Standard devices
Wireless access points connects a group of wireless devices to an adjacent wired LAN. An access point is similar to an ethernet 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. Most newer laptop computers are equipped with internal adapters. Internal cards are generally more difficult to install.
Wireless routers integrate WAP, 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 cable modem or 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 most usually an integrated web server which serves web pages 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 Ethernet bridges connect a wired network to a wireless network. This is different from an access point in the sense that 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. Range extenders can be strategically placed to elongate a signal area or allow for the signal area to reach around barriers such as those created in L-shaped corridors. Wireless devices connected through repeaters will suffer from an increased latency for each hop. Additionally, a wireless device at the end of chain of wireless repeaters will have a throughput that is limited by the weakest link within the repeater chain.
Most commercial devices (routers, access points, bridges, repeaters) designed for home or business environments use either RP-SMA or RP-TNC antenna connectors. PCI wireless adapters also mainly use RP-SMA connectors. Most PC card and USB wireless only have internal antennas etched on their printed circuit board while some have MMCX connector or MC-Card external connections in addition to an internal antenna. A few USB cards have a RP-SMA connector. Most Mini PCI wireless cards utilize Hirose U.FL connectors, but cards found in various wireless appliances contain all of the connectors listed. Many high-gain (and homebuilt antennas) utilize the Type N connector more commonly used by other radio communications methods.
Non-standard devices
USB-Wi-Fi adapters, food container "Cantennas", parabolic reflectors, and many other types of self-built antennas are increasingly made by do-it-yourselfers. For minimal budgets, as low as a few dollars, signal strength and range can be improved dramatically.
As of 2007, Long Range Wi-Fi kits have begun to enter the market. Companies like BroadbandXpress offer long range, inexpensive kits that can be setup with limited knowledge. These kits utilize specialized antennas which increase the range of Wi-Fi dramatically, up to the world record 137.2 miles (220 km). These kits are commonly used to get broadband internet to a place without direct broadband access.[4]
The longest link ever achieved was by the Swedish space agency. They attained 310 km, but used 6 watt amplifiers to reach an overhead stratospheric balloon.[citation needed] The longest link without amplification was 279 km in Venezuela, 2006.[5]
Embedded systems
Wi-Fi availability in the home is on the increase. This extension of the Internet into the home space will increasingly be used for remote monitoring. Examples of remote monitoring include security systems and tele-medicine. In all these kinds of implementation, if the Wi-Fi provision is provided using a system running one of operating systems mentioned above, then it becomes unfeasible due to weight, power consumption and cost issues.
Increasingly in the last few years (particularly as of early 2007), embedded Wi-Fi modules have become available which come with a real-time operating system and provide a simple means of wireless enabling any device which has and communicates via a serial port.
This allows simple monitoring devices – for example, a portable ECG monitor hooked up to a patient in their home – to be created. This Wi-Fi enabled device effectively becomes part of the internet cloud and can communicate with any other node on the internet. The data collected can hop via the home's Wi-Fi access point to anywhere on the internet.
These Wi-Fi modules are designed so that minimal Wi-Fi knowledge is required by designers to wireless enable their product.
Unintended and intended use by outsiders
During the early popular adoption of 802.11, providing open access points for anyone within range to use was encouraged to cultivate wireless community networks;[6] particularly since people on average use only a fraction of their upstream bandwidth at any given time. Later, equipment manufacturers and mass-media advocated isolating users to a predetermined whitelist of authorized users — referred to as "securing" the access point.[dubious – discuss]
Wikinews has related news:
Florida man charged with stealing WiFi
Measures to deter unauthorized users include suppressing the AP's service set identifier (SSID) broadcast, allowing only computers with known MAC addresses to join the network, and various encryption standards. Access points and computers using no encryption are vulnerable to eavesdropping by an attacker armed with packet sniffer software. If the eavesdropper has the ability to change his MAC address then he can potentially join the network by spoofing an authorised address.
WEP encryption can protect against casual snooping but may also produce a misguided sense of security since freely available tools such as AirSnort can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort will determine the encryption password in under a second.[7] The newer Wi-Fi Protected Access (WPA) and IEEE 802.11i (WPA2) encryption standards do not have the serious weaknesses of WEP encryption, but require strong passphrases for full security.
Recreational logging and mapping of other people's access points has become known as wardriving. It is also common for people to use open Wi-Fi networks without explicit authorization, termed piggybacking. These activities may be illegal in certain jurisdictions, but existing legislation and case-law is often unclear. A proposal to leave graffiti describing available services was called warchalking, but did not catch on.
Piggybacking is sometimes unintentional. Most access points are configured without encryption by default, and operating systems such as Windows XP SP2 and Mac OS X may be configured to automatically connect 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's signal is stronger. In combination with automatic discovery of other network resources (see DHCP and Zeroconf) this could possibly lead wireless users to send sensitive data to the wrong destination.[citation needed]
Wi-Fi vs. amateur radio
In the U.S., Canada and Australia, a portion of the 2.4 GHz Wi-Fi radio spectrum is also allocated to amateur radio users. In the U.S., FCC Part 15 rules govern non-licensed operators (i.e. most Wi-Fi equipment users). Under Part 15 rules, non-licensed users must "accept" (i.e. endure) interference from licensed users and not cause harmful interference to licensed users. Amateur radio operators are licensed users, and retain what the FCC terms "primary status" on the band, under a distinct set of rules (Part 97). Under Part 97, licensed amateur operators may construct their own equipment, use very high-gain antennas, and boost output power to 100 watts on frequencies covered by Wi-Fi channels 2-6. However, Part 97 rules mandate using only the minimum power necessary for communications, forbid obscuring the data, and require station identification every 10 minutes. Therefore, output power control is required to meet regulations, and the transmission of any encrypted data (for example https) is questionable.
In practice, microwave power amplifiers are expensive. On the other hand, the short wavelength at 2.4 GHz allows for simple construction of very high gain directional antennas. Although Part 15 rules forbid any modification of commercially constructed systems, amateur radio operators may modify commercial systems for optimized construction of long links, for example. Using only 200 mW link radios and high gain directional antennas, a very narrow beam may be used to construct reliable links with minimal radio frequency interference to other users.
Kamis, 27 September 2007
Advantages of Wi-Fi
Wi-Fi allows LANs to be deployed without cabling 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 2007 wireless network adapters are built into most modern laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in ever more devices. Wi-Fi has become widespread in corporate infrastructures, which also helps with the deployment of RFID technology that can piggyback on Wi-Fi.[2]
Different competitive brands of access points and client network interfaces are inter-operable at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards inter-operable. Wi-Fi is a global set of standards. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi is widely available in more than 250,000 public hotspots and tens of millions of homes and corporate and university campuses worldwide. WPA is not easily cracked if strong passwords are used and WPA2 encryption has no known weaknesses. 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.
Disadvantages of Wi-Fi
Spectrum assignments and operational limitations are not consistent 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, is now essentially homogeneous in this respect. A very confusing aspect is the fact a WiFI signal actually occupies five channels in the 2.4 GHz resulting in only 3 non-overlapped channels in the US: 1, 6, 11, and four in Europe: 1,5,9,13
Some countries, such as Italy, formerly required a 'general authorization' for any Wi-Fi used outside an operator's own premises, or require something akin to an operator registration.[citation needed] Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (0.1 W).
Power consumption is fairly high compared to some other low-bandwidth standards, such as Zigbee and Bluetooth, making battery life a concern.
The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be easily breakable even when correctly configured. Wi-Fi Protected Access (WPA and WPA2), which began shipping in 2003, aims to solve this problem and is now available on most products. Wi-Fi Access Points typically default to an open (encryption-free) mode. Novice users benefit from a zero-configuration device that works out of the box, but this default is without security enabled, providing open wireless access to their LAN. To turn security on requires the user to configure the device, usually via a software graphical user interface (GUI). Wi-Fi networks that are open (unencrypted) can be monitored and used to read and copy data (including personal information) transmitted over the network, unless another security method is used to secure the data, such as a VPN or a secure web page. (See HTTPS/Secure Socket Layer.)
