Whether you want to create a website for fun or for profit, you will need to find a reliable web host to support your site. While you shouldn't spend a fortune each month in hosting fees, you should expect to get what you pay for. But cost shouldn't be the only variable when it comes to choosing a host.Understanding what you need from a web host and visiting different host websites to see what they have to offer will give you some good information on which to make your choice. Below are four tips that can make this decision a little easier.Check Out Different Web Hosting PackagesBecause your needs will be different from a large corporations needs or a medium sized business' needs, many web hosts offer packages for small, medium and large businesses. When comparing packages, you will notice that the major differences are cost, amount of data transfer and disk space available, number of email addresses offered, and amount of bandwidth you will receive each month.If you're planning to upload lots of pictures, video or other media that takes up more space than text, you should determine how much space you'll need before choosing a web host.Quality Control PanelA good web host makes it as easy as possible for customers to upload files, manage email accounts, review site statistics and manage FTP accounts. Learn as much as you can about the control panel before choosing a web host. Learn which site statistics will be available so you can adequately monitor all marketing campaigns and incoming traffic. Lastly, make sure you can contact customer service at any time if you're experiencing problems.Moving Your Domain NameIf you're moving from one web host to another, keep in mind that you may have to pay to move your domain name. While some hosts offer to do this for you for free, others do not and will charge you for registration. When reviewing monthly fees and billing options, find out exactly what's included in these fees. If you don't have a domain name, you will have to register one in order to claim a web address so no one else can use it. Some web hosts include the domain registration fee in their monthly fees, while others charge service fees. Because your domain name needs to be renewed each year, find out who will be paying the renewal fee as well. Customer ServiceIf you can't get in contact with your web host if you're site goes down, there is very little you can do except wait until the site is up and running again. Choosing a web host that provides excellent customer service 24/7 via phone, live chat, email and tutorials found on their website can make downtime seem less frustrating. Since you're paying for their services, you should expect their customer service department to be efficient and easily accessible. Now that you know more about what to look for in a web host, you should be able to make an informed decision that will enable you to choose the very best hosting services for your website.
read more
0
comments
How To Select The Right Web Host?
The question every person who has just completed the design and about to launch his/her favorite website tend to ask oneself. Well, one must understand in the first place itself that selecting the right web host is not that simple a task. There are thousands of web hosting services existing in each country and many of them provide similar services at almost the same rates as well. Hence, it might take a while and some effort in studying and researching about each service provider before you could proclaim, 'yes, this is the right provider I was looking for'. In this article, we try to change this pattern a bit. The tips that are been included in the next few paragraphs would urge you to view the scenario more rationally and if you follow it precisely, then there is no reason to think why you can't find the right web hosting service provider. As a first step, see if the web hosting service provider is offering round the clock customer support. Remember, in the game of servers, memory, and bandwidth, glitches can happen anytime irrespective of the name and fame of the service provider and what matters is how quickly and efficiently the provider could fix it in less time. To test this facility, you just ring them up, their customer care. On a general scale, you will be surprised by the number of unanswered calls you find in the process. Always go for those with 24/7 customer care facilities. It is always a prudent idea to take into account the reviews about a web hosting service provider, especially if it had been written by one of its previous clients. But, at the same time, don't believe the writings found on the company's forums or in the hosting directories. Most of the times, such reviews will be partisan or might be favoring the company. Watch out for those web hosting companies that offer or boast a never ending backup of RAM and CPU. Another catch phrase employed by web hosting companies is 'unlimited bandwidth and memory space'. But, one should be intelligent enough to realize that these are just games involving numbers and practically, none of the web servers on this earth has such features in place. Further, if the rate of a web hosting plan and the offer they put forward in terms of server resources are not congruent, it can be safely assumed that the plan is a scam. More server resources definitely cost more. The moral of the story is, don't go by the plans entirely, but use one's discerning senses as well, to full use. Finally, go for a domain that is reasonably old in business. Chances for new domains going bust in the fast paced web hosting business race is high. In fact, that is the trend witnessed in the hosting industry with about 95% of the players going out of business within their first year itself. It is easy to be a hosting company, but the difficult part is in sustaining the business.
read more
0
comments
Web Hosting and Domain Names, Where To Start?
When you make the decision to start a website for your business, it is a big step. Going from the world of offline business where clients are limited to geographical locations to online where the entire world is a potential client can be overwhelming. There are many things to take into consideration. You have the products to sell, and the design of the website all planned out, now it is time to put it all together by choosing a web hosting company. The first thing you should decide on is a domain name. This is perhaps the single most important decision you can make. You want something that is professional; the domain name will reflect the nature of your business. Avoid using cute names; people tend to skip to the next website.Try to choose a name that is short and easy to remember. Think about your customers when they try to reach your web site. Will be easy to type? Can you spell your domain name at the phone without much trouble? This is going to be your presence in the internet from now on, so choose wisely.Choosing the web hosting company that is right for you is a long process. There will be millions of options, it is important to ask questions and that the web hosting company answers those questions adequately. The most crucial point of any web hosting company is their reliability. If the site does not offer enough space, then your website will be shut down for all or part of each month. This is not the goal you have set for your business. Ask the web hosting company if it offers an uptime guarantee. Usually if a company offers a guarantee of this type, their service is reliable. When you are new to Internet marketing, you will have a lot of question. Sometimes the questions you need to ask will not be during business hours. It is important that customer service is available by phone, email, or even a chat window twenty-four hours a day to answer any questions that you may have. Another service that is just as crucial as the rest is the storage and bandwidth that your website will need. Most likely, you will not know what your website is, but the web hosting company will. If you want a flashy site, you will need more bandwidth. It is important that you know before hand the ins and outs of web hosting companies. A good way to find your answers is to do some research. A Google search will yield you all of the information you need. The world is your potential client, reach out and make contact. It will ensure the success of your business.
