Sunday, August 30, 2009

VIRUS Announcement

You should be alert during the next few days. Do not open any message with an attachment entitled 'POSTCARD FROM BEJING', regardless of who sent it to you. It is a virus which opens A POSTCARD IMAGE, which 'burns' the whole hard disc C of your computer. This virus will be received from someone who has your e-mail address in his/her contact list. This is the reason why you need to send this e-mail to all your contacts.. It is better to receive this

message 25 times than to receive the virus and open it..

If you receive a mail called 'POSTCARD FROM BEJING,' even though sent to you by a friend, do not open it! Shut down your computer immediately.

This is the worst virus announced by CNN. It has been classified by Microsoft as the most destructive virus ever. This virus was discovered by McAfee yesterday, and there is no repair yet for this kind of virus. This virus simply destroys the Zero Sector of the Hard Disc, where the vital information is kept.More

Free WiFi

While commercial services attempt to move existing business models to Wi-Fi, many
groups, communities, cities, and individuals have set up free Wi-Fi networks, often adopting a common peering agreement in order that networks can openly share with each other. Free wireless mesh networks are often considered the future of the Internet.

Many municipalities have joined with local community groups to help expand free Wi-Fi networks (see Mu-Fi). Some community groups have built their Wi-Fi networks entirely based on volunteer efforts and donations.

For more information, see wireless community network, where there is also a list of the free Wi-Fi networks one can find around the globe. OLSR is one of the protocols used to set up free networks. Some networks use static routing; others rely completely on OSPF. Wireless Leiden developed their own routing software under the name LVrouteD for community wi-fi networks that consist of a completely wireless backbone. Most networks rely heavily on open source software, or even publish their setup under an open source license.

Some smaller countries and municipalities already provide free Wi-Fi hotspots and residential Wi-Fi internet access to everyone. Examples include Estonia which have already a large number of free Wi-Fi hotspots throughout their countries.

In Paris, France, OzoneParis offers free Internet access for life to anybody who contributes to the Pervasive Network’s development by making their rooftop available for the Wi-Fi Network.

Annapolis, Maryland is in the early phases (as of April 2006) of a pilot program to provide free, advertisement-financed Wi-Fi to all its residents. A private company, Annapolis Wireless Internet, will administrate the network. Users will only see local advertisements upon accessing the network.

Many universities provide free Wi-Fi internet access to their students, visitors, and anyone on campus. Similarly, some commercial entities such as Panera Bread and Culver's offer free Wi-Fi access to patrons. McDonald's Corporation also offers Wi-Fi access, often branded 'McInternet'. This was launched at their flagship restaurant in Oak Brook, Illinois, USA, and is also available in many branches in London, UK.

However, there is also a third subcategory of networks set up by certain communities such as universities where the service is provided free to members and guests of the community such as students, yet used to make money by letting the service out to companies and individuals outside. An example of such a service is Sparknet in Finland.

Sparknet also supports OpenSpark, a project where people can share their own wireless access point and become as a part of Sparknet and OpenSpark community in return for certain benefits.

Recently commercial Wi-Fi providers have built free Wi-Fi hotspots and hotzones. These providers hope that free Wi-Fi access would equate to more users and significant return
on investment.

Wifi Universal

Another business model seems to be making its way into the news. The idea is that users
will share their bandwidth through their personal wireless routers, which are supplied with specific software. An example is FON, a Spanish start-up created in November 2005. It aims to become the largest network of hotspots in the world by the end of 2006 with 70000 access points. The users are divided into three categories: linus share Internet access for free; bills sell their personal bandwidth; and aliens buy access from bills. Thus the system can be described as a peer-to-peer sharing service, which we usually relate to software.

