The Look At Wireless Lans Computer Science Essay

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Wireless technology has helped to simplify networking by enabling multiple computer users to simultaneously share resources in a home or business without additional or intrusive wiring. These resources might include a broadband Internet connection, network printers, data files, and even streaming audio have changed their habits from using single, and video. This kind of resource sharing has become more prevalent as computer users stand-alone computers to working on networks with multiple computers, each with potentially different operating systems and varying peripheral hardware. U.S. Robotics wireless networking products offer a variety of solutions to seamlessly integrate computers, peripherals, and data. Wireless networking technology has developed like most new technologies; business needs drive technology developments, which in turn drive new business needs, which in turn drive new technology developments. To keep this cycle from spinning out of control, several organizations have stepped forward to establish WLAN standards and certifications.

Wireless LANs are a boon for organizations that don't have time to setup wired LANs, make

networked- temporary offices a reality and remove the wire work that goes on in setting LANs. They are reported to reduce setting up costs by 15%. Wireless LANs (WLANs) are quickly gaining popularity due to their ease of installation and higher employee mobility. Together with personal digital assistants (PDA) and other mobility devices, they go on to improve the quality of life. Even at home, people have changed the way they live and learn. The Internet has become a standard in homes, right along with TV and phone service. Even the method of accessing the Internet has quickly moved from temporary modem dialup service to dedicated digital subscriber line (DSL) or cable service, which is always connected and is faster than dialup. In 2005, users of PCs purchased more Wi-Fi-enabled mobile laptops (i.e., products that are based on the IEEE 802.11 standards) than fixed-location desktops.

The most tangible benefit of wireless is the cost reduction. First, with a wireless infrastructure already in place, savings are realized when moving a person from one location in an office to another, or when moving from temporary locations or project sites. The second situation to consider is when a company moves into a new building that does not have a wired infrastructure. In this case, the savings from wireless is even more noticeable because running cables through walls, ceilings, and floors is a labor-intensive process.

2.0 Differences between WLANs and LANs

Although WLANs and LANs both provide connectivity between the end users, they have some key differences that include both physical and logical differences between the topologies. In WLANs, radio frequencies are used as the physical layer of the network. Differences also exist in the way the frame is formatted and in the transmission methods, detailed as follows:

1) WLANs use carrier sense multiple access with collision avoidance (CSMA/CA) instead of carrier sense multiple access collision detect (CSMA/CD), which is used by Ethernet LANs. Collision detection is not possible in WLANs, because a sending station cannot receive at the same time that it transmits and, therefore, cannot detect a collision. Instead, WLANs use the Ready To Send (RTS) and Clear To Send (CTS) protocols to avoid collisions.

2) WLANs use a different frame format than wired Ethernet LANs use. WLANs require additional information in the Layer 2 header of the frame. Radio waves cause problems not found in LANs, such as the following:

a) Connectivity issues occur because of coverage problems, RF transmission, multipath distortion, and interference from other wireless services or other WLANs.

b) Privacy issues occur because radio frequencies can reach outside the facility. In WLANs, mobile clients connect to the network through an access point, which is the equivalent of a wired Ethernet hub.

These connections are characterized as follows:

There is no physical connection to the network.

(ii) The mobile devices are often battery-powered, as opposed to plugged-in LAN devices. WLANs must meet country-specific RF regulations. The aim of standardization is to make WLANs available worldwide. Because WLANs use radio frequencies, they must follow country-specific regulations of RF power and frequencies. This requirement does not apply to wired LANs.

3.0 Different WLAN Technologies

As various wireless networking technologies have advanced over time, several WLAN technologies have emerged, including: narrowband, spread spectrum, frequency hopping spread spectrum, and direct sequence spread spectrum.

Narrowband

As the name suggests, narrowband technology uses a specific radio frequency (in the range of 50 cps [bytes per sec] to 64 Kbps [kilobytes per sec]) for data transmission.

Spread Spectrum

Originally developed for military use, spread spectrum technology allows for greater bandwidth by continually altering the frequency of the transmitted signal, thus spreading the transmission across multiple frequencies. Spread spectrum uses more bandwidth than narrowband, but the transmission is more secure, reliable, and easier to detect.

