Technology / Wireless Networking
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Autor: anton 24 November 2010
Words: 2346 | Pages: 10
While the term wireless network may technically be used to refer to any type of computer network that is wireless, the term is most commonly used to refer to a telecommunications network whose interconnections between nodes is implemented without the use of wires, such as a computer network (which is a type of communications network).Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or "layer" of the network.
An embedded Router Board 112 with U.FL-RSMA pigtail and R52 mini PCI Wi-Fi card widely used by wireless Internet service providers (WISPs) in the Czech Republic.
Wireless networks have had a significant impact on the world as far back as World War II. Through the use of wireless networks, information could be sent overseas or behind enemy lines easily and quickly and more reliably. Since then wireless networks have continued to develop and its uses have significantly grown. Cellular phones are part of huge wireless network systems. People use these phones daily to communicate with one another. Sending information over seas is possible through wireless network systems using satellites and other signals to communicate across the world. Emergency services such as the police department utilize wireless networks to communicate important information quickly. People and businesses use wireless networks to send and share data quickly whether it be in a small office building or across the world.
Another important use for wireless networks is as an inexpensive and rapid way to be connected to the Internet in countries and regions where the telecom infrastructure is poor or there is a lack of resources, like most developing countries.
Compatibility issues also arise when dealing with wireless networks. Different components not made by the same company may not work together, or might require extra work to fix compatibility issues. Wireless networks are typically slower than those that are directly connected through an Ethernet cable.
A wireless network is more vulnerable because anyone can try to break into a network broadcasting a signal. Many networks offer WEP - Wired Equivalent Privacy - security systems which have been found to be vulnerable to intrusion. Though WEP does block some intruders, the security problems have caused some businesses to stick with wired networks until security can be improved. Another type of security for wireless networks is WPA - Wi-Fi Protected Access. WPA provides more security to wireless networks than a WEP security set up. The use of firewalls will help with security breaches which can help to fix security problems in some wireless networks that are more vulnerable.
What is WLAN?
LAN stands for local area network, so a wireless LAN is simply a network linking two or more computers without wires (cables). In many offices today, computers communicate with each other and with printers and other devices by sending information along wires. Using newer technology, computers can be linked by the same method as your cordless telephone operates in your home - by transmitting the signal through air. Just as your cordless telephone frees you to make a phone call from anywhere in your home, the wireless LAN permits workers to use their computers anywhere in the network area, such as an office building or corporate campus. As with the wired network, the computer can access information stored in other computers in the office. Some wireless networks are designed to cover a broader area and are called wide area networks or WANS.
The commercial wireless LAN applications can be divided in five categories.
Ð²Ð‚Ñž LAN extension - indoor wire replacement
Ð²Ð‚Ñž Inter-LAN bridges - outdoor wire replacement
Ð²Ð‚Ñž Campus Area Networks (CAN) - wireless LANs with infrastructure
Ð²Ð‚Ñž Ad-hoc networking - wireless LANs without infrastructure
Ð²Ð‚Ñž Nomadic access - a wireless LAN service
Today's existing applications aims at four categories of applications.
Ð²Ð‚Ñž Healthcare industry
Ð²Ð‚Ñž Factory floors
Ð²Ð‚Ñž Banking industry
Ð²Ð‚Ñž Educational institutions
How does the wireless network works
The network operates by linking the computers to the wiring in the office using radio frequency energy, just as the `cordless' portable telephone in your home sends voice information to the telephone wiring in your home. Like the telephone system, it is a hybrid system using both wired and wireless communication. The antenna is small just a few inches, barely noticeable outside of the computer, and the power used is very low, comparable to your cordless telephone.
Is this technology new?
The ability to send information across distances by radio frequency energy, or radio waves, is not new. Non-cable television AM and FM radio, cellular telephones and pagers use this method. However, affordable technology to adapt these techniques for computers in offices has been developed only in the past few years.