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.
Wi-Fi networks have limited range. A typical Wi-Fi home 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. 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 range with improved (directional) antennas can be several kilometres or more with line-of-sight.
Wi-Fi pollution, or an excessive number of access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other access points by others, caused by overlapping channels in the 802.11g/b spectrum, as well as with decreased signal-to-noise ratio (SNR) between access points. This can be a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points. Additionally, other devices use the 2.4 GHz band: microwave ovens, cordless phones, baby monitors, security cameras, and Bluetooth devices can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a WiFi 5GHz product (802.11a) usually a dual band product as the 5GHz band is relatively unused and there are many more channels available. This also requires users to set up the 5GHz band to be the preferred network in the client and to configure each network band to a different name(SSID).
It is also an issue when municipalities,[3] or other large entities such as universities, seek to provide large area coverage. Everyone is considered equal for the base standard without 802.11e/WMM when they use the band. This openness is also important to the success and widespread use of 2.4 GHz Wi-Fi, but makes it unsuitable for "must-have" public service functions or where reliability is required.
Interoperability issues between brands or proprietary deviations from the standard can disrupt connections or lower throughput speeds on other user's devices that are within range. Additionally, Wi-Fi devices do not, as of 2007, pick channels to avoid interference.
As of 2007 wireless network adapters are built into most modern laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in ever more devices. Wi-Fi has become widespread in corporate infrastructures, which also helps with the deployment of RFID technology that can piggyback on Wi-Fi.[2]
Different competitive brands of access points and client network interfaces are inter-operable at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards inter-operable. Wi-Fi is a global set of standards. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi is widely available in more than 250,000 public hotspots and tens of millions of homes and corporate and university campuses worldwide. WPA is not easily cracked if strong passwords are used and WPA2 encryption has no known weaknesses. 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.
Disadvantages of Wi-Fi
Spectrum assignments and operational limitations are not consistent 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, is now essentially homogeneous in this respect. A very confusing aspect is the fact a WiFI signal actually occupies five channels in the 2.4 GHz resulting in only 3 non-overlapped channels in the US: 1, 6, 11, and four in Europe: 1,5,9,13
Some countries, such as Italy, formerly required a 'general authorization' for any Wi-Fi used outside an operator's own premises, or require something akin to an operator registration.[citation needed] Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (0.1 W).
Power consumption is fairly high compared to some other low-bandwidth standards, such as Zigbee and Bluetooth, making battery life a concern.
The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be easily breakable even when correctly configured. Wi-Fi Protected Access (WPA and WPA2), which began shipping in 2003, aims to solve this problem and is now available on most products. Wi-Fi Access Points typically default to an open (encryption-free) mode. Novice users benefit from a zero-configuration device that works out of the box, but this default is without security enabled, providing open wireless access to their LAN. To turn security on requires the user to configure the device, usually via a software graphical user interface (GUI). Wi-Fi networks that are open (unencrypted) can be monitored and used to read and copy data (including personal information) transmitted over the network, unless another security method is used to secure the data, such as a VPN or a secure web page. (See HTTPS/Secure Socket Layer.)
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.
Wi-Fi networks have limited range. A typical Wi-Fi home 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. 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 range with improved (directional) antennas can be several kilometres or more with line-of-sight.
Wi-Fi pollution, or an excessive number of access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other access points by others, caused by overlapping channels in the 802.11g/b spectrum, as well as with decreased signal-to-noise ratio (SNR) between access points. This can be a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points. Additionally, other devices use the 2.4 GHz band: microwave ovens, cordless phones, baby monitors, security cameras, and Bluetooth devices can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a WiFi 5GHz product (802.11a) usually a dual band product as the 5GHz band is relatively unused and there are many more channels available. This also requires users to set up the 5GHz band to be the preferred network in the client and to configure each network band to a different name(SSID).
It is also an issue when municipalities,[3] or other large entities such as universities, seek to provide large area coverage. Everyone is considered equal for the base standard without 802.11e/WMM when they use the band. This openness is also important to the success and widespread use of 2.4 GHz Wi-Fi, but makes it unsuitable for "must-have" public service functions or where reliability is required.
Interoperability issues between brands or proprietary deviations from the standard can disrupt connections or lower throughput speeds on other user's devices that are within range. Additionally, Wi-Fi devices do not, as of 2007, pick channels to avoid interference.
Channels of Wifi
Channels
Except for 802.11a/n, which operates at 5 GHz, Wi-Fi devices historically primarily use the spectrum in 2.4 GHz, which is standardized and unlicensed by international agreement, although the exact frequency allocations and maximum permitted power vary slightly in different parts of the world. Channel numbers, however, are standardized by frequency throughout the world, so authorized frequencies can be identified by channel numbers. The 2.4 GHz band is also used by microwave ovens, Bluetooth devices, Amateur radio, legal domestic videosenders, Security systems (including cordless CCTV), also (in North America) cordless phones and baby monitors.
The maximum number of available channels for Wi-Fi enabled devices are:
* 7 for Israel (only Channels 3 through 9 are permitted)
* 11 for North America. Only channels 1, 6, and 11 are recommended for 802.11b/g to minimize interference from adjacent channels.[1] (Note: In Mexico Channels 1 through 8 are reserved "for indoor use only")
* 13 for China and most countries in Europe. A typical channel layout for 802.11b would be 1/7/13 (or 1/6/11 for compatibility to devices bought in North America). For traffic that is predominantly 802.11g, 1/5/9/13 provides a fourth frequency enabling a much better frequency plan. (Note: In France only Channels 10 through 13 are available)
* 14 for Japan.
There are also restrictions on power levels and permitted antenna types which vary by country.
Wi-Fi on various operating systems
There are two sides to Wi-Fi support under an operating system: driver level support, and configuration and management support.
Driver support is usually provided by the manufacturer of the hardware or, in the case of Unix clones such as Linux and FreeBSD, sometimes through open source projects.
Configuration and management support consists of software to enumerate, join, and check the status of available Wi-Fi networks. This also includes support for various encryption methods. These systems are often provided by the operating system backed by a standard driver model. In most cases, drivers emulate an ethernet device and use the configuration and management utilities built into the operating system. In cases where built in configuration and management support is non-existent or inadequate, hardware manufacturers may include their own software to handle the respective tasks.
Microsoft Windows
Microsoft Windows has comprehensive driver-level support for Wi-Fi, the quality of which depends on the hardware manufacturer. Hardware manufactures almost always ship Windows drivers with their products. Windows ships with very few Wi-Fi drivers and depends on the original equipment manufacturers (OEMs)and device manufacturers to make sure users get drivers. Configuration and management depend on the version of Windows.
* Earlier versions of Windows, such as 98, ME and 2000 do not have built-in configuration and management support and must depend on software provided by the manufacturer
* Microsoft Windows XP has built-in configuration and management support. The original shipping version of Windows XP included rudimentary support which was dramatically improved in Service Pack 2. Support for WPA2 and some other security protocols require updates from Microsoft. There are still problems with XP support of Wi-Fi. (One simple interface problem is that if the user makes a mistake in the (case sensitive) passphrase, XP keeps trying to connect but never tells the user that the passphrase is wrong. A second problem is not allowing the user to see different BSSID's for the same ESSID; that is, it provides no way for the user to differentiate access points with the same name.) To make up for Windows’ inconsistent and sometimes inadequate configuration and management support, many hardware manufacturers include their own software and require the user to disable Windows’ built-in Wi-Fi support. See article "Windows XP Bedevils Wi-Fi Users" in Wired News.
* Microsoft Windows Vista has improved Wi-Fi support over Windows XP. The original betas automatically connected to unsecured networks without the user’s approval. The release candidate (RC1 or RC2) does not continue to display this behavior, requiring user permissions to connect to an unsecured network, as long as the user account is in the default configuration with regards to User Account Control.
