Wi-Fi is trademark of the Wi-Fi Alliance. However, the Alliance has generally enforced its use to describe only a narrow range of connectivity technologies including wireless local area network (WLAN) based on the IEEE 802.11 standards, device to device connectivity and a range of technologies that support PAN, LAN and even WAN connections

The technical term "IEEE 802.11" has been used interchangeably with Wi-Fi, however Wi-Fi has become a superset of IEEE 802.11 over the past few years. Wi-Fi is used by over 700 million people, there are over 750,000 hotspots (places with Wi-Fi Internet connectivity) around the world, and about 800 million new Wi-Fi devices every year. Wi-Fi products that complete the Wi-Fi Alliance interoperability certification testing successfully can use the Wi-Fi CERTIFIED designation and trademark.

Wi-Fi certified and compliant devices are installed in many personal computers, video game consoles, MP3 players, smartphones, printers, and other peripherals, and newer laptop computers.

This article focuses on the certification and approvals process and the general growth of wireless networking under the Wi-Fi Alliance certified protocols. For more on the technologies see the appropriate articles with IEEE, ANSI, IETF , W3 and ITU prefixes (acronyms for the accredited standards organizations that have created formal technology standards for the protocols by which devices communicate). Non-Wi-Fi-Alliance wireless technologies intended for fixed points such as Motorola Canopy are usually described as fixed wireless. Non-Wi-Fi-Alliance wireless technologies intended for mobile use are usually described as 3G, 4G or 5G reflecting their origins and promotion by telephone/cell companies.

Wi-Fi technology builds on IEEE 802.11 standards. The IEEE develops and publishes some of these standards, but does not test equipment for compliance with them

The term Wi-Fi suggests Wireless Fidelity, resembling the long-established audio-equipment classification term high fidelity Hi-Fi Even the Wi-Fi Alliance itself has often used the phrase Wireless Fidelity in its press releases and documents, the term also appears in a white paper on Wi-Fi from ITAA

Internet access

A roof-mounted Wi-Fi antenna

A Wi-Fi enabled device such as a personal computer, video game console, smartphone or digital audio player can connect to the Internet when within range of a wireless network connected to the Internet. The coverage of one or more (interconnected) access points — called hotspots — can comprise an area as small as a few rooms or as large as many square miles. Coverage in the larger area may depend on a group of access points with overlapping coverage. Wi-Fi technology has been used in wireless mesh networks, for example, in London, UK

In addition to private use in homes and offices, Wi-Fi can provide public access at Wi-Fi hotspots provided either free-of-charge or to subscribers to various commercial services. Organizations and businesses - such as those running airports, hotels and restaurants - often provide free-use hotspots to attract or assist clients

Routers that incorporate a digital subscriber line modem or a cable modem and a Wi-Fi access point, often set up in homes and other premises, can provide Internet access and internetworking to all devices connected (wirelessly or by cable) to them.

One can also connect Wi-Fi devices in ad-hoc mode for client-to-client connections without a router. Wi-Fi also connects places that would traditionally not have network access, for example bathrooms, kitchens and garden sheds.

City-wide Wi-Fi

An outdoor Wi-Fi access point in Minneapolis

An outdoor Wi-Fi access point in Toronto

Campus-wide Wi-Fi

Carnegie Mellon University built the first wireless Internet network in the world at their Pittsburgh campus in 1994,[24] long before Wi-Fi branding originated in 1999. Many traditional college campuses provide at least partial wireless Wi-Fi Internet coverage.

Drexel University in Philadelphia made history by becoming the United State's first major university to offer completely wireless Internet access across the entire campus in 2000. [25]

[edit] Direct computer-to-computer communications

Wi-Fi also allows communications directly from one computer to another without the involvement of an access point. This is called the ad-hoc mode of Wi-Fi transmission. This wireless ad-hoc network mode has proven popular with multiplayer handheld game consoles, such as the Nintendo DS, digital cameras, and other consumer electronics devices.

