WOLLO UNIVERSITY
KOMBOLCHA INSTITUTE OF TECHNOLOGY
SCHOOL OF ELECTRICAL AND COMPUTER ENGINEERING
Data communication and computer networks
Group 7: Wireless LANs
MOHAMED ABIB MOHAMOUD
Kombolcha, Ethiopia.
May, 2022.
Contents
1.0 OVERVIEW 3
1.1 background 4
1.2 Problem statement 4
1.3 Research Objectives 5
1.3.1 General Objectives 5
1.3.2 Specific Objectives 5
1.4 Significance of the Paper 5
1.4 Principal of wireless LAN 5
1.5 Wireless LAN Components 7
1.6 Categories for Wireless LANs and their transmission techniques 8
A. Infrared LANs 9
B. Spread Spectrum LANs 10
1.7 Wireless LAN Applications 11
1.8 Wireless LAN Requirements 12
Conclusion 13
References 14
Abstract
Wireless LANs technology are finding their way in all the verticals of life. More and more places, hospitals, airports are getting outfitted with them. Wireless medium is a shared medium, so as more and more devices demand the bandwidth, concentrating on performance becomes critical. As the wireless LANs are giving a competition to the ethernet, apart from speed it will also have to assure the Quality of Service, specially when dealing with voice, video and other real time services. These services are very sensitive to time delays, so extra care has to be taken while dealing with these.
The traditional LANs technology are based on twisted pair, coaxial cable, and optical fiber. Wireless LAN technology serves the same purpose as that of a wired or optical LAN: to convey information among the devices attached to the LAN. But with the lack of physical cabling to tie down the location of a node on a network. Thus, the network can be much more flexible, as moving a wireless node is always easier. Wireless LANs technology have a number of other advantages. It helps in case the physical makeup of a building does not allows to run wires in it. It is also more robust against disasters such as earthquake and fire. But nothing comes without a price. It has certain disadvantages.
In this papar, we will talk about the standard protocols and the enhanced protocols to provide support for such services. In this papar, we will first talk about Wireless LANs are generally categories according to the transmission technique that is used, application areas for wireless LANs Technology and wireless LAN technology requirements.
Keyboard: Wireless, LAN , technology
1.0 OVERVIEW
wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building. This gives users the ability to move around within the area and remain connected to the network. Through a gateway, a WLAN can also provide a connection to the wider Internet.
As the name suggests, a wireless LAN is one that makes use of a wireless transmission medium. Until relatively recently, wireless LANs were little used. The reasons for this included high prices, low data rates, occupational safety concerns, and licensing requirements. As these problems have been addressed, the popularity of wireless LANs has grown rapidly. In this section, we survey the key wireless LAN application areas and then look at the requirements for and advantages of wireless LANs.
1.1 background
The first IEEE working group was founded in 1991 and was set up the technical basics of the new standard. The first devices were working according to pre-802.11 standard but were not compatible to the later IEEE standard. The data rates of 2 Mbit/s were relatively modest. The technology could not be really established in the first years because the first WLAN cards were very expensive. This changed at the end of 1999 as Apple launched an iBook with an incorporated WLAN card. A base station at a reasonable price was also produced by Apple.
Norman Abramson, a professor at the University of Hawaii, developed the world's first wireless computer communication network, ALOHAnet. The system became operational in 1971 and included seven computers deployed over four islands to communicate with the central computer on the Oahu island without using phone lines.[1]
Wireless LAN hardware initially cost so much that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by technical standards, primarily the various versions of IEEE 802.11 (in products using the Wi-Fi brand name).
1.2 Problem statement
Wireless LANs technology are finding their way in all the verticals of life. More and more places, hospitals, airports are getting outfitted with them. Wireless medium is a shared medium, so as more and more devices demand the bandwidth, concentrating on performance becomes critical. As the wireless LANs are giving a competition to the ethernet, apart from speed it will also have to assure the Quality of Service, specially when dealing with voice, video and other real time services. These services are very sensitive to time delays, so extra care has to be taken while dealing with these.
