Monday, August 31, 2009

AntiVirus software






These are stand-alone programs that will protect your computer from viruses, worms and some trojans, and allow you to clean it should you become infected.

• Norton Antivirus (http://www.symantec.com/) Trial / Buy
• Mcafee Virus Scan (http://www.mcafee.com/) Trial / Buy
• PC-Cillin (http://www.trendmicro.com/) Trial / Buy
• Anti-Viral Toolkit Pro (http://www.kaspersky.com/) Trial / Buy
• AVG Anti-Virus (http://www.grisoft.com/) Free / Buy

Note that all of these websites (except grisoft.com) have areas that will conduct free online virus scans on your machine; however, only Trend Micro’s “House Call” page (housecall.trendmicro.com) will actually clean your machine if it finds any. In any case, these online scans are only band-aid solutions for disinfecting your machine after the fact – you should still be purchasing a realtime Anti-Virus software package (such as those listed above) to prevent viruses from getting into your system in the first place.


  • Update your virus/trojan definitions on a regular basis. Definition files are the
    database that your anti-virus/trojan software draw from to detect, identify and
    remove new viruses, worms and trojans. With new ones constantly emerging, new
    definition files are constantly being compiled and released by the software
    companies to keep up. Make sure you download these definitions regularly
    (weekly) from your company’s website to keep your software up-to-date for your
    own protection (ie, for Norton Anti-Virus you can use their “live update” feature).
  • Scan all downloaded files/attachments with Anti-Virus/Anti-Trojan software,
    before you open them.
  • Backup your data. No matter how safe you think you are, unless you back up
    your data prior to being infected, you may lose it during the infection/payload
    process (viruses/worms/trojans may delete or scramble files) or anti-virus/trojan
    cleaning process (files may need to be deleted to clean the machine). If there is
    important data that you need, make sure you back it up on a regular basis (either
    on diskette, CD-ROM or uploaded to a website).

Viruses, Worms, Trojans Preventative Solutions

  • Use common sense - don’t visit, or download programs from, people/websites you don’t know or trust.
  • Don’t open “spam” or unknown emails or attachments – delete them instead.
  • Check with your friend over the phone if you receive an email from them with
    an attachment you weren’t expecting – verify they did intend to send you the
    email/attachment, to make sure it wasn’t a worm sending it instead (many
    viruses/worms/trojans are sent from people unaware they’ve been infected).
  • Obtain the latest patches for Windows, Internet Explorer and Outlook Express
    to plug the many security holes and vulnerable exploits found in these programs.
  • Un-hide file extensions. This addresses the problem where Windows by default
    likes to hide the extensions of filenames; ie "susie.jpg" shows up as just "susie".
    The danger is that "susie.jpg.exe", which is an executable program, would be
    shown as "susie.jpg" which many would mistake for just a picture. This is
    potentially very dangerous and confusing.

In Windows 95 / 98:
- Open Explorer
- Under View menu, select Options
- Check "show all files"
- UNcheck "hide MSDOS file extensions that are registered"
- Click OK to finish
In Windows ME / 2000 / XP:
- select Start Settings Control Panels Folder Options
- select the View tab
- check "show hidden files and folders"
- UNcheck "hide file extensions for known file types"
- Click OK to finish

…or follow this illustrated guide: www.granneman.com/techinfo/windows/showexte

IMPORTANT EXCEPTION: Even after you unhide the extensions using the
above steps, you still cannot see certain hidden extensions for files ending with
.shs, .pif, and .lnk (blame Microsoft for its infinite lack of wisdom).
Unfortunately these files are executable, and are rapidly becoming the most
popular choices for many trojan horses, worms and viruses, such as
"Movie.avi.pif" which will look like "Movie.avi", and
"LIFE_STAGES.TXT.SHS" which will look like "LIFE_STAGES.TXT". Instead
of being a movie and text file, respectively, they are both dangerous programs.
Again, unless you know where the file you are getting comes from or who sent it,
do not download/accept, or open it.

Virus Suspicious

Computer Virus Suspicious File Types. Be wary if any of these show up in your email

•.ade: Microsoft Access projectextension
• .adp: Microsoft Access project
• .bas: Microsoft Visual Basic class module
• .bat: Batch file
• .chm: Compiled HTML Help file
• .cmd: Microsoft Windows NT Command script
• .com: Microsoft MS-DOS program
• .cpl: Control Panel extension
• .crt: Security certificate
• .exe: Program
• .hlp: Help file
• .hta: HTML program
• .inf: Setup Information
• .ins: Internet Naming Service
• .isp: Internet Communication settings
• .js: JScript file
• .jse: Jscript Encoded Script file
• .lnk: Shortcut
• .mdb: Microsoft Access program
• .mde: Microsoft Access MDE database
• .msc: Microsoft Common Console document
• .msi: Microsoft Windows Installer package
• .msp: Microsoft Windows Installer patch
• .mst: Microsoft Visual Test source files
• .pcd: Photo CD image, Microsoft Visual compiled script
• .pif: Shortcut to MS-DOS program
• .reg: Registration entries
• .scr: Screen saver
• .sct: Windows Script Component
• .shs: Shell Scrap object
• .shb: Shell Scrap object
• .url: Internet shortcut
• .vb: VBScript file
• .vbe: VBScript Encoded script file
• .vbs: VBScript file
• .wsc: Windows Script Component
• .wsf: Windows Script file
• .wsh: Windows Script Host Settings file

Computer Virus How you get infected?