Similarly, the Wi-Fi Alliance promotes a pending specification called Wi-Fi Direct for file transfers and media sharing through a new discovery- and security-methodology.[26]

[edit] Future directions

As of 2010 Wi-Fi technology has spread widely within business and industrial sites. In business environments, just like other environments, increasing the number of Wi-Fi access points provides network redundancy, support for fast roaming and increased overall network-capacity by using more channels or by defining smaller cells. Wi-Fi enables wireless voice-applications (VoWLAN or WVOIP). Over the years, Wi-Fi implementations have moved toward "thin" access points, with more of the network intelligence housed in a centralized

network appliance, relegating individual access points to the role of "dumb" transceivers. Outdoor applications may utilize mesh topologies.

[edit] Advantages and challenges

A keychain-size Wi-Fi detector

[edit] Operational advantages

Wi-Fi allows the deployment of local area networks (LANs) without wires for client devices, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.

As of 2010 manufacturers are building wireless network adapters into most laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in even more devices. Wi-Fi has become widespread in corporate infrastructures

Different competitive brands of access points and client network-interfaces can inter-operate at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards compatible. "Wi-Fi" designates a globally operative set of standards: unlike mobile phones, any standard Wi-Fi device will work anywhere in the world.

New protocols for quality-of-service (WMM) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video); and power saving mechanisms (WMM Power Save) improve battery operation.

Limitations

Spectrum assignments and operational limitations do not operate consistently worldwide. Most of Europe allows for an additional 2 channels beyond those permitted in the U.S. for the 2.4 GHz band. (1–13 vs. 1–11); Japan has one more on top of that (1–14). Europe, as of 2007, was essentially homogeneous in this respect. A very confusing aspect is the fact that a Wi-Fi signal actually occupies five channels in the 2.4 GHz band resulting in only three non-overlapped channels in the U.S.: 1, 6, 11, and three or four in Europe: 1, 5, 9, 13. Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (100 mW).

Reach

Wi-Fi networks have limited range. A typical wireless router using 802.11b or 802.11g with a stock antenna might have a range of 32 m (120 ft) indoors and 95 m (300 ft) outdoors. The IEEE 802.11n however, can exceed that range by more than two times.[28] Range also varies with frequency band. Wi-Fi in the 2.4 GHz frequency block has slightly better range than Wi-Fi in the 5 GHz frequency block. Outdoor ranges - through use of directional antennas - can be improved with antennas located several kilometres or more from their base. In general, the maximum amount of power that a Wi-Fi device can transmit is limited by local regulations, such as FCC Part 15 [29] in USA.

Due to reach requirements for wireless LAN applications, Wi-Fi has fairly high power consumption compared to some other standards. Technologies such as Bluetooth (designed to support wireless PAN applications) provide a much shorter propagation range of <10m[30] and so in general have a lower power consumption. Other low-power technologies such as ZigBee have fairly long range, but much lower data rate. The high power consumption of Wi-Fi makes battery life in mobile devices a concern.

Due to the complex nature of radio propagation at typical Wi-Fi frequencies, particularly the effects of signal reflection off trees and buildings, algorithms can only approximately predict Wi-Fi signal strength for any given area in relation to a transmitter.[31] This effect does not apply equally to long-range Wi-Fi, since longer links typically operate from towers that broadcast above the surrounding foliage.

[edit] Mobility

Speed vs. Mobility of wireless systems: Wi-Fi, HSPA, UMTS, GSM

The very limited practical range of Wi-Fi essentially confines mobile use to such applications as inventory-taking machines in warehouses or in retail spaces, barcode-reading devices at check-out stands, or receiving/shipping stations. Mobile use of Wi-Fi over wider ranges is limited, for instance, to uses such as in an automobile moving from one hotspot to another (known as Wardriving). Other wireless technologies are more suitable as illustrated in the graphic.