read more
0
comments
8 Ways To Host Your Site
There are 8 basic types of the web hosting available in the market today. Hosting even by IT standards, is not considered exciting, if it was a country it would be Belgium. If it was another business it would be fleet car leasing, where shared hosting would be company car pooling. Dedicated, leasing of cars to a sales force on a rolling annual rental contract or lease agreement. Like the gold rush in the Sierra Nevada in 49, nobody pays much attention to the stores the picks and shovels, but this is a mistake it can be vital to your sites success. It is crucial to security and in vital if maintaining site integrity, to have a hosting partner who will grow with you and react quickly and decisively to resolve problems when they arise. A good host can even be a source of revenue for your site. 1. Dedicated Server – rental as well as the exclusive use of an internet connection, server and software2. Shared hosting – Multiple websites are being hosted on just one remote hard drive and server3. Reseller hosting – reselling of hosting accounts for another web host under a brand of your own. You determine the pricing structure and other aspects of the offer.4. Virtual Private Server - You are not renting a real server, but you are rather splitting hardware with the other virtual servers running on the same machine. Many self contained virtual server can exist on one rented remote server.5. Free hosting – Service usually offered by ISP’s or compensated with advertisements on your website. Free hosting usually offers little or no support, bandwidth, space, or the free scripts or site building features you enjoy with shared and dedicated hosting.6. Managed Hosting - Expanded dedicated web server hosting. In dedicated servers, the client has to take care of his or her own server but in managed hosting, the provider would have the responsibility of doing that Unmanaged Hosting - Total remote control administration of your web server. The server's technical aspects are controlled by the designated administrator which you would select to manage and handle your website information.7. Colocation – Requires that you to bring your server to the data center of your host.8. Clustered hosting - Used by the biggest and most important websites, you buy manage and physically house the servers yourself. Clustered means that the same content would be served on a number of servers enabling better redundancy and resource. Works well for Google.As you can see there are many types of hosting account. Whether you are planning business web hosting or you intend to run a school site or maybe you are simply planning on getting a small hobby site up and running, you have a decision to make, what hosting package do you chose.This article abstract is published on behalf of www.123ftpdirectory.com an online web services company. We are the one stop web shop, everything you need to set up a site under one roof, we trawl through the web and review the best services and then publish just a select list of web services we try to restrict to just six service providers in each category.
read more
0
comments
What Should I Know About Web Hosting?
There has never been a better time to start your own website. Firstly, the web hosting offers are cheaper than ever, the technology behind web hosting accounts is as simple as it can get when it comes to administrating them and there are various types of free software and service support included into the hosting plan.To begin with, you have to ask yourself one thing: what is the purpose of your future website? Is it a personal site? Do you want to share pictures of you and your family? Do you plan on selling something?Once you know exactly what you plan to do with your website, and you find out what your visitors would like to see, you can easily choose the hosting offer to suit your needs. You can decide over your domain name, you can decide if you need a host that provides a site builder or you can make your own website.There are a couple of important questions you have to answer before starting your website. If your site's requirements are intense, you will probably like a web design company to work on it, or maybe a website consultant will help you understand exactly how the website will function and what you will need to start it off. On the other hand, if you want to develop a personal site or a blog, you can easily maneuver it following a few installing instruction provided by the host itself.Some people are attracted by free web hosting services. There are lots of places over the internet where you can build your own free website. For example, you will find free hosts that provide you even with 10 databases strictly crucial in order to develop a dynamic website. But usually no one will provide you with free web hosting space with MySQL database available for it. Websites installed on LINUX operating systems are by far the most common over the Internet.The key criteria you have to consider when choosing a hosting provider are three: pricing, uptime and customers support. Every web hosting company is basically selling the same thing, the differences come from the web space you will have available and the bandwidth. You will also have to make sure that if at any moment something wrong happens to your website there will be someone there to assist you in correcting the mistake. Such a web hosting company would be ideal, especially the ones that have a free phone line for customers, so they can receive support at any moment.With nowadays technology, you can easily start up your web hosting account via its control panel in less than 2 minutes and you can even install a blog very fast with the help of various free programs or build up a website in merely a half hour through the assisted steps most web hosts provide. It's up to you to decide if website time has come!
read more
0
comments
Webhosting Tips - Picking A Good Web Hosting Company
Picking a good web hosting company is important to keeping your website open and your costs down. There are many to choose from, as well as different pricing plans to look over. Depending on the amount of sites that you intend on building, you may want to consider a larger web space in the long run.You should start with the smallest web space that you can get to test the waters, just incase niche website Internet marketing does not work out for you. You may want to add on later, so make sure that your provider offers that option.You will want to choose a provider that has a reliable service. If your site is down or takes to long to open up when visitors are trying to get in, it may lead them to click out of your site and move on to the next one. They will also more than likely not visit in the future since they will remember their bad experience. For this reason, it is probably best to stick with a well known company who you can check reliable references on. Like anything larger companies have a reputation to uphold, so therefore they have more too loose and generally the bigger the better when it comes to web hosting companies as you will want the support asap shoudl you need it. With smaler companies web hosting support is sometimes lacking or delayed.There are many small hosting providers that offer space for as low as $.50 to $1 per month, however, you never know what you will be getting and many of them want you to pay for at least a years worth in advance.You will also want one that has the most affordable hosting. If you can create your own small site or have one made for you, then you will probably be able to find space for as low as $3 to $4 per month. However, if you need to choose a company that offers a What You See Is What You Get (WYSIWYG) website builder, then you will probably end up paying $10 to $15 per month for the smallest amount of space. But if this is the only way that you can build a site, then it is necessary.Some web hosting providers may also offer a deal on a yearly URL or other products when you make a web hosting purchase.Ultimately, whatever web hosting provider you choose will depend on your individual needs and what you can afford. Hopefully you will be able to snap up a well known provider at a low price who will allow you to upgrade your service as needed.
read more
0
comments
Choosing Your Web Host
It isn’t easy trying to choose the correct and best web hosting plan to best suit your needs. Even though there are so many web-hosting companies out there, some thought and careful consideration should be implemented. Two things you don’t want are:You don’t want to end up having to pay for extra features that you realise afterwards you needed.You don’t want your sites not showing up on the Internet due to excessive downtime by your hosting providers servers.When choosing your web host you also need to consider your requirements. You will need to consider:How many websites will you need?How much disk space and bandwidth do you need?What extras will you need eg email with auto-responders included?How much do you want to spend on web hosting?You should compare at least 5 hosting providers to see what they are offering. Here’s what you should look forA reasonable price for your needs - usually a monthly fee.Disk space and Bandwidth allowance – is your site or sites going to have audio, video or downloadable material? How Many Domains – look for unlimited.Sub Domains – look for unlimited.Does it have an in-built Website Builder? Comes in very handy if you don’t know much about building websites.24/7 email and phone support – this is important. Not everyone has this.At least a 99.5% uptime 99.9% is bestFree set-up – no hidden charges.Unlimited email accounts allowed.FTP accounts.Auto-responders included – you don’t want to pay extra to add on an auto-responder later.Compare all other special features even though you believe you may not need them likeCGI.FrontPage.Streaming Audio and Video.Hotlink protection.Web stats.When choosing a web host it’s important you take your time to compare hosting plans before you make the decision. There are some out there that are absolutely useless at web hosting, remember that anyone can become a web host. Your best bet is to go with a company that has been around a few years. Search for online reviews on the company you are considering. If you are considering a new web host I would recommend you include http://www.hostgator.bloggers-guide.comin your list of 5 web hosts to compare. – Visit the link. Go to “WEBHOSTING” Take a look at the plans – and when you make the comparison you’ll find that they will come out on top.