Although FON has received some financial support by companies like Google and Skype, it remains to be seen whether the idea can actually work. There are three main challenges for this service at the moment. The first is that it needs much media and community attention first in order to get through the phase of "early adoption" and into the mainstream. Then comes the fact that sharing your Internet connection is often against the terms of use of your ISP. This means that in the next few months we can see ISPs trying to defend their interests in the same way music companies united against free MP3 distribution. And third, the FON software is still in Beta-version and it remains to be seen if it presents a good solution of the imminent security issues.

WiFi Commercial

Commercial Wi-Fi services are available in places such as Internet cafes, coffee houses, hotels and airports around the world (commonly called Wi-Fi-cafés), although coverage is patchy in comparison with cellular.


• T-Mobile provides HotSpots in many partner retail locations including many Starbucks, Borders Books, and a variety of hotels and airports.

• a Columbia Rural Electric Association subsidiary offers 2.4 GHz Wi-Fi service across a 3,700 mi² (9,500 km²) region within Walla Walla and Columbia counties in Washington and Umatilla County, Oregon.

• WiSE Technologies provides commercial hotspots for airports, universities, and independent cafes in the US;

• Boingo Wireless has over 45,000 hotspots worldwide, including most major airports in the U.S.

• restaurant chain Panera Bread provides free Wi-Fi access at its restaurants.

• Other large hotspot providers include Wayport, iPass, and iBahn.

• There are also a number of aggregators of Wi-Fi, the main one being BOZII, they allow users access to over 250 networks including BT Openzone and Orange France, all with one username and password for a flat fee and no roaming charges.


• T-Mobile provides hotspots in many Starbucks and Airports in the UK too.

• BT Openzone provides many hotspots across the United Kingdom and Ireland, notably in most McDonalds restaurants, and have roaming agreements with TMobile UK and ReadyToSurf. Their customers are also able to access hotspots managed by The Cloud.

In France:

• Ozone and OzoneParis In France, in September 2003, Ozone started deploying the OzoneParis network across the City of Lights. The objective: to construct a wireless metropolitan network with full Wi-Fi coverage of Paris. Ozone is also deploying its network in Brussels (Belgium) and other cities in France like Rennes. Ozone Pervasive Network philosophy is based on a nationwide scale.

• als@tis One of the largest Wireless Internet Service Provider for rural areas in France.

In other places

• GlobeQUEST, under Globe Telecom, provides for prepaid Wi-Fi services for nearly all cafes in the Philippines
• Pacific Century Cyberworks provides hotspots in Pacific Coffee shops in Hong Kong;
• Vex offers a big network of hotspots spread over Brazil. Telefónica Speedy Wi-Fi has started its services in a new and growing network distributed over the state of São Paulo.
• Netstop provides hotspots in New Zealand;
• FatPort is Canada's oldest independent Wi-Fi HotSpot operator with coverage from coast to coast.

WiFi cellular

Some argue that Wi-Fi and related consumer technologies hold the key to replacing
cellular telephone networks such as GSM. Some obstacles to this happening in the near future are missing roaming and authentication features (see 802.1x, SIM cards and RADIUS), the narrowness of the available spectrum and the limited range of Wi-Fi. It is more likely that WiMax will compete with other cellular phone protocols such as GSM, UMTS or CDMA. However, Wi-Fi is ideal for VoIP applications e.g. in a corporate LAN or SOHO environment. Early adopters were already available in the late '90s, though not until 2005 did the market explode. Companies such as Zyxel, UT Starcomm, Sony, Samsung, Hitachi and many more are offering VoIP Wi-Fi phones for reasonable prices.

In 2005, low-latency broadband ISPs started offering VoIP services to their customers. Since calling via VoIP is free or low-cost, VoIP enabled ISPs have the potential to open up the VoIP market. GSM phones with integrated Wi-Fi & VoIP capabilities are being introduced into the market and have the potential to replace land line telephone services.

