How Skype Works

Skype is a software application that allows you to make free phone calls to more than 75 million people worldwide, and shockingly cheap calls to practically everywhere else on Earth! As a result of that, Skype has become the fastest growing service in the history of the Internet. Recently, the company was acquired by eBay, another step forward towards achieving the final goal of making Skype the world's largest communication company.

Skype is easy to install and use. It allows its users to make crystal clear calls, regardless of their location, send instant messages, switch seamlessly between text and voice communication, make video calls, conference calls, transfer files, call landlines and cell phones for a fraction of the cost of a traditional call. Skype is truly making a revolution in the way we communicate.

But how does it actually work? This article focuses on describing the Skype network and the technology behind it.

How Skype Works

Skype is a type of peer-to-peer Voice-Over-IP client, based on the Kazaa file sharing program. The developers of Skype claim that it provides better voice quality than similar applications like MSN and Yahoo Messenger. It also encrypts calls end-to-end.

There are two types of machines in the Skype network - ordinary host (Skype Client) and Super Node (SN). An ordinary host is the computer of a regular user who has the application installed and connects to the network in order to communicate with other users. The Super Nodes are the end-point of ordinary hosts in the network. In other words, ordinary hosts connect to the Super Nodes. Any computer with a public IP and proper hardware configuration can be a SN. An ordinary host must connect to a super node and must register itself with the Skype login server for a successful login. The Skype login server is the only central unit in the whole network. It stores the usernames and respective passwords of all Skype users. Nslookups have shown that this server is located in Denmark. All Super Nodes connect to the login server in attempt to verify the username password of the client. It stores your Skype Name, your e-mail address, and an encrypted representation of your password.

If you are a regular Skype user, then your computer is considered an 'ordinary host' that connects to a Super Node. The Super Nodes are servers, located in different parts of the world. But your Skype client, must know to which SN it has to connect. Therefore, every Skype client (SC) maintains a local table that contains the IPs and corresponding ports of Super Nodes. This is called a host cache and it stored in the Windows Registry of the given SC. So basically, every time you load up Skype, it reads the date from the host cache, takes the first IP and port from there and tries to connect to this SN. If the connection fails for some reason (the SN is offline; it is no longer part of the network, etc) then it reads the next line from the table. In case it fails to connect to any of the IPs listed, the Skype returns a login error upon start-up. Hence, the host cache must contain at least one valid entry in order for the application to connect to the network and work properly. Valid entry means an IP address and port number of an online Super Node. The path to the table in the Windows Registry is HKEY_CURRENT_USER / SOFTWARE / SKYPE / PHONE / LIB / CONNECTION / HOSTCACHE. You can verify that on your computer by opening the Start menu, then click Run and enter 'regedit', without the dashes. Of course, the exact path could be different in the next versions of the application.

As a concept, Super Nodes were introduced in the third-generation P2P networks. They allow improved search performance, reduced file-transfer latency, network scalability, and the ability to resume interrupted downloads and simultaneously download segments of one file from multiple peers. Basically, they help ordinary hosts connect to each other and guide efficiently the encrypted network traffic.

Super Nodes are also responsible for the 'Global Indexing'. This technology enables you to search for other users in the network. The company guarantees that it will find a user if he has registered and has logged in during the last 72 hours.

A very interesting moment about the Skype network is that it 'self-modifiable'. If you have the application installed, your computer may turn into a Super Node, without you even knowing it, because those capabilities don't have a noticeable impact on a computer's performance. SNs basically store the addresses of up to several hundred Skype users, without carrying any voice, text or file-transfer data. In that manner, the more Skype users come online, the more supernodes become available to expand the capacity of the network.

Skype routes the traffic intelligently by choosing the optimum data transfer path. Since it uses either TCP or UDP protocol, it breaks the whole data stream into separate packets, which can take different paths to the end destination. The final arrangement is done at the receiving end.

As far as safety and privacy are concerned, Skype uses Advanced Encryption Standard, known as Rijndel, used also by the U.S. Government organizations to protect sensitive data. Skype uses 256-bit encryption.

The programmers of Skype have implemented wideband codecs which allows it to maintain a good sound quality at a bandwidth of 32kb/s and allow frequencies between 5-8,000Hz to pass trough.

Your list of contacts, the application stores in the Windows Registry. This is called the Buddy list and once again, it is digitally encrypted. So, the list is local for every machine, or in other words, it's not downloaded from the central server.

Let's briefly describe the tasks of the Skype client. First it connects to the network. It then listens on particular ports for incoming calls, refreshes the host cache table, uses wideband codecs, maintains the buddy list, encrypts messages and determines if there is a firewall or not.