read more
0
comments
Web Hosting – What You Need to Know
Web hosting is a service that lets an individual or organization makes their website accessible in the World Wide Web. This service is made available by companies called web hosting providers. The web host has a server—where your website is run, which is connected to the internet, this way; anyone who has internet access can be connected to your website.There are mainly two types of web hosting, free and paid hosting service. Under paid hosting service, there are several types, which will be discussed later on in the article.Free web hosting enables the user to modify the content of his website by uploading the simplest kind of features in which capabilities are only limited to a certain degree. The web hosting provider makes money by advertisements displayed on the website. This type of web hosting doesn’t appear too professional since the site is under a sub domain or a directory, meaning, the website name is followed or preceded by the web hosting provider. This type of web hosting is advantageous for people who are newbie’s in the Internet and needing just a small site to get started especially with the upload tools that are very easy to use.Paid web hosting, on the other hand, provides more space and more features but you will be required to pay the web hosting provider fees to maintain your website. An advantage for this type is that the ads that appear on your website are those that you prefer and the revenue from it goes to you. You also get to have your own domain name. The different types of paid web hosting are the following:• Shared web hosting – wherein you share the same server and all other resources like software with other people. You only manage the design and content of your site.• Virtual Private Servers – here the idea is that a server is divided into small servers to enable the user to have their own. This is a cheaper alternative to dedicated servers and more expensive than shared web hosting.• Dedicated Server – this is not too popular for the common companies as it entails a lot of money. The owner gets full control over it. This is ideal for high-traffic websites.• Colocation web hosting – the individual purchases a server and passes it to the web hosting company for them to provide space, connection, and power. You must have your own administrator to check on your server.Other web hosting companies provide specific hosting and these would include blog hosting, video hosting, image hosting, and file hosting among others. When choosing a web hosting provider, consider the following:• Your needs – what type of hosting do you need, how much memory, bandwidth, etc.• How reliable is the web hosting company? Can they guarantee that your website is always up and running?• Development – in the future, can this company still provide for what you need? Do they have the latest technology?• Dependability – should there be any problems with your website and/or server.
read more
0
comments
Website Promotion Tricks
You have your own website, now what? In order to succeed online, you will need website promotion so your site would be visible to everyone connected to the Internet. It is a common belief that all websites are searchable by search engines. It’s not as simple as it seems. Website promotion entails a lot of work.Website promotion suggests that submitting your site to directories first is more important than submitting to search engines. These two are different in such a way that sites submitted to directories are only approved if it has high quality and useful content, whereas search engines just simply accept submissions of sites or pages. In submitting a website to the directory, make sure that you read and follow the directory’s rules and instructions. Keep in mind that the editors will be very discerning of your web content.Submitting to search engines definitely helps in website promotion but this takes quite a while, usually around 3-6 months. There are things to consider when submitting to search engines, you must prepare your website. Also, you will need to learn SEO or search engine optimization. You may do this by optimizing your website by improving the elements of web design like loading time, browser compatibility, etc. Another is keyword optimization wherein you make use of appropriate keywords; these would greatly help in your website. Other website promotion techniques are:• Link popularity - wherein you let people link your site to theirs. In this way, you can generate more new visitors and at the same time improve your ranking in search engines.• Write articles – that are useful to your website and let other people publish these like in article directories. You may also opt for email newsletters that include a link to your website. In this way, your subscribers are informed and updated on what’s going on in your website promotion.• Post to a forum or discussion boards. Forums are greatly increasing their popularity and this is a good way to spread the word about your website promotion.• In line with posting a forum, you may also want to use a signature file, a text that is appended at the end of your every post.• Improve website promotion through banner ads displayed in other websites related to your content. But be sure that your ad is well-designed.• Write a press release – this can definitely help in website promotion. You have to write an article about your website and submit it to different publications and you’ll get new visitors in no time at all!Now you know what to do, know what you have to avoid as well. One of the common mistakes made is relying on free web hosting service. It’s harder for search engines to detect your website if it is hosted on a free host. If you mean serious business and eyeing it as long-term, then paid web hosting is the way to go. There are some companies that promise to submit your website to thousands of search engines at a very low price, do not be fooled. Majority of these directories and engines have very minimal traffic. Website promotion can be tricky but with good research, you and your business will succeed before you know it.
read more
0
comments
How to Choose a Domain Name For Your Business?
Domain name provides access to information that you own or want to create for the public in the public domain. Therefore, there are a number of consideration in deciding and choosing the right name for your business as follows:-1)if you are in the business of selling or buying property for and/or on behalf of clients then your domain name should reflect that. An example of a domain name for a business that sells real estate is www.acresofrealestate.com If you rely on the internet for your business, lead generation, promotion or for information then having a name which describes your business and what you do is very important it would seem. But, this is also a very contentious point... There are counter arguments and we shall take a brief look at some shortly.2)If your offline business is called "Real Estate New York" then your internet business should in theory map that business exactly. Domains names such as:-A) realestatenewyork.comB) realestateny.comC) justrealestatenewyork.comD) totalrealestateny.comE) 123realestatenewyork.comThe names listed above (A to E) are all suitable for your business. However, the best practice according to Nathan Anderson; the America's foremost search engine optimization expert, in choosing name for ones domain name is to have the business name in the front. For example, realestateny.com is preferred choice over say the 123realestatenewyork.com name for search engine optimisation stand point.How do I then register my chosen domain name?There are a myriad of domain name registration companies all over the world. How do you choose one? Since you are interested in good service, you want to choose a company that specialises in domain registration. You will be able to decipher good companies from that ones that are not so good. This is my experience with domain registration companies:-" Cost is a major factor when you are registering a lot of domain names particularly when you have 100 or more domain names... I have therefore actively looked for companies that are the cheapest " Recently, I bought 2 domain names at $2.99 each but the supplier turned out to be very poor at providing service. As a direct result, I went back to my original supplier and paid nearly $10 for each domain. The point of this exercise "cheap turned out to be very expensive".What if my chosen domain name is already registered?This is sometimes the case. There are lots of realtors in New York and chances are that someone has already beaten you to it. Under this situation, I will be inclined to use a domain name that matches my business as closely as possible. Realestateny4you is not a bad choice. Arguably, this name is too similar to say another business; a competitor, for all intents and purposes. According to H. Anderson. "it matters less what the name of your chosen domain is the real issue is about promotion of the name ". I agree with this statement whole heartedly because a site regardless of its name does nothing for the business until such time that the site is actually promoted and that is the key to there being any meaning or value in the name.
