Definition
The LAN (Local Area Network) card is a 'door' to the network from a computer. Any type of network activity requires a LAN card: the Internet, network printer, connecting computers together, and so on. Today many devices contain a network card, including televisions for their Internet apps, Blu-ray players, mobile phones, VoIP, desk phones, and even refrigerators. LAN cards are hardware devices that can be added to a computer, or they can be integrated into the main hardware of the computer.
LAN Card Types
What does a LAN card look like? Some LAN cards look like credit cards.
Some cards, such as a PCMCIA card, can be used in a laptop. There are many other ways of connecting the LAN card to a computer. Some cards are connected via the USB port, some via the PCI port inside of the computer, and some are even embedded inside of the computer. Most laptops today have integrated LAN cards both for wired and wireless networking.
A PCI card goes inside of a PC computer. The card shows an Ethernet port, which is the spot where you plug in a network cable. The LAN card you select often determines the protocols that are used on the network. For example, an Ethernet card will allow communication via the Ethernet protocol. A coax card would allow for a bus topology network and a new set of protocols. A fiber cable would have a different cable plugin, and it would likely work with Wide Area Network protocols. The Ethernet port on a LAN card looks like a phone jack, but it is wider and has more pins.
A typical Ethernet cable, or network cable, is the plugin that goes into the LAN card, or the Network Interface Controller (NIC).
Function
The purpose of a LAN card is to create a physical connection to the network - to provide an open 'door,' as it were. The first interface supported by a LAN card is a physical interface through which the cable plugs into the card. The interface is well-defined in technical documentation, which is why standard network cables fit most standard LAN cards. The second function of a LAN card is to provide a data link. There is a theoretical model in computer networking called OSI (Open Systems Interconnection). This model, or way of explaining networks, includes seven layers. The first two layers are the physical layer and the data link. Each layer of the OSI model allows for other layers to be independent. Upgrading or changing one layer does not affect the others. This means that if plugins change for all LAN cards, other elements, like the protocols, don't have to change.
The data link function of a LAN card provides hardware-level sending and receiving of network binary data. Zeros and ones flow from the network into the network card. The card can recognize this flow and it can even check for errors. When you turn on a computer with a LAN card, it will have two lights, one green and one orange. The orange light will come on when the data link layer is activated. This means that the cable works, there is a network connected, and data bits are flowing. The second light, the green light, comes on once the next layer, the network layer (such as an IP network), is activated.
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