The login process:

The login process is the most important one and it consists of several phases. As mentioned, SC must connect to a valid SN in order to authenticate the username and password with the Central Server.

Skype gets the fist IP from the host cache, sends it a UDP packet and waits for response. If there is no response after 5 seconds, it sends a TCP packet to the same IP. It tries to establish a TCP connection to the HC IP address and port 80 (HTTP port). If still unsuccessful, it tried to connect to IP address and port 443 (HTTPS port). If this does not work either, it reads the next address in the HC. If Skype is unable to connect to a SN, it will report a login failure.

The application comes with several build-in addresses of different nodes, called bootstrap super nodes.

If the connection attempt is successful, the client must authenticate the user name and password with the Skype login server, which holds all user names and passwords and makes sure they are unique across the whole network. When the application connects to an SN, it receives an up-to-date list of other active SNs, so it has the most current information.

The Media Transfer process:

The video/voice communication through Skype is established through UDP. The trick here is that quite often, one of the users is behind a firewall or a router, hence it doesn't have a real IP address. But if both Skype clients are on real IPs, then the media traffic flows directly between them over UDP. The size of the voice packet is 67 bytes, which is actually the size of UDP payload. One second conversation results in roughly 140 voice packets being exchanged both ways, or 3-16 kilobytes/s.

If one of the callee or both of them do not have a public IP, then they send voice traffic to another online Skype node over UDP or TCP. The developers of Skype have preferred to use UDP for voice transmission as much as possible.

An interesting fact is that even if both sides are not speaking, voice packets will still be flowing between them. The purpose of these so called 'silent packages' is to keep the connection alive.

Conclusion:

There are several factors responsible for the success of Skype. First of all, the voice quality is better compared to other applications. It works without a problem on computers with firewall. It is very easy to install and use. Skype's security is also a big advantage. Everything that is being transferred across the network is being encrypted to ensure privacy. As a result of that, even if hackers intercept the data being transferred, they won't be able to decode it.

The Skype application does not include any adware or spyware. But, there are cases when third parties have managed to add such functionalities (not only for Skype), so it's really important that you download it from the right place. Therefore, do it either from the official website, or from respected sites as http://www.freesecuredownloads.com/skype/index.html.

How Skype Works
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Learn to Fly on Your Computer - RC Flight Simulator

Flying model aircraft via radio control (RC) has been a very popular hobby since the mid 1960s, with the advent of compact electronic radio control systems. However, in order to learn how to fly, all instruction had to be done with your model flying in the air. There was essentially no training that could be accomplished on the ground. As you can imagine, this method of learning to fly led to many accidents and crashed or damaged model aircraft.

With the availability today of powerful personal computers, practical radio control model airplane flight simulators are an everyday reality. For a very modest cost, you can purchase RC flight simulator software and hardware for home use. The hardware is a realistic replica of an RC transmitter (usually called the controller), plugged to your computer via the USB port. An RC flight sim produces extremely realistic images of flying sites, and the computer generated aircraft look and behave virtually like the real thing. You can even see the flight control surfaces move to your control stick's input.

The aspiring model airplane pilot uses the controller to taxi the airplane to the RC simulator's runway, increase the throttle, and take off just as if you were at the airfield. Of course, all engine sounds are realistically produced by the RC flight sim. The airplane becomes airborne, and the computer monitor's scene is automatically orientated such that you get a great view of the airplane in flight from your position "on the ground." It's just as if you were really at the field.

Learn to Fly on Your Computer - RC Flight Simulator

When learning to fly a radio control model airplane, it is always a very good idea to have an instructor for your first few actual flights. The RC flight sim, however, is invaluable in minimizing the time needed in the air to become an accomplished flyer. As a general guide, you can easily cut your flight practice time in half when an RC flight sim is an integral part of your training strategy.

Another model flight training area that RC sims have changed forever is learning and practicing advanced maneuvers. In the past, learning a new stunt had to be done at the field. You always risked a crash when practicing loops, rolls, inverted flight, etc. With the availability of the flight simulator on your computer, you can now safely practice these new maneuvers as much as you like in the privacy of your own home, without fear of damaging your aircraft. It is almost impossible to describe how quickly you can acquire new flying skills via this method.

In addition, most of the new RC flight sims have very useful video clips from experienced model airplane instructor pilots on how to perform these new flight maneuvers. They include maneuver descriptions of what you will be doing on the RC flight sim, as well as a discussion of common errors. They even discuss what you will be doing with your control sticks to perform these stunts.