Currently it seems unlikely that Wi-Fi will directly compete against cellular in areas that have only sparse Wi-Fi coverage. Wi-Fi-only phones have a very limited range, so setting up a covering network would be too expensive. Additionally, cellular technology allows the user to travel while connected, bouncing the connection from tower to tower (or "cells") as proximity changes, all the while maintaining one solid connection to the user. Many current Wi-Fi devices and drivers do not support roaming yet and connect to only one access point at a time. In this case, once you are out of range of one "hotspot", the connection will drop and will need to be re-connected to the next one each time.

For these reasons, Wi-Fi phones are still best suited for local use such as corporate or home networks. However, devices capable of multiple standards, called converged devices, (using SIP or UMA) may well compete in the market. Top-tier handset manufacturers have announced converged dual-radio handsets. Converged handsets present several compelling advantages to mobile carriers:

• Efficient spectrum allocation, as more data-intensive services come online and bandwidth demands increase
• Improved in-building coverage in markets such as the US, where dropped calls
are still a major cause of customer dissatisfaction
• Opportunities for mobile operators to offer differentiated pricing and services.

Range Extender

A wireless range extender (or wireless repeater) can increase the range of an existing
wireless network by being strategically placed in locations where a wireless signal is sufficiently strong and near by locations that have poor to no signal strength. An example location would be at the corner of an L shaped corridor, where the access point is at the end of one leg and a strong signal is desired at the end of the other leg. Another example would be 75% of the way between the access point and the edge of its useable signal. This would effectively increase the range by 75%.

Wireless ethernet Bridge

A wireless ethernet bridge connects 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.

WiFi Devices

Wireless Access Point (WAP)

A wireless access point (AP) connects a group of wireless stations to an adjacent wired
local area network (LAN). An access point is similar to an ethernet hub, but instead of
relaying LAN data only to other LAN stations, an access point can relay wireless data to
all other compatible wireless devices as well as to a single (usually) connected LAN
device, in most cases an ethernet hub or switch, allowing wireless devices to
communicate with any other device on the LAN.

WiFi works

The 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 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 influence 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 least 1 Mbit/s. Based on the settings (e.g. the SSID), the client may decide whether to connect to an AP. Also the firmware running on the client Wi-Fi card is of influence. Say two APs of the same SSID are in range of the client, the firmware may decide based on signal strength to which of the two APs it will connect. 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 the other. Since Wi-Fi transmits in the air, it has the same properties as a non-switched ethernet network. Even collisions can therefore appear like in non-switched ethernet LAN's.


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 frequencies for 802.11 b/g span 2.400 GHz to 2.487 GHz. Each channel is 22 MHz wide and 5 MHz spacers between the channels are required. With the required spacers, only 3 channels (1,6, and 11) can be used simultaneously without interference.

Wifi Origin

Despite the similarity between the terms "Wi-Fi" and "Hi-Fi", statements reportedly [3] made by Phil Belanger of the Wi-Fi Alliance contradict the popular conclusion that "Wi- Fi" stands for "Wireless Fidelity".

According to Mr. Belanger, the Interbrand Corporation developed the brand "Wi-Fi" for the Wi-Fi Alliance to use to describe WLAN products that are based on the IEEE 802.11 standards. In Mr. Belanger's words, "Wi-Fi and the yin yang style logo were invented by Interbrand. We (the founding members of the Wireless Ethernet Compatibility Alliance, now called the Wi-Fi Alliance) hired Interbrand to come up with the name and logo that we could use for our interoperability seal and marketing efforts. We needed something that was a little catchier than 'IEEE 802.11b Direct Sequence'."

The Wi-Fi Alliance themselves invoked the term "Wireless Fidelity" with the marketing of a tag line, "The Standard for Wireless Fidelity," but later removed the tag from their marketing. The Wi-Fi Alliance now seems to discourage propagation of the notion that "Wi-Fi" stands for "Wireless Fidelity" but includes it in their knowledge base:

To understand the value of Wi-Fi Certification, you need to know that Wi-Fi is short for "Wireless Fidelity," and it is the popular name for 802.11-based technologies that have passed Wi-FI certification testing. This includes IEEE 802.11a, 802.11b, 802.11g and upcoming 802.11n technologies.

