Network devices

From Wikiversity

[edit] Network Interface Controller (NIC) Card

• Typically when you think of a NIC Card, you should think of an NIC embedded onto the motherboard of your computer or an expansion card that is installed into an ISA,PCI, or PCI-Express slot inside your computer.

[edit] Repeater

• One of the limitations of computer networking is found in the transmission medium. Certain cables are only capable of transmitting a certain distance before a concept called Attenuation comes into play. If the distances of a cable run exceed the physical limitations of the medium, a repeater may be placed before the limitation distance to recondition and repeat the signal so that it may run the rest of the length of the cable.

[edit] Hubs

• Hubs are very basic devices that are made up of many NIC ports. They take the electrical signals that a computer transmits into them and repeats them out every port on the device except for the one the signals arrived in. Since hubs offer no services other than repeating signals to multiple ports, they are often called multiport repeaters.

[edit] Bridges

• A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model, and the term layer 2 switch is often used interchangeably with bridge. Bridges are similar to repeaters or network hubs, devices that connect network segments at the physical layer, however a bridge works by using bridging where traffic from one network is managed rather than simply rebroadcast to adjacent network segments. In Ethernet networks, the term "bridge" formally means a device that behaves according to the IEEE 802.1D standard—this is most often referred to as a network switch in marketing literature.

[edit] Switches

• Low-end network switches appear nearly identical to network hubs, but a switch contains more "intelligence" (and comes with a correspondingly slightly higher price tag) than a network hub. Network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately. By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth and offers generally better performance than a hub.

[edit] Routers

• A router allows connectivity to one or more computers, helping create a network. For home users, these are particularly useful for taking a single broadband internet account, and spreading it to at least two or more computers. Standard routers require the internet connection from a standalone modem but modem-routers are increasing in popularity, which can be plugged into any broadband-enabled phone line, reducing cable clutter, and only taking up one power socket.
• In the telecoms industry, industrial routers form the backbone of the internet. They work rather like telephone exchanges, passing data between network segments to form a connection. Each router has a configuration table, or routing table, containing information on which connections lead to certain groups of addresses, which connections have priority for usage, and rules for handling different kinds of traffic. A typical home/office router has a very small routing table, but the big routers that handle the main internet traffic can have huge complicated routing tables. Each time a router receives a packer of data it will attempt to send it along the best possible route to its destination, based on its routing table. If that connection is not currently available, it will send it along the next best route. In this way, the routers that form the internet can reconfigure the paths packages take to work around any problems with the network.
• The rules for handling traffic are an important part of internet security. A home/office router may have rules limiting how computers outside the network can connect to computers inside the network, as well as preventing private network traffic from spilling into the outside world. Many home routers include additional security features - they scan and filter all traffic that passes through them, usually through an integrated firewall in the hardware. Some may carry out other useful roles such as acting as a print server.
• Wireless routers have become more common. A wireless router does exactly the same job in the home as a regular wired (Ethernet) router, with the difference that a computer can be connected to it without needing to run Ethernet cable between the computer and the router. All you need is a wireless network adapter in each PC you want to connect, usually in the form of a card in your PCI slot (or a laptops PCMCIA card slot) or an adapter for USB. Wireless routers generally have four ports to connect Ethernet cable as well, so computers can be connected by whatever means is most convenient - you might want to use a cable for your desktop PC, which sits right next to the router, but use the wireless adapter in your laptop.

[edit] Firewalls

• A firewall is a dedicated appliance, or software running on another computer, which inspects network traffic passing through it, and denies or permits passage based on a set of rules. A firewall's basic task is to regulate some of the flow of traffic between computer networks of different trust levels. Typical examples are the Internet which is a zone with no trust and an internal network which is a zone of higher trust. A zone with an intermediate trust level, situated between the Internet and a trusted internal network, is often referred to as a "perimeter network" or Demilitarized zone (DMZ).

[edit] Other Devices

• IP Phone

An IP phone uses Voice over IP technologies allowing telephone calls to be made over an IP network such as the internet instead of the ordinary PSTN system. Calls can traverse the Internet, or a private IP Network such as that of a company.

[edit] Summary

In summary, according to this page, network devices primarily consist of:

1. Network Interface Controller (NIC) Card
2. Repeater
3. Hubs
4. Bridges
5. Switches
6. Routers
7. Firewalls
8. Other Devices