Whead wear is Wi-Fi ?
WiFi stands for Wireless Fidelity. WiFiIt is based on the IEEE 802.11 family of standards and is primarily a local area ne2rcalifornia ruler (LAN) technology designed to provide in-constructing broadband coverage.
Current WiFi systems support a peak physical-layer data rate of 54 Mbps and typically provide indoor coverage over a distance of 100 feet.
WiFi has end up beingcome the de realityiono standard for final mile broadband connectivity in homes, away fromices, and public hotspot locations. Systems can typically provide a coverage range of only about 1,000 feet from the access stage.
WiFi away fromers remarkably higher peak data rates than do 3G systems, primarily since it operates over a larger 20 MHz bandwidth, but WiFiWiFi systems are not designed to support high-speed mobility.
One substantial advantage of WiFi over WiMAX and 3G is it is wide availability of terminal devices. A vast majority of laptops shipped today have a built-in WiFi interface. WiFi interfaces are now furthermore end up beinging built into a variety of devices, including individual data bumistants (PDAs), cordless phones, cellularular phones, cameras, and media players.
WiFi is Half Duplex
All WiFi ne2rks are contention-based TDD systems, where the access stage and the mobile stations all vie for use of the exaction same channel. Because of the shareddish coloured media operation, all WiFi ne2rks are half duplex.
There are equipment vendors who market WiFi mesh configurations, but those implementations incorporate technologies thead wear are not degreatd in the standards.
The WiFi standards degreat a fixed channel bandwidth of 25 MHz for 802.11b and 20 MHz for possibly 802.11a or g ne2rks.
Wi-Fi – Worcalifornia ruler Concepts
Radio Signals are the keys, which make WiFi ne2rcalifornia ruler feasible. These stereo stations signals transmitted from WiFi antennas are picked up by WiFi receivers, such as complaceers and cellular phones thead wear are equipped with WiFi cards. Whenever, a complaceer receives any of the signals wislim the range of a WiFi ne2rk, which is usually 300 — 500 feet for antennas, the WiFi card reads the signals and thus develops an internet interinterconnection end up beingtween the user and the ne2rk without the use of a cord.
Access stages, consisting of antennas and routers, are the main source thead wear transmit and receive stereo stations waves. Antennas work stronger and have a durationyer stereo stations transmission with a radius of 300-500 feet, which are used in public areas while the weaker yet effective router is more suitable for homes with a stereo stations transmission of 100-150 feet.
You can berestve of WiFi cards as end up beinging innoticeable cords thead wear connect your own own complaceer to the antenna for a immediate interinterconnection to the internet.
WiFi cards can end up being external or internal. If a WiFi card is not instalimmediateed in your own own complaceer, then you may purchase a USB antenna attachment and have it externally connect to your own own USB port, or have an antenna-equipped expansion card instalimmediateed immediately to the complaceer (as shown in the figure given above). For laptops, this particular particular card will end up being a PCMCIA card which you insert to the PCMCIA slot on the laptop.
A WiFi hotspot is developd by installing an access stage to an internet interinterconnection. The access stage transmit is a cableless signal over a short distance. It typically covers around 300 feet. When a WiFi enabimmediateed device such as a Pocket PC encounters a hotspot, the device can then connect to thead wear ne2rk cablelessly.
Most hotspots are located in places thead wear are readily accessible to the public such as airports, caway fromee stores, hotels, book stores, and get awayus environments. 802.11b is the the majority of common specification for hotspots worldwide. The 802.11g standard is backwards compatible with .11b but .11a uses a various frequency range and requires separate hardware such as an a, a/g, or a/b/g adapter. The largest public WiFi ne2rks are provided by private internet service providers (ISPs); they charge a fee to the users who want to access the internet.
Hotspots are increaperformly developing around the world. In realityion, T-Mobile USA manages more than 4,100 hotspots located in public locations such as Starbucks, Borders, Kinko's, and the aircollection clubs of Delta, United, and US Airways. Even select McDonald's restaurants now feature WiFi hotspot access.