[edit] Data security risks

The most common wireless encryption-standard, Wired Equivalent Privacy (WEP), has been shown to be easily breakable even when correctly configured. Wi-Fi Protected Access (WPA and WPA2) encryption, which became available in devices in 2003, aimed to solve this problem. Wi-Fi access points typically default to an encryption-free (open) mode. Novice

users benefit from a zero-configuration device that works out-of-the-box, but this default does not enable any wireless security, providing open wireless access to a LAN. To turn security on requires the user to configure the device, usually via a software graphical user interface (GUI). On unencrypted Wi-Fi networks connecting devices can monitor and record data (including personal information), but such networks may use other means of protection, such as a virtual private network or secure Hypertext Transfer Protocol (HTTPS) and Transport Layer Security.

[edit] Population

Many 2.4 GHz 802.11b and 802.11g access-points default to the same channel on initial startup, contributing to congestion on certain channels. To change the channel of operation for an access point requires the user to configure the device.

A wireless access point (WAP) connects a group of wireless devices to an adjacent wired LAN. An access point resembles a network hub, relaying data between connected wireless devices in addition to a (usually) single connected wired device, most often an ethernet hub or switch, allowing wireless devices to communicate with other wired devices.

Wireless adapters allow devices to connect to a wireless network. These adapters connect to devices using various external or internal interconnects such as PCI, miniPCI, USB, ExpressCard, Cardbus and PC Card. As of 2010, most newer laptop computers come equipped with internal adapters. Internal cards are generally more difficult to install.

Wireless routers integrate a Wireless Access Point, ethernet switch, and internal router firmware application that provides IP routing, NAT, and DNS forwarding through an integrated WAN-interface. A wireless router allows wired and wireless ethernet LAN devices to connect to a (usually) single WAN device such as a cable modem or a DSL modem. A wireless router allows all three devices, mainly the access point and router, to be configured through one central utility. This utility is usually an integrated web server that is accessible to wired and wireless LAN clients and often optionally to WAN clients. This utility may also be an application that is run on a desktop computer such as Apple's AirPort.

Wireless network bridges connect a wired network to a wireless network. A bridge differs from an access point: an access point connects wireless devices to a wired network at the data-link layer. Two wireless bridges may be used to connect two wired networks over a wireless link, useful in situations where a wired connection may be unavailable, such as between two separate homes.

Wireless range-extenders or wireless repeaters can extend the range of an existing wireless network. Strategically placed range-extenders can elongate a signal area or allow for the signal area to reach around barriers such as those pertaining in L-shaped corridors. Wireless devices connected through repeaters will suffer from an increased latency for each hop. Additionally, a wireless device connected to any of the repeaters in the chain will have a throughput limited by the "weakest link" between the two nodes in the chain from which the connection originates to where the connection ends.

[edit] Distance records

Distance records (using non-standard devices) include 382 km (237 mi) in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3 MB of data between the mountain-tops of El Águila and Platillon.[33][34] The Swedish Space Agency transferred data 420 km (260 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon.[35]

[edit] Embedded systems

Embedded serial-to-Wi-Fi module

Increasingly in the last few years (particularly as of 2007), embedded Wi-Fi modules have become available that incorporate a real-time operating system and provide a simple means of wirelessly enabling any device which has and communicates via a serial port.[36] This allows the design of simple monitoring devices. An example is a portable ECG device monitoring a patient at home. This Wi-Fi-enabled device can communicate via the Internet.[37]

These Wi-Fi modules are designed[by whom?] so that implementers need only minimal Wi-Fi knowledge to provide Wi-Fi connectivity for their products.

Network securityThe main issue with wireless network security is its simplified access to the network compared to traditional wired networks such as ethernet. With wired networking one must either gain access to a building (physically connecting into the internal network) or break through an external firewall. Most business networks protect sensitive data and systems by attempting to disallow external access. Enabling wireless connectivity provides an attack vector, particularly if the network uses inadequate or no encryption.[38]

An attacker who has gained access to a Wi-Fi network router can initiate a DNS spoofing attack against any other user of the network by forging a response before the queried DNS server has a chance to reply.[39]

[edit] Securing methods

A common but unproductive measure to deter unauthorized users involves suppressing the access point's SSID broadcast. This is ineffective as a security method because the SSID is broadcast in the clear in response to a client SSID query. Another unproductive method is to only allow computers with known MAC addresses to join the network.[40] But intruders can

defeat this method because they can often (though not always) set MAC addresses with minimal effort (MAC spoofing). If eavesdroppers have the ability to change their MAC address, then they may join the network by spoofing an authorized address.