Frequency Hopping Spread Spectrum (FHSS)

Frequency hopping spread spectrum (FHSS) technology synchronizes the changing frequency of both the transmitter and receiver (using a narrowband carrier) to, in effect, produce a single transmission signal. This frequency "hopping" can occur as often as several times a second; it is constantly changing from one frequency to another, transmitting data for a certain period of time before changing frequency again. Like spread spectrum technology, FHSS technology consumes additional bandwidth, however, this is over the course of multiple carrier frequencies.

Direct Sequence Spread Spectrum (DSSS)

Direct sequence spread spectrum (DSSS) technology breaks down the transmitted stream of data into small pieces across a frequency channel. A redundant bit pattern (known as a chipping code) is generated for each bit transmitted. Generally, the longer the chipping code, the more likely it is that the original transmitted data will be properly received. DSSS technology uses more bandwidth than FHSS, but DSSS is considered more reliable and resists interference. Because of the chipping code, data can still be recovered without retransmission of the signal, even in the case of damaged data bits. U.S. Robotics wireless networking products utilize DSSS technology.

4.0 Types of WLAN

The 802.11 specification defines two types of operational modes: ad hoc (peer-to-peer) mode and infrastructure mode. In ad hoc mode, the wireless network is relatively simple and consists of 802.11 network interface cards (NICs). The networked computers communicate directly with one another without the use of an access point. In infrastructure mode, the wireless network is composed of a wireless access point(s) and 802.11 network interface cards (NICs). The access point acts as a base station in an 802.11 network and all communications from all of the wireless clients go through the access point. The access point also provides for increased wireless range, growth of the number of wireless users, and additional network security

Ad Hoc Mode

In ad hoc mode, also known as Independent Basic Service Set (IBSS) or peer-to-peer mode, all of the computers and workstations connected with a wireless NIC (network interface card) can communicate with each other via radio waves without an access point. Each computer in the LAN is configured at the same radio channel to enable peer-to-peer networking. Ad hoc mode is convenient for quickly setting up a wireless network in a meeting room, hotel conference center, or anywhere else sufficient wired infrastructure does not exist.

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Figure 1- Ad hoc mode

Infrastructure Mode

Infrastructure WLAN consists of wireless stations and access points. Access Points combined with a distribution system (such as Ethernet) support the creation of multiple radio cells that enable roaming throughout a facility. The access points not only provide communications with the wired network but also mediate wireless network traffic in the immediate neighborhood. This network configuration satisfies the need of large-scale networks arbitrary coverage size and complexities.

There are two infrastructure modes:

Basic Service Set (BSS): The communication devices that create a BSS are mobile clients using a single access point to connect to each other or to wire network resources. The Basic Service Set Identifier (BSSID) is the Layer 2 MAC address of the BSS access point's radio card. While the BSS is the single building block for wireless topology and the BSS access point is uniquely identified through a BSSID, the wireless network itself is advertised through a SSID, which announces the availability of the wireless network to mobile clients. The SSID is a wireless network name that is user configurable and can be made up of as many as 32 case-sensitive characters.

Extended Services Set (ESS): The wireless topology is extended with two or more BSSs connected by a distribution system (DS) or a wired infrastructure. An ESS generally includes a common SSID to allow roaming from access point to access point without requiring client configuration.

Figure 2: Infrastructure mode

4.1 WLAN standards

Several standards for WLAN hardware exist:

WLAN standard

Pros

Cons

802.11a

Faster data transfer rates (up to 54Mbps)

Supports more simultaneous connections

Less susceptible to interference

Short range (60-100 feet)

Less able to penetrate physical barriers

802.11b

Better at penetrating physical barriers

Longest range (70-150 feet)

Hardware is usually less expensive

Slower data transfer rates (up to 11Mbps)

Doesn't support as many simultaneous connections

More susceptible to interference

802.11g

Faster data transfer rates (up to 54Mbps)

Better range than 802.11b (65-120 feet)

More susceptible to interference

802.11n

The 802.11n standard was recently ratified by the Institute of Electrical and Electronics Engineers (IEEE), as compared to the previous three standards. Though specifications may change, it is expected to allow data transfer rates up to 600Mbps, and may offer larger ranges.

