Network Interface Controller (NIC)

A network interface card (NIC) is a hardware device that handles an interface to a computer network and allows a network-capable device to access that network. The NIC has a ROM chip that contains a unique number, the media access control (MAC) Address burned into it. The MAC address identifies the device uniquely on the LAN. The NIC exists on the 'Data Link Layer' (Layer 2) of the OSI model.

The OSI Model

This section serves as an introduction to the International Standards Organization/Open System Interconnection (ISO/OSI) model. You do not need to understand the OSI model in order to build a home network. However, it can be helpful to have a basic understanding of how your network works in order to troubleshoot future problems. We designed this section with more advanced users in mind.

The OSI model defines a networking framework for implementing protocols according to seven layers. Each layer is functionally independent of the others, but provides services to the layer above it and receives services from the layer below it. The seven OSI layers are explained in more detail below.

APPLICATION

The Application layer is the layer at which applications access network services. This layer represents the services that directly support applications such as software for file transfers, database access, email, and network games.

PRESENTATION

The Presentation layer translates data from the Application layer into a network format (and vice-versa). This layer also manages security issues by providing services such as data encryption and compression.

SESSION

The Session layer allows applications on different computers to establish, use, and end a session/connection. This layer establishes dialog control between the two computers in a session, regulating which side transmits, and when and how long it transmits.

TRANSPORT

The Transport layer handles error recognition and recovery. It also repackages long messages when necessary into small packets for transmission and at the receiving end, rebuilds packets into the original message. The receiving Transport layer also sends receipt acknowledgments.

NETWORK

The Network layer addresses messages and translates logical addresses and names into physical addresses. It also determines the route from the source to the destination computer and manages traffic problems (flow control), such as switching, routing, and controlling the congestion of data packets.

DATA LINK

The Data Link layer packages raw bits from the Physical layer into frames (logical, structures packets for data). This layer is responsible for transferring frames from one computer to another, without errors. After sending a frame, it waits for an acknowledgment from the receiving computer.

PHYSICAL

The Physical layer transmits bits from one computer to another and regulates the transmission of a stream of bits over a physical medium. This layer defines how the cable is attached to the network adapter and what transmission technique is used to send data over the cable.

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Purpose

A network interface card, network adapter, network interface controller (NIC), or LAN adapter is a computer hardware component designed to allow computers to communicate over a computer network. It is both an OSI layer 1 (physical layer) and layer 2 (data link layer) device, as it provides physical access to a networking medium and provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.

Although other network technologies exist (e.g. Token Ring), Ethernet has achieved near-ubiquity since the mid-1990s. Every Ethernet network card has a unique 48-bit serial number called a MAC address, which is stored in ROM carried on the card. Every computer on an Ethernet network must have a card with a unique MAC address. Normally it is safe to assume that no two network cards will share the same address, because card vendors purchase blocks of addresses from the Institute of Electrical and Electronics Engineers (IEEE) and assign a unique address to each card at the time of manufacture.

A 1990s Ethernet network interface controller card which connects to the motherboard via the now-obsolete ISA bus. This combination card features both a (now obsolete) bayonet cap BNC connector (left) for use in coaxial-based 10base2 networks and an RJ-45 connector (right) for use in twisted pair-based10baseT networks. (The ports could not be used simultaneously.)

Madge 4/16Mbps TokenRing ISA NIC.

Ethernet 10Base-5/2 ISA NIC.

Implementation

The card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet or token ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP.

There are four techniques used to transfer data, the NIC may use one or more of these techniques.

• Polling is where the microprocessor examines the status of the peripheral under program control.
• Programmed I/O is where the microprocessor alerts the designated peripheral by applying its address to the system's address bus.
• Interrupt-driven I/O is where the peripheral alerts the microprocessor that it's ready to transfer data.
• DMA is where an intelligent peripheral assumes control of the system bus to access memory directly. This removes load from the CPU but requires a separate processor on the card.

A network card typically has a RJ45, BNC, or AUI socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it. Network cards are typically available in 10/100/1000 Mbit/s varieties. This means they can support a notional maximum transfer rate of 10, 100 or 1000 Megabits per second.

Sometimes the words 'controller' and 'card' are used interchangeably when talking about networking because the most common NIC is the network interface card. Although 'card' is more commonly used, it is less encompassing. The 'controller' may take the form of a network card that is installed inside a computer, or it may refer to an embedded component as part of a computer motherboard, a router, expansion card, printer interface or a USB device.

A MAC address is a 48-bit network hardware identifier that is burned into a ROM chip on the NIC to identify that device on the network. The first 24-bit field is called the Organizationally Unique Identifier (OUI) and is largely manufacturer-specific. Each OUI allows for 16,777,216 Unique NIC Addresses. Smaller manufacturers that do not have a need for over 4096 unique NIC addresses may opt to purchase an Individual Address Block (IAB) instead. An IAB consists of the 24-bit OUI plus a 12-bit extension (taken from the 'potential' NIC portion of the MAC address.)


Network Interface Controller(NIC) Installation

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