Wired Equivalent Privacy (WEP) encryption was designed to protect against casual snooping, but is now deprecated. Tools such as AirSnort or Aircrack-ng can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort can determine the encryption password in under a second;[41] newer tools such as aircrack-ptw can use Klein's attack to crack a WEP key with a 50% success rate using only 40,000 packets.

To counteract this in 2002, the Wi-Fi Alliance approved Wi-Fi Protected Access (WPA) which uses TKIP as a stopgap solution for legacy equipment. Though more secure than WEP, it has outlived its designed lifetime and has known attack vectors.

In 2004, the IEEE ratified the full IEEE 802.11i (WPA2) encryption standards. If used with a 802.1X server or in pre-shared key mode with a strong and uncommon passphrase WPA2 is still considered[by whom?] secure, as of 2009.

Piggybacking

Piggybacking refers to access to a wireless Internet connection by bringing one's own computer within the range of another's wireless connection, and using that service without the subscriber's explicit permission or knowledge.

During the early popular adoption of 802.11, providing open access points for anyone within range to use was encouraged[by whom?] to cultivate wireless community networks,[42] particularly since people on average use only a fraction of their downstream bandwidth at any given time.

Recreational logging and mapping of other people's access points has become known as wardriving. Indeed, many access points are intentionally installed without security turned on so that they can be used as a free service. Providing access to one's Internet connection in this fashion may breach the Terms of Service or contract with the ISP. These activities do not result in sanctions in most jurisdictions; however, legislation and case law differ considerably across the world.

Piggybacking often occurs unintentionally, most access points are configured without encryption by default, and operating systems can be configured to connect automatically to any available wireless network. A user who happens to start up a laptop in the vicinity of an access point may find the computer has joined the network without any visible indication. Moreover, a user intending to join one network may instead end up on another one if the latter has a stronger signal.

General description

A Compaq 802.11b PCI card

The 802.11 family includes over-the-air modulation techniques that use the same basic protocol. The most popular are those defined by the 802.11b and 802.11g protocols, which are amendments to the original standard. 802.11-1997 was the first wireless networking standard, but 802.11b was the first widely accepted one, followed by 802.11g and 802.11n. Security was originally purposefully weak due to export requirements of some governments,[1] and was later enhanced via the 802.11i amendment after governmental and legislative changes. 802.11n is a new multi-streaming modulation technique. Other standards in the family (c–f, h, j) are service amendments and extensions or corrections to the previous specifications.

802.11b and 802.11g use the 2.4 GHz ISM band, operating in the United States under Part 15 of the US Federal Communications Commission Rules and Regulations. Because of this choice of frequency band, 802.11b and g equipment may occasionally suffer interference from microwave ovens, cordless telephones and Bluetooth devices. 802.11b and 802.11g control their interference and susceptibility to interference by using direct-sequence spread spectrum (DSSS) and orthogonal frequency-division multiplexing (OFDM) signaling methods, respectively. 802.11a uses the 5 GHz U-NII band, which, for much of the world, offers at least 19 non-overlapping channels rather than the 3 offered in the 2.4 GHz ISM frequency band.[2] Better or worse performance with higher or lower frequencies (channels) may be realized, depending on the environment.

The segment of the radio frequency spectrum used by 802.11 varies between countries. In the US, 802.11a and 802.11g devices may be operated without a license, as allowed in Part 15 of the FCC Rules and Regulations. Frequencies used by channels one through six of 802.11b and 802.11g fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption.[3]

[edit] History

802.11 technology has its origins in a 1985 ruling by the U.S. Federal Communications Commission that released the ISM band for unlicensed use.[4]

In 1991 NCR Corporation/AT&T (now Alcatel-Lucent and LSI Corporation) invented the precursor to 802.11 in Nieuwegein, The Netherlands. The inventors initially intended to use the technology for cashier systems; the first wireless products were brought on the market under the name WaveLAN with raw data rates of 1 Mbit/s and 2 Mbit/s.[citation needed]