5.0 Advantages and Disadvantages of WLANs

WLANs have advantages and disadvantages when compared with wired LANs. A WLAN will make it simple to add or move workstations and to install access points to provide connectivity in areas where it is difficult to lay cable. Temporary or semi permanent buildings that are in range of an access point can be wirelessly connected to a LAN to give these buildings connectivity. Where computer labs are used in schools, the computers (laptops) could be put on a mobile cart and wheeled from classroom to classroom, provided they are in range of access points. Wired network points would be needed for each of the access points. A WLAN has some specific advantages:

It is easier to add or move workstations.

It is easier to provide connectivity in areas where it is difficult to lay cable.

Installation is fast and easy, and it can eliminate the need to pull cable through walls and ceilings.

Access to the network can be from anywhere within range of an access point.

Portable or semi permanent buildings can be connected using a WLAN.

Although the initial investment required for WLAN hardware can be similar to the cost of wired LAN hardware, installation expenses can be significantly lower.

When a facility is located on more than one site (such as on two sides of a road), a directional antenna can be used to avoid digging trenches under roads to connect the sites.

In historic buildings where traditional cabling would compromise the façade, a WLAN can avoid the need to drill holes in walls.

Long-term cost benefits can be found in dynamic environments requiring frequent moves and changes.

Moreover, WLANs also have some disadvantages:

As the number of computers using the network increases, the data transfer rate to each computer will decrease accordingly.

As standards change, it may be necessary to replace wireless cards and/or access points.

Lower wireless bandwidth means some applications such as video streaming will be more effective on a wired LAN.

Security is more difficult to guarantee and requires configuration.

Devices will only operate at a limited distance from an access point, with the distance determined by the standard used and buildings and other obstacles between the access point and the user.

A wired LAN is most likely to be required to provide a backbone to the WLAN; a WLAN should be a supplement to a wired LAN and not a complete solution.

Long-term cost benefits are harder to achieve in static environments that require few moves and changes.

6.0 What are Benefits of a Wireless Network?

Wireless LANs offer the following productivity, convenience, and cost advantages over wired networks:

Mobility: Wireless LAN systems can provide LAN users with access to real-time information anywhere in their organization. This mobility supports productivity and service opportunities not possible with wired networks.

There are now thousands of universities, hotels and public places with public wireless connection. These free you from having to be at home or at work to access the Internet.

Installation Speed and Simplicity: Installing a wireless LAN system can be fast and easy and can eliminate the need to pull cable through walls and ceilings.

Reduced Cost-of-Ownership: While the initial investment required for wireless LAN hardware can be higher than the cost of wired LAN hardware, overall installation expenses and life-cycle costs can be significantly lower. Long-term cost benefits are greatest in dynamic environments requiring frequent moves and changes.

Scalability: Wireless LAN systems can be configured in a variety of topologies to meet the needs of specific applications and installations. Configurations are easily changed and range from peer-to-peer networks suitable for a small number of users to full infrastructure networks of thousands of users that enable roaming over a broad area.

7.0 Technology of WLAN

WLAN links two or more devices together using some wireless distribution method and usually providing a connection through an access point (device that links a wireless network to a wired LAN) to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network. WLAN uses radio signals instead of traditional network cabling. Using radio frequency (RF) technology, wireless LANs transmit and receive data over the air, thereby minimizing the need for wired connections. Most modern WLANs are based on IEEE (Institute of Electrical and Electronic Engineers) 802.11 standards, marketed under the Wi-Fi brand name which is the industry name for wireless LAN communication technology.

Examples 1: For WLANs that connect to the Internet, Wireless Application Protocol (WAP) technology allows Web content to be more easily downloaded to a WLAN and rendered on wireless clients like cell phones and PDAs. (WLAN)

C:\Users\vandana\Desktop\l.gif (wireless networking)

Figure 3: WLAN networking

Example 2: WLANs are most often used on mobile systems as an extension to a wired LAN, as illustrated in Figure 4.