read more
0
comments
Domain Registration
Since most businesses have a desire to have a web site, the first step is finding a Domain Names and then registering that name. Picking an available domain name can be easy, but what tends to confuse first time users is the registration process. There are a number of domain name registration services out there that can help make this process virtually pain free. With a little knowledge, and patience domain name registration can be an easy process.When starting the process you may come across many terms that may not make sense to you. A couple of key terms are Nameserver and Whois that you will need to be aware of.
What is nameserver?Nameservers actually are web hosting companies that host the account where your domain name will belong or point towards. Each domain name must have an IP address. When servers have IP addresses they can actually hold multiple domain names with shared hosting. Without this, your domain name wouldn’t be found on the internet.
What is Whois?The owner of the domain name is what is considered Whois. When you register your domain name, you will need to provide information that will distinguish you the owner. You may need to keep privacy in mind when providing this information.
Here is a short list of things you will need to do to register your domain name and the steps to do so.
1. List of Domain Names – By having a list of multiple domain names, it is easier to select anavailable domain name from the list ensuring that one will not be already taken. Most sites have a built in tool to allow for cross checking if the domain name is already taken. Pick your domain name and purchase. You are on your way! 2. Deciding on what time frame you want to register your domain name can be of utmost importance. Registering for multiple years usually saves money over all and reduces the chance of missing a re-register date the following year. You want to make sure you secure the use of your domain for as many years as you think necessary.3. Payment Methods – Many companies allow you to use a check or money order, but the fastest payment method is paying with a credit or debit card. Make sure this is a secure transaction! By paying with the fastest method, this allows you the guarantee that your domain name will be available once it’s paid for instantly. 4. Contact information – Keep your privacy at bay, but make sure you have a valid email address for correspondence. This will allow the registrar a way to contact you if needed and to send your instructions on how to access your account. By having valid contact information, you should hear back from the registrar within 24-48 hours. If for some reason your registration doesn’t succeed, it may be due to someone else registering the same name at the same time frame as you did. 5. Lock your domain name – Locking secures your domain name and prevents anyone from transferring your domain to another registrar. Make sure you read carefully all links that are provided upon registration. Most companies require the lock, but many wont if you don’t specify to do so.
read more
What is nameserver?Nameservers actually are web hosting companies that host the account where your domain name will belong or point towards. Each domain name must have an IP address. When servers have IP addresses they can actually hold multiple domain names with shared hosting. Without this, your domain name wouldn’t be found on the internet.
What is Whois?The owner of the domain name is what is considered Whois. When you register your domain name, you will need to provide information that will distinguish you the owner. You may need to keep privacy in mind when providing this information.
Here is a short list of things you will need to do to register your domain name and the steps to do so.
1. List of Domain Names – By having a list of multiple domain names, it is easier to select anavailable domain name from the list ensuring that one will not be already taken. Most sites have a built in tool to allow for cross checking if the domain name is already taken. Pick your domain name and purchase. You are on your way! 2. Deciding on what time frame you want to register your domain name can be of utmost importance. Registering for multiple years usually saves money over all and reduces the chance of missing a re-register date the following year. You want to make sure you secure the use of your domain for as many years as you think necessary.3. Payment Methods – Many companies allow you to use a check or money order, but the fastest payment method is paying with a credit or debit card. Make sure this is a secure transaction! By paying with the fastest method, this allows you the guarantee that your domain name will be available once it’s paid for instantly. 4. Contact information – Keep your privacy at bay, but make sure you have a valid email address for correspondence. This will allow the registrar a way to contact you if needed and to send your instructions on how to access your account. By having valid contact information, you should hear back from the registrar within 24-48 hours. If for some reason your registration doesn’t succeed, it may be due to someone else registering the same name at the same time frame as you did. 5. Lock your domain name – Locking secures your domain name and prevents anyone from transferring your domain to another registrar. Make sure you read carefully all links that are provided upon registration. Most companies require the lock, but many wont if you don’t specify to do so.
0
comments
Simple Strategies for Web Site Promotion
When you want to spread the word about your web site, you need some tips on web site promotion. Denver area businesses are often wondering whether they should follow their competitor’s advertising strategies or if there’s a simpler way to get the word out. Luckily, you don’t need to spend a lot of time or a lot of money on web site promotion. Here are some simple ways that you can generate a buzz without creating a dent in your business budget.The first way to promote your web site is to create a blog. These journaling web sites are easy to set up, simple to use, and are often more visited than larger web sites. You can find many blogging systems to be free of charge and with a little study, you can make them as complicated or as simple as you like. In terms of web site promotion, Denver blogs work well because they address the reader on a more casual level. Instead of trying to force information onto someone, the goal of a blog is to create a discussion that will entice readers to want to find out more – and then you add a link to your site. Here are some things that you can add to your blog:· Links to your business web site· Links to related informational web sites (as long as you as permission)· Comments feature that will allow readers to interact· RSS feed so that readers can get instant updates whenever you add an entry· Quality content that allows readers to learn more about your product or businessAnother simple way to begin to advertise your web site is to add a small link at the end of all of your emails – both personal and business. This will help to spread the word about your website, even if the reader is not interested. Often enough, people will forward e-mails instead of writing new ones, so your web site link will be able to travel far without any help from you. In terms of web site promotion, Denver businesses find this method to be the simplest, but not always the most effective.For some of the best web site promotion, Denver businesses like to use forums to help introduce themselves to potential customers. What you’ll do is register on a forum that will include people that are interested in your business topic and then begin to make regular postings. This isn’t the time to necessarily promote your business, but rather you should try to establish yourself as an expert on the topic. And by subtly adding your web site link under your signature, you will entice people to click on the link if they appreciate the knowledge you do demonstrate.In terms of web site promotion, Denver businesses understand that it’s not necessarily the biggest things that make the most impact. It’s knowing how these small tips work to reach the customers that will be interested in your product – that’s the key to your success.