Vic Hayes, who held the chair of IEEE 802.11 for 10 years and has been called the "father of Wi-Fi" was involved in designing the initial 802.11b and 802.11a standards within the IEEE.[citation needed]

In 1992, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) obtained a patent in Australia for wireless data transfer technology. In 1996, they obtained a patent for the same technology in the US.[5] Wi-Fi uses the mathematical formula in the patents. In April 2009, 14 tech companies including Intel, Microsoft, HP, Dell, agreed to pay CSIRO $250 million for their Wi-Fi patent infringements.[6]

[edit] Protocols

[hide]802.11 network standards v • d • e 

802.11Protoco

l

Release[7]

Freq.(GHz

)

Bandwidth

(MHz)

Data rate per stream(Mbit/s)

[8]

Allowable

MIMO streams

Modulation

Approximate indoor

range[citation

needed]

Approximate Outdoor range[citation

needed]

(m) (ft) (m) (ft)

– Jun 1997 2.4 20 1, 2 1 DSSS, FHSS 20 66 100 330

a Sep 1999

5

20

6, 9, 12, 18, 24, 36, 48,

54

1 OFDM

35 115 120 390

3.7[y] -- -- 5,000

16,000[y]

b Sep 1999 2.4 20 5.5, 11 1 DSSS 38 125 140 460

g Jun 2003 2.4 20

6, 9, 12, 18, 24, 36, 48,

54

1 OFDM, DSSS 38 125 140 460

n Oct 2009 2.4/5

20

7.2, 14.4, 21.7, 28.9, 43.3,

57.8, 65, 72.2[z] 4 OFDM

70 230 250 820[9]

40

15, 30, 45, 60, 90, 120,

135, 150[z]

70 230 250 820[9]

y IEEE 802.11y-2008 extended operation of 802.11a to the licensed 3.7 GHz band. Increased power limits allow a range up to 5000m. As of 2009, it is only being licensed in the United States by the FCC.

z Assumes Short Guard interval (SGI) enabled, otherwise reduce each data rate by 10%.

[edit] 802.11-1997 (802.11 legacy)

Main article: IEEE 802.11 (legacy mode)

The original version of the standard IEEE 802.11 was released in 1997 and clarified in 1999, but is today obsolete. It specified two net bit rates of 1 or 2 megabits per second (Mbit/s), plus forward error correction code. It specified three alternative physical layer technologies: diffuse infrared operating at 1 Mbit/s; frequency-hopping spread spectrum operating at 1 Mbit/s or 2 Mbit/s; and direct-sequence spread spectrum operating at 1 Mbit/s or 2 Mbit/s. The latter two radio technologies used microwave transmission over the Industrial Scientific Medical frequency band at 2.4 GHz. Some earlier WLAN technologies used lower frequencies, such as the U.S. 900 MHz ISM band.

Legacy 802.11 with direct-sequence spread spectrum was rapidly supplanted and popularized by 802.11b.

[edit] 802.11a

Main article: IEEE 802.11a-1999

The 802.11a standard uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface (physical layer). It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net achievable throughput in the mid-20 Mbit/s[citation needed]

Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively unused 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: the effective overall range of 802.11a is less than that of 802.11b/g. In theory, 802.11a signals are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength and, as a result, cannot penetrate as far as those of 802.11b. In practice, 802.11b typically has a higher range at low speeds (802.11b will reduce speed to 5 Mbit/s or even 1 Mbit/s at low signal strengths). However, at higher speeds, 802.11a often has the same or greater range due to less interference.[citation needed]

[edit] 802.11b

Main article: IEEE 802.11b-1999

802.11b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard)

along with simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.

802.11b devices suffer interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include: microwave ovens, Bluetooth devices, baby monitors and cordless telephones.