Apple Mac OS
Apple was an early adopter of Wi-Fi, introducing its AirPort product line, based on the 802.11b standard, in July 1999. Apple then introduced AirPort Extreme as an implementation of 802.11g. All Macs starting with the original iBook included AirPort slots for which an AirPort card can be used, connecting to the computer's internal antenna. All Intel-based Macs either come with built-in Airport Extreme or a slot for an AirPort card. In late 2006, Apple began shipping Macs with Broadcom Wi-Fi chips that also supported the Draft 802.11n standard which can be unlocked through buying a $2 driver released by Apple at the January 2007 Macworld Expo. The driver is also included for free with Apple's 802.11n AirPort Extreme.
Apple makes the Mac OS operating system, the computer hardware, the accompanying drivers, AirPort WiFi base stations, and configuration and management software, simplifying Wi-Fi integration. The built-in configuration and management is integrated throughout many of the operating system's applications and utilities. Mac OS X has Wi-Fi support, including WPA2, and ships with drivers for Apple’s Broadcom-based AirPort cards. Many third-party manufacturers make compatible hardware along with the appropriate drivers which work with Mac OS X’s built-in configuration and management software. Other manufacturers distribute their own software.
Apple's older Mac OS 9 does not have built in support for Wi-Fi configuration and management nor does it ship with Wi-Fi drivers, but Apple provides free drivers and configuration and management software for their AirPort cards for OS 9, as do a few other manufacturers. Versions of Mac OS before OS 9 predate Wi-Fi and do not have any Wi-Fi support, although some third-party hardware manufacturers have made drivers and connection software that allows earlier OSes to use Wi-Fi.[3]
Open source Unix-like systems
Linux, FreeBSD and similar Unix-like clones have much coarser support for Wi-Fi. Due to the open source nature of these operating systems, many different standards have been developed for configuring and managing Wi-Fi devices. The open source nature also fosters open source drivers which have enabled many third party and proprietary devices to work under these operating systems. See Comparison of Open Source Wireless Drivers for more information on those drivers.
* Linux has patchy Wi-Fi support.[4] Native drivers for many Wi-Fi chipsets are available either commercially or at no cost,[5] although some manufacturers don't produce a Linux driver, only a Windows one. Consequently, many popular chipsets either don't have a native Linux driver at all, or only have a half-finished one. For these, the freely available NdisWrapper and its commercial competitor DriverLoader[6] allow Windows x86 and 64 bit variants NDIS drivers to be used on x86-based Linux systems but not on other architectures. As well as the lack of native drivers, some Linux distributions do not offer a convenient user interface and configuring Wi-Fi on them can be a clumsy and complicated operation compared to configuring wired Ethernet drivers.[7] This is changing with NetworkManager, a utility that allows users to automatically switch between networks without using the command line.
* FreeBSD has Wi-Fi support similar to Linux. Support under FreeBSD is best in the 6.x versions, which introduced full support for WPA and WPA2, although in some cases this is driver dependent. FreeBSD comes with drivers for many wireless cards and chipsets, including those made by Atheros, Ralink, Cisco, D-link, Netgear, and many Centrino chipsets, and provides support for others through the ports collection. FreeBSD also has "Project Evil", which provides the ability to use Windows x86 NDIS drivers on x86-based FreeBSD systems as NdisWrapper does on Linux, and Windows amd64 NDIS drivers on amd64-based systems. ndisgen.
* NetBSD, OpenBSD, and DragonFly BSD have Wi-Fi support similar to FreeBSD. Code for some of the drivers, as well as the kernel framework to support them, is mostly shared among the 4 BSDs.
* Haiku has no Wi-Fi support at all as of April 2007.
Except for 802.11a/n, which operates at 5 GHz, Wi-Fi devices historically primarily use the spectrum in 2.4 GHz, which is standardized and unlicensed by international agreement, although the exact frequency allocations and maximum permitted power vary slightly in different parts of the world. Channel numbers, however, are standardized by frequency throughout the world, so authorized frequencies can be identified by channel numbers. The 2.4 GHz band is also used by microwave ovens, Bluetooth devices, Amateur radio, legal domestic videosenders, Security systems (including cordless CCTV), also (in North America) cordless phones and baby monitors.
The maximum number of available channels for Wi-Fi enabled devices are:
* 7 for Israel (only Channels 3 through 9 are permitted)
* 11 for North America. Only channels 1, 6, and 11 are recommended for 802.11b/g to minimize interference from adjacent channels.[1] (Note: In Mexico Channels 1 through 8 are reserved "for indoor use only")
* 13 for China and most countries in Europe. A typical channel layout for 802.11b would be 1/7/13 (or 1/6/11 for compatibility to devices bought in North America). For traffic that is predominantly 802.11g, 1/5/9/13 provides a fourth frequency enabling a much better frequency plan. (Note: In France only Channels 10 through 13 are available)
* 14 for Japan.
There are also restrictions on power levels and permitted antenna types which vary by country.
Wi-Fi on various operating systems
There are two sides to Wi-Fi support under an operating system: driver level support, and configuration and management support.
Driver support is usually provided by the manufacturer of the hardware or, in the case of Unix clones such as Linux and FreeBSD, sometimes through open source projects.
Configuration and management support consists of software to enumerate, join, and check the status of available Wi-Fi networks. This also includes support for various encryption methods. These systems are often provided by the operating system backed by a standard driver model. In most cases, drivers emulate an ethernet device and use the configuration and management utilities built into the operating system. In cases where built in configuration and management support is non-existent or inadequate, hardware manufacturers may include their own software to handle the respective tasks.
Microsoft Windows
Microsoft Windows has comprehensive driver-level support for Wi-Fi, the quality of which depends on the hardware manufacturer. Hardware manufactures almost always ship Windows drivers with their products. Windows ships with very few Wi-Fi drivers and depends on the original equipment manufacturers (OEMs)and device manufacturers to make sure users get drivers. Configuration and management depend on the version of Windows.
* Earlier versions of Windows, such as 98, ME and 2000 do not have built-in configuration and management support and must depend on software provided by the manufacturer
* Microsoft Windows XP has built-in configuration and management support. The original shipping version of Windows XP included rudimentary support which was dramatically improved in Service Pack 2. Support for WPA2 and some other security protocols require updates from Microsoft. There are still problems with XP support of Wi-Fi. (One simple interface problem is that if the user makes a mistake in the (case sensitive) passphrase, XP keeps trying to connect but never tells the user that the passphrase is wrong. A second problem is not allowing the user to see different BSSID's for the same ESSID; that is, it provides no way for the user to differentiate access points with the same name.) To make up for Windows’ inconsistent and sometimes inadequate configuration and management support, many hardware manufacturers include their own software and require the user to disable Windows’ built-in Wi-Fi support. See article "Windows XP Bedevils Wi-Fi Users" in Wired News.
* Microsoft Windows Vista has improved Wi-Fi support over Windows XP. The original betas automatically connected to unsecured networks without the user’s approval. The release candidate (RC1 or RC2) does not continue to display this behavior, requiring user permissions to connect to an unsecured network, as long as the user account is in the default configuration with regards to User Account Control.
Apple Mac OS
Apple was an early adopter of Wi-Fi, introducing its AirPort product line, based on the 802.11b standard, in July 1999. Apple then introduced AirPort Extreme as an implementation of 802.11g. All Macs starting with the original iBook included AirPort slots for which an AirPort card can be used, connecting to the computer's internal antenna. All Intel-based Macs either come with built-in Airport Extreme or a slot for an AirPort card. In late 2006, Apple began shipping Macs with Broadcom Wi-Fi chips that also supported the Draft 802.11n standard which can be unlocked through buying a $2 driver released by Apple at the January 2007 Macworld Expo. The driver is also included for free with Apple's 802.11n AirPort Extreme.