In each case, viruses/worms/trojans can all be spread in the guise of literally ANYTHING people find desirable, such as a free game, movie, song, etc. Victims typically downloaded the file from a website, via file sharing programs such as KaZaa, over instant messaging (such as MSN), or by just carelessly opening some email attachment without thinking. Although these programs can also be exchanged on floppy disks, today the Internet has taken precedent as the distribution medium of choice.

• Viruses, worms and trojans often masquerade under files with various extensions, the most common of which are .exe (executable program – beware!), .com, .vbs, .pif, and .js. Be very suspicious if files with the following extensions arrive in your email without you expecting them, as they could contain a virus, worm or trojan.

• Macro viruses may arrive in the form of Microsoft Word (.doc), Microsoft Excel (.xls), and Microsoft Powerpoint (.ppt) files. Also, be wary of .htm and .html files; because they can access the Internet, they may direct you to a website that will forcibly attempt your machine to download unsafe files or exploit an un-patched security hole in Windows or Internet Explorer.


• In the case of worms, it is also possible to get one that activates just by reading an email, even when there is no attachment. A recent worm spread by taking advantage of a security hole in Microsoft Outlook Express that allowed it to run, even though there was no attachment in the email.

Trojan Types


Again, just as with viruses and worms, there are many types of Trojan programs - the most popular being “Back Orifice”, “Netbus” and “SubSeven”. Depending on the type of trojan installed and the motives of someone who gains access to an infected machine, the results can be disastrous: trojans can allow someone to see what you are seeing (on their screen), to transfer files from your computer to theirs, to delete your files and crash your computer, to use keyloggers to track (log) what you type in order to steal passwords/bank account/credit card info, to open and close CD-ROM drives, take control of your mouse, turn the machine and monitor on/off, and much more.

Almost all trojans will attempt to open a “port” (metaphorically, an open port is like an open door to a house) to broadcast the presence of an infected machine to “port scanners” (people looking for open ports on infected machines, to break into). Some trojans are also programmed to establish a direct connection to a specific person/computer, or to commit illegal DoS (Denial of Service) attacks on specific websites. Firewalls (see futher in this document) are particularly useful to block Trojans from trying to access the Internet, and from people trying to gain access to your machine.

What is computer Trojan



In today's computer world, a Trojan horse is often defined as a program that seemingly does one thing, but its true function is hidden in order to fool you. For example, you download what appears to be a movie or music file, but when you click to open it, you unleash a program that could do any number of things. Trojans usually operate silently, in the background - the most common purpose for them is that they can allow someone to gain access and control your computer over the Internet, and use it for whatever purposes they wish, often without your knowledge.

Computer Worm Types

There are many types of worm programs, many of which are quite insidious - they can compromise the security of an infected machine and leave it vulnerable to future attacks, collect passwords and other confidential information (which can then be automatically emailed to other people), or be programmed to delete files or deface websites.


Worms are particularly well-known for scanning through a person’s computer for email addresses, and then propagating themselves to the addresses found. Some worms will also send a file from your computer to every person they propagate to, which could be disastrous if the attached file is confidential/personal information.

Computer Worms


Worms are programs that once run, take advantage of a computer’s ability to send and receive information. They use this ability to propagate themselves automatically (usually through email) over a network such as the Internet, and cause massive congestion (slow response time, server overloads) in the process. They can also do more malicious acts, and slow down your machine.

Computer Virus types

  • Boot Sector Virus: replaces or implants itself in the boot sector - an area of the hard drive (or any other disk) accessed when you first turn on your computer. This kind of virus can prevent you from being able to boot your hard disk/computer.
  • File Virus: infects applications. These executables then spread the virus by infecting associated documents and other applications whenever they're opened or run.
  • Macro Virus: Written using a simplified macro programming language, these virusesaffect Microsoft Office applications, such as Word (.doc) and Excel (.xls). A document infected with a macro virus generally modifies a pre-existing, commonly used command (such as Save) to trigger its payload upon execution of that command.
  • Multipartite Virus: infects both files and the boot sector - a double whammy that can
    reinfect your system dozens of times before it's caught.
  • Polymorphic Virus: changes code whenever it passes to another machine; in theory these
    viruses should be more difficult for antivirus scanners to detect, but in practice they're
    usually not that well written.
  • Stealth Virus: hides its presence by making an infected file not appear infected, but
    doesn't usually stand up to antivirus software.

Depending on the virus, some will perform more malicious deeds than others. Examples include deleting and renaming of files, scrambling contents of the entire hard drive (so you can’t access your data), or not letting the machine boot into Windows. Some viruses also slow down your machine, disable certain functions, or cause erratic system behavior and crashes.

Viruses, Worms, Trojans What are they?

Virus:
Simply put, viruses are (primarily) destructive computer programs created by someone that once run, attempt to destroy the data (files) on your computer. A virus spreads when an infected program is run (executing the virus code), which in turn infects more files on the same machine. This usually happens silently and without your knowledge until its too late. In general, viruses have 1) an infection phase where they reproduce widely, 2) an attack/trigger phase (such as a certain date or time) which causesthem to 3) deliver their “payload”, and do whatever damage they have been programmed to do (if any).

Spyware What is it?


Spyware is any application that collects information about your computer activities and then sends that information to another individual or company without your knowledge or permission. Spyware often arrives bundled with freeware (free) or shareware (trial) programs, through email or instant messenger, as an Active X install, or by someone with access to your computer. Once on your drive, spyware secretly installs itself and goes to work. Spyware can be difficult to detect, and difficult (if not impossible) for the average user to remove.