A number of applications already exist in which computers are connected by using radio waves instead of wires. Some are wide area networks and some are local area networks. You may have encountered these without noticing. For example, trucks that carry packages for express delivery are liked to the main office by wireless technology. Similarly, an appliance repairman can set up his portable computer in your home and check with the local warehouse to see if the parts needed to fix your refrigerator are available. Wireless LANs are used at airports, by local police and other public service organizations, and in hospitals for nurses and doctors to enter or obtain data at the patient's bedside.
Wireless local area network speed
The speed at which a WLAN performs depends on the products within the network and configuration of those products. The number of users, the distance between network components, the type of WLAN system used and the efficiency of wired network components all influence the overall speed and performance of the WLAN.
Wired network speeds differ as well, but most commercial wired LANs operate at around 10 megabits per second (10BaseT) to 100 Mbps (100BaseT). WLAN components that use the 802.11a high data rate standard perform at speeds as high as 54 Mbps, a nearly five-fold increase from the 802.11b standard.
802.11 refer to a family of specifications developed by the IEEE for wireless LAN technology. 802.11 specify an over-the-air interface between a wireless client and a base station or between two wireless clients. 802.11b is an extension to 802.11 that provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4GHz band.
The 802.11a standard, also an extension of 802.11, operates on a new, wider band of the frequency spectrum Ð²Ð‚â€œ between 5.15 and 5.35GHz Ð²Ð‚â€œ that experiences considerably less contention than the 2.4GHz band. The combined results of faster speeds and cleaner air space translate into increased capacity for large file transfers, streaming video and other types of bandwidth-intensive content.
Wireless local area network Standards
Home and business net workers looking to buy wireless local area network (WLAN) gear face some difficult choices. Vendors sell many products that conform to different wireless standards such as 802.11,802.11a, 802.11b, 802.11g, and Bluetooth. To make an educated network building decision, one must understand the relative pros and cons of each of these technologies.
1) In 1997, the Institute of Electrical and Electronics Engineers (IEEE) created the first WLAN standard. They called it 802.11 after the name of the group formed to oversee its development. Unfortunately, 802.11 only supported a maximum bandwidth of 2 Mbps - too slow for most applications.
2) For this reason, ordinary 802.11 wireless products are no longer being manufactured.
Wireless local area network Topologies
Wireless LANs can be built with either of two topologies:
Ð¿Ñ“? Access point-based.
Ð¿Ñ“? point-to-point or point-to-multipoint bridge
In a peer-to-peer topology, client devices within the wireless cell communicate directly to each other as depicted in Figure 1.
Fig 1.In a peer-to-peer topology, wireless devices create a LAN by communicating directly with each other
2. Access point-based.
An access point is a bridge that connects a Wireless client device to the wired network. An access point-based topology uses access points to bridge traffic onto a wired (Ethernet or Token Ring) or wireless backbone as shown in Figure 2.The access point enables a wireless client device to communicate with any other wired or wireless device on the network. The access point topology is more commonly used, demonstrating that WLANs do not replace wired LANs; they extend Connectivity to mobile devices
Figure 2. In a topology based on access points, wireless devices can connect to the wired LAN backbone for communication with both wired and wireless nodes.
3. Point-to-point or point-to-multipoint Bridge.
A bridge is defined as a node (or pair of nodes) with a transceiver client device that connects two networks using similar protocols. Wireless bridges connect a LAN in one building to a LAN in an-other, even if the buildings are many miles apart (see Figures 3 and 4). These connections require a clear line-of-sight (i.e., no obstacles, such as buildings, hills or trees) between the buildings. The line-of-sight range varies based on the type of wireless bridge and antenna used as well as environmental conditions. WLAN clients are available in a number of form factors for use in any of these network topologies. Personal computers (PCs) can connect to a WLAN using PCI, PCMCIA, and USB dongles cards. Wireless modems can attach to parallel ports, RS232, 10BaseT, or other popular physical interfaces on a PC or other device. In this con-figuration, the client device communicates via the physical interface (e.g. PCI, RS232, etc.) to the radio device, which in turn provides the physical interface to the WLAN. For portable applications, the most common configurations are PCMCIA adapter cards for laptop computers and integrated LAN modules for application-specific, hand-held terminals.
