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Wednesday, April 4, 2007
Wi-Fi: How it Works
Wi-Fi: How it Works
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 who 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 which of the two APs to make a connection to. 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 a packet exchange (RTS/CTS used for Collision Avoidance or CA) to try to avoid collisions.' Wi-Fi networks use radio technologies called IIEE 802.11a, 802.11b or 802.11g to provide secure, reliable, fast wireless connectivity. 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 and 5 GHz radio bands, with an 11 Mbps (802.11b) or 54 Mbps (802.11a) date rate or with products that contain both bands (dual band). They can provide real world performance similar to the basic 10BaseT wired ethernet networks.
Channels
Except for 802.11a, which operates at 5 GHz, Wi-Fi uses the spectrum near 2.4 GHz, which is standardized and unlicensed by international agreement, although the exact frequency allocations vary slightly in different parts of the world, as does maximum permitted power. However, channel numbers are standardized by frequency throughout the world, so authorized frequencies can be identified by channel numbers.
The maximum number of available channels for Wi-Fi enabled devices are:
* 13 for Europe
* 11 for North America. Only channels 1, 6, and 11 are recommended for 802.11b/g to minimize interference from adjacent channels.[1]
* 14 for Japan [2]
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 who 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 which of the two APs to make a connection to. 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 a packet exchange (RTS/CTS used for Collision Avoidance or CA) to try to avoid collisions.' Wi-Fi networks use radio technologies called IIEE 802.11a, 802.11b or 802.11g to provide secure, reliable, fast wireless connectivity. 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 and 5 GHz radio bands, with an 11 Mbps (802.11b) or 54 Mbps (802.11a) date rate or with products that contain both bands (dual band). They can provide real world performance similar to the basic 10BaseT wired ethernet networks.
Channels
Except for 802.11a, which operates at 5 GHz, Wi-Fi uses the spectrum near 2.4 GHz, which is standardized and unlicensed by international agreement, although the exact frequency allocations vary slightly in different parts of the world, as does maximum permitted power. However, channel numbers are standardized by frequency throughout the world, so authorized frequencies can be identified by channel numbers.
The maximum number of available channels for Wi-Fi enabled devices are:
* 13 for Europe
* 11 for North America. Only channels 1, 6, and 11 are recommended for 802.11b/g to minimize interference from adjacent channels.[1]
* 14 for Japan [2]
Advantages n Disadvantages of Wi-Fi
Advantages of Wi-Fi
* Allows LANs to be deployed without cabling, 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.
* Built into all modern laptops
* Wi-Fi chipset pricing continues to come down, making Wi-Fi a very economical networking option and driving inclusion of Wi-Fi in an ever-widening array of devices.
* Wi-Fi products are widely available in the market. Different brands of access points and client network interfaces are interoperable at a basic level of service. Products designated as Wi-Fi CERTIFIED by the Wi-Fi Alliance are interoperable and include WPA2 security.
* Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.
* Widely available in more than 250,000 public hot spots and millions of homes and corporate and university campuses worldwide.
* As of 2006, WPA and WPA2 encryption are not easily crackable if strong passwords are used
* New protocols for Quality of Service (WMM) and power saving mechanisms (WMM Power Save) make Wi-Fi even more suitable for latency-sensitive applications (such as voice and video) and small form-factor
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 US (1-13 vs 1-11); Japan has one more on top of that (1-14) - and some countries, like Spain, prohibit use of the lower-numbered channels. Furthermore some countries, such as Italy, used to require 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 standards, making battery life and heat a concern.
* The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be 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 generally available.
* 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 might not intend to provide open wireless access to their LAN.
* Many 2.4 GHz 802.11b and 802.11g Access points default to the same channel, contributing to congestion on certain channels.
* 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 45 m (150 ft) indoors and 90 m (300 ft) outdoors. Range also varies with frequency band, as Wi-Fi is no exception to the physics of radio wave propagation. Wi-Fi in the 2.4 GHz frequency block has better range than Wi-Fi in the 5 GHz frequency block, and less range than the oldest Wi-Fi (and pre-Wi-Fi) 900 MHz block. Outdoor range with improved antennas can be several kilometres or more with line-of-sight.
* Wi-Fi pollution, meaning interference of a closed or encrypted access point with other open access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other open 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.
* It is also an issue when municipalities or other large entities such as universities seek to provide large area coverage. Everyone is considered equal when they use the band (except for amateur radio operators who are the primary licensee). This openness is also important to the success and widespread use of Wi-Fi, but makes it unsuitable for "must have" public service functions.
* Interoperability issues between brands or deviations from the standard can disrupt connections or lower throughput speeds on other user's devices within range. Wi-Fi Alliance programs test devices for interoperability and designate devices which pass testing as Wi-Fi CERTIFIED.