Spyware can:
• Track your online surfing habits, profile your shopping preferences, gather personal information (age, sex, etc, possibly credit card info, PIN numbers)

• Send your email address to the company/person that made the spyware; that company/person can now send spam to your email account.

• Decrease your connection speed/hog your internet connection by sending information about you and your computer to the company/person that made the spyware

• Hijack your web browser’s start page, bombard you with pop-up advertisement boxes
• Run in the background and slow your computer down, alter important system files, make your computer unstable and crash

Spyware comes in many flavors including:

• Trojan Horses

As mentioned previously, Trojans are malicious programs that appear asharmless or desirable applications. Trojans are often designed to cause loss or theft of computer data. Some Trojans called RATs (Remote Administration Tools) allow an attacker to gain unrestricted access of your computer whenever you are online. The attacker can perform activities such as file transfers, adding/deleting files or programs, and controlling your mouse and keyboard. Trojans are generally distributed as a desirable program or file, in email attachments or bundled with another software program.

System Monitors/Keyloggers

System monitors are applications designed to monitor computer activity to various degrees. These programs can capture virtually everything you do on your computer including recording all keystrokes, emails, chat room dialogue, web sites visited, and programs run. System monitors usually run in the background so that you do not know that you are being monitored. The
information gathered by the system monitor is stored on your computer in an encrypted log file for later retrieval. Some programs are capable of emailing the log files to another location/person. System monitors can be installed by someone that shares your computer, or come disguised as email attachments or "freeware" software products.

Dialers

Dialers are a type of software typically used by vendors serving pornography via the Internet. Once dialer software is installed, the user is disconnected from their usual Internet service provider and then redirected by the dialer program to call into another phone number where the user is billed per minute. Dialers do not "spy" on their intended victims, but these malevolent programs can rack up significant long distance phone charges, costing victims time and money.

Adware

Adware is advertising-supported software that displays pop-up advertisements whenever the program is running. The software is usually available via free download from the Internet, and it is the advertisements that create revenue for the company. Although seemingly harmless (aside from intrusiveness and annoyance of pop-up ads), adware can install components onto your computer that track personal information (including your age, gender, location, buying preferences, surfing habits, etc.). Most advertising supported software doesn't inform you that it installs adware on your system, other than through a buried reference in a license agreement. In many cases the software will not function without the adware component. Some Adware will install itself on your computer even if you decline the offer.

Adware Cookies

Cookies are pieces of information that are generated by a web server and stored on your computer for future access. Cookies were originally implemented to allow you to customize your web experience, and continue to serve a useful purpose in enabling a personalized web experience. However, some web sites now issue “adware” cookies, which allow multiple web sites to store and access cookies that may contain personal information (including surfing habits, user names and passwords, areas of interest, etc.), and then simultaneously share the information they contain with other web sites. This sharing of information allows marketing firms to create a user profile based on your personal information, which they then sell it other firms. Adware cookies are almost always installed and accessed without your knowledge or consent.

A list of some common spyware programs:
• Bonzai Buddy
• Comet Cursor
• Download Accelerator
• Go!Zilla
• Gator
• Hotbar
• Huntfly
• Lop.com
• Web3000 programs
• Xupiter Toolbar
- Spyware components can also be found in many popular file-sharing programs such as KaZaa, BearShare, LimeWire, iMesh and Grokster.

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 :www.mcafee.com

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.

IN USA

• 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.


IN UK

• 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.

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 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
VLAN 1.

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.

VLAN


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.

Saturday, August 29, 2009

ATM


ATM, which stands for Asynchronous Transfer Mode is a ”de facto standard” developed
by the ATM Forum and is a switching method of communication, which can be used in both
LANs and WANs.

ATM specifications are being written to ensure that ATM smoothly integrates numerous
existing network technologies.

Today, in many instances, separate networks are used to carry voice, data and video
information, mostly because these traffic types have different characteristics. For instance,
data traffic tends to be "bursty" while voice and video tend to be more "continuous".
With ATM, separate networks will not be required. ATM is the only technology which
from the beginning, was designed to accommodate the simultaneous transmission of data,
voice and video.

ATM is available at various speeds but the most commonly used are 25, 155 and 622 Mbps.

Fiber Data


FDDI stands for Fiber Distributed Data Interface. FDDI standard was developed by ANSI,
the American National Standards Institute. It is based on the use of double optical fiber cable
and provides for a token-passing ring configuration, operating at 100 Mbps.
FDDI is being developed to deal with the requirements of high-speed LANs, MANs and
backbone networks. Since FDDI consists of two fiber rings, primary and secondary ring,
there is good redundancy and high availability. Normally traffic only flows on the primary
ring, but if the primary ring is broken then the secondary ring is used.

Token Ring

Token Ring is mainly used to connect equipment from IBM and Novell.
In this picture you have two environments, IBM and Novell, co-existing on a single Token
Ring. Although these two environments cannot communicate with each other in this
configuration, they can still use the same Token Ring.

Token Ring Novell

A normal way for an organization to go from mainframes to more modern computers is to
use the existing Token Ring network but to change the earlier IBM devices to personal
computers.

Novell was one of the first to see this market and they are using Token Ring to connect their
servers and clients together.

In the picture you can see a typical configuration with different types of personal computers
working as Novell clients and servers.