read more
0
comments
Useful Tips for Buying Used Computers
In this modern era, high tech devices that are very expensive like the computers can be replaced with cheaper ones. Such cheap computers mostly come in the form of used computers. Used computers can be found in abundance in the used computer warehouses in various places, even in the local area of the prospective buyer’s residence. However there is no guarantee of quality when buying a used computer. The buyer has to take his own personal risk in doing so. But, if the buyer is ready to spend some money in upgrading the level of the used computer and also some time checking the quality of the used computer before purchase, it will save him from loss. Used computers can save a lot of money for the buyer when compared to buying a new computer. There are many who cannot afford to buy a new computer like the students who do not have any source of income but definitely require computers. For such people, used computers come as a boon.Also, used computers need not always be second hand computers. They can also be recertified or refurbished computers. Refurbished or recertified computers are those, which are checked for any faults, if any corrected and sold with a warranty ensuring the working condition of the computer to be perfect. Hence, such computers are considered to be the safest form of buying a used computer. Refurbished computers can be bought from many of the online stores at very less prices. Quality computer manufacturers also sell such kind of recertified or refurbished computers. However, certain measures need to be taken while buying such kind of computers. The prime aspect to be considered while purchasing a used or refurbished computer is to look for a good branded one. There are various companies who sell used computers or refurbished computers. The main reasons for opting for a branded one is that it comes with a warranty and also the buyer can be sure that the parts used are of good quality. While buying used or refurbished computers related software documents, licenses and paperwork have to be got from the seller as this will avoid stolen computers being passed off as used computers to the buyer. If possible working for some time on the used computer will determine its efficiency. Most of the reputed dealers would allow the purchaser to use the computer for a shorter period to check the quality before purchase.While checking for the efficiency of the used computer, it is good to check if the booting process is smooth, as most of the problems occur during booting and also to check all the sound drivers, video, graphics, monitor, mouse, keyboard etc. CD drives and hard disks also need to be checked. Another aspect is the support system offered for the used computer whether technical or non-technical, support staff capabilities and the number of support staff which determine the quality of service offered. If the purchaser is not satisfied, he can very well think of another choice.
read more
0
comments
Broadband Internet Access - In The Age Of Broadband Technology Rapid Development
Broadband technology and developmentBroadband technology development from low speed modems to broadband internet access as well as broadband telephone connections make substantial differences in our lives.In this age of rapid growth and transformation, regardless of whether in science, technology, transportation or diffusion of information, speed is the driving force behind each tremendous change in advancement. With the innovation of broadband access, we are connected at a neck breaking speed and tasks can be completed within a few seconds. The internet has made astonishing contributions in the transmission and communication of data and information as well as making it possible for business to be conducted in every corner of the planet. Business partners such as the buyers, sellers or agents do not have to meet together in person to discuss and agree on their business arrangements. They make use of modern technology as tools of communication, broadband internet access being one of them.However, before the introduction of broadband internet access, access to the internet was restricted and limited to dial-up connections only. In addition to the cost of installing a separate telephone line for the access, it is also very time consuming. Uploading and downloading of information or files were done at a snail's pace, with a low speed 28.8 Kbps modems. Basically, broadband internet access is a high capacity and high-speed transmission medium. It provides the user with a low cost but higher data-transmission rate internet connection in terms of speed but with no compromise on the quality. Broadband internet access transfers data over a broad bandwidth connection from multiple independent network carriers. This broadband technology is usually done by establishing the different bandwidth channels on fiber-optic cable connections, through telephone lines or via complex satellite systems. These huge volumes of data are transmitted in the form of signals. Such connection supports a wide range of frequencies and usually allows two or more signals to share a medium simultaneously.The biggest effect of broadband access is in the transmission of data, video and voice over long distances. It is ideal for a variety of different purposes such as streaming multimedia including the downloading of large files of video pictures, movies, music and various forms of computer games as well as the broadband telephone connections or VoIP.The broadband internet access provides broadband telephone connections of high quality long distance conversations. This is a type of voice based communications system and is more efficient as well as very much cheaper than the traditional telephone line. The accessories needed are a broadband connection, a connecting adapter and a normal touch-tone telephone. The broadband technology is a cost saving instrument for communication through voice and video.
read more
0
comments
Carrer in IT
Information Technology is a discipline that has a major influence on how everyone lives. It entails almost all forms of technological advancements which are often used to create, save, interchange and make use of information in its different forms. This may include business data, still images, motion pictures and multimedia presentations. It has proved to be of immense significance, as its presence seems to be apparent in almost every section of life. ApplicationsIt is next to impossible to think of a day without computers and communications. Most of the common applications of information technology includes storage of information, data processing, analysis of statistics, word- processing, communications, designing, accounting, management of information systems, financial forecasts and the control over the manufacturing procedure. There is a continuous development mainly in two sectors, namely, computing and communications.Basic skillsInformation Technology is in a revolutionary phase of development. It is a great industry with respect to employment opportunities. Similar to many other fields, IT recruits hardworking, dedicated, talented and forthright people with some training and working experience. In order to be successful in this field you need to possess the following characteristics. They are:a) Good Communication Skillsb) An inclination towards problem solvingc) Team spiritd) Creativitye) Respect for deadlinesf) Analytical and logical reasoning ability Job OpportunitiesMany career options in Information Technology are available. People with high as well as medium skills can also find jobs depending on their areas of interest. Some of the main positions in IT sector are as follows:a) Systems Analysts And Designers: Systems analysts and designer's main jobs are to examine and analyze a business problem, design an appropriate system in order to deal with a particular problem, install and check the systems. b) Software Engineering And Design: It requires a substantial amount of technical experience. Software engineers and designers work on very complicated and advanced forms of software that are used to control high- tech equipment and on usage of programs for business purposes. c) Computer Programmers: Computer programmers are those professionals who feed data for the computers in a language that can be easily interpreted by the computer. They even design programs from the detailed description provided by the system analysts and carry out the logical steps that can be used to do a job.d) End-User And Technical Support: People who have the experience both regarding computer systems as well as a specific business sector. It can be of immense significance for people without any technical qualifications in IT.e) Database Controller/ Manager: A database controller/manager's job is to ensure that the database is accurate, user-friendly and is in accordance with the latest ideas and technology. f) Computer Sales: You need to have basic knowledge of computer fundamentals, salesmanship, and around seven years of experience in computing in order to be eligible to become a computer sales person.g) Information Technology Manager: The main responsibility of an Information technology manager is to ensure the availability of right equipment and properly trained staffs in the organization along with arranging for the requirements within the allocated budget, negotiating with the suppliers and adapting to the latest developments. Information technology has become one of the largest fields in today's world and offers good job prospects. You need to have the zeal to stay as well as enable others to stay connected with the world all the time, in order to succeed in this field.