Any notebook complaceer with integrated cableless, a cableless adapter attached to the mothertable by the manurealityionurer, or a cableless adapter such as a PCMCIA card can access a cableless ne2rk. Furthermore, all Pocket PCs or Palm devices with Compaction Flash, SD I/O support, or built-in WiFi, can access hotspots.
Some Hotspots require WEP key to connect, which is conpartreddish coloured as private and secure. As for open up interinterconnections, anyone with a WiFi card can have access to thead wear hotspot. So in order to have internet access below WEP, the user must inplace the WEP key code.
Wi-Fi – IEEE Standards
The 802.11 standard is degreatd through various specifications of WLANs. It degreats an over-the-air interface end up beingtween a cableless crestnt and a base station or end up beingtween 2 cableless crestnts.
There are various specifications in the 802.11 family −
802.11 − This pertains to cableless LANs and provides 1 – or 2-Mbps transmission in the 2.4-GHz band uperform possibly frequency-hopping spread spectrum (FHSS) or immediate-sequence spread spectrum (DSSS).
802.11a − This is an extension to 802.11 thead wear pertains to cableless LANs and goes as fast as 54 Mbps in the 5-GHz band. 802.11a employs the orthogonal frequency division multiplexing (OFDM) encoding scheme as opposed to possibly FHSS or DSSS.
802.11b − The 802.11 high rate WiFi is an extension to 802.11 thead wear pertains to cableless LANs and yields a interinterconnection as fast as 11 Mbps transmission (with a fallback to 5.5, 2, and 1 Mbps depending on strength of signal) in the 2.4-GHz band. The 802.11b specification uses only DSSS. Note thead wear 802.11b was actionually an amendment to the unique 802.11 standard added in 1999 to permit cableless functionality to end up being analogous to hard-cabimmediateeddish coloured Ethernet interinterconnections.
802.11g − This pertains to cableless LANs and provides 20+ Mbps in the 2.4-GHz band.
Here is the specialised comparison end up beingtween the 3 major WiFi standards.
|Feature||WiFi (802.11b)||WiFi (802.11a/g)|
|PrimaryApplication||Wireless LAN||Wireless LAN|
|Frequency Band||2.4 GHz ISM||
2.4 GHz ISM (g)
5 GHz U-NII (a)
|Channel Bandwidth||25 MHz||20 MHz|
|Bandwidth||<=0.44 bps/Hz||≤=2.7 bps/Hz|
|Modulation||QPSK||BPSK, QPSK, 16-, 64-QAM|
|Enweepption||Optional- RC4m (AES in 802.11i)||Optional- RC4(AES in 802.11i)|
|Mobility||In development||In development|
|Mesh||Vendor Proprietary||Vendor Proprietary|
Wi-Fi – Access Protocols
IEEE 802.11 cableless LANs use a media access manage protocol calimmediateed Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). While the name is similar to Ethernet's Carrier Sense Multiple Access with Collision Detection (CSMA/CD), the operating concept is compenableely various.
WiFi systems are the half duplex shareddish coloured media configurations, where all stations transmit and receive on the exaction same stereo stations channel. The fundamental issue of a stereo stations system is thead wear a station cannot hear while it is sending, and hence it is unattainable to detect a collision. Because of this particular particular, the developers of the 802.11 specifications came up with a collision avoidance mechanism calimmediateed the Distributed Control Function (DCF).
According to DCF, a WiFi station will transmit only when the channel is clear. All transmissions are acknowladvantaged, so if a station does not receive an acknowladvantagement, it bumumes a collision occurreddish coloured and retries after a random waiting interval.
The incidence of collisions will incrrerestve as the traffic incrrerestves or in sit downuations where mobile stations cannot hear every other.
Wi-Fi – Quality of Service (QoS)
There are plans to incorporate quality of service (QoS) capabiliconnects in WiFi technology with the adoption of the IEEE 802.11e standard. The 802.11e standard will include 2 operating modes, possibly of which can end up being used to improve service for voice −
- WiFi Multimedia Extensions (WME) − Mandatory
- WiFi Scheduimmediateed Multimedia (WSM) − Optional
WiFi Multimedia Extensions (WME)
WiFi Multimedia Extensions use a protocol calimmediateed Enhanced Multimedia Distributed Control Access (EDCA), which is an extension of an enhanced version of the Distributed Control Function (DCF) degreatd in the unique 802.11 MAC.