Apple makes the Mac OS operating system, the computer hardware, the accompanying drivers, AirPort WiFi base stations, and configuration and management software, simplifying Wi-Fi integration. The built-in configuration and management is integrated throughout many of the operating system's applications and utilities. Mac OS X has Wi-Fi support, including WPA2, and ships with drivers for Apple’s Broadcom-based AirPort cards. Many third-party manufacturers make compatible hardware along with the appropriate drivers which work with Mac OS X’s built-in configuration and management software. Other manufacturers distribute their own software.
Apple's older Mac OS 9 does not have built in support for Wi-Fi configuration and management nor does it ship with Wi-Fi drivers, but Apple provides free drivers and configuration and management software for their AirPort cards for OS 9, as do a few other manufacturers. Versions of Mac OS before OS 9 predate Wi-Fi and do not have any Wi-Fi support, although some third-party hardware manufacturers have made drivers and connection software that allows earlier OSes to use Wi-Fi.[3]
Open source Unix-like systems
Linux, FreeBSD and similar Unix-like clones have much coarser support for Wi-Fi. Due to the open source nature of these operating systems, many different standards have been developed for configuring and managing Wi-Fi devices. The open source nature also fosters open source drivers which have enabled many third party and proprietary devices to work under these operating systems. See Comparison of Open Source Wireless Drivers for more information on those drivers.
* Linux has patchy Wi-Fi support.[4] Native drivers for many Wi-Fi chipsets are available either commercially or at no cost,[5] although some manufacturers don't produce a Linux driver, only a Windows one. Consequently, many popular chipsets either don't have a native Linux driver at all, or only have a half-finished one. For these, the freely available NdisWrapper and its commercial competitor DriverLoader[6] allow Windows x86 and 64 bit variants NDIS drivers to be used on x86-based Linux systems but not on other architectures. As well as the lack of native drivers, some Linux distributions do not offer a convenient user interface and configuring Wi-Fi on them can be a clumsy and complicated operation compared to configuring wired Ethernet drivers.[7] This is changing with NetworkManager, a utility that allows users to automatically switch between networks without using the command line.
* FreeBSD has Wi-Fi support similar to Linux. Support under FreeBSD is best in the 6.x versions, which introduced full support for WPA and WPA2, although in some cases this is driver dependent. FreeBSD comes with drivers for many wireless cards and chipsets, including those made by Atheros, Ralink, Cisco, D-link, Netgear, and many Centrino chipsets, and provides support for others through the ports collection. FreeBSD also has "Project Evil", which provides the ability to use Windows x86 NDIS drivers on x86-based FreeBSD systems as NdisWrapper does on Linux, and Windows amd64 NDIS drivers on amd64-based systems. ndisgen.
* NetBSD, OpenBSD, and DragonFly BSD have Wi-Fi support similar to FreeBSD. Code for some of the drivers, as well as the kernel framework to support them, is mostly shared among the 4 BSDs.
* Haiku has no Wi-Fi support at all as of April 2007.
Wi-Fi Technical Information
Evolution of Wi-Fi standards
The IEEE standard that governs Wi-Fi technology is IEEE 802.11; that standard has gone through several generations since its inception in 1997.
802.11. The original version of the standard, released in 1997, specifies two raw data rates of 1 and 2 megabits per second (Mbit/s) to be transmitted via infrared (IR) signals or by either frequency hopping or direct-sequence spread spectrum in the Industrial Scientific Medical frequency band at 2.4 GHz. IR remains a part of the standard but has no actual implementations.
802.11a. The 802.11a amendment to the original standard was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard and yields realistic throughput in the mid-20 Mbit/s. Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points.
802.11b. The 802.11b amendment to the original standard was ratified in 1999. 802.11b has a maximum raw data rate of 11 Mbit/s and uses the same CSMA/CA media access method defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.
802.11g. In June 2003, a third standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbit/s, or about 24.7 Mbit/s net throughputs (like 802.11a). Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones.
802.11n. 802.11n builds upon previous standards by adding MIMO (multiple-input multiple-output). MIMO uses multiple transmitter and receiver antennas to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity, through coding. On January 19, 2007, the IEEE 802.11 Working Group unanimously approved 802.11n to issue a new Draft 2.0 of the proposed standard.
Wi-Fi: How it Works
Wi-Fi networks use radio technologies called IEEE 802.11 to provide secure, reliable, fast wireless connectivity. A typical Wi-Fi setup contains one or more Access Points (APs) and one or more clients. An AP broadcasts its SSID (Service Set Identifier, "Network name") via packets that are called beacons, which are usually broadcast every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of relatively short duration and therefore do not have a significant effect on performance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that the client that receives the beacon can communicate at at least 1 Mbit/s. Based on the settings (e.g. the SSID), the client may decide whether to connect to an AP. If two APs of the same SSID are in range of the client, the client firmware might use signal strength to decide with which of the two APs to make a connection.
The Wi-Fi standard leaves connection criteria and roaming totally open to the client. This is a strength of Wi-Fi, but also means that one wireless adapter may perform substantially better than another. Since Wi-Fi transmits in the air, it has the same properties as a non-switched wired Ethernet network, and therefore collisions can occur. Unlike a wired Ethernet, and like most packet radios, Wi-Fi cannot do collision detection, and instead uses an acknowledgment packet for every data packet sent. If no acknowledgement is received within a certain time a retransmission occurs. Also, a medium reservation protocol can be used when excessive collisions are experienced or expected (RequestToSend/ClearToSend used for Collision Avoidance or CA) in an attempt to try to avoid collisions.
A Wi-Fi network can be used to connect computers to each other to the internet and to wired networks (which use IEEE 802.3 or Ethernet). Wi-Fi networks operate in the unlicensed 2.4 (802.11b/g) and 5 GHz (802.11a/h) radio bands, with an 11 Mbit/s (802.11b) or 54 Mbit/s (802.11a or g) data rate or with products that contain both bands (dual band). They can provide real world performance similar to the basic 10BaseT wired Ethernet networks.
The IEEE standard that governs Wi-Fi technology is IEEE 802.11; that standard has gone through several generations since its inception in 1997.
802.11. The original version of the standard, released in 1997, specifies two raw data rates of 1 and 2 megabits per second (Mbit/s) to be transmitted via infrared (IR) signals or by either frequency hopping or direct-sequence spread spectrum in the Industrial Scientific Medical frequency band at 2.4 GHz. IR remains a part of the standard but has no actual implementations.
802.11a. The 802.11a amendment to the original standard was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard and yields realistic throughput in the mid-20 Mbit/s. Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points.
802.11b. The 802.11b amendment to the original standard was ratified in 1999. 802.11b has a maximum raw data rate of 11 Mbit/s and uses the same CSMA/CA media access method defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.
802.11g. In June 2003, a third standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbit/s, or about 24.7 Mbit/s net throughputs (like 802.11a). Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones.
802.11n. 802.11n builds upon previous standards by adding MIMO (multiple-input multiple-output). MIMO uses multiple transmitter and receiver antennas to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity, through coding. On January 19, 2007, the IEEE 802.11 Working Group unanimously approved 802.11n to issue a new Draft 2.0 of the proposed standard.
Wi-Fi: How it Works
Wi-Fi networks use radio technologies called IEEE 802.11 to provide secure, reliable, fast wireless connectivity. A typical Wi-Fi setup contains one or more Access Points (APs) and one or more clients. An AP broadcasts its SSID (Service Set Identifier, "Network name") via packets that are called beacons, which are usually broadcast every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of relatively short duration and therefore do not have a significant effect on performance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that the client that receives the beacon can communicate at at least 1 Mbit/s. Based on the settings (e.g. the SSID), the client may decide whether to connect to an AP. If two APs of the same SSID are in range of the client, the client firmware might use signal strength to decide with which of the two APs to make a connection.