* Wi-Fi networks can be monitored and used to read and copy data (including personal information) transmitted over the network unless encryption such as WPA or VPN is used.
* For desktop machines that have wired ethernet built in, the speed and reliability of the wired connection might be worth the hassle of running the wire, versus the cost of buying a wireless adapter.
* Allows LANs to be deployed without cabling, 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.
* Built into all modern laptops
* Wi-Fi chipset pricing continues to come down, making Wi-Fi a very economical networking option and driving inclusion of Wi-Fi in an ever-widening array of devices.
* Wi-Fi products are widely available in the market. Different brands of access points and client network interfaces are interoperable at a basic level of service. Products designated as Wi-Fi CERTIFIED by the Wi-Fi Alliance are interoperable and include WPA2 security.
* Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.
* Widely available in more than 250,000 public hot spots and millions of homes and corporate and university campuses worldwide.
* As of 2006, WPA and WPA2 encryption are not easily crackable if strong passwords are used
* New protocols for Quality of Service (WMM) and power saving mechanisms (WMM Power Save) make Wi-Fi even more suitable for latency-sensitive applications (such as voice and video) and small form-factor
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 US (1-13 vs 1-11); Japan has one more on top of that (1-14) - and some countries, like Spain, prohibit use of the lower-numbered channels. Furthermore some countries, such as Italy, used to require 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 standards, making battery life and heat a concern.
* The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be 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 generally available.
* 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 might not intend to provide open wireless access to their LAN.
* Many 2.4 GHz 802.11b and 802.11g Access points default to the same channel, contributing to congestion on certain channels.
* 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 45 m (150 ft) indoors and 90 m (300 ft) outdoors. Range also varies with frequency band, as Wi-Fi is no exception to the physics of radio wave propagation. Wi-Fi in the 2.4 GHz frequency block has better range than Wi-Fi in the 5 GHz frequency block, and less range than the oldest Wi-Fi (and pre-Wi-Fi) 900 MHz block. Outdoor range with improved antennas can be several kilometres or more with line-of-sight.
* Wi-Fi pollution, meaning interference of a closed or encrypted access point with other open access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other open 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.
* It is also an issue when municipalities or other large entities such as universities seek to provide large area coverage. Everyone is considered equal when they use the band (except for amateur radio operators who are the primary licensee). This openness is also important to the success and widespread use of Wi-Fi, but makes it unsuitable for "must have" public service functions.
* Interoperability issues between brands or deviations from the standard can disrupt connections or lower throughput speeds on other user's devices within range. Wi-Fi Alliance programs test devices for interoperability and designate devices which pass testing as Wi-Fi CERTIFIED.
* Wi-Fi networks can be monitored and used to read and copy data (including personal information) transmitted over the network unless encryption such as WPA or VPN is used.
* For desktop machines that have wired ethernet built in, the speed and reliability of the wired connection might be worth the hassle of running the wire, versus the cost of buying a wireless adapter.
Uses Of Wi-Fi
A person with a Wi-Fi enabled device such as a computer, cell phone or PDA can connect to the Internet when in proximity of an access point. The region covered by one or several access points is called a hotspot. Hotspots can range from a single room to many square miles of overlapping hotspots. 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.
A term for certain types of wireless local area networks (WLAN) that use specifications conforming to IEEE
Wi-Fi At Home
Home Wi-Fi infrastructure devices typically fall into the category of a multifunction piece of networking equipment, with wireless being only one of many features proved more information. Home Wi-Fi clients come in many shapes and sizes, from stationary PCs to digital cameras. The trend today and into the future will be to enable wireless into every device where mobility is prudent.
Wi-Fi devices are often used in home or consumer-type environments in the following manner:
* Termination of a broadband connection into a single router which services both wired and wireless clients
* Ad-hoc mode for client to client connections
* Built into non-computer devices to enable simple wireless connectivity to other devices or the Internet
Wi-Fi in gaming
The gaming consoles and handhelds make use of Wi-Fi technology to enhance the gaming experience:
* The Nintendo DS handheld is Wi-Fi compatible. The majority of its Wi-Fi compatible games use only WEP encryption.
* The PlayStation Portable is Wi-Fi compatible, and uses this for local multiplayer as well as connecting to wireless networks for online gameplay.
* The Xbox 360 can be made Wi-Fi compatible if the user purchases a separate wireless adapter.
* The PlayStation 3 Premium model features built-in Wi-Fi, while the Basic model can be upgraded with a separate wireless adapter.
* The Wii is Wi-Fi compatible.
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.
