Wireless Local Area Networks: History and Types of WLAN
Wireless Local Area Networks (WLANs) Definition: A wireless LAN (or WLAN, for wireless local area network, sometimes referred to as LAWN, for local area wireless network) is one in which a mobile user can connect to a local area network (LAN) through a wireless (radio) connection. The IEEE 802. 11 group of standards specify the technologies for wireless LANs. 802. 11 standards use the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing and include an encryption method, the Wired Equivalent Privacy algorithm.
Introduction Wireless Local Area Networks (WLANs) have moved quickly to the mainstream and are now found in many educational institutions, homes, businesses and public areas. Organizations and consumers have been keen to take advantage of the flexibility adding wireless networks can offer. A recent report from In-Stat predicts that the wireless market will grow from 140 million wireless chipsets a year in 2005 to 430 million in 20091. The emergence of new security standards has also increased confidence in WLANs.
Users are becoming more familiar with the technology and are increasingly expecting wireless access to be available. There is a wide range of products and standards involved in WLAN technology and more continue to emerge. This paper will focus on wireless LANs and the issues surrounding their implementation. History In 1970, Norman Abramson, a professor at the University of Hawaii, developed the world’s first computer communication network, ALOHA net, using low-cost ham- like radios.
With a bidirectional star topology, the system connected seven computers deployed over four islands to communicate with the central computer on the Oahu Island without using phone lines. “In 1979, F. R. Gfeller and U. Bapst published a paper in the IEEE Proceedings reporting an experimental wireless local area network using diffused infrared communications. Shortly thereafter, in 1980, P. Ferrert reported on an experimental application of a single code spread spectrum radio for wireless terminal communications in the IEEE National Telecommunications Conference.
In 1984, a comparison between infrared and CDMA spread spectrum communications for wireless office information networks was published by Kaveh Pahlavan in IEEE Computer Networking Symposium which appeared later in the IEEE Communication Society Magazine. In May 1985, the efforts of Marcus led the FCC to announce experimental ISM bands for commercial application of spread spectrum technology. Later on, M. Kavehrad reported on an experimental wireless PBX system using code division multiple access.
These efforts prompted significant industrial activities in the development of a new generation of wireless local area networks and it updated several old discussions in the portable and mobile radio industry. The first generation of wireless data modems was developed in the early 1980s by amateur radio operators, who commonly referred to this as packet radio. They added a voice band data communication modem, with data rates below 9600-bit/s, to an existing short distance radio system, typically in the two meter amateur band.
The second generation of wireless modems was developed immediately after the FCC announcement in the experimental bands for non- military use of the spread spectrum technology. These modems provided data rates on the order of hundreds of KB/s. The third generation of wireless modem then aimed at compatibility with the existing LANs with data rates on the order of MB/s. Several companies developed the third generation products with data rates above 1 MB/s and a couple of products had already been announced by the time of the first IEEE Workshop on Wireless LANs. 54 MB/s WLAN PCI Card (802. 11g). The first of the IEEE Workshops on Wireless LAN was held in 1991. At that time early wireless LAN products had just appeared in the market and the IEEE 802. 11 committee had just started its activities to develop a standard for wireless LANs. The focus of that first workshop was evaluation of the alternative technologies. By 1996, the technology was relatively mature, a variety of applications had been identified and addressed and technologies that enable these applications were well understood. Chip sets aimed at wireless LAN implementations and applications, a key enabling technology for rapid market growth, were emerging in the market.
Wireless LANs were being used in hospitals, stock exchanges, and other in building and campus settings for nomadic access, point-to-point LAN bridges, ad-hoc networking, and even larger applications through Internetworking. The IEEE 802. 11 standard and variants and alternatives, such as the wireless LAN interoperability forum and the European Hiper LAN specification had made rapid progress, and the unlicensed PCS Unlicensed Personal Communications Services and the proposed SUPER Net, later on renamed as U-NII, bands also presented new opportunities. WLAN hardware was initially so expensive that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industryspecific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards, primarily the various versions of IEEE 802. 11 (Wi-Fi). An alternative ATM-like 5 GHz standardized technology, Hiper LAN/2, has so far not succeeded in the market, and with the release of the faster 54 MB/s 802. 11a (5 GHz) and 802. 11g (2. 4 GHz) standards, almost certainly never will.
What is a WLAN? A wireless local area network (WLAN) is two or more computers joined together using radio frequency (RF) transmissions. This differs from a wired LAN, which uses cabling to link together computers in a room, building, or site to form a network. Although WLANs can be independent they are more typically an extension to a conventional wired network. They can allow users to access and share data, applications, internet access or other network resources in the same way as wired networks. Currently, Wireless LAN technology is significantly slower than wired LAN.