IBM implementation

In this picture we see an IBM implementation of Token Ring. An IBM mainframe 3090
cannot directly communicate with the Token Ring. To do that it needs an NCP which is a
dedicated computer that only handles the communication between the mainframe and the
Token Ring network.

The users sitting on terminals can access the data from the mainframe through a terminal
server. There can be several thousand terminals connected to a mainframe.

Another possibility is to use mini computers such as AS/400. These mini computers can be
accessed by directly connected terminals as in the picture, or from a terminal server.

Token ring Network

Token Ring was introduced by IBM in 1987 and became their main architecture. The
standard for Token Ring from IEEE came in 1989.

Token Ring is physical star and logical ring topology. This means that you connect the
computers physically in a star configuration to the hub, but the computers still pass the
access rights with help of a token in a ring.

The bandwidths used in Token Ring are 4 or 16 Mbps.

Ethernet

Ethernet can be used to connect equipment from different vendors. Different protocols can
also be used at the same time on Ethernet. For example Novell’s IPX/SPX can be used
together with TCP/IP. Almost all modern computers, printers and network components can
connect to Ethernet.

In this picture you have three environments, Novell, SUN and Digital, co-existing at the
same time on a single Ethernet. Although these three environments cannot communicate with
each other in this configuration, they can still use the same Ethernet.

Sun microsystems

Sun microsystems was one of the earliest manufacturers of UNIX workstations. Sun had an
early vision that ”The network is the computer”. SUN is using Ethernet and TCP/IP as a
strategic platform. Since every UNIX workstation and UNIX server comes with an Ethernet
card and TCP/IP software, it is ready for direct connection to the network.
For the PC market, SUN has developed PCNFS software, so that a PC can communicate
with SUN equipment.

Ethernet Digital


Ethernet, as defined in IEEE 802.3 standard, can use both star and bus topology with bandwidths between 10 and 100 Mbps. Ethernet is today the most common technique used
in Local Area Networks.

Digital uses Ethernet for communication between their products. This picture represents an
early implementation by Digital. You can see that Vax computers can be accessed by VT220
terminals, through a terminal server.

LAN Technologies

This diagram shows what has happened to the development of the two most used LAN technologies today, Ethernet and Token ring. 10 Megabits Ethernet exists in two versions. Version two as specified by Digital. Intel and Xerox, is the most commonly used version and IEEE standard 802.3 which is not so commonly used. These two versions are not compatible, because the frame format differs.

Fast Ethernet, which is specified in IEEE 802.3u, offers 100 Mbps. Fast Ethernet is a modern version of Ethernet and is often used in LAN backbone networks today (that is 1999), but is still not so commonly used for clients.

Gigabit Ethernet over fiber, is specified in IEEE 802.3z, offers 1000 Mbps. Gigabit Ethernet is not so common today (that is 1999). Gigabit Ethernet is only used in LAN backbone networks because it is expensive and there is not any need today for so high bandwidth to clients.


Gigabit Ethernet over twisted pair cable, is specified in IEEE 802.3ab, offers 1000 Mbps. This standard is not fully specified today, that is in the spring 1999. Gigabit Ethernet is the future of LAN development, because Ethernet is simple, reliable and will become cheap.

Token ring as specified in IEEE 802.5 offers 4 and 16 Mbps. The use of token ring technology is diminishing even though a new standard, called high speed token ring, offering 100 Mbps, has been specified.

CSMA/CD


CSMA/CD stands for "Carrier Sense Multiple Access with Collision Detect”. CSMA/CD
is a random control access method.

The CSMA/CD access method is used as the access control method in Ethernet and is defined in a standard from IEEE. The CSMA/CD algorithm is quite simple and the efficiency for an ordinary Ethernet is about 65%. This means that the effective bandwidth for a 10 Mbps Ethernet is about 6.5 Mbps. The rest is lost, mainly due to collisions.


Before one host will transmit it must ”listen” on the medium whether or not another host is
transmitting. If the medium is ”quiet” the host can send its data. The term "Carrier Sense" indicates that a host listens before it transmits.

"Multiple Access" means that many hosts can be connected to the network and all hosts
have the same right to transmit.

With CSMA/CD, it occasionally happens that two hosts send their packets at the same
time. This will make a collision on the network. The information about the collision is
detected by all the other hosts on the network. This is called "Collision Detect". If a host
detects a collision it will wait a random period of time before it tries to transmit again.

Access Methods


A characteristic common to all Local Area Networks is that multiple hosts have to share access to a single physical transmission medium. Several methods can be employed to control the sharing of access to the transmission medium. The various access control methods can be characterized by where in the network the transmission control function is performed. An access method can use following forms of transmission control:


1. Random control
With random control any host can transmit and permission is not required. A host may
check the medium to see if it is free before beginning to transmit.

2. Distributed control
With distributed control only one host at a time has the right to transmit and that right is
passed from host to host. This is usually done by passing on a small piece of data called a
token. The host that has the token, is the one that has the right to transmit.

Transmission


IEEE standards for LANs describe different types of transmission media. It could be cable,
fiber or wireless.


Cables:
Cables typically come in two flavors: twisted pair cables or coaxial cables.


Twisted pair cables
A twisted-wire consists of two insulated strands of copper wire that have been braided.
Often a number of twisted-wire pairs are grouped together into a twisted pair cable. Twisted
pair cables are used both for data communication and telephony.
In the picture the twisted pair cables would typically be used in the star topology in the
middle, that is between the hub and the connected hosts.