[edit] 802.11g

Main article: IEEE 802.11g-2003

In June 2003, a third modulation standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b), but uses the same OFDM based transmission scheme as 802.11a. It operates at a maximum physical layer bit rate of 54 Mbit/s exclusive of forward error correction codes, or about 22 Mbit/s average throughput.[10] 802.11g hardware is fully backwards compatible with 802.11b hardware and therefore is encumbered with legacy issues that reduce throughput when compared to 802.11a by ~21%.

The then-proposed 802.11g standard was rapidly adopted by consumers starting in January 2003, well before ratification, due to the desire for higher data rates as well as to reductions in manufacturing costs. By summer 2003, most dual-band 802.11a/b products became dual-band/tri-mode, supporting a and b/g in a single mobile adapter card or access point. Details of making b and g work well together occupied much of the lingering technical process; in an 802.11g network, however, activity of an 802.11b participant will reduce the data rate of the overall 802.11g network .

Like 802.11b, 802.11g devices suffer interference from other products operating in the 2.4 GHz band, for example wireless keyboards.

[edit] 802.11-2007

In 2003, task group TGma was authorized to "roll up" many of the amendments to the 1999 version of the 802.11 standard. REVma or 802.11ma, as it was called, created a single document that merged 8 amendments (802.11a, b, d, e, g, h, i, j) with the base standard. Upon approval on March 8, 2007, 802.11REVma was renamed to the current base standard IEEE 802.11-2007.[11]

[edit] 802.11n

Main article: IEEE 802.11n-2009

802.11n is a recent amendment which improves upon the previous 802.11 standards by adding multiple-input multiple-output antennas (MIMO). 802.11n operates on both the 2.4GHz and the lesser used 5GHz bands. The IEEE has approved the amendment and it was published in October 2009.[12][13] Prior to the final ratification, enterprises were already migrating to 802.11n networks based on the Wi-Fi Alliance's certification of products conforming to a 2007 draft of the 802.11n proposal.

[edit] Channels and international compatibility

See also: List of WLAN channels

Graphical representation of Wi-Fi channels in 2.4 GHz band

802.11 divides each of the above-described bands into channels, analogously to how radio and TV broadcast bands are sub-divided but with greater channel width and overlap. For example the 2.4000–2.4835 GHz band is divided into 13 channels each of width 22 MHz but spaced only 5 MHz apart, with channel 1 centered on 2.412 GHz and 13 on 2.472 GHz to which Japan adds a 14th channel 12 MHz above channel 13.

Availability of channels is regulated by country, constrained in part by how each country allocates radio spectrum to various services. At one extreme, Japan permits the use of all 14 channels (with the exclusion of 802.11g/n from channel 14), while at the other Spain initially allowed only channels 10 and 11 and France allowed only 10, 11, 12 and 13 (now both countries follow the European model of allowing channels 1 through 13[14][15]). Most other European countries are almost as liberal as Japan, disallowing only channel 14, while North America and some Central and South American countries further disallow 12 and 13. For more details on this topic, see List of WLAN channels.

Besides specifying the centre frequency of each channel, 802.11 also specifies (in Clause 17) a spectral mask defining the permitted distribution of power across each channel. The mask requires that the signal be attenuated by at least 30 dB from its peak energy at ±11 MHz from the centre frequency, the sense in which channels are effectively 22 MHz wide. One consequence is that stations can only use every fourth or fifth channel without overlap, typically 1, 6 and 11 in the Americas, and in theory, 1, 5, 9 and 13 in Europe although 1, 6, and 11 is typical there too. Another is that channels 1-13 effectively require the band 2.401–2.483 GHz, the actual allocations being, for example, 2.400–2.4835 GHz in the UK, 2.402–2.4735 GHz in the US, etc.

Spectral masks for 802.11g channels 1-14 in the 2.4 GHz band

Since the spectral mask only defines power output restrictions up to ±11 MHz from the center frequency to be attenuated by -50 dBr, it is often assumed that the energy of the channel

extends no further than these limits. It is more correct to say that, given the separation between channels 1, 6, and 11, the signal on any channel should be sufficiently attenuated to minimally interfere with a transmitter on any other channel. Due to the near-far problem a transmitter can impact a receiver on a "non-overlapping" channel, but only if it is close to the victim receiver (within a meter) or operating above allowed power levels.