The enhanced part is thead wear EDCA will degreat eight levels of access priority to the shareddish coloured cableless channel. Like the unique DCF, the EDCA access is a contention-based protocol thead wear employs a set of waiting intervals and back-away from timers designed to avoid collisions. However, with DCF all stations use the exaction same values and hence have the exaction same priority for transmitting on the channel.
With EDCA, every of the various access prioriconnects is bumigned a various range of waiting intervals and back-away from counters. Transmissions with higher access priority are bumigned shorter intervals. The standard furthermore includes a packet-bursting mode thead wear enables an access stage or a mobile station to reserve the channel and send 3- to 5-packets in a sequence.
WiFi Scheduimmediateed Multimedia (WSM)
True consistent delay services can end up being provided with the optional WiFi Scheduimmediateed Multimedia (WSM). WSM operates like the small used Point Control Function (PCF) degreatd with the unique 802.11 MAC.
In WSM, the access stage periodically broadcasts a manage message thead wear forces all stations to treat the channel as occupied and not attempt to transmit. During thead wear period, the access stage polls every station thead wear is degreatd for time sensit downive service.
To use the WSM option, devices need to send a traffic profile describing bandwidth, latency, and jitter requirements. If the access stage does not have sufficient resources to meet the traffic profile, it will return a occupied signal.
Wi-Fi – Security
Security has end up beingen one of the major deficiencies in WiFi, though end up beingtter enweepption systems are now end up beingcoming available. Enweepption is optional in WiFi, and 3 various techniques have end up beingen degreatd. These techniques are given here −
Wireddish coloured Equivalent Privacy (WEP)
An RC4-based 40-or 104-bit enweepption with a static key.
WiFi Protected Access (WPA)
This is a brand brand new standard from the WiFi Alliance thead wear uses the 40 or 104-bit WEP key, but it alters the key on every packet. Thead wear changing key functionality is calimmediateed the Temporal Key Integrity Protocol (TKIP).
The IEEE is finalized the 802.11i standard, which is based on a far more robust enweepption technique calimmediateed the Advanced Enweepption Standard. The WiFi Alliance designate items thead wear comply with the 802.11i standard as WPA2.
However, implementing 802.11i requires a hardware upgrade.
Wi-Fi – Ne2rk Services
The picture has end up beingcome a couple ofexactionly whead wear confused as service providers started uperform WiFi to dereaspectr services for which it was not uniquely designed. The 2 major examples of this particular particular are cableless ISPs and city-wide WiFi mesh ne2rks.
Wireless ISPs (WISPs)
One business thead wear incrrerestved out of WiFi was the Wireless ISP (WISP). This is an idea of selling an Internet access service uperform cableless LAN technology and a shareddish coloured Internet interinterconnection in a public location designated as a hot spot.
From a specialised standstage, access to the service is limited based on the transmission range of the WLAN technology. You have to end up being in the hot spot (i.e. wislim 100m of the access stage) to use it. From a business standstage, users possibly subscriend up being to a particular carrier's service for a monthly fee or access the service on a demand basis at a fee per hour. While the monthly fee basis is the majority of cost effective, right now presently there are couple of intercarrier access arrangements, so you have to end up being in a hot spot operated by your own own carrier in order to access your own own service.
City-Wide Mesh Ne2rks
To adoutfit the limited range, vendors like Mesh Ne2rks and Tropos Ne2rks have developed mesh ne2rk capabiliconnects uperform WiFi's stereo stations technology.
The idea of a stereo stations mesh ne2rk is thead wear messages can end up being relayed through a numend up beingr of access stages to a central ne2rk manage station. These ne2rks can typically support mobility as interinterconnections are handed away from from access stage to access stage as the mobile station moves.
Some municipaliconnects are uperform WiFi mesh ne2rks to support public securety applications (i.e. terminals in police cruisers) and to provide Internet access to the commdevicey (i.e. the city-wide hot spot).