WiFi History

Wi-Fi uses both single carrier direct-sequence spread spectrum radio technology, part of the larger family of spread spectrum systems and multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) radio technology. Unlicensed spread spectrum was first authorized by the Federal Communications Commission in 1985 and these FCC regulations were later copied with some changes in many other countries enabling use of this technology in all major countries. These regulations then enabled the development of Wi-Fi, its onetime competitor HomeRF, and Bluetooth.

The precursor to Wi-Fi was invented in 1991 by NCR Corporation/AT&T (later Lucent & Agere Systems) in Nieuwegein, the Netherlands. It was initially intended for cashier systems; the first wireless products were brought on the market under the name Wave LAN with speeds of 1 Mbit/s to 2 Mbit/s. Vic Hayes, who was the primary inventor of Wi-Fi and has been named the 'father of Wi-Fi,' was involved in designing standards such as IEEE 802.11b, 802.11a and 802.11g. In 2003, Vic retired from Agere Systems. Agere Systems suffered from strong competition in the market even though their products were high quality, as many opted for cheaper Wi-Fi solutions. Agere's 802.11a/b/g all-inone chipset (code named: WARP) never made it to market, and Agere Systems decided to quit the Wi-Fi market in late 2004.

About Wifi

Wi-Fi, also, WiFi, Wi-fi or wifi, is a brand originally licensed by the Wi-Fi Alliance to describe the underlying technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications.

Wi-Fi was developed to be used for mobile computing devices, such as laptops, in LANs, but is now increasingly used for more applications, including Internet and VoIP phone access, gaming, and basic connectivity of consumer electronics such as televisions and DVD players, or digital cameras. There are even more standards in development that will allow Wi-Fi to be used by cars in highways in support of an Intelligent Transportation System to increase safety, gather statistics, and enable mobile commerce IEEE 802.11p.

A person with a Wi-Fi device, such as a computer, telephone, or personal digital assistant (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 Wireless mesh network. Both architectures are used in Wireless community network, municipal wireless networks like Wireless Philadelphia [1], and metro-scale networks like M-Taipei [2].

Wi-Fi also allows connectivity in peer-to-peer 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 another brand "Wi-Fi CERTIFIED" to denote products are interoperable with other products displaying the "Wi-Fi CERTIFIED" brand.

User Base

In the future there will be other VLAN solutions. One promissing solution, that many poeple wait for, is user based VLAN. When a user logs on a particular host, the user identity is anylized by the switch and then the host becomes a part of a particular VLAN. For example, the user Bob logs on the host P in the picture with his own user ID and password. The switch A decides that Bob belongs to VLAN 1.

Protocol based

Protocol based VLAN means that a host belongs to a particular VLAN based on which
protocol it uses for communication. For example, the host P in the picture is a Netware
client which normally uses IPX protocol, which means that it belongs to IPX VLAN.

Mac based

Mac based VLAN means that a host belongs to a particular VLAN based on which MAC
address the host has. MAC based VLAN is independent of which physical switch port the
host is connected to. For example, the host P in the picture has the MAC address 00-10-4-
B-62-1E-A4, which means that host P belongs to VLAN 1, as can be seen in the left table.
As you can see the same MAC address of the host P is also in the table for switch B. This
means that if we connect host P to any port of switch B, the host P will still belong to

Port based

There are a number of different sollutions to create VLAN. Port based solution means that a
host belongs to a particular VLAN based on which physical port in the switch the host is
connected to. For example, the host P in the picture is connected to port 4 of switch A,
which means that host P belongs to VLAN 1, as can be seen in the left table.