The Wi-Fi standard leaves connection criteria and roaming totally open to the client. This is a strength of Wi-Fi, but also means that one wireless adapter may perform substantially better than another. Since Wi-Fi transmits in the air, it has the same properties as a non-switched wired Ethernet network, and therefore collisions can occur. Unlike a wired Ethernet, and like most packet radios, Wi-Fi cannot do collision detection, and instead uses an acknowledgment packet for every data packet sent. If no acknowledgement is received within a certain time a retransmission occurs. Also, a medium reservation protocol can be used when excessive collisions are experienced or expected (RequestToSend/ClearToSend used for Collision Avoidance or CA) in an attempt to try to avoid collisions.
A Wi-Fi network can be used to connect computers to each other to the internet and to wired networks (which use IEEE 802.3 or Ethernet). Wi-Fi networks operate in the unlicensed 2.4 (802.11b/g) and 5 GHz (802.11a/h) radio bands, with an 11 Mbit/s (802.11b) or 54 Mbit/s (802.11a or g) data rate or with products that contain both bands (dual band). They can provide real world performance similar to the basic 10BaseT wired Ethernet networks.
Wireless
Wi-Fi, also unofficially known as Wireless Fidelity, is a wireless technology brand owned by the Wi-Fi Alliance intended to improve the interoperability of wireless local area network products based on the IEEE 802.11 standards.
Common applications for Wi-Fi include Internet and VoIP phone access, gaming, and network connectivity for consumer electronics such as televisions, DVD players, and digital cameras.
Wi-Fi Alliance is a consortium of separate and independent companies agreeing to a set of common interoperable products based on the family of IEEE 802.11 standards. Wi-Fi certifies products via a set of established test procedures to establish interoperability. Those manufacturers that are members of Wi-Fi Alliance whose products pass these interoperability tests can mark their products and product packaging with the Wi-Fi logo.
According to the brand style guide of the Wi-Fi Alliance (the owner of the Wi-Fi brand):
Products which successfully pass the Wi-Fi Alliance testing may use the Wi-Fi CERTIFIED brand. The Alliance tests and certifies the interoperability of wireless LAN products based on the IEEE 802.11 standards. Studies show that 88% of consumers prefer products that have been tested by an independent organization.
Wi-Fi technologies have gone through several generations since their inception in 1997. Wi-Fi is supported to different extents under Microsoft Windows, Apple Macintosh and open source Unix and Linux operating systems. Contrary to popular belief, Wi-Fi is not an abbreviation for "Wireless Fidelity" .
Uses
A Wi-Fi enabled device such as a PC, game console, cell phone, MP3 player or PDA can connect to the Internet when within range of a wireless network connected to the Internet. The area covered by one or more interconnected access points is called a hotspot. Hotspots can cover as little as a single room with wireless-opaque walls or as much as many square miles covered by overlapping access points. Wi-Fi can also be used to create a mesh network. Both architectures are used in community networks.[citation needed]
Wi-Fi also allows connectivity in peer-to-peer (wireless ad-hoc network) mode, which enables devices to connect directly with each other. This connectivity mode is useful in consumer electronics and gaming applications.
When the technology was first commercialized there were many problems because consumers could not be sure that products from different vendors would work together. The Wi-Fi Alliance began as a community to solve this issue so as to address the needs of the end user and allow the technology to mature. The Alliance created the branding Wi-Fi CERTIFIED to show consumers that products are interoperable with other products displaying the same branding.
Many consumer devices use Wi-Fi. Amongst others, personal computers can network to each other and connect to the Internet, mobile computers can connect to the Internet from any Wi-Fi hotspot, and digital cameras can transfer images wirelessly.
Routers which incorporate a DSL or cable modem and a Wi-Fi access point are often used in homes and other premises, and provide Internet access and internetworking to all devices connected wirelessly or by cable into them. Devices supporting Wi-Fi can also be connected in ad-hoc mode for client-to-client connections without a router.
Business and industrial Wi-Fi is widespread as of 2007. In business environments, increasing the number of Wi-Fi access points provides redundancy, support for fast roaming and increased overall network capacity by using more channels or creating 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 be simply 'dumb' radios. Outdoor applications may utilize true mesh topologies. As of 2007 Wi-Fi installations can provide a secure computer networking gateway, firewall, DHCP server, intrusion detection system, and other functions.
In addition to restricted use in homes and offices, Wi-Fi is publicly available at Wi-Fi hotspots provided either free of charge or to subscribers to various providers. Free hotspots are often provided by businesses such as hotels, restaurants, and airports who offer the service to attract or assist clients. Sometimes free Wi-Fi is provided by enthusiasts, or by organizations or authorities who wish to promote business in their area. Metropolitan-wide WiFi (Mu-Fi) already has more than 300 projects in process.
Common applications for Wi-Fi include Internet and VoIP phone access, gaming, and network connectivity for consumer electronics such as televisions, DVD players, and digital cameras.
Wi-Fi Alliance is a consortium of separate and independent companies agreeing to a set of common interoperable products based on the family of IEEE 802.11 standards. Wi-Fi certifies products via a set of established test procedures to establish interoperability. Those manufacturers that are members of Wi-Fi Alliance whose products pass these interoperability tests can mark their products and product packaging with the Wi-Fi logo.
According to the brand style guide of the Wi-Fi Alliance (the owner of the Wi-Fi brand):
Products which successfully pass the Wi-Fi Alliance testing may use the Wi-Fi CERTIFIED brand. The Alliance tests and certifies the interoperability of wireless LAN products based on the IEEE 802.11 standards. Studies show that 88% of consumers prefer products that have been tested by an independent organization.
Wi-Fi technologies have gone through several generations since their inception in 1997. Wi-Fi is supported to different extents under Microsoft Windows, Apple Macintosh and open source Unix and Linux operating systems. Contrary to popular belief, Wi-Fi is not an abbreviation for "Wireless Fidelity" .
Uses
A Wi-Fi enabled device such as a PC, game console, cell phone, MP3 player or PDA can connect to the Internet when within range of a wireless network connected to the Internet. The area covered by one or more interconnected access points is called a hotspot. Hotspots can cover as little as a single room with wireless-opaque walls or as much as many square miles covered by overlapping access points. Wi-Fi can also be used to create a mesh network. Both architectures are used in community networks.[citation needed]
Wi-Fi also allows connectivity in peer-to-peer (wireless ad-hoc network) mode, which enables devices to connect directly with each other. This connectivity mode is useful in consumer electronics and gaming applications.
When the technology was first commercialized there were many problems because consumers could not be sure that products from different vendors would work together. The Wi-Fi Alliance began as a community to solve this issue so as to address the needs of the end user and allow the technology to mature. The Alliance created the branding Wi-Fi CERTIFIED to show consumers that products are interoperable with other products displaying the same branding.
Many consumer devices use Wi-Fi. Amongst others, personal computers can network to each other and connect to the Internet, mobile computers can connect to the Internet from any Wi-Fi hotspot, and digital cameras can transfer images wirelessly.
Routers which incorporate a DSL or cable modem and a Wi-Fi access point are often used in homes and other premises, and provide Internet access and internetworking to all devices connected wirelessly or by cable into them. Devices supporting Wi-Fi can also be connected in ad-hoc mode for client-to-client connections without a router.
Business and industrial Wi-Fi is widespread as of 2007. In business environments, increasing the number of Wi-Fi access points provides redundancy, support for fast roaming and increased overall network capacity by using more channels or creating 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 be simply 'dumb' radios. Outdoor applications may utilize true mesh topologies. As of 2007 Wi-Fi installations can provide a secure computer networking gateway, firewall, DHCP server, intrusion detection system, and other functions.
In addition to restricted use in homes and offices, Wi-Fi is publicly available at Wi-Fi hotspots provided either free of charge or to subscribers to various providers. Free hotspots are often provided by businesses such as hotels, restaurants, and airports who offer the service to attract or assist clients. Sometimes free Wi-Fi is provided by enthusiasts, or by organizations or authorities who wish to promote business in their area. Metropolitan-wide WiFi (Mu-Fi) already has more than 300 projects in process.