Wireless LANs more robust against disasters such as earthquake and fire. It3 convey information among the devices attached to the LAN. But with the lack of physical cabling to tie down the location of a node on a network. Thus, the network can be much more flexible, as moving a wireless node is always easier. Wireless LANs technology has a number of other advantages. It helps in case the physical makeup of a building does not allows to run wires in it.
1.3 Research Objectives
1.3.1 General Objectives
The general objective is Wireless LANs technology
1.3.2 Specific Objectives
To discuss and describe wireless LANs and principle operations.
To categorize Wireless LANs generally according to the transmission technique that is used.
To urvey the key wireless LAN application areas and then look at the requirements for and advantages of wireless LANs.
1.4 Significance of the Paper
This paper will provide significant guidance to the government, lectures and students also support researchers of the subject matter as this will provide relevant literature review for students researching in this area.
Wireless LANs technology are finding their way in all the verticals of life. More and more places, hospitals, airports are getting outfitted with them. Wireless medium is a shared medium, so as more and more devices demand the bandwidth, concentrating on performance becomes critical.
1.4 Principal of wireless LAN
In short, a wireless local area network (WLAN) provides access to the Internet without the need for cables or other wires hooking directly into your computer. Instead, an access point (AP) connects other wireless devices to your local area network (LAN). Then high-frequency radio waves transmit the signal from the LAN to your mobile computer. Figure 5-1 shows you an overview of this process.
WLANs use radio, infrared and microwave transmission to transmit data from one point to another without cables. Therefore WLAN offers way to build a Local Area Network without cables. This WLAN can then be attached to an allready existing larger network, the internet for example.
A wireless LAN consists of nodes and access points. A node is a computer or a peripheral (such as a printer) that has a network adapter, in WLANs case with an antenna. Access points function as transmitters and receivers between the nodes themselves or between the nodes and another network.
1.5 Wireless LAN Components
User Devices
Users of wireless LANs operate a multitude of devices, such as PCs, laptops, and PDAs. The use of wireless LANs to network stationary PCs is beneficial because of limited needs for wiring.
Access Points
An access point contains a radio card that communicates with individual user devices on the wireless LAN, as well as a wired NIC that interfaces to a distribution system, such as Ethernet. s. Figure 2 shows an example of access-point hardware.
Routers
By definition, a router transfers packets between networks. The router chooses the next best link to send packets on to get closer to the destination. Routers use Internet Protocol (IP) packet headers and routing tables, as well as internal protocols, to determine the best path for each packet.
Repeaters
Access points, which require interconnecting cabling, generally play a dominant role for providing coverage in most wireless LAN deployments. Wireless repeaters, however, are a way to extend the range of an existing wireless LAN instead of adding more access points. There are few standalone wireless LAN repeaters on the market, but some access points have a built-in repeater mode.
Antennae
Most antennae for wireless LANs are omnidirectional and have low gain. Nearly all access points, routers, and repeaters come standard with omnidirectional antennae. Omnidirectional antennae satisfy most coverage requirements; however, consider the use of optional directive antennae to cover a long, narrow area. In some cases, the antenna is integrated within a radio card or access point and there is no choice to make. If a need exists to use a directive antenna (higher gain), ensure that the radio card or access point has an external antenna connector.
1.6 Categories for Wireless LANs and their transmission techniques
Wireless LANs are generally categorized according to the transmission technique that is used.All current wireless LAN products fall into one of the following categories:
• Infrared (IR) LANs: An individual cell of an IR LAN is limited to a single room,because infrared light does not penetrate opaque walls.
• Spread spectrum LANs: This type of LAN makes use of spread spectrum transmission technology. In most cases, these LANs operate in the ISM (industrial, scientific, and medical) microwave bands so that no Federal Communications Commission (FCC) licensing is required for their use in the United States.
A. Infrared LANs
Optical wireless communication in the infrared portion of the spectrum is commonplace in most homes, where it is used for a variety of remote control devices.
More recently, attention has turned to the use of infrared technology to construct wireless LANs. In this section, we begin with a comparison of the characteristics of infrared LANs with those of radio LANs and then look at some of the details of infrared LANs.