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Figure 4: Example of a standard wireless LAN topology

8.0 Wireless LAN applications in business fields

In just the past few years, wireless LANs have come to occupy a significant niche in the local area network market. Increasingly, organizations are finding that wireless LANs are an indispensable adjunct to traditional wired LANs, to satisfy requirements for mobility, relocation, ad hoc networking, and coverage of locations difficult to wire.

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.

Wireless LANs Applications

Early wireless LAN products, introduced in the late 1980s, were marketed as substitutes for traditional wired LANs. A wireless LAN saves the cost of the installation of LAN cabling and eases the task of relocation and other modifications to network structure. In a number of environments, there is a role for the wireless LAN as an alternative to a wired LAN. Examples include buildings with large open areas, such as manufacturing plants, stock exchange trading floors, and warehouses; historical buildings with insufficient twisted pair wiring or where drilling holes for new wiring is prohibited; and small offices where installation and maintenance of wired LANs is not economical. In all of these cases, a wireless LAN provides an effective and more attractive alternative.

In most of these cases, an organization will also have a wired LAN to support servers and some stationary workstations. For example, a manufacturing facility typically has an office area that's separate from the factory floor but that must be linked to it for networking purposes. Therefore, typically, a wireless LAN will be linked into a wired LAN on the same premises. Thus, this application area is referred to as a LAN extension.

Figure 5 shows a simple wireless LAN configuration that's typical of many environments. A backbone wired LAN, such as Ethernet, supports servers, workstations, and one or more bridges or routers to link with other networks. In addition, a control module (CM) acts as an interface to a wireless LAN. The control module includes either bridge or router functionality to link the wireless LAN to the backbone. It also includes some sort of access-control logic, such as a polling or token-passing scheme, to regulate the access from the end systems. Notice that some of the end systems are standalone devices, such as a workstation or a server. Hubs or other user modules (UMs) that control a number of stations off a wired LAN may also be part of the wireless LAN configuration.

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Figure 5: Single-cell wireless LAN configuration.

The configuration of Figure 5 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 is a multiple-cell wireless LAN. In this case, multiple control modules are 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.

Another use of wireless LAN technology is to support nomadic access by providing 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 of these cases, users may move around with their portable computers and may want access to the servers on a wired LAN from various locations.

Another example of a wireless LAN application is an ad hoc network, which 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 (Stallings, 2001).

Moreover, the prior implementation of wireless LAN would be because it is cost effective compare to wired LAN. But most businesses apply the wireless LAN as an alternative solution, in other words most businesses do work on a cabling LAN system and keep the wireless LAN as an alternative ad hoc network.

However, the wireless LAN are mostly applied in building with large open areas such as the manufacturing plant, stock exchange trading floor or warehouses. Hence the following are the prior applications of the wireless LAN:

Communication- indeed, employees and employers can rather communicate via laptops, mobiles or palm computers hands free without any cables connected. So this can fasten the communication mode in emergency problem or to solve unstructured problems,

Conferencing- in large businesses, sometimes managers in the same building do not have to move on to the conference room due to lateness if ever for an important meeting,

Ad hoc network- many business use the wireless LAN as an important alternative to solve specific problems in the organization,

Wireless LAN is very useful for historical building with insufficient twisted pair cabling or where drilling of new holes are prohibited,

Wireless LAN is also appropriate for small businesses or offices where the installation and maintenance of wired LAN is not economical.

There are some more examples of business fields whereby WLAN can be implemented:

Inventory Control

Many businesses profit from using wireless LANs when managing their manufacturing processes. This lowers operating costs. Because the connections between the manufacturing equipment and main control systems are wireless, the company can reconfigure the assembly process at anytime from anywhere, saving time and money.

Through the use of a wireless LAN, a company can track and update inventory in real time, enabling efficiency and accuracy to increase dramatically. In a retail environment, as soon as a clerk purchases or stocks a product, a wireless management solution can update the inventory. In a manufacturing setting, the company can keep the raw materials and finished product statistics up-to-date. Employees equipped with wireless-enabled bar code scanners can check or change product prices or check the number in stock.