Selasa, 18 September 2007
Types, Format of Ringtones
Types of Ringtones
* Monophonic
A Monophonic ringtone is a ringtone that can play only one type of musical tone at a time.
* Polyphonic
A Polyphonic ringtone is a ringtone that can play several types of tones at a time (up to 72 in recent phones). The first polyphonic ringtones used sequenced recording methods such as MIDI. Such recordings specify what instrument should play a note at a given time, but the actual instrument sound is dependent upon the playback device.
* Realtone
A Truetone is a Ring tone which has been encoded with a high fidelity format such MP3, AAC, or WMA format, and represents the latest evolution of the ringtone. It is often also referred to as a Mastertone, a Realtone or a Superphonic Ringtone. Real tones, which are often excerpts from pop songs, have become popular as ringtones. A recent innovation is the singtone, whereby the user’s voice is recorded to a popular track and then “tuned-up” automatically to sound in key. This can then be downloaded as a ringtone or sent to another user’s mobile phone.
Ringtone formats
* eMelody - Older Ericsson format.
* iMelody - Most new phones that don't do Nokia's Smart Messaging are using this format.
* KWS - Kyocera's ringer format.
* MID / MIDI - Popular sound format.
* Morse code - Text files with a .MORSE extension get converted into morse code songs
* MOT - An older ringer format for Motorola phones.
* MP3 - Some phones support ringtones that are mp3 format.
* Nokia / SCKL / OTT - Nokia Smart Messaging format. Nokia phones can receive ringtones as a text message. Ringtone tools can create these text messages. This allows anyone with a compatible phone to load their own ringtones in without a data cable. There are other phones besides Nokia that use this.
* PDB - Palm database. This is the format used to load ringtones on PDA phones such as the Kyocera 6035 and the Handspring Treo
* QCP - File format generated by Qualcomm PureVoice software.
* RTTTL - A popular text format for ringtones.
* RTX - Similar to rtttl with some advanced features. Also the octaves are different on rtx.
* Samsung1 & Samsung2 - Samsung keypress format.
* Siemens Keypress - Can create and read in a Siemens text file format.
* Siemens SEO - Siemens SEO binary format.
* SMAF - Yamaha music format that combines MIDI with instrument sound data (ala Module files). Filenames have the extension "MMF."
* AAC - Some phones like the Sony Ericsson W810i support ring tones in ".m4a" AAC format.
* Monophonic
A Monophonic ringtone is a ringtone that can play only one type of musical tone at a time.
* Polyphonic
A Polyphonic ringtone is a ringtone that can play several types of tones at a time (up to 72 in recent phones). The first polyphonic ringtones used sequenced recording methods such as MIDI. Such recordings specify what instrument should play a note at a given time, but the actual instrument sound is dependent upon the playback device.
* Realtone
A Truetone is a Ring tone which has been encoded with a high fidelity format such MP3, AAC, or WMA format, and represents the latest evolution of the ringtone. It is often also referred to as a Mastertone, a Realtone or a Superphonic Ringtone. Real tones, which are often excerpts from pop songs, have become popular as ringtones. A recent innovation is the singtone, whereby the user’s voice is recorded to a popular track and then “tuned-up” automatically to sound in key. This can then be downloaded as a ringtone or sent to another user’s mobile phone.
Ringtone formats
* eMelody - Older Ericsson format.
* iMelody - Most new phones that don't do Nokia's Smart Messaging are using this format.
* KWS - Kyocera's ringer format.
* MID / MIDI - Popular sound format.
* Morse code - Text files with a .MORSE extension get converted into morse code songs
* MOT - An older ringer format for Motorola phones.
* MP3 - Some phones support ringtones that are mp3 format.
* Nokia / SCKL / OTT - Nokia Smart Messaging format. Nokia phones can receive ringtones as a text message. Ringtone tools can create these text messages. This allows anyone with a compatible phone to load their own ringtones in without a data cable. There are other phones besides Nokia that use this.
* PDB - Palm database. This is the format used to load ringtones on PDA phones such as the Kyocera 6035 and the Handspring Treo
* QCP - File format generated by Qualcomm PureVoice software.
* RTTTL - A popular text format for ringtones.
* RTX - Similar to rtttl with some advanced features. Also the octaves are different on rtx.
* Samsung1 & Samsung2 - Samsung keypress format.
* Siemens Keypress - Can create and read in a Siemens text file format.
* Siemens SEO - Siemens SEO binary format.
* SMAF - Yamaha music format that combines MIDI with instrument sound data (ala Module files). Filenames have the extension "MMF."
* AAC - Some phones like the Sony Ericsson W810i support ring tones in ".m4a" AAC format.
Free Ringtone for Your Mobile
Ringtone
A ringtone or ring tone (ringing tone in the British Isles) is the sound made by a telephone to indicate an incoming call. The term, however, is most often used to refer to the customizable sounds available on mobile phones. This facility was originally provided so that people would be able to determine when their phone was ringing when in the company of other mobile phone owners.
A phone only rings when a special "ringing signal" is sent to it. For regular telephones, the ringing signal is a 90-volt, 20-hertz, AC wave generated by the switch to which the telephone is connected. For mobile phones, the ringing signal is a specific, radio-frequency signal.
A telephone ring is the sound generated when an incoming telephone call is received. The term originated from the fact that telephones notified the household of an incoming call by repeatedly striking a bell or bells, producing a ringing sound.
This "Magneto" bell system is still in widespread use; newer telephones use electronic sounders to produce other noises, but the term "ring" is still used. The ringing signal sent to a customer's telephone is AC at around 90 volts (at 20 hertz in North America, because of the use of 60 Hz mains; other regions with 50 Hz mains use 25 Hz); modern telephones electronically produce a warbling or chirping sound. The signal is sent for every ring and allows phone operators to provide several services with different kinds of rings (for example, rings with a shorter interval between them might be used to signal a call from a given number). When a home phone rings, it may carry Caller ID information and present it on a screen.
The ringing cadence differs between telephone administrations: the UK and many countries of the British Commonwealth use "brr-brr" at 2s intervals; north America and much of continental Europe use "brr" with a variety of intervals.
A ringtone or ring tone (ringing tone in the British Isles) is the sound made by a telephone to indicate an incoming call. The term, however, is most often used to refer to the customizable sounds available on mobile phones. This facility was originally provided so that people would be able to determine when their phone was ringing when in the company of other mobile phone owners.
A phone only rings when a special "ringing signal" is sent to it. For regular telephones, the ringing signal is a 90-volt, 20-hertz, AC wave generated by the switch to which the telephone is connected. For mobile phones, the ringing signal is a specific, radio-frequency signal.
A telephone ring is the sound generated when an incoming telephone call is received. The term originated from the fact that telephones notified the household of an incoming call by repeatedly striking a bell or bells, producing a ringing sound.
This "Magneto" bell system is still in widespread use; newer telephones use electronic sounders to produce other noises, but the term "ring" is still used. The ringing signal sent to a customer's telephone is AC at around 90 volts (at 20 hertz in North America, because of the use of 60 Hz mains; other regions with 50 Hz mains use 25 Hz); modern telephones electronically produce a warbling or chirping sound. The signal is sent for every ring and allows phone operators to provide several services with different kinds of rings (for example, rings with a shorter interval between them might be used to signal a call from a given number). When a home phone rings, it may carry Caller ID information and present it on a screen.
The ringing cadence differs between telephone administrations: the UK and many countries of the British Commonwealth use "brr-brr" at 2s intervals; north America and much of continental Europe use "brr" with a variety of intervals.
Senin, 17 September 2007
Types of shoes
Dress and casual shoes
Dress shoes are categorized by smooth and supple leather uppers, leather soles, and narrow sleek shape. Casual shoes are characterized by sturdy leather uppers, non-leather outsoles, and wide profile.