Although the statement that channels 1, 6, and 11 are "non-overlapping" is limited to spacing or product density, the 1–6–11 guideline has merit. If transmitters are closer together than channels 1, 6, and 11 (for example, 1, 4, 7, and 10), overlap between the channels may cause unacceptable degradation of signal quality and throughput.[16] However, overlapping channels may be used under certain circumstances. This way, more channels are available.[17]

WiFi Modes

Generally there are two well known WiFi modes by means of connectivity to get access to internet and for file sharingWireless technology has modified the means for us to connect to internet via remote or local computers.  It has permitted the accomplishment of thoughts away from the restrictions. . Wireless adapter or network interface are network cards having best 802.11 standards. These wireless adapters are available in various formats like PCI, PCMCIA, USB, Compact flash etc. 802.11 standards having two operating modes one is WiFi ad-hoc mode which is also known as peer-to-peer WiFi mode, which is a very easy to install and least hardware required for it, and second is WiFi Infrastructure mode in which hardware and software are both required for configuration as a part of design. Infrastructure mode is little hard to configure then ad hoc mode.

WiFi Infrastructure Mode

Infrastructure mode is one of the two methods for linking to cable less networks .Wi-Fi modes permitted devices such I-phone laptops, PDA’s which are used to connect with wireless network with the help of Access Point(AP). Wireless Access Points are generally routers which are used to connect with computer via Ethernet port. Infrastructure mode is the requirements of Wireless Access points. It is essential to use SSID when you are going to configure Access Point(AP). The basic security key of WiFi is SSID which facilitate to avoid

UN official access to WLAN. When you are using WiFi network then you can use multiple access points can be added in the WLAN.

 

The Infrastructure mode of WiFi is supporting a large number of wireless clients. The configuration of Infrastructure mode for wireless network is not very hard just follow simple step and setting up your Infrastructure mode. Write the URL in your any browser which you are using and then give user name and password in coming window. Typically in WiFi wireless network default setting is used which is admin password and admin user name. After putting it write name the connection in appeared screen. Infrastructure mode will be enabled and then assign SSID in the switch for transmit. Now scan adopter to see any wireless network availability. If appear click on it for connect and provide it SSID information to make possible file sharing and internet browsing. Infrastructure makes available much more evenness, scalability, ease of supervision and enhanced security.

WiFi Ad-hoc Mode

WiFi Ad hoc Mode is the other type of WiFi modes of connectivity. By using Ad hoc Mode direct communication of devices can be possible. No need of any Access Point such as routers, switches for communication purposes .All devices in Ad hoc Modes connect in peer to peer communication mode therefore each machines act as client and AP at the same type. The setting of Ad hoc Mode wireless adaptors are required to configure it. In ad hoc mode you need to use same channel name and same SSID for a live connection. You can set Ad hoc Mode in small is alike homes, building etc because you never need to use extra hardware. In Ad hoc Mode if there are two different stations range then it will not be able to communicate. Ad hoc Mode is a limited wireless network which invites people in the same room for exchanging data.

 

Both modes provide various benefits depend on the environment. Infrastructure mode and ad hoc mode has no giving out system that can throw data from one location to another location but in short it is a constrained wireless network. The configuration of WiFi modes become possible and ease because Wi-Fi Alliance has standardized these modes via Wi-Fi Protected Setup.

Configuring a Wifi Network

WiFi network technology is most popular and widely used now days. WiFi facilitates the user to connect with internet over a distance of 32 to 95 meters depending on the environment. WiFi technology is providing two types of operating modes such as Ad hoc mode which is a peer to peer mode and connects two systems with wireless adapters to one another, and second is infrastructure mode which make possible to join two computers via wired network by using access points.

  

Configuration of WiFi network

First of all you have to need different equipments which can support at least three wireless technologies such as 802.11a, 802.11b, and 802.11g but for Wifi the best suit is 802.11g, because it provides high quality performance and compatible with almost everything. You have to require a broadband internet connection; wireless router. And a computer with built in wireless network adapter. A wifi network can be configuring by using following process or method.