The improved accuracy provided by using a wireless LAN to manage inventory creates a chain reaction of benefits. Because the clerks enter the information directly into the main computer through handheld scanners, there is no paperwork to deal with. This significantly reduces human error when entering data, which leads to accurate financial records. This is important to manufacturing companies because accurate financial records ensure correct taxes are paid and fines (and possible law suits) are kept to a minimum.

Health Care

More and more hospitals are deploying wireless networks to improve operational efficiency and convenience. In most cases, hospitals deploy wireless LANs in high patient-traffic areas including emergency rooms, critical care wards, nursing stations, as well as in doctor's offices and patient waiting areas. Hospital staff can use mobile computer devices to increase efficiency and accuracy when caring for patients.

Health-care centers must maintain accurate records to ensure quality patient care. A simple mistake can cost someone's life. As a result, doctors and nurses must carefully record test results, physical data, pharmaceutical orders, and surgical procedures. This paperwork often overwhelms health-care staff, taking 50-70 percent of their time. The use of a mobile data collection device that wirelessly transmits the data to a centralized database significantly increases accuracy and raises the visibility of the data to those who need the information.

Doctors and nurses are also extremely mobile, going from room to room caring for patients. The use of electronic patient records, with the ability to input, view, and update patient data from anywhere in the hospital, increases the accuracy and speed of health care. This improvement is possible by providing each nurse and doctor with a wireless pen-based computer, such as a tablet or PDA, coupled with a wireless network to databases that store critical medical information about the patients.

A doctor caring for someone in the hospital, for example, can place an order for a blood test by keying the request into a handheld computer. The laboratory receives the order electronically and dispatches a lab technician to draw blood from the patient. The laboratory runs the tests requested by the doctor and enter the results into the patient's electronic medical record. The doctor can then check the results via the handheld appliance from anywhere in the hospital.

Another hospital application is tracking of pharmaceuticals. The use of mobile handheld bar code printing and scanning devices dramatically increases the efficiency and accuracy of all drug transactions, such as receiving, picking, dispensing, inventory, and expiration dates. Most importantly, however, it ensures that hospital staff can administer the right drug to the right person in a timely fashion.

Education

Many colleges and elementary schools are finding beneficial reasons to install wireless LANs, mostly to provide mobile network applications to their students. In fact, schools have begun using the existence of wireless LAN access as a competitive advantage. These schools are targeting the growing number of students with laptops and expectations of accessing the Internet and school resources from anywhere on campus, such as classrooms, libraries, quads, and dormitories. Students are able to readily check e-mail, surf the Web, access specialized school applications, check grades, and view transcripts. As a result, students make better use of their time.

It's expensive to establish and maintain computer labs for students to utilize for accessing the Internet and completing assignments. Students must often wait in line for using a computer in a lab, which cuts into other activities. A wireless LAN, however, gives students access to needed resources using their own laptop from anywhere on campus at any time, even after the traditional computer lab closes. This more evenly distributes network access to all students, enhancing student efficiency. Of course, the school can also save the costs of running the computer lab.

Real Estate

Real estate salespeople perform a great deal of their work away from the office, usually talking with customers at the property being sold or rented. Before leaving the office, salespeople normally identify a few sites to show a customer, print the Multiple Listing Service (MLS) information that describes the property, and then drive to each location with the potential buyer. If the customer is unhappy with that round of sites, the real estate agent must drive back to the office and run more listings. Even if the customer decides to purchase the property, they must both go back to the real estate office to finish paperwork that completes the sale.

Wireless networking makes the sale of real estate much more efficient. The real estate agent can use a computer away from the office to access a wireless MLS record. An agent can also use a portable computer and printer to produce contracts and loan applications for signing at the point of sale.

