Wireless Networks

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Computer Studies wireless router

Wireless networks use radio, microwaves and infrared light as transmission media, with wireless technology you can connect cell phones, PDAs or Personal digital assistants, laptops etc together, but the disadvantage of a wireless network is it's a much greater security risk, wireless technologies are implemented at the data link and physical layers of the OSI model, wireless networks work on the IEEE 802.11standard.There are three types of wireless topologies Ad-Hoc which uses a peer to peer connection, Infrastructure where all the devices connect via an access point, and a Bridge topology which connects two wireless or wired networks together. Wireless devices use one of three transmission methods DSSS or Direct sequence spread spectrum used in the 802.11b wireless radios, FHSS or Frequency hopping spread spectrum these transmissions jump between several frequencies at a pre-determined rate or interval and OFDM or Orthogonal frequency division multiplexing used by 802.11a and 802.11g networks this transmits data using multiple carrier waves, each wave carries part of the message, DSSS and FHSS can penetrate walls and are less prone to interference and can transmit data over greater distances, OFDM offers a higher data rate over a smaller bandwidth, with resistance to interference with more non-overlapping channels.

Wireless hardware

Wireless hardware can include PCMCIA cards, Express cards, PC cards, USB or internal PCI cards and mini-PCI cards for laptops, wireless access points, cell phones, and PDAs, you can expand the computers functionality by inserting a wireless network interface card into a PC, modern laptops now come with wireless functionality already built in but there may be legacy devices that would need to use network cards like compact flash cards, PCMCIA cards or external USB devices to give the laptop wireless capability, Windows 2000 does not have wireless support built in but Windows XP has built in wireless support known as Windows wireless zero configuration, Wireless on Linux machines can be problematic a utility called NDISwrapper can be used but doesn't always work, and MACs use AirPort Extreme wireless cards with their computers to add built in wireless capabilities, network cards are built around chipsets, the older cards use Hermes or Prism2 chipsets and modern cards use Broadcom or Cisco chipsets among a few other well known brands. For more information on PCMCIA

Antennas are also an important feature in wireless networks utilising many different shapes, sizes and characteristics, the Omni-directional dipole antenna is used with most common wireless access points which resembles a doughnut shaped sphere of signal transmission covering 360 degrees, there are also semi-directional antennas used to direct the signal to specific areas for precise coverage examples of these include the patch, panel and yagi antennas, antennas can work by line of site both visual and with RF radio frequency, the Fresnel zone is a elliptical zone that should be free of RF obstructions and interference, Effected isotropic radiated power EIRP is a measure of transmitted radio signal power as it leaves the antenna, antennas suffer from interference from electrical devices, weather, attenuation is where the signal weakens over distance, multi-path signals is where reflection and refraction can cause problems, to increase coverage of the network boosters and extenders can be used to amplify the signal enabling you to receive, amplify and retransmit the wireless signal increasing the range of the network.

The wireless access point is used to receive signals to forward on to other devices on the network, hubs, switches, computers, printers etc. Wireless access points are a key piece of hardware that make wireless networks feasible, they can provide basic to advanced connection functions, routing and security they can be as simple as hubs or as complicated as routers, firewalls, switches and bridges that employ security, authentication, encryption and proxying functions, they are interoperable with multiple wireless standards, usually easily configured through a web interface and can provide both wired and wireless access, a lot of modern access points are multifunctional utilising routers, switches and bridges in one device as well as firewall and proxy functionality, their capable of NAT Network address translation which translates IP addresses into MAC addresses, configuring IP addresses to block or allow traffic, to block ports and protocols.

Wireless security issues have additional problems to that of a wired network because they are not enclosed or contained they are physically open because they utilise the airwaves, radio frequencies making it possible to circumvent security devices, firewalls, routers etc, with radio transmission security becomes more important, you need to use encryption and access control, authentication, authorisation and accounting also play an important role in keeping the network secure.

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