What are Network Devices?
Network devices are components used to connect computers or other electronic devices together so that they can share files or resources like printers or fax machines. Devices used to setup a Local Area Network (LAN) are the most common type of network devices used by the public. A LAN requires a hub, router, cabling or radio technology, network cards, and if online access is desired, a high-speed modem. Happily this is much less complicated than it might sound to someone new to networking.
In a network, one computer is designated as the server, and the others, clients. The server is connected to an external hub, which the clients are also connected to. Now that the computers each have one foot in a common electronic door (the hub), they can use the hub to pass signals back and forth. To direct these signals, the hub contains a device known as a router. The router is the equivalent of an electronic traffic cop that handles data traffic between the computers.
Sounds good, but how does the router know one computer from another? The answer is that every computer in the network must have a network card installed. These network devices each contain a unique address. In a hard-wired network, special cabling called Ethernet runs from the network card to the hub. In a wireless network the network cards and router/hub communicate using radio waves.
Network cards identify themselves on the network, sending all requests to the router with the unique return-address included. The router reads the "To" address and "From" address, and routes the traffic accordingly. In other types of networks all requests made on the local network are broadcast by the router to all machines on the network, but only the machine with the matching address responds, however this is not as secure because other machines can trap traffic that is not addressed to them.
Online access is optional in a local area network, but if included, a single online account can be shared by all computers on the network. When online access is available, the router not only directs traffic on the local network, but also handles requests made to the Internet and subsequent replies. The router acts as a gateway to the Internet, and also serves as a hardware firewall to keep unsolicited traffic from flowing back into the network from the wild.
One can add online access to a LAN by either attaching a router/hub to a high-speed modem, or by acquiring a high-speed modem that has a router/hub built-in. The high-speed modem must be compatible with the online service. Most modems are designed specifically for use with DSL, cable or fiber optics, though some models might be made to work with more than one technology, such as being DSL and cable compatible.
When setting up a LAN all network devices must be compatible. If building a hard-wired LAN using Ethernet cabling, the network cards will be designed with an Ethernet port. If building a wireless LAN, all network devices must not only be designed for wireless use, but must speak the same wireless language or protocol. As of spring 2009 the fastest and most current protocol available is 802.11n, while the older protocol still in widespread use is 802.11g. The router/modem and network cards must all be compatible with the same protocol to communicate with one another.
Wireless network devices can also carry Wi-Fi certification, guaranteed to be fully compliant with the standards or protocol(s) that the product supports. Wi-Fi certification comes from the Wi-Fi Alliance, the organization responsible for developing wireless protocols. Many wireless network devices are marketed as being compatible with one or more protocols, but lack certification. The guarantee might be an important consideration when setting up a business LAN, but probably isn't a concern for home LANs.
Resource : http://www.wisegeek.com/