Network Interface Card: Types, Functions and Buying Guide

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What is a network interface card?

The network interface card is equipped with a processor and memory (including RAM and ROM). The communication between the network interface card and the local area network is carried out in a serial transmission mode through a cable or a twisted pair. The communication between the network interface card and the computer is carried out in parallel transmission through the I/O bus on the computer motherboard. Therefore, an important function of the network interface card is to perform serial/parallel conversion. Because the data rate on the network and the data rate on the computer bus are not the same, the network interface card must be equipped with a memory chip that caches the data.

The network interface card used to be plugged into the computer bus as an expansion card. Most new computers feature integrated network interfaces on the motherboard due to their low cost and the broad availability of Ethernet standards. These motherboards either integrate the Ethernet function in the motherboard chip or use a cheap network interface card connected to the motherboard via PCI (or the newer PCI-Express bus). Unless you need multiple interfaces or use other types of networks, you no longer need a separate network interface card. Even newer motherboards may contain built-in dual network (Ethernet) interfaces.

network interface card

A network interface card is a piece of computer hardware designed to allow computers to communicate on a computer network. Because it has a MAC address, it belongs between the first and second layers of the OSI model. It allows users to connect to each other via cable or wirelessly. Each network interface card has a unique 48-bit serial number called the MAC address, which is written in a ROM on the card. Every computer on the network must have a unique MAC address. No two network interface cards produced have the same address. This is because the Institute of Electrical and Electronics Engineers (IEEE) is in charge of assigning unique MAC addresses to network interface controller (network interface card) providers.

What are the main functions of a network interface card?

1. Encapsulation and decapsulation of data

When it sending data, it adds the header and tail to the data passed by the upper layer to become an Ethernet frame. And it strips the header and tail of the Ethernet frame when receiving data, and then sends it to the upper layer.

2. Link management

Link management is mainly achieved by CSMA/CD protocol (Carrier Sense Multiple Access with Collision Detection, Carrier Sense Multiple Access with Collision Detection).

3. Data encoding and decoding

That is Manchester encoding and decoding. Manchester code is a popular binary code line encoding method used by the physical layer to encode the clock and data of a synchronized bitstream. In communication technology, it’s a code used to indicate the combination of data and timing signals in the bitstream to be sent. Ethernet communication, train bus control, industrial bus, and other areas all use it.

Detailed function explained

When installing the network interface card, the device driver for the management network interface card must be installed in the computer's operating system. This driver will tell the network interface card in the future where the data block transferred from the LAN should be stored in the memory. The network interface card must also be able to implement the Ethernet protocol.

The network interface card is not an independent autonomous unit, because the network interface card itself does not have a power supply but must use the power supply of the inserted computer and be controlled by the computer. Therefore, the network interface card can be regarded as a semi-autonomous unit.

When the network interface card receives an error frame, it discards the frame without notifying the computer it is inserted into. When the network interface card gets a valid frame, it sends an interrupt to the computer and delivers it to the protocol stack's network layer. The protocol stack assembles it into a frame and sends it down to the network interface card, which then sends it to the local area network when the computer wants to send an IP data packet.

With the continuous improvement of integration, the number of chips on the network interface card continues to decrease. Although there are many types of network interface cards produced by various manufacturers, their functions are similar.

What are the types of network interface cards?

According to the different physical layer standards and host interfaces supported by the network interface card, the network interface card can be divided into different types, such as Ethernet cards and token ring network interface cards. According to the connection mode of the network interface card and the bus on the motherboard, the transmission rate of the network interface card, and the interface between the network interface card and the transmission medium, the network interface card is divided into different types.

The network interface card is classified as either a standard Ethernet card or a PCMCIA network interface card, depending on the type of computer it supports. Standard Ethernet cards are used for desktop computer networking, while PCMCIA network interface cards are used for notebook computers.

According to the classification of the transmission rate supported by the network interface card, it is mainly divided into four types: 10Mbps network interface card, 100Mbps network interface card, 10/100Mbps adaptive network interface card, and 1000Mbps network interface card. According to the requirements of the transmission rate, the 10Mbps and 100Mbps network interface cards only support the transmission rates of 10Mbps and 100Mbps.