Strengths and Weaknesses
Infrared offers a number of significant advantages over microwave approaches.The spectrum for infrared is virtually unlimited, which presents the possibility of achieving extremely high data rates. This has two advantages: First, infrared communications can be more easily secured against eavesdropping than microwave; and second, a separate infrared installation can be operated in every room in a building without interference, enabling the construction of very large infrared LANs. Another strength of infrared is that the equipment is relatively inexpensive and simple. Infrared data transmission typically uses intensity modulation, so that IR receivers need to detect only the amplitude of optical signals, whereas most microwave receivers must detect frequency or phase. The infrared medium also exhibits some drawbacks. Many indoor environments experience rather intense infrared background radiation, from sunlight and indoor lighting. This ambient radiation appears as noise in an infrared receiver, requiring the use of transmitters of higher power than would otherwise be required and also limiting the range. However, increases in transmitter power are limited by concerns of eye safety and excessive power consumption.
Transmission Techniques
Three alternative transmission techniques are in common use for IR data transmission: the transmitted signal can be focused and aimed (as in a remote TV control); it can be radiated omnidirectionally; or it can be reflected from a light-colored ceiling.
Directed-beam IR can be used to create point-to-point links. In this mode, the range depends on the emitted power and on the degree of focusing.A focused IR data link can have a range of kilometers.Such ranges are not needed for constructing indoor wireless LANs. However, an IR link can be used for cross-building interconnect between bridges or routers located in buildings within a line of sight of each other. One indoor use of point-to-point IR links is to set up a ring LAN.A set of IR transceivers can be positioned so that data circulate around them in a ring configuration. Each transceiver supports a workstation or a hub of stations, with the hub providing a bridging function.
An omnidirectional configuration involves a single base station that is within line of sight of all other stations on the LAN.Typically,this station is mounted on the ceiling. The base station acts as a multiport repeater.The ceiling transmitter broadcasts an omnidirectional signal that can be received by all of the other IR transceivers in the area. These other transceivers transmit a directional beam aimed at the ceiling base unit.
In a diffused configuration, all of the IR transmitters are focused and aimed at a point on a diffusely reflecting ceiling. IR radiation striking the ceiling is reradiated omnidirectionally and picked up by all of the receivers in the area.
B. Spread Spectrum LANs
Currently, the most popular type of wireless LAN uses spread spectrum techniques. Configuration Except for quite small offices, a spread spectrum wireless LAN makes use of a multiple-cell arrangement, as was illustrated in Figure 17.2.Adjacent cells make use of different center frequencies within the same band to avoid interference. Within a given cell, the topology can be either hub or peer to peer. The hub topology is indicated in Figure 17.2. In a hub topology, the hub is typically mounted on the ceiling and connected to a backbone wired LAN to provide connectivity to stations attached to the wired LAN and to stations that are part of wireless LANs in other cells. The hub may also control access, as in the IEEE 802.11 point coordination function, described subsequently.The hub may also control access by acting as a multiport repeater with similar functionality to Ethernet multiport repeaters. In this case, all stations in the cell transmit only to the hub and receive only from the hub. Alternatively, and regardless of access control mechanism, each station may broadcast using an omnidirectional antenna so that all other stations in the cell may receive; this corresponds to a logical bus configuration. One other potential function of a hub is automatic handoff of mobile stations. At any time, a number of stations are dynamically assigned to a given hub based on proximity.When the hub senses a weakening signal, it can automatically hand off to the nearest adjacent hub. A peer-to-peer topology is one in which there is no hub.
Transmission Issues A desirable,though not necessary,characteristic of a wireless LAN is that it be usable without having to go through a licensing procedure. The licensing regulations differ from one country to another,which complicates this objective. Within the United States, the FCC has authorized two unlicensed applications within the ISM band: spread spectrum systems.
1.7 Wireless LAN Applications
[PAHL95] lists four application areas for wireless LANs: LAN extension, crossbuilding interconnect, nomadic access, and ad hoc networks. Let us consider each of these in turn.
LAN Extension
Typically, a wireless LAN will be linked into a wired LAN on the same premises.Thus, this application area is referred to as LAN extension. Figure 17.1 indicates a simple wireless LAN configuration that is typical of many environments. There is a backbone wired LAN, such as Ethernet, that supports servers, workstations, and one or more bridges or routers to link with other networks.on. The configuration of Figure 17.1 can be referred to as a single-cell wireless LAN; all of the wireless end systems are within range of a single control module. Another common configuration,suggested by Figure 17.2,is a multiple-cell wireless LAN. In this case, there are multiple control modules interconnected by a wired LAN. Each control module supports a number of wireless end systems within its transmission range. For example, with an infrared LAN, transmission is limited to a single room; therefore, one cell is needed for each room in an office building that requires wireless support.