Coaxial cables
Coaxial cables consist of a central conducting copper core that is surrounded by insulating
material. The insulation is surrounded by a second conducting layer, which can consist of
either a braided wire mesh or a solid sleeve. In the picture, the coaxial cable would typically
be used for the bus network seen on the top.


Optical fiber:
Optical fibers can be used to carry data signals in the form of modulated light beams with
high bandwidth. An optical fiber consists of an extremely thin cylinder of glass, called the
core, surrounded by a concentric layer of glass. In the picture, the optical fiber would
typically be used for the backbone network.

Wireless:
Different types of radio LANs are available on the market. This is an expensive type of
LAN technique. In the picture, wireless connection is used between the two hosts with
antennas. Wireless LAN connections are often used in old historical buildings where you are
not allowed to install cables.

Networks


The topology of a network concerns the physical configuration of the devices and the cables
that connect them.

Three principle topologies are used for local area networks:


1. Bus network
On the bus network all connected hosts are sharing the same cable. All the hosts must use
the same communication speed and every host ”hears” all traffic on the cable.

2. Ring network
In the ring topology all hosts are connected into a ring. Every host in the ring receives all data
that is passing. If the data has another destination address, the host will re-transmit the data
into the ring. The data will continue to travel in this way until it reaches the destination host.

3. Star network
A star configuration includes a central controller which could be a hub or a switch. Every
host is directly connected to a port on the central controller.

The History of Local Area Networks, LAN

In the mid 70's Robert Metcalf and David Boggs at Xerox experimented with communication
between the computers. This became the first implementation of Ethernet.

In 1982, the second version of Ethernet was implemented by Digital, Intel and Xerox. This is
the version of Ethernet that is still in use today.

In the mid 80's the first PC-networks started to appear. Network components such as
bridges and routers were now available on the market.

The normal bandwidth of the Local Area Network today is 10 Mbps.

In the near future we will see higher bandwidths, such as 100 to 1000 Mbps.

Wednesday, August 26, 2009

Tuesday, August 25, 2009

Satellite


With some broadband systems, data signals travel from a computer to a satellite and are then beamed to the ISP where the request is processed. The main advantage of satellite broadband is that it is available to nearly anyone who has an unobstructed view of the southern sky, since satellites orbit the Earth near the Equator. Rural customers who may not have access to other broadband technology can usually receive service via satellite.

Satellite Satellite broadband has several limitations including upload and download delays, inclement weather disruptions, physical obstruction concerns, and costs to purchase, maintain and operate the necessary equipment. Due to the distance from the computer to the satellite, there is a delay of a half-second or more between information sent and data received. Inclement weather can increase the delay or disrupt satellite service altogether. Objects such as trees and buildings can severely restrict or prevent reception of satellite signals.

T Lines


T-1 Lines A T-1 line is a dedicated line supporting data rates up to 1.544 Mbps - using 24 individual channels with each supporting 64 Kbps. An individual channel can carry voice or data traffi c, while a customer switching unit/ digital switching unit (CSU/DSU) is necessary toconnect the channel to the four wires that carry the information. The CSU/DSU sends the data signal to
the router which connects it to a server that may send it to the Internet via other servers. Lines
Repeaters must be in place every 6,000 feet or less to help prevent data signal degeneration (as diagrammed below).

Telephone companies, in general, allow customers to buy individual channels in increments of 56 Kbps (8 Kbps per channel is used for data management). A full T-1 connection can theoretically accommodate 200+ users and other provider services.

T-1 lines use copper wire and offer a popular option to businesses and smaller Internet service providers (ISPs) wanting to connect to the Internet and the Internet backbone (such as faster T-3 connections). Because of costs, T-1 service is generally not considered an effective method for reaching most rural areas or residential customers.

Coaxial


Cable television companies (Comcast, Insight, Brighthouse, Time Warner, etc.) are now competing
with traditional telephone services by providing service over their own networks, usually Voice over Internet Protocol (VoIP). For more information on VoIP please refer to the OUCC’s VoIP fact sheet.

Coaxial Cable If a consumer uses a cable service for broadband access, a cable modem connects the user’s personal computer to a shared network, connecting the computer to the Internet via the cable company’s main offi ce (as shown below). Cable modems adhere to industry standards known as DOCSIS (Data Over Cable Service Interface Specifi cation). These standards allow them to interact with other DOCSIS-certifi ed equipment to ensure data privacy. Cable companies can install new service to customers very quickly and easily if those customers are already using cable TV. In general, cable companies offer faster download and upload speed than traditional DSL if the network is not congested. Cable modems can accommodate data speeds up to 27 Mbps downstream and 10 Mbps upstream, but typical speeds generally average 1 to 3 Mbps. Cable broadband speeds can be limited by congestion on the network, limiting providers’ ability to guarantee broadband speeds. The cost of deploying cable can hinder providers’ ability to extend service into low-density areas.

DSL

Digital Subscriber Line (DSL)

DSL Digital Subscriber Line (DSL) provides a dedicated digital circuit between a user’s premises and the Internet through the telephone company’s central offi ce via ordinary copper telephone wires. The two primary forms of DSL are Asymmetric Digital Subscriber Line (ADSL) and Symmetric Digital Subscriber Line (SDSL). ADSL has a higher download speed (1.544 to 6.1 Mbps downstream) and a lower upload speed (16 Kbps to 1.5 Mbps). SDSL’s download and upload speeds (1.544 Mbps) are equal. SDSL does not provide voice capabilities. ADSL – which is more widely used and available – must be within 18,000 feet of the central offi ce while SDSL users must be within 12,000 feet. Some companies, however, have begun to use new technologies such as fi ber lines and/or repeaters to extend DSL capabilities up to 25,000 feet.