A switch makes it possible to configure something called VLAN. A VLAN, which stands for Virtual Local Area Network, is a logical LAN consisting of a group of hosts. One physical LAN can be divided into several VLANs. A VLAN can be configured by one or several switches, which makes it possible to be geographically distributed but having a logical presence. Users of the same VLAN can communicate with each other at LAN speeds and with no router latency.

There are different solutions for communication between VLANs, but the most common way is to use a router. The router is sometimes integrated in the switch.

LAN Switching

Fast Forward
Fast forward or cut-through switching is the fastest way of forwarding packets thorough a
switch. The switch forwards the packets as soon as the switch is able to determine the
destination MAC address. Although this generally reduces network latency, fast forward
switching doesn't verify the checksum and consequently allows bad packets to pass, which
can reduce the available bandwidth. In fast forward switching the sending direction is never
established which means that two hosts can send to each other simultaneously which will
lead to a collision.

Store and Forward
In Store and forward switching the switch waits until the entire packet is received before
sending it to the destination. This lets the switch verify the packet's checksum and eliminate
the possibility of forwarding bad packets. While the packet is stored in the buffer of the
switch, the transmission direction is established, which means that no collisions can occur.
A disadvantage with store and forward switching is that a delay occurs because the switch
needs time to buffer and analyze the packet.

Fragment Free
The fragment free switch works just like fast forward, but it buffers 64 bytes of every
packet in order to avoid collisions.

LAN Components

A hub is a commonly used device for connecting hosts to each other, using bus or ring topology. Each host is attached to a hub via a port. When a hub receives a signal on one port it transmits that signal to all other ports. Many hubs also regenerate and amplify weak signals before re-transmitting them.

A switch is a multiport device that handles routing between different hosts based on their MAC addresses. A switch ”learns” MAC addresses from the hosts that are connected to the switch, and stores them in an internal table. When two hosts communicate with each other, the switch creates a temporary connection path between them. This means that only two hosts will hear each other and not like the hub where everyone hears everything. For example if host A and host B have a conversation with each other, then host C and D can also communicate at the same time without any disturbance from host A or B. There is also possibility for one host to broadcast, which means that the packets will be transmitted on all ports in the switch.

Switches improve the performance of a LAN in two ways. First they increase the available bandwidth for each host, since the collisions are avoided.The second improvement is the security. A user on a host connected via a hub, can by using a sniffer software, hear other conversations. This is not possible in a switched network.


Assignment Lanka Tag Cloud
Computer Networks The History of Local Area Networks, LAN, The Topologies of a Networks, LANs describe different types of transmission Medias, Local Area Networks Access Methods, Carrier Sense Multiple Access with Collision Detect, Development of LAN Technologies. LAN -Token Ring, LAN Ethernet Digital, LAN - Ethernet Sun microsystems, LAN - Ethernet Mixed Environment, LAN - Token Ring was introduced by IBM LAN - IBM implementation of Token Ring, Token Ring Novell, LAN Token Ring - in a mixed environment, LAN - Fiber Distributed Data Interface, LAN - ATM, LAN Components, LAN Switching Methods, Virtual Local Area Network, Port based VLAN, Mac based VLAN, Protocol based VLAN, User Base VLAN, PC networks Components, PC networks Shared resources, PC Network operating systems, PC networks Novell Netware, PC networks Windows NT, PC networks IBM LAN Server Computer Programming Languages HTML Language, The Generations of Programming Languages, Different types of High Level Languages, Different types of High Level Languages Disadvantages
Computer Networks - IBM LAN Server, Windows NT Networks, Novell Netware, Network operating systems, Networks Shared, Networks Components, User Base, Protocol based, Mac based, Port based, VLAN, LAN Switching, LAN Components, ATM, Fiber Data, Token Ring, Token Ring Novell, IBM implementation, Ethernet, Sun microsystems, Ethernet Digital, Token passing, LAN Technologies, CSMA/CD, Access Methods, Transmission, Networks, The History of Local Area Networks, LAN