Text F. Wireless networks
3.13 Before you read the text try to answer these questions:
1) What is a WAN?
2) How can computers be linked up over a long distance?
3) What are the advantages of optical-fiber cables over telephone lines?
4) What is the function of communications satellites?
3.14 Now read the passage and find out if your answers were correct:
For long-distance or worldwide communications, computers and LANs are usually connected into a wide area network (WAN) to form a single, integrated network. The largest WAN in existence is the Internet.
Networks can be linked together by either telephone lines orfiber-opticcables. An optical-fiber network transmits data at great speed - 100 megabits per second. A variation called FDDT transmits data at 200 Mbps. FDDI networks are typically used as backbones for wide area networks.
Modern telecommunications use fiber-optic cables because data can be transmitted at a very high speed through the extremely wide bandwidths of glass fibers. The fiber system operates by transmitting light pulses at high frequencies along the glass fiber. This offers considerable advantages:
- the cables require little physical space;
- they are safe because they don't carry electricity;
- they avoid electromagnetic interference.
Networks on different continents can also be connected viasatellite. Computers are connected by a modem either to ordinary telephone wires or fiber-optic cables, which are linked to a dish aerial. This aerial has a large concave reflector for the reception and sending of signals. Then, when signals are received by the satellite, they are amplified and sent on to workstations in another part of the world.
Wireless (WiFi) networks are just like fixed LANs but instead of using cables, devices are linked by radio waves.
Each computer in a wireless network requires a wireless network interface card (NIC). These can be built in or you can use plug-in adapters. These allow each component in the network to communicate with a wireless access point (AP) to create a wireless local area network (WLAN). The AP operates like a router in a fixed LAN. It also provides a bridge which plugs into the hub of a fxed LAN allowing both fixed and wireless users to talk to each other. If your LAN is connected to the Internet, the WLAN can also use it. If not, you can connect the WLAN to the Internet via an ADSL or cable modem.
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What are the advantages of a wireless network? You don’t need cabling. In older buildings it can be expensive to install cables and access points. With WiFi, one access point can cover an entire floor or even a building. You can work anywhere within range of the access point. On a sunny day you could work outside. You can make any room in the house your study. There are now hotspots in hotels, libraries and airports, so you can link to a network away from home or your officce.
There are disadvantages. Fixed LANs can run at 1000 Mbps. Wireless networks are much slower and the further you are from an access point, the slower the rate. Although there are savings on the cost of cabling, wireless NICs are more expensive than the wired versions. Then there is the problem of interference, if a neighbour uses the same channel, and security. Other users may be able to intercept your data. Encription programs like Wired Equivalent Privacy (WEP) can help.
3.15 Write a list of the advantages and disadvantages of using wireless networks.
3.16 Look through the texts above and correct the following statements.
1. In a client-server architecture, all the workstations have the same
2. LANs link computers and other devices that are placed far apart.
3. The word protocol refers to the shape of the network.
4. Routers are used to link two computers.
5. Access points don’t need to be connected to a wired LAN.
6. Wireless adapters are optional when you using a WLAN.
7. Hotspots can only be found inside a building.
8. The Internet is an example of a LAN.
9. Wireless WANs use fiber and cable as linking devices.
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