When using unshielded twisted pair UTP as the transmission medium, the 10Mbps network interface card is usually used in conjunction with the Type 3 UTP, and the 100Mbps network interface card is connected with the Type 5 UTP. The 10/100Mbps adaptive network interface card automatically detects the transmission rate of the network by the network interface card to ensure the compatibility of two different transmission rates in the network. As the transmission rate of local area networks continues to increase, 1000Mbps network interface cards are mostly used in high-speed servers.

According to the bus types supported by the network interface card, it can be divided into ISA, EISA, PCI, etc... Because of the rapid development of computer technology, the use of ISA bus interface network interface cards is less and less. The network interface card of the EISA bus interface can transmit 32-bit data in parallel, and the data transmission speed is fast, but the price is more expensive. The CPU occupancy rate of the PCI bus interface network interface card is relatively low. The theoretical transmission rate of the commonly used 32-bit PCI network interface card is 133Mbps, so the supported data transmission rate can reach 100Mbps.

Buying guide for the network interface card

Whether the network interface card can be correctly selected, connected, and set up during assembly is often a prerequisite and necessary condition for the correct connection to the network. Generally speaking, the following factors should be considered when purchasing a network interface card:

Network Type

The more popular ones are Ethernet, token ring network, FDDI network, etc. The corresponding network interface card should be selected according to the type of network.

Transmission rate

The network interface card's transmission rate should be determined by the server or workstation's bandwidth requirements as well as the maximum transmission rate that the physical transmission medium can provide. Taking Ethernet as an example, the selectable rates are 10Mbps, 10/100Mbps, 1000Mbps, and even 10Gbps. Configuring a 1000M network interface card for a computer connected to a twisted pair cable with a transmission speed of only 100M is a waste of money because it can only achieve a maximum transmission rate of 100M.

Bus type

Common bus slot types in computers are ISA, EISA, VESA, PCI, and PCMCIA, etc. In servers, PCI or EISA bus smart network interface cards are usually used. Workstations use ordinary network interface cards that can use PCI or ISA bus. Notebook computers use PCMCIA bus network interface cards or portable network interface cards with parallel interfaces. Basically, PCs no longer support ISA connections. Therefore, when buying a network interface card for your PC, you should never buy an outdated ISA network interface card, but a PCI network interface card.

Cable interface supported by the network interface card

The network interface card is ultimately connected to the network, so there must be an interface for the network cable to connect with other computer network equipment through it. Different network interfaces are suitable for different network types. Common interfaces mainly include Ethernet RJ-45 interface, thin coaxial cable BNC interface, and thick coaxial electrical AUI interface, FDDI interface, ATM interface, etc. In addition, some network interface cards provide two or more types of interfaces in order to be suitable for a wider range of application environments. If some network interface cards provide RJ-45, BNC, or AUI interfaces at the same time.

(A) RJ-45 interface: This is the most common and the most widely used interface type network interface card, which is mainly due to the popularity of twisted-pair Ethernet applications. This RJ-45 interface type network interface card is used in the Ethernet with twisted pair as the transmission medium. The network interface card also comes with two status indicator lights, and the working status of the network interface card can be preliminarily judged by the colors of these two indicator lights.

(B) BNC interface: This interface network interface card is used in Ethernet or token network that uses thin coaxial cable as the transmission medium. This type of network interface card is uncommon because few networks use narrow coaxial cables as their transmission medium.

(C) AUI interface: This network interface card is utilized in Ethernet or token networks using thick coaxial cable as the transmission medium, and it is even more uncommon.

(D) FDDI interface: The network interface card of this interface is adapted to the FDDI (Fiber Distributed Data Interface) network. This network has a bandwidth of 100Mbps. The transmission medium it uses is optical fiber, so the interface of this FDDI interface network interface card also has a fiber-optic interface. With the advent of Fast Ethernet, its speed superiority no longer exists.

(E) ATM interface: This interface type network interface card is used in ATM (Asynchronous Transfer Mode) optical fiber (or twisted pair) network. It can provide a physical transmission speed of 155Mbps.