How NICs work

Specifically: Nic
Work on the MAC Sub-layer in the data link layer, rather than the physical layer. Nic is used to convert parallel lines. That is, the MAC Sub-layer specifies how frame is transmitted on a physical line. The role of LLC is to identify
Encapsulation is performed based on different protocol types. The MAC address is burned into the NIC. Therefore, the NIC works on the data link layer.
I. MAIN FEATURES OF NICs
Network interface card (NIC), also known as network adapter, is a device connecting a computer and a LAN. A network card is required to connect to a LAN, whether it is a common computer or a high-end server. If necessary, two or more NICs can be installed on one computer.

Figure 1 A 10/100 Mbps PCI Nic
When computers communicate with each other, data is transmitted in frames instead of streams. We can regard frame as a data packet, which not only contains data information, but also contains
It has data sending and receiving locations and data validation information. An ENI consists of two layers of the OSI model: the physical layer and the data link layer. The physical layer defines the electrical and optical signals required for data transmission and reception,
Line status, clock reference, data encoding, and circuit, and provides standard interfaces to data link layer devices. The data link layer provides addressing mechanism, data frame construction, data error check, transmission control, and
Provides standard data interfaces and other functions.
Two main functions of the network adapter are as follows: first, the computer data is encapsulated into frames and data is sent to the network through the network cable (electromagnetic waves for wireless networks; the second is to receive messages from other devices on the network.
And re-combine the frames into data and send them to the computer. The network adapter can receive all signals transmitted over the network, but normally only accept frames and broadcast frames sent to the computer, and discard the remaining frames.
Then, it is sent to the system CPU for further processing. When the computer sends data, the network adapter waits for the appropriate time to insert the group into the data stream. Whether the computer message received by the system is completely sent. If any problem occurs,
The recipient will be requested to resend the request.
2. Graphic Nic

Figure 2 graphic PCI Nic
Taking the most common PCI interface Nic as an example, a card consists of a PCB circuit board, a main chip, data mercury, and a golden finger (bus slot interface), bootrom, EEPROM, crystal oscillator, RJ45 interface, indicator light, fixed chip, and some diodes, resistance and capacitance. Next, let's take a look at the main components.
● Main chip

Figure 3 most common 8139d Chip
The main control chip of the network card is the core component of the network card. The performance of a network card is good or bad, and the strength of the function is many, mainly depends on the quality of this chip. Launched by common RealTek companies
For example, rtl8139c and rtl8139d are slightly different in encapsulation. The former is 128pin.
QFP/lqfp, while the latter is 100pin. Secondly, 8139c has more support for 93c56 than the latter, while 8139d is 93c46. However
The 8139d is more powerful. It provides support for PCI multi-function and PCI-bridge I/F, PCI
Multi-function allows the rtl8139d chip and other functional chips (such as hardware modulation and demodulation chips) to work collaboratively on the same PCB to form different types of functions.
Card, in which 8139 is used to identify the LAN signal or PCI bus signal; 8139d also enhances the power management function.
If the speed is determined by the speed of the main chip of the NIC, common 10/100 M Adaptive Nic chips include RealTek 8139 series/810x series,
Vt610 * series, Intel 82550pm/82559 series, Broadcom 44xx series, 3Com 3c920 series, and davicom
Dm9102, mxic mx98715, etc.
Common 10/100/8254 M Adaptive Nic chips include Intel's * series, Broadcom's bcm57 ** series, and Marvell's
88e8001/88e8053/88e806 * series, RealTek RTL8169S-32/64, RTL8110S-32/64 (LOM ),
Rtl8169sb, rtl8110sb (LOM), rtl8168 (PCI Express), rtl8111 (Lom, PCI
Express) series, via vt612 * series, and so on.

Figure 4 vt6120 Gigabit chip of

Figure 5 Marvell 88e8001 Gigabit Chip
It should be noted that the NIC chip also has the "soft and hardware", especially for Nic chips with motherboard board-mounted (LOM). What is the problem? As you know, Ethernet interfaces can be divided into the protocol layer and the physical layer.
The protocol layer is implemented by a single module called the MAC (media access layer) controller.
The physical layer consists of two parts: the physical layer and the transmitter.
The common Nic chips integrate Mac and PHY into one chip. However, currently, many nanqiao chips on the Main Board contain Ethernet MAC control functions, but do not provide physical layer interfaces. Therefore,
An external PHY chip is required to provide an Ethernet access channel. This type of PHY network chip is commonly known as the "soft Nic chip". The commonly used PHY function chips include rtl8201bl and vt6103.
.