New aircraft are constantly being added to RC flight sim programs. One can experience flying a wide variety of model aircraft with a click of your computer mouse button. These planes can range from lightweight electric powered park flyers to turbine jet fighters. The sounds, control feel and performance of these various airplanes within the RC flight sim are very accurately reproduced.

Whether you are just starting out learning to fly radio control model aircraft, wish to improve your flying skills, or just want to have some fun flying indoors on a cold, windy winter's night, the new generation of RC flight sims is an ideal way to enter the fascinating world of computer flight training.

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Tim McKay has been an avid model airplane enthusiast for the past 35 years. Further information on ready to fly indoor radio control model airplanes can be found at http://IndoorFlyingModel.com/

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Alienware X51 Dell PC Guide - A Mini-Desktop With Plenty of Power, Speed, and Space

The Alienware X51 PC is a mini-gaming desktop by Dell. You can easily place it anywhere in your home due to its compact size. The tower can be placed vertically or horizontally on any flat surface. Don't think that its compact size holds it back, however, as it's still faster and more powerful than the average desktop. It's also highly customizable and upgradable, so you can add more hardware to it later on down the road.

It comes with a variety of advanced features, such as the AlienFX lighting technology and AlienFusion management controls. The lighting technology gives users access to 8,000 unique lighting combinations. It's up to you how you want to customize the lighting scheme of your desktop. As for the AlienFusion, the user is in charge of power management controls. Lower the settings when you want to preserve energy and crank them up whenever you need an extra boost of power.

The great thing about Alienware X51 is that it's inexpensive compared to other gaming desktops. It's a great starter entertainment PC. Despite its small sizes, it's still expandable. The components can be upgraded later on down the road. There is plenty of room for an additional graphics card, CPU, and memory. Keep the machine up to date by adding new hardware when you need it.

Alienware X51 Dell PC Guide - A Mini-Desktop With Plenty of Power, Speed, and Space

There are a number of dual and quad-core processors from which you can choose. The desktop can handle up to a 2nd generation Intel Core i7 processor with Turbo Boost technology. Its CPU should be able to handle any program you throw at it. An i3 model is the default option. If you need more than this, you can simply select an i5 or i7 when placing your order online.

Processors deliver the power, and memory delivers the speed. Your memory options go up to 8 GB dual-core channel with 1333 MHz (system memory). This is enough memory to take on high-performance multimedia and gaming applications with ease.

No entertainment PC is complete without a NVIDIA video card. This one comes with a 1 GB NVIDIA GeForce GT 640. You won't have to worry about your games lagging or your videos getting choppy. With this kind of graphics power, you can easily run your favorite multimedia smoothly. Thanks to a 1 TB SATA hard drive, you'll be able to save all of you files on the computer. It's almost impossible to run out of space!

If you read any Alienware X51 reviews, you'll see that consumers are very happy with the amount of power they are getting. It really is a great PC that's designed to last for a very long time. Its expandability alone makes it worth every penny.

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Now that you know what to expect from this desktop, you can take a look at Alienware X51 discount offers to learn how to save. Dell is really great when it comes to providing online shoppers with deals and promotional offers. You can save on an Alienware computer and accessories.

To find out more about this computer along with coupons and discounts to make your purchase less heavy on the wallet, visit George's website - http://www.gripbuy.com/Electronics/dell.html

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Computer Cookies: Are They Good or Bad?

Explaining "Cookies" (the non caloric ones that reside in your computer!)

You can't talk about all those nasty 'things' that can 'attack' your computer while you are surfing the Internet, like viruses or spyware, without talking about 'Cookies'. But what are they and are they really bad for my computer?

Ok, first let's define the term, and then we'll explain the good and the bad about it.

Computer Cookies: Are They Good or Bad?

Cookie(s):

A small data (text and numbers) file (piece of information) created by a Web server (large computer that stores web sites) that is stored on your computer either temporarily for that session only (the time that you spend on a web site) or permanently on the hard disk (persistent cookie). Cookies provide a way for the Web site that you visit and go back to visit again, to identify users and keep track of their preferences. Amazon and Barnes and Noble online are very creative in the use of their cookies that get generated when you visit.

Here's an example from my computer from visiting the Disney.com website:

CP null*disneyworld.disney.go.com/1088 1761935360 30785590 403215680 29726670*

Notice that the only thing in that string of text and numbers that you can recognize is the name of the website. The rest of the information is simply a set of numbers that only a computer can understand.

Why are cookies important to you? Well, you would not be able to browse through the Web as you are currently used to if you had cookies restricted on your computer.