Utilities

Utility companies operate and maintain a highly distributed system that delivers power and natural gas to industries and residences. Utility companies must continually monitor the operation of the electrical distribution system, gas lines, and water consumption, and must check usage meters at least monthly to calculate bills. Traditionally, this means a person must travel from location to location, visit residences and company facilities, record information, and then enter the data at a service or computing center.

Today, utility companies employ wireless WANs to support the automation of meter reading and system monitoring. Instead of a meter reader recording the data on a sheet of paper to later enter in a computer for processing, the meter can periodically transmit the data through the wireless WAN to the utility company. This saves time and reduces overhead costs by eliminating the need for human meter readers.

Field Service

Field service personnel spend most of their time on the road installing and maintaining systems or inspecting facilities under construction. To complete their jobs, these individuals need access to product documentation and procedures. Traditionally, field service employees have had to carry several binders of documentation with them to sites that often lacked a phone and even electricity.

In some cases, the field person might not be able to take all the documents to a job site, causing delay while obtaining the proper information. On long trips, this information might also become outdated. Updates require delivery that might take days to reach the person in the field. Wireless WAN access to documentation can definitely enhance field service. A field service employee, for example, can carry a portable computer that connects to the office LAN that contains accurate documentation of all applicable information.

Field Sales

Sales professionals are always on the move and meeting with customers. While on site with a customer, a salesperson needs access to vast information that describes products and services. Salespeople must also place orders, provide status-such as meeting schedules-to the home office, and maintain inventories.

With wireless access to the main office network, a salesperson can view centralized contact information, retrieve product information, produce proposals, create contracts, and stay in touch with office staff and other salespeople. This contact permits salespeople to complete the entire sale directly from the customer site, which increases the potential for a successful sale and shortens the sales cycle.

Vending

Beverage and snack companies place vending machines in hotels, airports, and office buildings to enhance the sales of their products. Vending machines eliminate the need for a human salesclerk. These companies, however, must send employees around to stock the machines periodically. In some cases, machines might become empty before the restocking occurs because the company has no way of knowing when the machine runs out of a particular product.

A wireless WAN can support the monitoring of stock levels by transporting applicable data from each of the vending machines to a central database that can be easily viewed by company personnel from a single location. Such monitoring allows companies to be proactive in stocking their machines, because they always know the stock levels at each machine. This enables the vending company to schedule appropriate stops for people who refill the machines.

9.0 Range of coverage and cost aspects of WLAN

9.1 Range of coverage

The distance over which RF (radio frequency) and IR (infrared) waves can communicate depends on product design (including transmitted power and receiver design) and the propagation path, especially in indoor environments. Interactions with typical building objects, such as walls, metal, and even people, can affect the propagation of energy, and thus also the range and coverage of the system. IR is blocked by solid objects, which provides additional limitations. Most wireless LAN systems use RF, because radio waves can penetrate many indoor walls and surfaces. The range of a typical WLAN node is about 100 m. Coverage can be extended, and true freedom of mobility achieved via roaming. This means using access points to cover an area in such a way that their coverages overlap each other.

Thereby the user can wander around and move from the coverage area of one access point to another without even knowing he has, and at the same time seamlessly maintain the connection between his node and an access point.

9.2 Cost aspects

Finally, the cost of installing and maintaining a WLAN is on average lower than the cost of installing and maintaining a traditional wired LAN, for two reasons. First, WLAN eliminates the direct costs of cabling and the labor associated with installing and repairing it. Second, because WLANs simplify moving, additions, and changes, the indirect costs of user downtime and administrative overhead are reduced.

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Figure 6: Traditional wired LAN and WLAN

A diagram has been illustrated below showing the in-door and out-door solutions:

Home Users

Edimax's wireless devices have been taken as example which are an ideal, no-hassle, no-wires alternative for networking computers and Internet appliances in your home. They install easily, expand quickly and reduce the cost of setting up a wired network. With a small investment, you can enjoy the same advantages of a wireless LAN in your home that small businesses now a day rely on for their commerce.