Figure 6 rtl8201bl PHY Chip
"Soft network card" generally transfers the operation part of the network control chip to the processor or nanqiao chip to simplify the line design and reduce the cost, but it will occupy more system resources.
Bootrom
Bootrom socket, also known as the diskless boot ROM interface, is used to construct a diskless workstation through the Remote Boot service. Remoteboot
RPL) makes it possible to use software on the server's hard disk to boot a workstation on the network instead of the workstation's hard disk. An RPL (remote program
Load Remote initializationProgram The ROM chip can be loaded to enable diskless boot.
Rom chips are made for a specific type of network interface card and cannot be exchanged between them. A network interface card with RPL sends a broadcast (broadcasts) of the boot record request, and the server automatically
To respond to it and load the MS-DOS Startup file into the workstation's memory.

Figure 7 bootrom socket and 93c46 EEPROM chip in its center
In addition, there is usually a 93c46, 93lc46 or 93c56 EEPROM chip in the bootrom slot Center (93c56 is 128 * 16bit
EEPROM, while 93c46 is 64*16 bit EEPROM), which is equivalent to the BIOS of the NIC, which records the ID of the supplier of the NIC chip, the ID of the subsystem supplier, and the ID of the NIC
MAC address and nic configurations, such as the PHY address on the bus, bootrom capacity, and whether to enable the bootrom boot system. General information about the eeprom of the board Nic on the motherboard
Integrated into the motherboard BIOS.
● LED indicator

Figure 8
Generally, each network card has more than one led (light emitting)
LEDs are used to indicate the different working states of the network card, so that we can check whether the network card works normally. Typical led indicators include link/Act, full,
Power. Link/Act indicates the connection activity status, and full indicates whether full duplex (full
Duplex), while power is a power indicator (mainly used on a USB or PCMCIA Nic.
● Network wake-up Interface

Figure 9 reserved Wol interfaces on some NICs
Early NICs also had a dedicated 3-core Socket network wake-up (Wol) interface (pci2.1 standard Nic), wake on
LAN (Network wake-up) provides the ability to remotely wake up computers. It is an advanced management alliance established by IBM and Intel in October 1996.
Manageability
Alliance) is a result that allows administrators to remotely wake up computers during non-work hours and enable them to automatically complete some management services, such as software updates or virus scans. It is also
Part of the wired for management basic specification. The principle of network wake-up is that a management software package sends a magic-based
Packet standard wake-up frame. After receiving the wake-up frame, the network card can analyze it and determine whether the frame contains the MAC address of the network card. If the MAC address of this Nic is included
The system automatically enters the boot status.
Currently, mainstream independent NICs or motherboard onboard NICs comply with pci2.2 and later specifications. Therefore, you do not need this interface and need to enable the network wake-up function, you only need to enable the "Wake on PCI Card" function in the BIOS of the motherboard.
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 on one network card. One is the number of data transmitted.
It filters the differential signals sent by PHY with the difference mode coupled coil to enhance the signal, and coupling to the other end of the Connection Network at different levels through the electromagnetic field conversion; first, isolate the network connection.
Different levels of network equipment to prevent transmission of different voltages through the network cable from damaging the device. In addition, data mercury can also protect the equipment against lightning.
● Crystal Oscillator