Some designs of dress shoes can be worn by either gender. The majority of dress shoes have an upper covering, commonly made of leather, enclosing most of the lower foot, but not covering the ankles. This upper part of the shoe is often made without apertures or openings, but may also be made with openings or even itself consist of a series of straps, e.g. an open toe featured in women's shoes. Shoes with uppers made high to cover the ankles are also available; a shoe with the upper rising above the ankle is usually considered a boot but certain styles may be referred to as high-topped shoes or high-tops. Usually, a high-topped shoe is secured by laces or zippers, although some styles have elastic inserts to ease slipping the shoe on.
Shoes made from real crocodile skin, in a conservation exhibit at Bristol Zoo, England
Shoes made from real crocodile skin, in a conservation exhibit at Bristol Zoo, England
Men's shoes
Men's shoes can be categorized by how they are closed:
* Balmorals - the vamp has a V-shaped slit to which the laces are attached; also known as "closed lacing." In England, the balmoral is known as the Oxford. The word "Oxford" is used by American clothing companies to market shoes that are not Oxfords, such as rubber-sole bluchers.
* Blüchers - the laces are tied to two pieces of leather independently attached to the vamp; also known as "open lacing." In England, the Blucher is known as the Derby shoe.
* Monk-straps - a buckle and strap instead of lacing
Various other closings exist but are less popular such as side-elastic closings.
Men's shoes can also be decorated in various ways:
* Plain-toes - have a sleek appearance and no extra decorations on the vamp.
* Cap-toes - has an extra layer of leather that 'caps' the toe. This is possibly the most popular decoration
* Wing-tips - The toe of the shoe is covered with a perforated panel, the wing-tip, which extends down either side of the shoe. Wing-tips can be found in both balmoral and blucher styles. In England this is called a brogue.
Women's shoes
There is a large variety of shoes available for women. Some broad categories are:
Pumps, known in the US as ballerinas or skimmers, are shoes with a very low heel and a relatively short vamp, exposing much of the instep. They are popular for warm-weather wear, and may be seen as more comfortable than shoes with a higher heel.
High heels may be shoes with heels 2 inches (5 cm) or higher. They are often seen as having more sex appeal than low heels (see article for discussion) and are thus commonly worn by women for formal occasions or social outings.
* Sneaker boot and sneaker pump - a shoe that looks like an athletic shoe, but is equipped with a heel, making it a kind of novelty dress shoe
Either gender
Women's sandals.
Women's sandals.
* Clog
* Platform shoe - shoe with very thick soles and heels
* Moccasin - originated by American Indians, a soft shoe without a heel and usually made of leather.
* Sandals - open shoes consisting of a sole and various straps, leaving much of the foot exposed to air. They are thus popular for warm-weather wear, because they let the foot be cooler than a closed-toed shoe would.
* Saddle shoe - leather shoe with a contrasting saddle-shaped band over the instep, typically white uppers with black "saddle"
* Loafer - a dress or casual shoe without laces; often with tassels, buckles, or coin-holders (penny loafers)
* Boating shoes, also known as boat shoes and deck shoes - similar to a loafer, but more casual. Laces, if present, are usually simple leather (often two-tone) with no frills. Often made of canvas or featuring a white sole. They have soft soles/heels to avoid marring or scratching a boat deck.
A pair of leather roper boots
A pair of leather roper boots
* Boots - Long shoes (covering the ankle) frequently made of leather. Some are designed to be used in times of bad weather, or simply as an alternate style of casual or dress wear. Styles include rubber boots and snow boots, as well as work boots and hiking boots.
* Slippers - Usually for night use, commonly worn with pajamas
Athletic shoes
Men's and women's athletic shoes and special function shoes often have less difference between the sexes than in dress shoes. In many cases these shoes can be worn by either sex. Emphasis tends to be more on function than style.
A shoe for right foot
A shoe for right foot
* Sneakers/trainers (also called gym shoes or tennis shoes) - general purpose athletic shoes; made out of rubber, cloth, and/or plastic to be lightweight, flexible, and have good traction. Special varieties available for basketball or tennis.
* Running shoes - very similar to above, with additional emphasis on cushioning.
* Track shoes - lightweight; often with plastic or metal cleats
* Cleats - a type of shoe featuring molded or removable studs. Usually worn while playing sports such as rugby, football, American football, or baseball
* Golf shoes - with "spikes" for better grip in grass and wet ground. Originally the spikes or "cleats" were made of metal but replacable "soft spikes" made of synthetic plastic-like materials with prongs distributed radially around the edge of each spike are much more common today (and are required on many golf courses since they cause less damage to the greens)
* Bowling shoes - intermediate style between ordinary dress shoes and athletic shoes. They have harder rubber soles/heels so as not to damage bowling alley floors. They are often rented or loaned at bowling alleys.
* Climbing shoes, also known as hiking shoes or boots - usually have a high somewhat stiff upper with many lace eyelets, to provide ankle support on uneven terrain, with extra large traction on the sole.
* Walking shoes - have a more flexible sole than the running shoe, lighter in weight than the hiking boot, may have air holes, may not be water proof.
* Skating shoes - typically called skates. They have various attachments for skating on the bottom of the shoe portion.
o Ice skates
o Roller skates
o Inline skates
* Ski boot - a large, thick plastic boot specially designed for attachment to the ski.
* Skateboarding shoes have flat soles for a better grip on a skateboard. They are very wide and have extra layers of padding to protect the skateboarders feet. Many young people wear them for comfort.
* Cycling shoes are equipped with a metal cleat to interface with clipless pedals, as well as a stiff sole to maximize power transfer and support the foot.
* Snowshoes are special shoes for walking in thick snow. In temperate climates, snowshoes are used for mostly recreational purposes in winter.
Dress shoes are categorized by smooth and supple leather uppers, leather soles, and narrow sleek shape. Casual shoes are characterized by sturdy leather uppers, non-leather outsoles, and wide profile.
Some designs of dress shoes can be worn by either gender. The majority of dress shoes have an upper covering, commonly made of leather, enclosing most of the lower foot, but not covering the ankles. This upper part of the shoe is often made without apertures or openings, but may also be made with openings or even itself consist of a series of straps, e.g. an open toe featured in women's shoes. Shoes with uppers made high to cover the ankles are also available; a shoe with the upper rising above the ankle is usually considered a boot but certain styles may be referred to as high-topped shoes or high-tops. Usually, a high-topped shoe is secured by laces or zippers, although some styles have elastic inserts to ease slipping the shoe on.
Shoes made from real crocodile skin, in a conservation exhibit at Bristol Zoo, England
Shoes made from real crocodile skin, in a conservation exhibit at Bristol Zoo, England
Men's shoes
Men's shoes can be categorized by how they are closed:
* Balmorals - the vamp has a V-shaped slit to which the laces are attached; also known as "closed lacing." In England, the balmoral is known as the Oxford. The word "Oxford" is used by American clothing companies to market shoes that are not Oxfords, such as rubber-sole bluchers.
* Blüchers - the laces are tied to two pieces of leather independently attached to the vamp; also known as "open lacing." In England, the Blucher is known as the Derby shoe.
* Monk-straps - a buckle and strap instead of lacing
Various other closings exist but are less popular such as side-elastic closings.
Men's shoes can also be decorated in various ways:
* Plain-toes - have a sleek appearance and no extra decorations on the vamp.
* Cap-toes - has an extra layer of leather that 'caps' the toe. This is possibly the most popular decoration
* Wing-tips - The toe of the shoe is covered with a perforated panel, the wing-tip, which extends down either side of the shoe. Wing-tips can be found in both balmoral and blucher styles. In England this is called a brogue.
Women's shoes
There is a large variety of shoes available for women. Some broad categories are:
Pumps, known in the US as ballerinas or skimmers, are shoes with a very low heel and a relatively short vamp, exposing much of the instep. They are popular for warm-weather wear, and may be seen as more comfortable than shoes with a higher heel.