Small Business

Using Edimax's devices to setup a wireless network can save small businesses time and money. Edimax's wireless equipments are easy to install, can augment your existing network and can reduce the costs, planning time and implementation time in expanding your wired network. With Edimax's wireless devices, small businesses can take advantage of a cost-effective and flexible network infrastructure solution.http://www.edimax.at/images/meuser.gif

IN-DOOR SOLUTIONSEnterprise

Edimax's wireless devices allow enterprise networks to keep workers connected to the network, giving them real-time access to information whether they are at or away from their desks. Mobile workers become more productive because they can access information when they need it, whether they are using the Internet, doing email or accessing a corporate database. 

With Edimax's wireless devices, IT professionals can easily solve end-user's requests by providing immediate connectivity without having to install wiring as workers move within buildings or from building to building. Edimax's wireless devices make dynamic moves, additions and changes within your network extremely easy to implement.http://www.edimax.at/images/app-soffice.gifhttp://www.edimax.at/images/app-inter.gif

Out Door Solution :  Point to multi point/ Point to point /

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LAN-to- LAN bridging

Edimax's wireless devices is an easy and cost effective way to connect separate networks in different locations. Point-to-point and point-to-multi-point connections allow users in different locations the opportunity to access the Internet, share files, and access network resources without wires. Building-to-Building or LAN-to-LAN wireless networks are being used by many industries serving diverse applications such as: Telco and Internet Service Providers ,Corporate Enterprise ,Education, Healthcare and Travelhttp://www.edimax.at/images/app-p2p.gif

10.0 Security issues and challenges

10.1 Wireless LAN Security Threats

With the lower costs of IEEE 802.11b/g systems, it is inevitable that hackers have many more unsecured WLANs from which to choose. Incidents have been reported of people using numerous open source applications to collect and exploit vulnerabilities in the IEEE 802.11 standard security mechanism, Wired Equivalent Privacy (WEP). Wireless sniffers enable network engineers to passively capture data packets so that they can be examined to correct system problems. These same sniffers can be used by hackers to exploit known security weaknesses.

10.2 Mitigating Security Threats

To secure a WLAN, the following components are required:

1) Authentication

802.11 specify two authentication mechanisms:

a) Open system authentication

b) Shared key authentication

• Open system authentication

A client needs an SSID (Service Set Identifier) for successful Association. Any new client that comes in an EBSS area is provided with an SSID. This is equivalent to no security.

Fig 7: Open System Authentication

• Shared system authentication

The client cannot authenticate himself if he doesn't have the WEP shared secret key. WEP protocol is used for encryption.

Fig 7.1: Shared key authentication

2) Association

An SSID is used to differentiate two networks logically. To successfully associate to a WS, one

must have the SSID of the other WS. This was not intended to be a security feature, and in

fact SSID is sent in open in the beacon frame of the AP (access point).

3) Encryption and Decryption-The WEP Protocol

The WLAN administrator has an option (if the administrator decides to send the packets

unencrypted) to make all the communication over the air encrypted, i.e. every frame that is

below the Ethernet Header is encrypted using the WEP protocol. The WEP protocol has three

components:

• A shared secret key, k (40bit /104 bit): The fact that the secret key is shared helps

reduce the load on AP, while simultaneously assuming that whoever is given the secret

key is a trusted person. This shared key is never sent over the air.802.11 doesn't

discuss the deployment of this key onto Work Stations. It has to be installed manually

at each WS/AP. Most APs can handle up to four shared secret keys.

• Initialization vector, IV (24 bit): IV is a per-packet number that is sent in clear over the

air. This number is most effective if generated randomly, because it is used as one of

the inputs to the RC4 algorithm. 802.11 don't specify generation of IV. In fact, many

cards generate IVs in linear fashion, i.e., 1,2,3…

• RC4 algorithm, RC4 (IV, k): This algorithm is used to generate a key stream K, length

equal to that of the message to be transmitted by the data-link layer. It takes the IV

and k as inputs

Fig 7.2: Encryption & Decryption on WEP

10.3 Attacks on WEP

WEP is considered to be very vulnerable to attackers. Any attacker sitting in the parking lot of

a building can attack the building's WLAN security. This is unlike the wired case whereby the

attacker needs a physical access to the wires. The following known attacks have been

employed on WEP.