Figure 11
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.
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, and sealing of the crystal oscillator are now
Important technical indicators are good and are no longer prone to faults, but you can still pay attention to the quality of the Crystal Oscillator when selecting.
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.
As close as possible to the main chip, the signal cabling length is greatly shortened, and the reliability is further increased. If the inferior crystal oscillator is used, this can reduce the cost of the NIC, but it is easy to cause problems due to the accuracy of the frequency.
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. Interface selection and network cabling
In a small shared LAN, the BNC port Nic is directly connected to other computers and servers through a coaxial cable; The RJ-45 port Nic is connected to the hub or switch through a twisted pair wire, and then through the set
A wire or switch connects to other computers and servers.
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. The RJ-45 is a 8-core wire while
The telephone line interface is 4-core, usually only 2-core (the ISDN telephone line is 4-core); but you can take a closer look, in fact, 10 m network card RJ-45 plug also used only 1, 2, 3, 6 four
And M or M Nic is the eight needles are all, this is also a way to distinguish between 10 M and m nic (see 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 layer of metal isolation film, which can reduce electromagnetic interference during data transmission, so its stability
High. 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) is mainly divided into 3 categories and 5 categories, UTP (unshielded twisted pair)
Cables) are mainly divided into 3 categories/4 categories/5 categories/over 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
The cables belong to unshielded twisted pair wires. Compared with common category 5 twisted pair wires, over 5 twisted pairs have lower attenuation and stronger anti-interference capabilities when transmitting signals. In a m network, the user's device is only subject to interference of ordinary Category 5 lines.
1/4, which is also the mainstream application.
Bus Interface
The NIC must be connected to the computer before it can be used normally, and various interfaces on the computer emerge one after another, which also leads to a variety of bus interfaces used by the NIC. In addition, when talking about bus interfaces, we need to note that
This kind of interface is commonly called "golden finger". Why is it called a golden finger? The reason is that the pin of this plug-in card uses titanium plating (or other metals), which ensures reliable contact during repeated plugging and increases the anti-dry performance of the card.
Interference capability reduces interference with other devices.
For your convenience, we will illustrate the network interfaces of common interface types.
① ISA interface Nic

Figure 13
ISA is a bus interface used by early NICs. The ISA Nic communicates with the CPU by program request I/O. In this mode, the network transmission rate is low, CPU resources are occupied, and many
10 m network card, at present in the market basically do not see ISA bus type network card, I found several ISA network card from the old parts heap, D-LINK products, actually use an eraser to clean the Gold finger computer
And later.
② PCI interface Nic

Figure 14
PCI (Peripheral Component
Interconnect) bus slots are still the most basic interfaces on the current motherboard. It is based on a 32-Bit Data Bus and can be expanded to 64-bit. Its operating frequency is 33 MHz/66 MHz. Data Transmission
The input rate is 132 MB per second (32*33 MHz/8 ). At present, PCI interface NICs are still the absolute mainstream in the household consumption market.
③ PCI-X interface Nic

Figure 15
PCI-X is an extended architecture of the PCI bus. Unlike the PCI bus, the PCI bus must frequently exchange data between the target device and the bus, while the PCI-X allows the target
The device looks exchanged only on a single PCI-X device, and if the PCI-X device does not have any data transfer, the bus automatically removes the PCI-X device to reduce the wait cycle between PCI devices.
Therefore, at the same frequency, the PCI-X will be able to provide 14-35% higher performance than PCI. Currently, the server Nic often uses this type of interface Nic.
PCI-E Interface Card

Figure 16
The PCI Express 1x interface has become a required interface for mainstream mainboards. Different and parallel transmission, PCI
The express interface adopts a point-to-point serial connection mode. The PCI Express interface varies with the bus interface's bit width requirements.
1x (Standard 250 Mb/s, bidirectional 500 Mb/s), 2x (Standard 500 Mb/s), 4X (1 Gb/s), 8x (2 Gb/s), 16x (4 Gb/s), 32x
(8 Gb/s ). Most NICs using PCI-E interfaces are Gigabit NICs.
⑤ USB interface Nic

Figure 17
On the current computer, it is difficult to find the USB Interface
USB Bus is classified into USB and USB. The theoretical value of the USB standard transmission rate is 12 Mbps, while the USB standard transmission rate
The transmission rate can be up to 480 Mbps. Currently, most USB wired NICs are USB standard.
⑥ PCMCIA Interface Nic

Figure 18
The PCMCIA Interface is a dedicated interface for laptops. The PCMCIA bus is divided into two types: one is a 16-bit PCMCIA Interface and the other is a 32-bit cartana interface. The maximum throughput of the carw.nic is close to 90 Mbps, it is currently the mainstream commercial laptop network card.
7. Mini-PCI interface Nic

Figure 19
The minipci interface is an interface standard extended based on the desktop PCI interface for laptops. Its speed is equivalent to the PCI standard, and many such products are wireless NICs.
In addition, there are network cards for interfaces such as Amr on the market, which will not be described in this article due to the limited length and popularity.