High heels may be shoes with heels 2 inches (5 cm) or higher. They are often seen as having more sex appeal than low heels (see article for discussion) and are thus commonly worn by women for formal occasions or social outings.
* Sneaker boot and sneaker pump - a shoe that looks like an athletic shoe, but is equipped with a heel, making it a kind of novelty dress shoe
Either gender
Women's sandals.
Women's sandals.
* Clog
* Platform shoe - shoe with very thick soles and heels
* Moccasin - originated by American Indians, a soft shoe without a heel and usually made of leather.
* Sandals - open shoes consisting of a sole and various straps, leaving much of the foot exposed to air. They are thus popular for warm-weather wear, because they let the foot be cooler than a closed-toed shoe would.
* Saddle shoe - leather shoe with a contrasting saddle-shaped band over the instep, typically white uppers with black "saddle"
* Loafer - a dress or casual shoe without laces; often with tassels, buckles, or coin-holders (penny loafers)
* Boating shoes, also known as boat shoes and deck shoes - similar to a loafer, but more casual. Laces, if present, are usually simple leather (often two-tone) with no frills. Often made of canvas or featuring a white sole. They have soft soles/heels to avoid marring or scratching a boat deck.
A pair of leather roper boots
A pair of leather roper boots
* Boots - Long shoes (covering the ankle) frequently made of leather. Some are designed to be used in times of bad weather, or simply as an alternate style of casual or dress wear. Styles include rubber boots and snow boots, as well as work boots and hiking boots.
* Slippers - Usually for night use, commonly worn with pajamas
Athletic shoes
Men's and women's athletic shoes and special function shoes often have less difference between the sexes than in dress shoes. In many cases these shoes can be worn by either sex. Emphasis tends to be more on function than style.
A shoe for right foot
A shoe for right foot
* Sneakers/trainers (also called gym shoes or tennis shoes) - general purpose athletic shoes; made out of rubber, cloth, and/or plastic to be lightweight, flexible, and have good traction. Special varieties available for basketball or tennis.
* Running shoes - very similar to above, with additional emphasis on cushioning.
* Track shoes - lightweight; often with plastic or metal cleats
* Cleats - a type of shoe featuring molded or removable studs. Usually worn while playing sports such as rugby, football, American football, or baseball
* Golf shoes - with "spikes" for better grip in grass and wet ground. Originally the spikes or "cleats" were made of metal but replacable "soft spikes" made of synthetic plastic-like materials with prongs distributed radially around the edge of each spike are much more common today (and are required on many golf courses since they cause less damage to the greens)
* Bowling shoes - intermediate style between ordinary dress shoes and athletic shoes. They have harder rubber soles/heels so as not to damage bowling alley floors. They are often rented or loaned at bowling alleys.
* Climbing shoes, also known as hiking shoes or boots - usually have a high somewhat stiff upper with many lace eyelets, to provide ankle support on uneven terrain, with extra large traction on the sole.
* Walking shoes - have a more flexible sole than the running shoe, lighter in weight than the hiking boot, may have air holes, may not be water proof.
* Skating shoes - typically called skates. They have various attachments for skating on the bottom of the shoe portion.
o Ice skates
o Roller skates
o Inline skates
* Ski boot - a large, thick plastic boot specially designed for attachment to the ski.
* Skateboarding shoes have flat soles for a better grip on a skateboard. They are very wide and have extra layers of padding to protect the skateboarders feet. Many young people wear them for comfort.
* Cycling shoes are equipped with a metal cleat to interface with clipless pedals, as well as a stiff sole to maximize power transfer and support the foot.
* Snowshoes are special shoes for walking in thick snow. In temperate climates, snowshoes are used for mostly recreational purposes in winter.
Shoe
A shoe is an item of footwear. Shoes may vary from a simple flip-flop to a complex boot. Shoes may have high or low heels, although in western cultures, high heels are considered a woman's style. Shoe materials include leather or canvas. Athletic shoe soles may be made of rubber.
Contents
The earliest known shoe dates from about 7000 BCE and was found in California. However, the materials used for making shoes does not normally last for thousands of years, so shoes were probably in use long before this. Physical anthropologist Erik Trinkaus believes he has found evidence that the use of shoes began in the period between about 40,000 and 26,000 years ago, based on the fact that the thickness of the bones of the toes (other than the big toe) decreased during this period, presumably because going barefoot results in greater bone growth before this period
Parts of a shoe
Gluing a new outsole to an athletic shoe.
Gluing a new outsole to an athletic shoe.
Sole
The bottom of a shoe is named the sole.
Insole
The insole is the interior bottom of a shoe, which sits directly beneath the foot. Many shoes have removable and replaceable insoles, and extra insoles are often added for comfort or health reasons (to control the shape, moisture, or smell of the shoe).
Outsole
The outsole is the layer in direct contact with the ground. The material of the outsole depends on the function, dressiness, and quality of the shoe, but is generally very durable material, since it experiences the most stress. Dress shoes have leather outsoles; casual or work-oriented shoes have outsoles made of natural rubber or a synthetic imitation. The outsole may comprise a single piece, or may comprise separate pieces of different materials. Often the heel of the sole is rubber for durability and traction, while the front is leather for style. Specialized shoes will often have modifications on this design: athletic cleats have spikes embedded in the outsole to grip the ground; many kinds of dancing shoes have much softer or harder soles. These soles can be as hard as concrete, and very sturdy.
Heel
The bottom rear part of a shoe is the heel. These come in a variety of sizes and are usually made to support the large stresses applied to the heel of the foot. They are often made of the same material as the sole of the shoe.This part can be high to make the person look taller, or flat.
Vamp, or upper
Any shoe has an upper part that helps hold the shoe onto the foot. In the simplest cases, such as sandals or flip flops, this may be nothing more than a few straps for holding the sole in place. Closed footwear, such as boots, sneakers and most men's shoes, will usually have a more complex upper. This part is normally decorated or is made in a certain style to look fashionable and attractive for the buyer.
Contents
The earliest known shoe dates from about 7000 BCE and was found in California. However, the materials used for making shoes does not normally last for thousands of years, so shoes were probably in use long before this. Physical anthropologist Erik Trinkaus believes he has found evidence that the use of shoes began in the period between about 40,000 and 26,000 years ago, based on the fact that the thickness of the bones of the toes (other than the big toe) decreased during this period, presumably because going barefoot results in greater bone growth before this period
Parts of a shoe
Gluing a new outsole to an athletic shoe.
Gluing a new outsole to an athletic shoe.
Sole
The bottom of a shoe is named the sole.
Insole
The insole is the interior bottom of a shoe, which sits directly beneath the foot. Many shoes have removable and replaceable insoles, and extra insoles are often added for comfort or health reasons (to control the shape, moisture, or smell of the shoe).
Outsole
The outsole is the layer in direct contact with the ground. The material of the outsole depends on the function, dressiness, and quality of the shoe, but is generally very durable material, since it experiences the most stress. Dress shoes have leather outsoles; casual or work-oriented shoes have outsoles made of natural rubber or a synthetic imitation. The outsole may comprise a single piece, or may comprise separate pieces of different materials. Often the heel of the sole is rubber for durability and traction, while the front is leather for style. Specialized shoes will often have modifications on this design: athletic cleats have spikes embedded in the outsole to grip the ground; many kinds of dancing shoes have much softer or harder soles. These soles can be as hard as concrete, and very sturdy.
Heel
The bottom rear part of a shoe is the heel. These come in a variety of sizes and are usually made to support the large stresses applied to the heel of the foot. They are often made of the same material as the sole of the shoe.This part can be high to make the person look taller, or flat.
Vamp, or upper
Any shoe has an upper part that helps hold the shoe onto the foot. In the simplest cases, such as sandals or flip flops, this may be nothing more than a few straps for holding the sole in place. Closed footwear, such as boots, sneakers and most men's shoes, will usually have a more complex upper. This part is normally decorated or is made in a certain style to look fashionable and attractive for the buyer.
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