The Good "Cookies" (non calorie type)

Cookies are commonly used to "maintain the state" (the current or last-known status) of the session (time that you spend on a site) as a user browses around on the site. For example, if you filled out a form and decided to leave that for a moment to view another page, when you come back to that form, the information that you already filled in would still be there. Without cookies, the site would not know who you were.

On the 2 web sites that I mentioned, Amazon and Barnes and Noble, they both use a combination of cookies and online database to recognize you when you return to the site as well as "remember" your earlier choices and from those choices recommend possible book or music choices for you on your current visit.

Imagine, if you will, walking into a local Barnes and Noble store where a clerk immediately recognizes you, walks up to you as she calls you by name and walks you over to your own table of books and music. You see that they have put all of your favorite kinds of books and musicians on the table, both new and old works, all laid out for your quick viewing pleasure!

And, on the next table, is a sign saying "Other people who bought these items also purchased these items" so that you may find interesting items that you may never have seen but might find interesting. Wouldn't that make shopping a great experience?

Well, that is exactly what it is like to shop online with a sophisticated shopping web site like Barnes and Noble and Amazon! And it's only because of cookies remembering who you are that allows this type of service to occur.

The Bad Side of Cookies

Actually, as you have just seen, cookies on your computer are not a bad thing; it's just that the information that they contain can be quite enticing to unscrupulous people. Quite a bit of personal data may reside in the cookie files in your computer, such as ID and Password information. As a result, this storehouse of private information is sometimes the object of attack, which is what happens with some types of spyware.

The default (Default refers to a value automatically assigned to a computer program or device), settings in your Web browser typically allow "first-party" cookies that do not contain any personal information, but not "third-party" cookies.

First-party cookies are ones that are created by the Web site you are visiting. Third-party cookies are created by a Web site other than the one you are currently visiting; for example, by a third-party advertiser on that site (pop-up or banner). The purpose of such cookies is usually to track your surfing habits, which is why third-party cookies are considered an invasion of privacy and riskier than first-party cookies. In some instances cookies are used to consolidate and track user behavior across different sites, which provide marketers with private information about you without your knowledge. These are what are referred to as Tracking Cookies.

Aha, now we're getting somewhere!

Because, a Tracking Cookie is a somewhat new term for a cookie that has been design by the above mentioned 'unscrupulous' people that do business on the Web. It is part of the unfortunate phenomenon known as Spyware! But, that's a topic for another whole article!

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What Is A Blog And How Does It Work? A Detailed Guide

So what is a blog and how does it work anyway? You're hearing more and more about the "blogging phenomenon" and the explosion of blogging online, and you might even fancy it as a way of earning a side income. Blogging is certainly an online publishing strategy that's here to stay, and here are 3 key characteristics of a blog that sets it apart from any other site:

What Is A Blog And How Does It Work? #1: It's A Simple Push Button Website

A blog is an easy way for anyone (and I mean anyone) with a computer and access to the internet to publish whatever they want on the internet without learning HTML or doing any kind of website development of their own. There are literally hundreds of different blogging platforms out there that provides free hosting for your blog, such as Blogger, WordPress and Tumblr, just to name a few. You also have the option of hosting your own blog on your own website, but you will have to buy the domain name and find a hosting provider of course.

What Is A Blog And How Does It Work? A Detailed Guide

What Is A Blog And How Does It Work? #2: It's A Publishing Tool

A blog has a unique way of displaying content, in that is shows up all your latest posts right at the top of the page, and older posts further down at the bottom. Most people started out using it as an online diary or journal, but since then many people have used it to showcase their expertise about various topics like gardening, stock trading and cooking, just to name a few. The beauty of a blog as a publishing tool is that you always see the newest content first, which is convenient for new and repeat visitors alike.

What Is A Blog And How Does It Work? #3: It's A Public Forum

You might be thinking "Okay, there's nothing all that special about a blog, it's just a glorified website... right?" Well, in addition to it being a push button website and a handy publishing tool, it also acts as a forum for your visitors. Anyone and everyone can comment on your posts, and many popular blogs have hundreds of comments on their posts every single day! That means that there are a lot of opinions being aired, which adds to the value of your content, and a strong community spirit being built, because people are personally invested in the blog.

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What Is A Blog And How Does It Work? #4: It's A Source Of Income

Just like any other publishing tool and community, you can make money from blogging if you know how to do it properly. Once you have a good understanding of what is a blog and how does it work?, you can easily leverage it to make money with your blog.

You can get free expert advice on making money blogging and many more blogging tips by signing up to my E-Bloggers' Essentials newsletter. Just follow the links above.

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