Figure 3. A point-to-multipoint bridge topology is useful for a campus or nearby buildings.
Figure 4. A wireless bridge connects the LAN backbones in separate buildings or locations.
Wireless local area network Technologies
The technologies available for use in WLANs include infrared, UHF (narrowband) radios, and spread spectrum radios. Two spread spectrum techniques are currently prevalent: frequency hopping and direct sequence. In the United States, the radio bandwidth used for spread spectrum communications falls in three bands (900 MHz, 2.4 GHz, and 5.7 GHz), which the Federal Communications Commission (FCC) approved for local area commercial communications in the late 1980s. In Europe, ETSI, the European Telecommunications Standards Institute, introduced regulations for 2.4 GHz in 1994, and Hiperlan is a family of standards in the 5.15-5.7 GHz and 19.3 GHz frequency bands
Health and Safety
Ð¿Ñ“? Wireless LANs operate at very low power (1watt or lower), less energy than is used for most cellular telephones.
Ð¿Ñ“? Wireless LANs cover relatively short distances, so they can operate using very weak radio waves.
Ð¿Ñ“? These weak radio waves are far below the exposure limits set by safety standards.
Wireless Wide Area Network (WWAN)
A wireless wide area network (WWAN) is a digital network that extends over a large geographical area. A WWAN receives and transmits data using radio signals over cellular sites and satellites, which make the network accessible to mobile computer systems. At the switching center, the WWAN splits off into the Segments and then connects to either a specialized public or private network via telephone or other high-speed communication links .The data then is linked to an organizationÐ²Ð‚â„¢s existing LAN/WAN infrastructure. The Coverage area for a WWAN is normally measured in miles (or kilometers) and it is therefore more susceptible to environmental factors, like weather and terrain, than wired networks.
A WWAN is a fully bidirectional wireless network capable of data transfer at speed in excess of 100 Mbps for a cost comparable with most DSL connections. Usually, basic WWAN services offer connection speeds between 1 and 10 Mbps. With dedicated equipment, the speeds can reach 100 Mbps. A WWAN system requires an antenna tuned to receive the proper radio frequency (RF). Through the propriate Web sites or e-mail addresses with a WWAN system, a signal originates from the provider at a centralized transmission unit. The company will interface with the carrier using a dish antenna connected to a transceiver device through a coaxial cable. The other side of the transceiver is a port for a typical CAT5 Ethernet cable that connects to a LAN bridge that also contains a multiport hub. The hub will allow speeds of 100 Mbps for use by the LAN.
Figure 5. Wireless connectivity between WLAN and WAN
Satellite services provide two-way data communications between the customer and the Internet. Many places in the world do not have a telephone network that can support broadband, nor do they have cellular coverage. For these locations, and for those who require Internet access while traveling, satellite connections are the answers, and they are becoming more affordable. Worldwide, 13 percent of ISP links to the Internet backbone and to customers use satellite communications. In fact, it is estimated that 10 percent of the worldwide broadband traffic in 2003 involved satellite communications.
Satellite connections are suitable for large businesses and for small officers, cyber-cafes, and homes. They also are used by the armed forces, business, and individuals for mobile communications. This wireless service is always on, unlike dial-up connections.
When an individual or organization contracts with an ISP for a satellite server, an earth-based communications station is installed. The generic name for this station is very small aperture terminal (VSAT). It includes two parts: a transceiver (a satellite dish) that is placed
Figure 6 .A signal travels from VSAT to a satellite then back to earth.
outdoors in direct line of sight to one of several special data satellites in geostationary orbit around the earth and a modem-like device that is connected to the dish, placed indoors, and connected to a computer or LAN. In a mobile implementation, the dish may be mounted on a land- or water- same speed as the earthÐ²Ð‚â„¢s rotation and it is always positioned over the same place on the earth. Therefore the dish can be focused precisely on the satellite.
The satellite links to large hub stations where the VSAT operators, and now various ISPs, are located along with their very-high-speed backbones for cross country network connectivity.
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