. RJ-45 is an 8-core line, while the telephone line interface is 4-core, usually only 2-core line (ISDN phone line is connected to 4-core line); but you can take a closer look, in fact, the RJ-45 socket of the 10M network card Only four pins 1, 2, 3, and 6 are used. For 100M or 1000M network cards, all eight pins are used. This is also a way to distinguish between 10M and 100M network cards.
8. Transmission media type
Twisted-pair cable is a data transmission line composed of many pairs of wires in an insulating jacket. Its characteristic is that it is cheap. Most of the current network cards use twisted-pair wires as transmission cables. Twisted pair cables are generally used for the wiring connection of star networks. RJ-45 heads (crystal heads) are installed at both ends to connect the network card and the hub. The maximum length of the network cable is about 100 meters.
There are two types of twisted pair: STP (shielded twisted pair) and UTP (unshielded twisted pair). There is a metal isolation film in the twisted pair of STP, which can reduce electromagnetic interference during data transmission, so its stability is high. But there is no such metal film in UTP, so its stability is poor, but its advantage is that it is cheap. Among them, STP (shielded twisted pair) is mainly divided into two types: 3 and 5, and UTP (unshielded twisted pair) is mainly divided into 3 types/4 types/5 types/super 5 types/6 types, general The network mainly uses Category 5 twisted-pair cables. The outer protective rubber of Category 5 twisted-pair cables is thick, and the words "CAT5" are marked on the rubber. Category 5 twisted pair is an unshielded twisted pair. Compared with ordinary Category 5 twisted pair, Category 5 twisted pair has a smaller attenuation and stronger anti-interference ability when transmitting signals. In a 100M network, the user equipment The degree of interference is only 1/4 of that of ordinary Category 5 cables, which is also the mainstream of current applications.
9. Bus interface The
network card can only be used normally if it is connected to the computer. Various interfaces on the computer emerge in an endless stream, which also causes the variety of bus interface types used by the network card. In addition, when it comes to bus interfaces, it needs to be explained that people generally call this type of interface "golden finger". Why is it called golden finger? This is because the pins of this type of card are made of titanium-plated gold (or other metal). Ensure the safe contact during repeated plugging and unplugging, which not only increases its own anti-interference ability but also reduces the interference to other equipment.
In order to facilitate your understanding, we will illustrate the common network cards with various interface types below.
①ISA interface network card
ISA is a kind of bus interface used by early network cards. ISA network card uses program request I/O to communicate with CPU. This method has low network transmission rate and large CPU resource usage. Most of them are 10M network cards. There are basically no ISA bus type network cards on the market. The author found several ISA network cards from the old parts list. D-LINK products can still be used after cleaning the golden fingers with an eraser.
②PCI interface network card
PCI (peripheral component interconnect) bus slot is still the most basic interface on the motherboard. It is based on a 32-bit data bus, which can be expanded to 64 bits, and its operating frequency is 33MHz/66MHz. The data transfer rate is 132MB per second (32*33MHz/8). At present, the PCI interface network card is still the absolute mainstream in the home consumer market.
③PCI-X interface network card
PCI-X is an expansion architecture of the PCI bus. It is different from the PCI bus in that the PCI bus must frequently exchange data between the target device and the bus, while PCI-X allows the target device to only be A single PCI-X device seems to have been exchanged. At the same time, if the PCI-X device does not have any data transfer, the bus will automatically remove the PCI-X device to reduce the waiting period between PCI devices. Therefore, under the same frequency, PCI-X will be able to provide 14-35% higher performance than PCI. At present, server network cards often use network cards with such interfaces.
④PCI-E interface network card
PCI Express 1X interface has become a necessary interface for mainstream motherboards. Different from parallel transmission, the PCI Express interface adopts a point-to-point serial connection. The PCI Express interface varies according to the different requirements of the bus interface for bit width. It is divided into PCI Express 1X (standard 250MB/s, two-way 500MB/s), 2X (standard 500MB/s), 4X (1GB/s), 8X (2GB/s), 16X (4GB/s), 32X (8GB/s). Most network cards with PCI-E interface are gigabit network cards.
⑤USB interface network card
It is difficult to find a USB interface (Universal Serial Bus) on the current computer. The USB bus is divided into USB2.0 and USB1.1 standards. The theoretical value of the transmission rate of the USB1.1 standard is 12Mbps, and the transmission rate of the USB2.0 standard can be as high as 480Mbps. The current USB wired network cards are mostly USB2.0 standard.
⑥PCMCIA interface network card
PCMCIA interface is a special interface for notebook computers. The PCMCIA bus is divided into two types, one is 16-bit PCMCIA and the other is 32-bit CardBus. The maximum throughput of CardBus network card is close to 90Mbps, which is currently a commercially available notebook. The mainstream of the network card.
⑦Mini-PCI interface network card
MiniPCI interface is an interface standard suitable for notebook computers based on the desktop PCI interface. Its speed is equivalent to the PCI standard. Many of these products are wireless network cards.
In addition, there are network cards with AMR and other interfaces on the market. Due to space and popularity, this article will not introduce them one by one.