 

Installing a Wireless Router

Wireless router used to support a wireless network and you have to need it if you are building you first home network, or you want to rebuild to be all wireless, you want to keep simple and easy installation .Now install a wireless router by using following method.

Always install your wireless router in a central location of a network and keep the computers closer to the router for better speed.

Now connect your router to a power outlet .normally all router support broadband modem but some of them support phone line and if you need a dial up support then for it you have to need a RS-232 serial port. A wireless router contain a built in access point so you can easily connect a wire to hub or switch.

Now select your network name which is called the SSID and all the computers used in network share the same SSID. By default router shipped with a name but for security reason you should change it .Then follow the documentation of router to enable web security, and turn on firewall.

Installing a Wireless Access Point

For Wifi network install wireless access point and one access point supports one wireless local area network and you have to use it if you need additional features from wireless router, if you want to extend existing wired home Ethernet .You have to need at least for or more than wireless computers dispersed all through the home. Now install aces point by using following procedure

Start installation your access point from central location Now connect dial up and power connection and then cable the access point to your LAN router,

hub or switch. Now set a network name and make enable WEP on access point.

 

Configuring the Wireless Adapters

After installation of router and access point you have to install WiFi adapter which have need of TCP/IP be setting up on the host computer. Each adapter has their own configuration utilities and for windows adapter have their GUI accessible from the start menu after hardware installation. Now set the name SSID and turn on WEP or any other parameters .All adapter uses the same parameters for the setting of WLAN for appropriate functionality.

 

Configuring an Ad-Hoc home WLAN

For a Wifi adapter you have to choose the mode that is the infrastructure also called access point and ad hoc mode called peer to peer. When you are using a wireless router configure each wireless adapter for infrastructure mode because it detects and set WLAN channels automatically which are best suit the router. If you are using ad hoc mode then you have to need a separate setting of channels. Ad hoc mode is best for home where only few computers are situated close to each other.

 

Configuring Software Internet Connection Sharing

Now after all necessary installation and configuration you can share your internet connection transversely an ad hoc network. Now appoint one of your computer as the host which has modem and be powered on whenever the network in use. ICS offering by Microsoft windows that works with ad hoc wireless local area network.

Ns is a discrete event simulator targeted at networking research. Ns provides substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless (local and satellite) networks.

Ns began as a variant of the REAL network simulator in 1989 and has evolved substantially over the past few years. In 1995 ns development was supported by DARPA through the VINT project at LBL, Xerox PARC, UCB, and USC/ISI. Currently ns development is support through DARPA with SAMAN and through NSF with CONSER, both in collaboration with other researchers including ACIRI. Ns has always included substantal contributions from other researchers, including wireless code from the UCB Daedelus and CMU Monarch projects and Sun Microsystems. For documentation on recent changes, see the version 2 change log.

While we have considerable confidence in ns, ns is not a polished and finished product, but the result of an on-going effort of research and development. In particular, bugs in the software are still being discovered and corrected. Users of ns are responsible for verifying for themselves that their simulations are not invalidated by bugs. We are working to help the user with this by significantly expanding and automating the validation tests and demos.

• NS is a discrete event simulator for networking research. It provides substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless (local and satellite) networks.

• NS is under /net/cs455/ns

• Let your path point to the directory with ns executable. Add the appropriate directory to your PATH environment variable.

• For bash, add the following to your ~/.bash_profile:

   if [ `uname` = "SunOS" ]; then

     export PATH=${PATH}:/net/cs455/ns2/Solaris

   elif [ `uname` = "Linux" ]; then

     export PATH=${PATH}:/net/cs455/ns2/Linux

   fi 

• For csh and tcsh, add the following to your ~/.login:

   if ( `uname` == "SunOS" ) then

     setenv PATH ${PATH}:/net/cs455/ns2/Solaris

   else if ( `uname` == "Linux" ) then

     setenv PATH ${PATH}:/net/cs455/ns2/Linux

  endif 

   rehash