An ADSL modem has a “plain old telephone service” POTS) splitter and a channel separator. The POTS splitter divides the phone line into two channels (voice and data) and the channel separator divides the data channel into two sections (downstream and upstream). Data are transported to another ADSL modem in the central offi ce. This modem sends the voice calls to the public switched telephone network (PSTN) and sends the data to the digital subscriber line access multiplexer DSLAM). The DSLAM connects many ADSL lines to a single asynchronus transfer mode (ATM) line or switch. This ATM line acts as both a traffi c aggregator and as a multiservice switch that is capable of forwarding traffi c in different ways, depending on needs. The ATM line then sends the data over the Internet.

3G history

First generation wireless, or 1G, refers to analogue networks introduced in the mid-1980s.
Examples include advanced mobile phone service (AMPS) used in North America and total access
communications system (TACS) used in the UK. In South Africa we had the C450 mobile system
run by Telkom which was relatively expensive and took ten years to achieve ten thousand subscribers. Most 1G technologies and systems were country or region-specifi c and thus offered
limited coverage.As mobile communications grew in popularity, networks often became
overloaded, resulting in busy signals and dropped calls. The solution was second-generation
wireless, or 2G, which emerged in the early 1990s. 2G technologies were digital and offered
the much-needed capacity that 1G analogue systems did not afford. Several technologies were
widely used:


• GSM was and still is popular in Europe and Asia Pacifi c, and Latin America
• TDMA was used in the Americas and is still used in Latin America
• CDMA IS-95 or cdmaOne was used primarily in the Americas and Asia Pacific

However, these 2G technologies are incompatible with each other. Thus, mobile service subscribers were still often limited to using their phones in a single country or region. In an effort to standardise future digital wireless communications and make global roaming with a single handset possible, the ITU established a single standard for wireless networks in 1999. Called IMT-2000, which is commonly referred to today as 3G, the initiative set forth the requirements (mentioned above) for the third generation of wireless networks.

3G standard

3G stands for third-generation wireless technology and networks. It is based on the International Telecommunication Union (ITU) initiative for a single global wireless standard called International Mobile Telecommunications-2000 (IMT-2000). This concept of a single standard evolved into a family of fi ve 3G wireless standards. Of those fi ve, the most widely accepted are CDMA2000, WCDMA (UMTS) and TD-SCDMA. According
to the ITU and IMT-2000, a wireless standard must meet minimum bit-rate requirements to be considered 3G:


• 2 Mbps in fixed or in-building environments
• 384 kbps in pedestrian or urbanenvironments
• 144 kbps in wide area mobileenvironments
• Variable data rates in large geographic areasystems (satellite)


In addition to providing faster bit rates and greater capacity over previous-generation technologies, 3G standards excel by effectively:


• Delivering mobile data
• Offering greater network capacity
• Operating with existing second-generation technologies
• Enabling rich data applications such as VoIP, video telephony, mobile multimedia,interactive gaming and more.

Monday, August 24, 2009

3G Option


With its comparatively low power consumption and robust techniques for dealing with interference, 3G fixed wireless technology remains a very attractive competitive carrier option. Combined with Internet Protocol, 3G technology can be leveraged to support the voice and data requirements of the most demanding residential and business users. While standards groups continue to finalize mobility 3G standards for roaming and other mobile applications, an extraordinary opportunity now exists to leverage the mature, lower-level 3G physical capabilities for fixed-point
wireless. These open solutions, combined with IP-enabled networking, computing platforms offering varied API support, plus an open services gateway concept, lay the groundwork for a more comprehensive, differentiated set of residential and business services than has ever been attempted.

In sum, 3G fixed wireless technology offers the potential for consumers and telecommuters to get the bandwidth and services of sophisticated private network users — at very reasonable cost. For competitive service providers, 3G can help launch a low cost, comparatively lower-risk service creation platform, and an overthe- air infrastructure based on a software-defined softswitch model that bypasses the expensive Class 5 PSTN switch. With implementations of 3G happening now, next generation fixed wireless represents a great leap forward. Real fixed-point implementations will be possible by mid-2000, and within the next few years, a revolution in competitive residential access could result.

3G Advantages

Although 3G fixed implementations have not yet been finalized, there are both technical and economic advantages to the technology that seem ideal as an entry point to competitive residential services. Vendors are already developing radio transmission systems for 3G that correct some of the weaknesses of other wireless local loop technology. For example, previous WLL systems that are not based on 3G have required line-of-sight or near line-of-sight from the radio transmitter to the home or building being served. Common weather conditions such as heavy rainstorms, dense fog and blizzards can adversely affect transmission.

By contrast, fixed wireless systems based on 3G technology are designed without line-of-sight limitations or requirements. Unlike wireless local loop solutions, which required use of externally mounted antennas, a 3G-based solution can use an integrated antenna in the home terminal unit. This is a significant benefit, enabling self-installation and over-the-air service activation. This can save consumers and carriers significant cost — $700 to $750 today per home.