read more
0
comments
10 benefits of Blue Tooth
Here, listed, are 10 advantages and reasons to use Bluetooth technology.1. Wireless.As you are probably already aware, there are many benefits and bonuses to using wireless devices. Along with improving safety as a consequence of eliminating wires once a necessity, wireless also offers you plenty of alternate advantages. If you are traveling and carrying your laptop or other wireless devices, you'll no longer need to worry unecessarily about bringing connecting cables.2. Bluetooth is very affordable.The technology of Bluetooth is cost-effective for companies to implement, which results in lower expenses for the company. These savings are then passed from the company on to you.3. Bluetooth is fully automated.Bluetooth doesn't have you set up a connection or push any buttons. When two or more devices enter a range of up to 30 feet of each other, they may certainly begin to contact each other without you having to do anything. 4. Highly Compatible .Bluetooth is standardized wireless, meaning that a high level of compatibility among devices is guaranteed. Bluetooth will connect devices to each other, even if they aren't the same model.5. Low interference.Bluetooth devices invariably avoid interference from other wireless devices. Bluetooth uses a practise known as frequency hopping, and also low grade wireless signals.6. Low power consumption.Consequently, because of Bluetooth using low power signals, the technology requires very little energy and will use less battery or electrical power as a result. This is an excellent benefit for mobile devices, as Bluetooth won't flatten the battery.7. Sharing voice and information.The standard for Bluetooth will allow compatible devices to share information and voice communications. This is great for cell phones and head-sets, as Bluetooth makes it simple to be driving and talking on your cell handset.8. Personal Network.You can connect up to seven Bluetooth devices to each other within a range of up to 30 feet, forming a Personal Network. For a single room, you can also set up multiple Networks.9. Upgradeable.Upgradeable is the standard for Bluetooth. There are newer versions of Bluetooth in the works, which offer many new advantages and backward compatible with older versions.10. The technology stays.Bluetooth technology is a world wide, widespread wireless standard. With it now as popular as it is, you can rely on it being a standard for years to come. As more and more devices start to use Bluetooth technology, more manufacturers will be eager to make their products compatible. A chain reaction will occur, making Bluetooth the standard for cutting edge wireless
read more
0
comments
What is Distance Learning?
Teachers and counselors need to know: what is distance learning technology? They should be prepared to answer this question. Education is not confined to the classroom anymore and distance learning technologies allow students to decide where, when and how they want to study.Types of Distance Learning TechnologyDistance learning technology can be divided into four basic categories - print, audio, video and computer. Many of them overlap and combinations of these technologies may be used for some programs.Print-based distance learning programs use text books, work books, study guides, fax, etc. Printed materials were used for correspondence courses, the original form of distance learning. Print still remains an important component of most programs.Many new methods are now being used and before you select a distance learning course, try to learn a little about what is distance learning technology.Audio-based distance learning programs use audio tapes, radio, audio conferences, the telephone, etc.Video-based distance learning programs use satellite delivery, video tape, desktop video, broadcast video, microwave, etc.Computer-based distance learning programs use CD-ROM, collaboration software, web-based software, video conferences and e-mail. Before signing-up for a computer-based distance learning program, find out what is distance learning technology.Advantages and Disadvantages of Different Types of TechnologyPrinted materials are cost-effective, and can be used anywhere. They are easily available and learners are generally comfortable using them. However, they offer no interaction and there are no audio/visual elements. It takes time to deliver them and students require reading skills.Audio-based methods are cheap, accessible and easy-to-use. The downside is that they lack visual information, need to be scheduled and tend to be impersonal.Video-based distance learning programs offer both audio as well as video communication. They allow instructors and students to see body language, expressions, etc, and allow a higher level of interaction. The downside is that they require technical support and are expensive. They also need preparation, planning and scheduling.Computer-based distance learning programs are inexpensive, allow students to move at their own pace and provide a high level of interaction. There is a written record and they can be accessed from anywhere. They offer graphics, text, audio and video. However, they often rely on written communication; need planning, a computer and an internet connection. There is also a danger of viruses and of computer network failure.To select a suitable distance learning course, you need to know what is distance learning technology. Be sure to select a course which uses the technology that maximizes your learning experience.
read more
A full list of Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment
A full list of Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment
read more
A full list of Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment
0
comments
What is Peer to peer network?
A peer-to-peer, commonly abbreviated to P2P, is any distributed network architecture composed of participants that make a portion of their resources (such as processing power, disk storage or network bandwidth) directly available to other network participants, without the need for central coordination instances (such as servers or stable hosts).[1] Peers are both suppliers and consumers of resources, in contrast to the traditional client-server model where only servers supply, and clients consume.
Peer-to-peer was popularized by file sharing systems like Napster. Peer-to-peer file sharing networks have inspired new structures and philosophies in other areas of human interaction. In such social contexts, peer-to-peer as a meme refers to the egalitarian social networking that is currently emerging throughout society, enabled by Internet technologies in general.
Architecture of P2P systems
Peer-to-peer networks are typically formed dynamically by ad-hoc additions of nodes. In an 'ad-hoc' network, the removal of nodes has no significant impact on the network. The distributed architecture of an application in a peer-to-peer system provides enhanced scalability and service robustness.
Peer-to-peer systems often implement an Application Layer overlay network on top of the native or physical network topology. Such overlays are used for indexing and peer discovery. Content is typically exchanged directly over the underlying Internet Protocol (IP) network. Anonymous peer-to-peer systems are an exception, and implement extra routing layers to obscure the identity of the source or destination of queries.
In structured peer-to-peer networks, connections in the overlay are fixed. They typically use distributed hash table-based (DHT) indexing, such as in the Chord system (MIT).[citation needed]
Unstructured peer-to-peer networks do not provide any algorithm for organization or optimization of network connections.[citation needed] In particular, three models of unstructured architecture are defined. In pure peer-to-peer systems the entire network consists solely of equipotent peers. There is only one routing layer, as there are no preferred nodes with any special infrastructure function. Hybrid peer-to-peer systems allow such infrastructure nodes to exist, often called supernodes [2]. In centralized peer-to-peer systems, a central server is used for indexing functions and to bootstrap the entire system.[citation needed] Although this has similarities with a structured architecture, the connections between peers are not determined by any algorithm. The first prominent and popular peer-to-peer file sharing system, Napster, was an example of the centralized model. Gnutella and Freenet, on the other hand, are examples of the decentralized model. Kazaa is an example of the hybrid model.