A term for certain types of wireless local area networks (WLAN) that use specifications conforming to IEEE
Wi-Fi At Home
Home Wi-Fi infrastructure devices typically fall into the category of a multifunction piece of networking equipment, with wireless being only one of many features proved more information. Home Wi-Fi clients come in many shapes and sizes, from stationary PCs to digital cameras. The trend today and into the future will be to enable wireless into every device where mobility is prudent.
Wi-Fi devices are often used in home or consumer-type environments in the following manner:
* Termination of a broadband connection into a single router which services both wired and wireless clients
* Ad-hoc mode for client to client connections
* Built into non-computer devices to enable simple wireless connectivity to other devices or the Internet
Wi-Fi in gaming
The gaming consoles and handhelds make use of Wi-Fi technology to enhance the gaming experience:
* The Nintendo DS handheld is Wi-Fi compatible. The majority of its Wi-Fi compatible games use only WEP encryption.
* The PlayStation Portable is Wi-Fi compatible, and uses this for local multiplayer as well as connecting to wireless networks for online gameplay.
* The Xbox 360 can be made Wi-Fi compatible if the user purchases a separate wireless adapter.
* The PlayStation 3 Premium model features built-in Wi-Fi, while the Basic model can be upgraded with a separate wireless adapter.
* The Wii is Wi-Fi compatible.
Tuesday, January 16, 2007
I will be back ....
I m not able to post new updates because i m upgrading
ma server so tht i can serve more users. I will be up
after two weeks so Plz do come back.....
Enjoy!!!
ma server so tht i can serve more users. I will be up
after two weeks so Plz do come back.....
Enjoy!!!
Sunday, January 7, 2007
BitTorrent Revisited
Guys this is awsome i hv experienced da power of Bit torrents.I was downloading
friends (complete season2) thru torrent n hv got such a nice speed ma speed of downloading n uploading was 110 kbs and 9 to 16 kbps respectively. I hv downloaded
1.3GB of content n uploaded around 565 MB.
This was possible only coz of many people downloadin da same file.
So it means if ur downlodin a popular stuff then u would get good speed.
How exactly does BitTorrent Sharing work?
Answer: Torrent sharing is about "swarming and tracking", where users download many small bits from many different sources at once. Because this format compensates for bottleneck points, it is actually faster than downloading a large file from a single source.
* “Swarming” is about splitting large files into hundreds of smaller “bits”, and then sharing those bits across a “swarm” of dozens of linked users.
* “Tracking” is when specific servers help swarm users find each other.
* Swarm members use special Torrent client software to upload, download, and reconstruct the many file bits into complete usable files.
* Special .torrent text files act as pointers during this whole process, helping users find other users to swarm with, and enforcing quality control on all shared files.
To read more on this Plz see da post "BitTorrent"
published on 19 December 2006
friends (complete season2) thru torrent n hv got such a nice speed ma speed of downloading n uploading was 110 kbs and 9 to 16 kbps respectively. I hv downloaded
1.3GB of content n uploaded around 565 MB.
This was possible only coz of many people downloadin da same file.
So it means if ur downlodin a popular stuff then u would get good speed.
How exactly does BitTorrent Sharing work?
Answer: Torrent sharing is about "swarming and tracking", where users download many small bits from many different sources at once. Because this format compensates for bottleneck points, it is actually faster than downloading a large file from a single source.
* “Swarming” is about splitting large files into hundreds of smaller “bits”, and then sharing those bits across a “swarm” of dozens of linked users.
* “Tracking” is when specific servers help swarm users find each other.
* Swarm members use special Torrent client software to upload, download, and reconstruct the many file bits into complete usable files.
* Special .torrent text files act as pointers during this whole process, helping users find other users to swarm with, and enforcing quality control on all shared files.
To read more on this Plz see da post "BitTorrent"
published on 19 December 2006
Shahrukh Khan - King Khan Rocks AT 41
Shahrukh Khan the most saleable actor in the business today.
Shahrukh Khan was born on 2nd november 1965. He was brought up in Delhi. He had done his schooling from 'St. Columba's school' and from 'Jamia Millia Islamia' he had done Mass Communication.
Shahrukh started his career on a TV serial called "Fauji" which has given him instant recognition. He also acted in TV soaps called "Circus" and "Doosra Keval".......
To read more n know more abt SRK visit dis writeup by my friend
Milind : http://milindreach4dstars.blogspot.com/
Shahrukh Khan was born on 2nd november 1965. He was brought up in Delhi. He had done his schooling from 'St. Columba's school' and from 'Jamia Millia Islamia' he had done Mass Communication.
Shahrukh started his career on a TV serial called "Fauji" which has given him instant recognition. He also acted in TV soaps called "Circus" and "Doosra Keval".......
To read more n know more abt SRK visit dis writeup by my friend
Milind : http://milindreach4dstars.blogspot.com/
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