Type of Attacks

The following known attacks are known to be effective:

1) Passive Attacks

Passive threats do not require an adversary to do anything other than sit back and take

advantage of what is already in place and being used.

Passive threats include but are not limited to exploits such as the following:

- tapping of communications links (wire line, RF);

- exploitation of software vulnerabilities; or

- traffic analysis.

An example of a passive threat would be the interception of data being sent via radio

frequencies. An adversary would point an antenna and tune a receiver to intercept the data.

Rather than trying to break in or cause an upset, this type of passive threat is performed

unbeknownst to the entity under attack. Encrypting the data over the radio link would

effectively eliminate this threat.

A passive threat may also take advantage of a software vulnerability such as when a worm

infects a system and migrates to other systems, all the while disclosing information to

whoever cares to listen. Protecting the systems, as discussed in the active threat section,

using anti-virus software, firewalls, intrusion detection/prevention systems, etc., will help

counter this threat.

Another type of passive attack would be traffic analysis: the ability to determine, in loose

terms, what is going on between communicating entities simply by virtue of how and when

they are communicating without necessarily being able to see or understand the data being

communicated. This threat can be countered by totally obscuring the link communications

either by what is called 'full-period traffic security', or by frequency hopping and spread

spectrum technologies. In full-period traffic security, the link would always appear busy

whether or not 'real' traffic was being sent. In this way, a passive adversary would not be

able to determine when 'real' data was being sent since it would appear that data was being

sent 100% of the time. Frequency hopping and spread spectrum attempt to hide the

transmission by jumping around the frequency spectrum resulting in the passive attacker's

not being able to lock onto the data without the hopping or spreading settings.

2) Active attacks

An active threat requires an adversary to initiate a sequence of events to attempt to exploit a

vulnerability. During an active attack, the adversary attempts to probe the system, or cause

mischief or upsets in order to compromise the system(s).

Active threats include but are not limited to exploits such as the following:

- communications system jamming (resulting in denial of service);

- attempting access to an otherwise access-controlled system resulting in unauthorized

access;

- replay of recorded authentic communications traffic at a later time with the hope that

the authorized communications will provide data;

- masquerading as an authorized entity in order to gain access;

- the exploitation of software vulnerabilities (bugs);

- unauthorized modification or corruption of data; and

- malicious software such as a virus, worm, Distributed Denial-Of-Service (DDOS)

agent, or Trojan horse.

Active threats may be carried out against both spacecraft and ground systems. In the case of

ground systems, it is imperative that they are operated as controlled networks. That is, in

general they should not be connected to open, external networks such as the Internet without

any safeguard. If a connection across an open network is required, it should be accomplished

through the use of formal risk assessment and technical security controls (e.g., secure Virtual

Private Network (VPN), firewalls, anti-virus, anti-spyware). Only personnel who have been

screened (e.g., national agency checks) should be provided access to the closed ground

system network.

As with other networks, the active attacks are riskier but provide greater powers to the

Passive Attacks

No risk involved Riskier

No need to be the part of networks, because the WLAN cards support monitor mode, whereby one can listen to the communication without being a part of the network

The attacker can only listen to whatever is

going on. He cannot fiddle with the network

Active attacks

Riskier

The attacker has to first get into the network, before doing damages

The attacker can interrupt, hijack and control the network at his willattacker.

Fig 7.3: Passive vs. Active attacks

Fig7.3: Passive v/s Active attacks

11.0 Conclusion

Wireless LAN security has a long way to go. Current Implementation of WEP has proved to be

flawed. Further initiatives to come up with a standard that is robust and provides adequate

security are urgently needed. Like most advances, wireless LANs poses both opportunities and risks. The technology can represent a powerful complement to an organization's networking capabilities, enabling increased employee productivity and reducing IT costs. To minimize the attendant risks, IT administrators can implement a range of measures, including establishment of wireless security policies and practices, as well as implementation of various LAN design and implementation measures. Achieving this balance of opportunity and risk allows enterprises to confidently implement wireless LANs and realize the benefits this increasingly viable technology offers.

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