P2P networks are typically used for connecting nodes via largely ad hoc connections.[citation needed] Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and real time data, such as telephony traffic, is also passed using P2P technology.
A pure P2P network does not have the notion of clients or servers but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client-server model where communication is usually to and from a central server. A typical example of a file transfer that is not P2P is an FTP server where the client and server programs are quite distinct: the clients initiate the download/uploads, and the servers react to and satisfy these requests.
The P2P overlay network consists of all the participating peers as network nodes. There are links between any two nodes that know each other: i.e. if a participating peer knows the location of another peer in the P2P network, then there is a directed edge from the former node to the latter in the overlay network. Based on how the nodes in the overlay network are linked to each other, we can classify the P2P networks as unstructured or structured.
[edit] Structured systems
Structured P2P network employ a globally consistent protocol to ensure that any node can efficiently route a search to some peer that has the desired file, even if the file is extremely rare. Such a guarantee necessitates a more structured pattern of overlay links. By far the most common type of structured P2P network is the distributed hash table (DHT), in which a variant of consistent hashing is used to assign ownership of each file to a particular peer, in a way analogous to a traditional hash table's assignment of each key to a particular array slot.
[edit] Distributed hash tables
Distributed hash tables
Distributed hash tables (DHTs) are a class of decentralized distributed systems that provide a lookup service similar to a hash table: (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key. Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption. This allows DHTs to scale to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures.
DHTs form an infrastructure that can be used to build peer-to-peer networks. Notable distributed networks that use DHTs include BitTorrent's distributed tracker, the Kad network, the Storm botnet, YaCy, and the Coral Content Distribution Network.
Some prominent research projects include the Chord project, the PAST storage utility, the P-Grid, a self-organized and emerging overlay network and the CoopNet content distribution system (see below for external links related to these projects).
DHT-based networks have been widely utilized for accomplishing efficient resource discovery[3][4] for grid computing systems, as it aids in resource management and scheduling of applications. Resource discovery activity involve searching for the appropriate resource types that match the user’s application requirements. Recent advances in the domain of decentralized resource discovery have been based on extending the existing DHTs with the capability of multi-dimensional data organization and query routing. Majority of the efforts have looked at embedding spatial database indices such as the Space Filling Curves (SFCs) including the Hilbert curves, Z-curves, k-d tree, MX-CIF Quad tree and R*-tree for managing, routing, and indexing of complex Grid resource query objects over DHT networks. Spatial indices are well suited for handling the complexity of Grid resource queries. Although some spatial indices can have issues as regards to routing load-balance in case of a skewed data set, all the spatial indices are more scalable in terms of the number of hops traversed and messages generated while searching and routing Grid resource queries.
[edit] Unstructured systems
An unstructured P2P network is formed when the overlay links are established arbitrarily. Such networks can be easily constructed as a new peer that wants to join the network can copy existing links of another node and then form its own links over time. In an unstructured P2P network, if a peer wants to find a desired piece of data in the network, the query has to be flooded through the network to find as many peers as possible that share the data. The main disadvantage with such networks is that the queries may not always be resolved. Popular content is likely to be available at several peers and any peer searching for it is likely to find the same thing. But if a peer is looking for rare data shared by only a few other peers, then it is highly unlikely that search will be successful. Since there is no correlation between a peer and the content managed by it, there is no guarantee that flooding will find a peer that has the desired data. Flooding also causes a high amount of signaling traffic in the network and hence such networks typically have very poor search efficiency. Many of the popular P2P networks are unstructured.
In pure P2P networks: Peers act as equals, merging the roles of clients and server. In such networks, there is no central server managing the network, neither is there a central router. Some examples of pure P2P Application Layer networks designed for file sharing are Gnutella (pre v0.4) and Freenet.
There also exist hybrid P2P systems, which distribute their clients into two groups: client nodes and overlay nodes. Typically, each client is able to act according to the momentary need of the network and can become part of the respective overlay network used to coordinate the P2P structure. This division between normal and 'better' nodes is done in order to address the scaling problems on early pure P2P networks. Examples for such networks are for example Gnutella (after v0.4) or G2.
An other type of hybrid P2P network are networks using on the one hand central server(s) or bootstrapping mechanisms, on the other hand P2P for their data transfers. These networks are in general called 'centralized networks' because of their lack of ability to work without their central server(s). An example for such a network is the eDonkey network (eD2k).
[edit] Indexing and resource discovery
Older peer-to-peer networks duplicate resources across each node in the network configured to carry that type of information. This allows local searching, but requires much traffic.
Modern networks use central coordinating servers and directed search requests. Central servers are typically used for listing potential peers (Tor), coordinating their activities (folding@home), and searching (Napster, eMule). Decentralized searching was first done by flooding search requests out across peers. More efficient directed search strategies, including supernodes and distributed hash tables, are now used.
Many P2P systems use stronger peers (super-peers, super-nodes) as servers and client-peers are connected in a star-like fashion to a single super-peer.
[edit] Peer-to-peer-like systems
In modern definitions of peer-to-peer technology, the term implies the general architectural concepts outlined in this article. However, the basic concept of peer-to-peer computing was envisioned in earlier software systems and networking discussions, reaching back to principles stated in the first Request for Comments, RFC 1.[5]
A distributed messaging system that is often likened as an early peer-to-peer architecture is the USENET network news system that is in principle a client-server model from the user or client perspective, when they read or post news articles. However, news servers communicate with one another as peers to propagate Usenet news articles over the entire group of network servers. The same consideration applies to SMTP email in the sense that the core email relaying network of Mail transfer agents has a peer-to-peer character, while the periphery of e-mail clients and their direct connections is strictly a client-server relationship. Tim Berners-Lee's vision for the World Wide Web, as evidenced by his WorldWideWeb editor/browser, was close to a peer-to-peer design in that it assumed each user of the web would be an active editor and contributor creating and linking content to form an interlinked web of links. This contrasts to the broadcasting-like structure of the web as it has developed over the years.