Cross-Building Interconnect
Another use of wireless LAN technology is to connect LANs in nearby buildings, be they wired or wireless LANs. In this case, a point-to-point wireless link is used between two buildings.The devices so connected are typically bridges or routers. This single point-to-point link is not a LAN per se, but it is usual to include this application under the heading of wireless LAN.
Nomadic Access
Nomadic access provides a wireless link between a LAN hub and a mobile data terminal equipped with an antenna, such as a laptop computer or notepad computer. One example of the utility of such a connection is to enable an employee returning from a trip to transfer data from a personal portable computer to a server in the office. Nomadic access is also useful in an extended environment such as a campus or a business operating out of a cluster of buildings. In both ofthese cases, users may move around with their portable computers and may wish access to the servers on a wired LAN from various locations.
Ad Hoc Networking
An ad hoc network is a peer-to-peer network (no centralized server) set up temporarily to meet some immediate need. For example, a group of employees, each with a laptop or palmtop computer, may convene in a conference room for a business or classroom meeting.The employees link their computers in a temporary network just for the duration of the meeting.
Figure Peer-to-Peer or ad hoc wireless LAN
1.8 Wireless LAN Requirements
A wireless LAN must meet the same sort of requirements typical of any LAN. In addition, there are a number of requirements specific to the wireless LAN environment. The following are among the most important requirements for wireless LANs:
• Throughput: The medium access control protocol should make as efficient use as possible of the wireless medium to maximize capacity.
• Number of nodes: Wireless LANs may need to support hundreds of nodes across multiple cells.
• Connection to backbone LAN: In most cases,interconnection with stations on a wired backbone LAN is required. For infrastructure wireless LANs, this is easily accomplished through the use of control modules that connect to both types of LANs.
• Transmission robustness and security: Unless properly designed, a wireless LAN may be especially vulnerable to interference and eavesdropping.
• Collocated network operation: As wireless LANs become more popular, it is quite likely for two or more wireless LANs to operate in the same area or in some area where interference between the LANs is possible.
• License-free operation: Users would prefer to buy and operate wireless LAN products without having to secure a license for the frequency band used by the LAN.
• Handoff/roaming: The MAC protocol used in the wireless LAN should enable mobile stations to move from one cell to another.
• Dynamic configuration: The MAC addressing and network management aspects of the LAN should permit dynamic and automated addition, deletion, and relocation of end systems without disruption to other users.
Conclusion
Wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building. This gives users the ability to move around within the area and remain connected to the network. Through a gateway, a WLAN can also provide a connection to the wider Internet.
WLANs use radio, infrared and microwave transmission to transmit data from one point to another without cables. A wireless LAN consists of nodes and access points. A node is a computer or a peripheral (such as a printer) that has a network adapter, in WLANs case with an antenna. Wireless LANs are generally categorized according to the transmission technique that is used.All current wireless LAN products fall into one of the following categories: Infrared (IR) LANs: An individual cell of an IR LAN is limited to a single room,because infrared light does not penetrate opaque walls. Spread spectrum LANs: This type of LAN makes use of spread spectrum transmission technology.
Finally, lists four application areas for wireless LANs: LAN extension, crossbuilding interconnect, nomadic access, and ad hoc networks. there are a number of requirements specific to the wireless LAN environment. The following are among the most important requirements for wireless LANs they are Throughput, Number of nodes, Connection to backbone LAN, Transmission robustness and security ,Collocated network operation, License-free operation, Handoff/roaming and Dynamic configuration
References
DATA COMMUNICATIONS AND NETWORKING Fourth Edition BehrouzA. Forouzan DeAnzaCollege with Sophia Chung Fegan Mc Grew Hill HigherEducation
(1) "History of Wireless". Johns Hopkins Bloomberg School of Public Health. Archived from the original on 2007-02-10. Retrieved 2007-02-17.