Wireless LANs have a nominal data transfer rate of between 11 and 54 Megabits per second (Mbps) compared to most wired LANs in schools which operate at 100Mbps or 1000Mbps. Wireless LANs are typically used with wireless enabled mobile devices such as notebook computers, PDAs and Tablet PCs. This allows users to take advantage of the flexibility, convenience and portability that WLANs can provide. Wireless networking is also appearing on other devices such as mobile phones, digital cameras, handheld games consoles and other consumer electronics.
There are several wireless technologies in existence, but most wireless LANs use wireless Ethernet technologies based on IEEE 802. 11 standards (see: Current Standards). The term Wi-Fi (Wireless Fidelity) is often used to refer to 802. 11 wireless networks. It comes from the testing and certification program run by the Wi-Fi Alliance (see below) to ensure wireless products from different manufacturers comply with standards and are interoperable. Types of Wireless LAN The Project 802. 11 committee distinguished between two types of wireless LAN: “ad-hoc” and “infrastructred” networks.
Ad-hoc Networks This network can be set up by a number mobile users meeting in a small room. It does not need any support from a wired/wireless backbone. There are two ways to implement this network. Broadcasting/Flooding Suppose that a mobile user A wants to send data to another user B in the same area. When the packets containing the data are ready, user A broadcasts the packets. On receiving the packets, the receiver checks the identification on the packet. If that receiver was not the correct destination, then it rebroadcasts the packets.
This process is repeated until user B gets the data. Temporary Infrastructure In this method, the mobile users set up a temporary infrastructure. But this method is complicated and it introduces overheads. It is useful only when there is a small number of mobile users. What are the advantages and disadvantages of a WLAN? A wireless LAN has some specific advantages over wired LAN: • Access to the network can be from anywhere in the school within range of an access point, giving users the freedom to use ICT where and when it is needed. It is typically easier and quicker to add or move devices on the network (once in place, a wired LAN can be difficult to move and expensive to cha nge. ) Increasing the overall network coverage of the wireless LAN can often be achieved by adding further access points. • Small dynamic ad hoc networks can be created very quickly and relatively easily. • It is typically easier and quicker to provide connectivity to the network in areas where it is difficult or undesirable to lay cable or drill through walls. Instances might be:-where a school is located on more than one site or is made up of several buildings. when implementation is anticipated to be temporary or semi-permanent -when only one device is required at a remote part of a building or site -in historic buildings where traditional cabling would be difficult to install or inappropriate • Where wireless enabled laptop computers are used, any classroom in range of an access point(s) can become a ‘computer suite’, potentially increasing the use of ICT across the curriculum • While the initial investment required for wireless LAN hardware can be similar to the cost of wired LAN hardware, installation expenses can be significantly lower. Wireless provides increased flexibility for teachers. A teacher with a wireless enabled laptop can access the wireless network to show students work, share resources, obtain information from the internet from anywhere within range of an AP, without being tied to a wired PC. This flexibility is further enhanced when combined with a wireless projector. • Portability. They allow computer devices to move around the school with the pupil rather than the pupil going to a specific place to use a device.
This allows for outdoor field work and work in non-classroom spaces (common areas, library, canteen, gymnasium/sports hall, and playground). Wireless LANs also have some issues: • • • The current data rates of wireless networks means that high bandwidth activities are better done on wired networks As the number of devices using the network increases, the data transfer rate to each device will decrease accordingly. As wireless standards change, it may be necessary, or at least desirable, to upgrade to higher specifications of wireless which could mean replacing wireless equipment (wireless NICs, access points etc).
Currently, wireless standards are changing more quickly than wired standards. Security is more difficult to guarantee. Devices will only operate at a limited distance from an access point, with the distance largely determined by the standard used. Obstacles between the access point and the user, like walls, glass, water, trees and leaves can also determine the distance of operation. Poor signal reception has been experienced around reinforced concrete school buildings; these may require higher numbers of access points which in turn increases overall cost.
In practice, a wireless LAN on its own is not a complete solution and will still require a wired LAN to be in place to provide a network backbone. Data speeds drop as the user moves further away from the access point It is generally easier to make a wired network ‘future proof’ for future requirements As the number of people using wireless devices increases, there is the risk that certain radio frequencies used for wireless will become congested and prone to interference; particularly the 2. 4GHz. frequency. • • • • • • Conclusion
Wireless LAN provides high speed data communication. The minimum data rate specified by the IEEE Project 802. 11 is 1Mbps. NCR’s wave LAN operates at 2Mbps, while Motorola’s ALTAIR operates at 15Mbps. Because of their limited mobility and short transmission range, wireless LANs can be used in confined areas such as a conference room. In the U. S, almost all WLANs products use spread spectrum transmission. Therefore they transmit information on the ISM band. But with this frequency band, users can experience interference from other sources using this band.