Another related advantage of 3G service is spectrum reuse. A 3G network, though requiring a wider “spread” of bandwidth thanconventional 2G technologies, uses spectrum more efficiently. In the case of wideband CDMA, the technology takes advantage of “voice quiet” periods to boost communications capacity. No single user is assigned a particular channel (as in analog wireless);
onversations are encoded and reassembled at the receiver site, so that the full spread of bandwidth is utilized. In effect, any user can gain access to the entire channel that is thought of as a shared radio resource.

3G fixed wireless is also sparing in the use of frequency; in other words, it is spectrally efficient. A 3G fixed system allows for oneto- one spectrum reuse; which means that multiple base stations and multiple sectors within a base station can operate on the same frequency. This contrasts with cellular networks, which must be carefully designed today so that adjacent cells do not operate on the same frequency. Since this issue does not arise with 3G, network planning is much simpler. In the case of wideband CDMA, cell splitting and sectorization are also both enhanced by W-CDMA’s ability to cope with the resulting signal overlap and interference. This helps improve signal penetration and increases the level of noise immunity.

3G Spectrum

Although spectrum (roughly 155 MHz in the core band around 2GHz) for 3G has been allocated specifically in Europe and many other parts of the world, the US has not yet finalized a 3G spectrumplan. While the FCC has announced it will free up spectrum located in the 700 MHz band for 3G auctioning later this year, further allocations will be required to accommodate a range of competitive 3G service providers in different parts of the country. However, because of 3G’s ability to be implemented across any number of bands, operators and the FCC are working toward a solution. As yet, the FCC has not completed all spectrum considerations, and the question of whether to provide new allocations remains open. Importantly, infrastructure providers are currently working to create solutions that will deliver the same functionality as 3G without requiring the extra spectrum.

3G Required


imperative, enabling network engineers to embark on massive 3GTo achieve this level of wireless connectivity over wide areas – a continent or oceans, for example, basic core networks must be interconnected. Cooperation among industry 3G groups has been harmonization efforts to promote IMT-2000 compatibility worldwide. These efforts include developing software and hardware upgrades to core networks that prepare for highbandwidth multimedia services; as well as developing systems to harmonize two different emerging 3G CDMA operating solutions. Both will ultimately talk to each other across the global network space.

The two solutions include W-CDMA (wideband CDMA), a standard that supports fixed network speeds up to 2 MHz, and is endorsed by European standards groups and NTT DoCoMo, the largest wireless carrier in Japan, which has led the first 3G tests and commercial implementations. The second 3G operating solution is CDMA-2000, which is an evolution of the North American IS-95 CDMA standard (also supported under the IMT-2000 3G specification.). Ultimately, both standards will accommodate the high data rates (up to 2 Mbps for fixed apps) specified in IMT- 2000 in both fixed and mobile modes. Figure 3 illustrates the commonly used wireless air interfaces as currently defined in the ITU’s IMT- 2000 Harmonization specification.

The five primary air links have been integrated into the core carrier specification. The five evolved standards are:

1. IMT-DS (W-CDMA direct spread spectrum)
2. IMT-MC (cdma2000 multi-carrier)
3. IMT-TC (TDD-SCDMA time-code division multiplex)
4. IMT-SC (TDMA IS-136 single carrier EDGE)
5. IMT-FT (DECT frequency time division)

In practical terms, the expectation today is that Fixed Wireless Access will become a mainstay of developing countries without adequate wired infrastructure. In developed countries, however, 3G residential wireless represents a new horizon for competitive access providers. The advent of cable modems and DSL has raised the bar substantially for data services, which means that users now readily expect a wireless connection to provide somewhere between 1.5 Mbps and 2 Mbps. In the US, some of the alternative providers are considering broadband, fixed wireless options. But these fixed systems are economical only when shared among small to medium-size businesses, and many have stringent line of sight requirements and suffer from weather-induced impairments. Theresidential and business marketplace is still ripe for a wireless access alternative such as fixed 3G which can be deployed in many different spectrum bands, offers superior in-building penetration, and provides better noise immunity and signal strength than other fixed wireless options.

3G Wireless

The IMT-2000 specification makes specific provisions for 3G Fixed Wireless Access (FWA). The International Telecommunications Union specifies that “IMT-2000 aims to exploit the potential synergy between the digital mobile telecommunications technologies being developed as part of the dramatic growth of personal telecommunications, and those rapidly evolving for Fixed
Wireless Access.” According to the ITU, this means that IMT-2000 will offer wireless access to the global telecommunications infrastructure which will serve both mobile and fixed users in both public and private networks.

Fixed wireless 3G is a converged, multimedia-driven technology that surpasses early concepts of wireless local loop which relied principally on RF and line-of-sight connections to deliver basic
POTS and narrowband data (mostly to under-served or sparsely populated areas). In fixed mode, 3G utilizes a point-to-multipoint network architecture that can transmit data and voice
simultaneously at high speeds across core wireless infrastructure. Potential applications for 3G fixed services include SOHO, business and home networking which creates a high-speed
interface/gateway between an in-building ‘network of networks’ (e.g., wireless interworking of telephony, data, video, home energy monitoring, and security networks) and the outside world – e.g., the Internet and the PSTN.

3G Concept

While some carriers announce plans to migrate to high-speed broadband wireless in incremental steps, international standards groups are busy finalizing 3G mobile and fixed standards.

