| | | Network Hardware Networks require a wide range of peripheral devices in order to function. This course will examine various pieces of hardware and look at what there functions are and how they work including providing links to other reliable sources to further enhance understanding.
| | | | 1 | Is a card that will normally plug into one of the PCI slots in the motherboard which will allow the computer to connext to a network. The card will normally be an ethernet card but there are other types such as a card which would allow the computer to use token rings. 
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| | | 2 | A server is a computer which provides services to other computers such as applications, file sharing, storage space, internet, printing and a variety of other tasks. As networks grow dedicated servers are required for the various tasks such as: File Servers: Stores and manages files including access rights and levels of access rights to users Print Servers: Manages printers and print requests Web Servers: Allows access to requested web pages Mail Servers: Provides email services and manages mail boxes |
| | | 3 | Linking hardware refers to hardware which allowsparts of a network or connecting networks to link or use various peripheral devices. Linking hardware refers to bridges, switches, routers, hubs and gateways. - Hubs: Traditionally a hub is one of the most critical devices for a LAN because it was normally the point of central connection of all shared devices, however they are largely being superseded by switches. A typical LAN will have multiple ports to which devices will connect. A hub will not be intelligent. In other words any packet received will be sent to all connected devices but only the device which it is addressed to will answer. Because of its lack of ability to address packets for the intended computer a hub will not be as efficient as other devices.
- Switches: Are similar to routers but will also amplify the signal like a repeater. Most switches are normally thought of as being a device which filters and forwards segments within LAN segments. These swictes worked on the layer 2 of the OSI model. Layer 2 is the data layer. This meant that switches could not transfer data between networks because they did not have access to the protocols. The new switches are also refrred to as routing switches and work at OSI layer 3 which is the network layer and can actually perform the same functions as a router. (Microsoft: networking Essentials Plus, 3rd edition pages 312-316 ATM switches), (webopedia: routing switches )
- Routers : Routers are located at gateways, the places where two or more networks connect. Routers also have the added intelligence of providing an alternate path to a node. ROUTERS WORK BY USING IP ADDRESSES STORED IN A TABLE. Unlike hubs, routers are intelligent devices which rout packets of data directly to the intended computer. A large network may have 25 LANs with large numbers of users on each of them and may support 500 or thousands of users. If we were depending on hubs relaying every message out to every computer and waiting for the correct computer to accept the message the network would collapse with only minimal amount of traffic ever able to use it. That is why routers are critical.
- Gateways: A gateway connects a LAN to the internet and external traffic. It may be a router with a hardware configured firewall or a server may act as a gateway.
- Repeaters: amplify the signal when a LAN is spread over a larger area than normal. A repeater will not filter or join different LANs. All they can do is amplify a signal
- Bridges: Join two or more LANS and are a cobination of hardware and software. They are similar to routers but can only make binary decision dependent on information stored in its Address table. UNLIKE ROUTERS BRIDGES WORK BY USING THE MAC ADDRESS A bridge will not allow traffic to pass unless it is addressed to one of the addresses in that table. Because of this bridges can be used as a security device to stop traffic between different parts of a LAN.
- Network Interface Card : The network interface card (NIC) allows computers to connect through an ethernet. An ethernet cable will connect to the NIC and then directly to another computer in a P2P connection or to a router, hub, switch etc...
List of Networking Devices, Bettscomputers, How Stuff Works, Wikipedia How routers work
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| | | 4 | There are 2 categories of transmission mediums: - Cable Mediums: (twisted pair, coaxial cable, fibre optic cable)
Left: This a picture of a twisted pair cable. This is also called STP (shielded twisted pair) and there is another one which looks very similar but without the shielding which is UTP. It may also be referred to as Cat 10T. This is the slowest of the transmission mediums. 
RIGHT: This is Coaxial Cable. This is the thick black ugly cables hanging off telegraph poles which are used for broadband and cable television. They are often underground and can be together in bundles. They are a much higher bandwidth to Cat 10T 
- LEFT: This is a picture of fibre optic cable. The cable is no more than the thickness of a human hair yet can carry huge numbers of users at the same time and can be used in 10 Gigabit Ethernet transmissions capable networks. It is often not used over short distance because of costs yet some areas require light weight, security or a medium which will not be susceptible to radiation or other trasnmission noise. In these cases even over short distance optic fibre would be the prefrred medium. It is becoming more common as prices begin to fall.
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| | | 5 | Twisted Pair (telephone cable) Twisted pair cable is the cabling which runs from a junction box on the footpath to a building. A twisted-pair cable consists of two thin insulated copper wires, twisted to form a spiral. Twisting reduces the amount of interference from other cabling. Twisted-pair cable is used over short distances, such as connecting a modem to a wall socket. Twisted-pair cables can transmit data in millions of bits per second for short distance. Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for most networks . The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky. Shielded twisted pair is often used on networks using Token Ring topology. |
| | | 6 | Coaxial Cable A number of very thin copper wires are enclosed within an outer protective cover to form the cable. They are individually wrapped in insulation so that they do not touch each other and short out. A cable can handle several thousand calls at one time. Coaxial cable has been laid on the seabed and is also usede for communication between continents. |
| | | 7 | Fibre Optic Cable Optic fibre is gradually replacing coaxial cable. In this technology, the data is converted into pulses of visible, laser light. This is transmitted to its destination by repeated reflections through very fine, optically pure glass fibre through which light can be reflected to transmit images or data from one end to the other. This fibre is no thicker than a human hair and the transmission is without distortion or interference. Although expensive to produce and install, optical fibres can carry more data than traditional cables, and are less susceptible to interference. Standard optical fibre transmitters can send up to 10 billion bits of information per second by switching a laser beam on and off. Bundles of such tubes are enclosed in a protective covering to form a cable, but one that is much thinner and cheaper to produce and maintain than a standard coaxial cable. Optical fibres are increasingly being used to replace metal communications cables, the messages being encoded as digital pulses of light rather than as fluctuating electric current. Current research is investigating how optical fibres could replace wiring inside computers. Bundles of optical fibres are also used in endoscopes to inspect otherwise inaccessible parts of machines or of the living body Fibre-optics technology uses very fine glass fibres to transmit data or images, and has increasingly come to replace metal communications cables. Fibre optics are also used in endoscopes (instruments used to visualize the body's organs), in which different bundles of fibres are used to illuminate the area under examination and to transmit the image. |
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