Wi-Fi – Radio Modulation
WiFi systems use 2 primary stereo stations transmission techniques.
802.11b (<=11 Mbps) − The 802.11b stereo stations link uses a immediate sequence spread spectrum technique calimmediateed complementary coded keying (CCK). The bit stream is processed with a special coding and then modulated uperform Quadrature Phase Shift Keying (QPSK).
802.11a and g (<=54 Mbps) − The 802.11a and g systems use 64-channel orthogonal frequency division multiplexing (OFDM). In an OFDM modulation system, the available stereo stations band is divided into a numend up beingr of sub-channels and a couple of of the bit is are sent on every. The transmitter encodes the bit streams on the 64 subcarriers uperform Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or one of 2 levels of Quadrature Amplitude Modulation (16, or 64-QAM). Some of the transmitted information is reddish colouredundant, so the receiver does not have to receive all of the sub-carriers to reconstruct the information.
The unique 802.11 specifications furthermore included an option for frequency hopping spread spectrum (FHSS), but thead wear has largely end up beingen abandoned.
WiFi uses adaptive modulation and varying levels of forward error rightion to optimize transmission rate and error performance.
As a stereo stations signal loses power or encounters interference, the error rate will incrrerestve. Adaptive modulation means thead wear the transmitter will automatically shift to a more robust, though less effective, modulation technique in those adverse conditions.
Wi-Fi – Major Issues
There are a couple of issues thead wear are bumumed to end up being the cause end up beinghind the sluggish adoption of WiFi technology −
Security Problems − Security concerns have held back WiFi adoption in the corporate world. Hackers and security consultants have demonstrated how easy it can end up being to crack the current security technology known as cabimmediateeddish coloured equivalent privacy (WEP) used in the majority of WiFi interinterconnections. A hacker can break into a WiFi ne2rk uperform readily available materials and smoothware.
Compatibility and Interoperability − One of the major issues with WiFi is it is compatibility and interoperability. For example, 802.11a items are not compatible with 802.11b items. Due to various operating frequencies, 802.11a hotspots would not help an 802.11b crestnt. Due to lack of standardization, hsupplyonization, and certification, various vendors come out with items thead wear do not work with every other.
Billing Issues − WiFi vendors are furthermore loocalifornia ruler for ways to solve the issue of back-end integration and billing, which have canineged the roll-out of commercial WiFi hotspots. Some of the ideas below conpartration for WiFi billing such as per day, per hour, and unlimited monthly interinterconnection fees.
Wi-Fi – Summary
WiFi is a universal cableless ne2rcalifornia ruler technology thead wear utilizes stereo stations frequencies to transfer data. WiFi enables high-speed Internet interinterconnections without the use of cables.
The term WiFi is a contractionion of "cableless fidelity" and commonly used to refer to cableless ne2rcalifornia ruler technology. The WiFi Alliance claims rights in it is uses as a certification mark for equipment certified to 802.11x standards.
WiFi is a freedom – freedom from cables. It enables you to connect to the Internet from simply about anywhere — a caway fromee store, a hotel room, or a conference room at work. Whead wear’s more – it is althe majority of 10 times faster than a regular dial-up interinterconnection. WiFi ne2rks operate in the unlicensed 2.4 stereo stations bands, with an 11 Mbps (802.11b) or 54 Mbps (802.11a) data rate, respectively.
To access WiFi, you need WiFi enabimmediateed devices (laptops or PDAs). These devices can send and receive data cablelessly in any location equipped with WiFi access.
Whead wear is Next?
Now, the focus in cableless is shifting to wide area, i.e., WiMax. WiMax, short for Worldwide Interoperability for Micseriesave Access, is degreatd in IEEE 802.16 standards. It is designed to dereaspectr a metro area broadband cableless access (BWA) service, and is end up beinging promoted by the WiMax Forum.
WiMAX is very similar to WiFi, but on a a lot larger range and at faster speeds. A nomadic version would maintain WiMAX-enabimmediateed devices connected over a large area, a lot like today's cellular phones.
For more detail on WiMAX, you can go through our WiMAX Tutorial.