In 1998, for example, working groups at the European Telecommunications Standards Institute (ETSI) and the International Telecommunications Union (ITU) in Geneva, the
reigning worldwide standards body, assembled to evaluate no less than five competing proposals for 3G wireless networks. Some of the proposals offered backward compatibility with existing 2G
networks; others did not. Today, the 3G international standard, known as IMT-2000 (or UMTS), represents an amalgam of many international interests. Groups as diverse as the GSM Association, the Universal Wireless Communications Consortium (UWCC), ETSI, the North American CDMA Development Group, the ITU, and the Third Generation Partnership Project (3GPP) have provided technical input into the IMT-2000 specification, which is still undergoing modification.

ITU defines the combined 3G wireless standard as “a comprehensive set of terrestrial and satellite radio interfaces,” a standard that actually encompasses specs for both narrowband and
wideband CDMA and TDMA (the spec was originally approved by the European Telecommunications Union). The specification accommodates fixed, mobile and Internet wireless users. IMT-2000 is a “standard that allows operators the freedom of radio access methods and core networks to openly implement and evolve their systems depending on the regulatory, market or business requisites,” ITU states. Key features of the 3G standard include
compatibility of services within IMT-2000 mobile and fixed networks; high voice quality; small terminals for worldwide use; worldwide roaming; and the capability of supporting multimedia
applications and services, such as videoconferencing, high-speed Internet, e-commerce, voice calling, and high-rate data.

Evolution to Wireless 3G Networks


First generation wireless referred to analog cellular transmission, which became popular in North America throughout the 1980s and early 1990s. Second generation wireless refers to the current, most common forms of digital cellular and personal communications services (PCS) primarily voice transmission technologies that utilize digital encoding and provide some low-speed, circuitswitched data for such handheld applications as phone-based email, news and stock services, and short message service (SMS). By contrast, 3G wireless is a form of sophisticated broadband transmission that in addition to handling vast amounts of voice capacity, is optimized for transmission of data and multimedia.

Development of third generation wireless air interfaces and switches has been going on intensively in universities, research centers, and wireless manufacturer settings in Europe, Japan and North America since the early 1990s. The International Telecommunications Union (ITU) released its first studies on 3G in 1994. By 1996, however, most wireless infrastructure providers recognized the need for a more robust network technology that could surpass the “second-generation” mobility concept of PCS.

Interim data strategies, sometimes known as 2.5G services have since been devised to accommodate wireless users’ needs for higher speed data and image transmissions over currently available spectrum. Among these 2.5G networks which are being deployed on a selective basis are GPRS (General Packet Radio Standard, an evolution of GSM technology which transmits data up to 115 Kbps) and EDGE — Enhanced Data Rate for Global Evolution, a TDMA evolution which delivers 384 Kbps for mobile applications.


In the CDMA world, a data-only 2.5G standard, known as HDR (High Data Rate), will deliver as much as 1.4 Mbps to wireless data customers in fixed mode. Concurrently, 1XRTT, an advanced version of IS-95 for mobile users, delivers transmission speeds up to 144 Kbps and is the first step in a perceived evolution to fullblown, multimedia-capable 3G networks.

Sunday, August 23, 2009

Standardization

It is also possible to compare the two technologies with respect to the extent to which they are standardized. Broadly, it appears that the formal standards picture for 3G is perhaps more clear than for WLAN. For 3G, there is a relatively small family of internatio nally sanctioned standards, collectively referred to as WCDMA. However, there is still uncertainty as to which of these (or even if multiple ones) will be selected by service providers. In contrast, WiFi is one of the family of continuously evolving 802.11x wireless Ethernet standards, which is itself one of many WLAN technologies that are under development. Although it appears that WiFi is emerging as the market winner, there is still a substantial base of HomeRF and other open standard and proprietary technologies that are installed and continue to be sold to support WLANs. Thus, it may appear that the standards picture for WLANs is less clear than for 3G, but the market pressure to select the 802.11x family of technologies appears much less ambiguous – at least today.

Because ubiquitous WLAN access coverage would be constructed from the aggregation of many independent WLANs, there is perhaps a greater potential for the adoption of heterogeneous WLAN technologies than might be the case with 3G. With 3G, although competing service providers may adopt heterogeneous and incompatible versions of 3G, there is little risk that there will be incompatibilities within a carriers own 3G network. Of course in the context of a mesh of WLANs, reliance on IP as the basic transport layer may reduce compatibility issues at the data networking level, although these could be significant at the air interface (i.e., RF level). Unless coordinated, this could be a significant impediment to realizing scale economies and network externality benefits in a bottom- up, decentralized deployment of WiFi local access infrastructure.

Support for Services

Another important difference between 3G and WiFi is their embedded support for voice services. 3G was expressly designed as an upgrade technology for wireless voice telephony networks, so voice services are an intrinsic part of 3G. In contrast, WiFi provides a lower layer data communications service that can be used as the substrate on which to layer services such as voice telephony. For example, with IP running over WiFi it is possible to support Voice-over-IP telephony. However, there is still great market uncertainty as to how voice services would be implemented and quality assured over WLAN networks.

Another potential advantage of 3G over WiFi is that 3G offers better support for secure/private communications than does WiFi. However, this distinction may be more apparent than real. First, we have only limited operational experience with how secure 3G communications are. Hackers are very ingenious and once 3G systems are operating, we will find holes that we were not previously aware of. Second, the security lapses of WiFi have attracted quite a bit of attention and substantial resources are being devoted to closing this gap. Although wireless communications may pose higher risks to privacy (e.g., follow-me anywhere tracking capabilities) and security (i.e., passive monitoring of RF transmissions is easier) than do wireline networks, we do not believe that this is likely to be a long-term differentiating factor between 3G and WiFi technologies.

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