[edit] Advantages and weaknesses
In P2P networks, all clients provide resources, which may include bandwidth, storage space, and computing power. As nodes arrive and demand on the system increases, the total capacity of the system also increases. This is not true of a client-server architecture with a fixed set of servers, in which adding more clients could mean slower data transfer for all users.[citation needed]
The distributed nature of P2P networks also increases robustness,[citation needed] and—in pure P2P systems—by enabling peers to find the data without relying on a centralized index server[citation needed]. In the latter case, there is no single point of failure in the system.[citation needed]
As with most network systems, unsecure and unsigned codes may allow remote access to files on a victim's computer or even compromise the entire network.[citation needed] In the past this has happened for example to the FastTrack network when anti P2P companies managed to introduce faked chunks into downloads and downloaded files (mostly MP3 files) were unusable afterwards or even contained malicious code.[citation needed] Consequently, the P2P networks of today have seen an enormous increase of their security and file verification mechanisms. Modern hashing, chunk verification and different encryption methods have made most networks resistant to almost any type of attack, even when major parts of the respective network have been replaced by faked or nonfunctional hosts.
Internet service providers (ISPs) have been known to throttle P2P file-sharing traffic due to the high-bandwidth usage [6]. Compared to Web browsing, e-mail or many other uses of the internet, where data is only transferred in short intervals and relative small quantities, P2P file-sharing often consists of relatively heavy bandwidth usage due to ongoing file transfers and swarm/network coordination packets.
A possible solution to this is called P2P caching, where a ISP stores the part of files most accessed by P2P clients in order to save access to the Internet.
[edit] Social and economic impact
Main article: Peer-to-peer (meme)
The concept of P2P is increasingly evolving to an expanded usage as the relational dynamic active in distributed networks, i.e., not just computer to computer, but human to human. Yochai Benkler has coined the term commons-based peer production to denote collaborative projects such as free software. Associated with peer production are the concepts of:
peer governance (referring to the manner in which peer production projects are managed)
peer property (referring to the new type of licenses which recognize individual authorship but not exclusive property rights, such as the GNU General Public License and the Creative Commons licenses)
peer distribution (or the manner in which products, particularly peer-produced products, are distributed)
Some researchers have explored the benefits of enabling virtual communities to self-organize and introduce incentives as a resource sharing and cooperation, arguing that what is missing from today's peer-to-peer systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered.[7] Ongoing research efforts for designing effective incentive mechanisms in P2P systems, based on principles from game theory are beginning to take on a more psychological and information-processing direction.
[edit] Applications
This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (October 2007)
Active peer-to-peer technologies include:
Many file sharing networks, including Gnutella, G2 and FastTrack. Peer-to-peer file sharing popularized peer-to-peer technologies. As of 2009, it is the largest contributor of network traffic on the Internet.
Completely decentralized networks of peers: Usenet (1979) and WWIVnet (1987).
Free, independ internet in form of a Wireless community network or Netsukuku
Software publication and distribution (Linux, several games); via file sharing networks.
Research like the Chord project, the PAST storage utility, the P-Grid, and the CoopNet content distribution system.
Distributed hash tables
In bioinformatics, drug candidate identification. The first such program was begun in 2001 the Centre for Computational Drug Discovery at the University of Oxford in cooperation with the National Foundation for Cancer Research. There are now several similar programs running under the United Devices Cancer Research Project.
The sciencenet P2P search engine.
Pennsylvania State University, MIT and Simon Fraser University are carrying on a project called LionShare designed for facilitating file sharing among educational institutions globally.
The U.S. Department of Defense has started research on P2P networks as part of its modern network warfare strategy.[8] In May, 2003 Dr. Tether. Director of Defense Advanced Research Project Agency testified that U.S. Military is using P2P networks.
Kato et al.’s studies indicate over 200 companies with approximately $400 million USD are investing in P2P network. Besides File Sharing, companies are also interested in Distributing Computing, Content Distribution.
delivery of TV content over a P2P network (P2PTV)
Skype, one of the most widely used internet phone applications is using P2P technology.
Osiris (Serverless Portal System) allows its users to create anonymous and autonomous web portals distributed via P2P network.
VoIP (using application layer protocols such as SIP)
Streaming media. P2PTV and PDTP. Applications include TVUPlayer, Joost, CoolStreaming, Cybersky-TV, PPLive, LiveStation
Instant messaging and online chat
An earlier generation of peer-to-peer systems were called "metacomputing" or were classed as "middleware". These include: Legion, Globus
Domain Name System, for Internet information retrieval. ee Comparison of DNS server software
JXTA, for Peer applications. See Collanos Workplace (Teamwork software), Sixearch
Peercasting for multicasting streams. See PeerCast, IceShare, FreeCast, Rawflow
Usenet for distributed discussion. See also list of Usenet newsreaders
Windows Peer-to-Peer. Distributed peer application development, collaboration[9] Shipped with Advanced Networking Pack for Windows XP,[10] Windows XP SP2, Windows Vista. This is a Windows component that runs only over IPv6 and provides a 'meta' peer-to-peer network that applications can utilize. It does not have file sharing support but third-parties can develop one.[9] It also includes the Peer Name Resolution Protocol that allows dynamic domain name publication and resolution of names to endpoints. Windows Meeting Space and the People Near Me feature of Windows Vista use this protocol. It can be used to setup a Windows Internet Computer Name (WICN) using netsh p2p.[11] Windows Remote Assistance and HomeGroup features of Windows 7 also use it.[12]
cloud computing
[edit] Examples
Usenet and SMTP servers are connected in a P2P structure, with users connecting to these servers as clients, in the standard client-server arch.
Tim Berners-Lee's vision for the World Wide Web was close to a P2P network in that it assumed each user of the web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links.[citation needed] This contrasts to the current broadcasting-like structure of the web.[citation needed]
Some networks and channels such as Napster, OpenNAP and IRC serving channels use a client-server structure for some tasks (e.g. searching) and a P2P structure for others. Networks such as Gnutella or Freenet use a P2P structure for nearly all tasks, with the exception of finding peers to connect to when first setting up.
P2P architecture embodies one of the key technical concepts of the Internet, described in the first Internet Request for Comments, RFC 1, "Host Software" dated April 7, 1969. More recently, the concept has achieved recognition in the general public in the context of the absence of central indexing servers in architectures used for exchanging multimedia files.
read more
Peer-to-peer was popularized by file sharing systems like Napster. Peer-to-peer file sharing networks have inspired new structures and philosophies in other areas of human interaction. In such social contexts, peer-to-peer as a meme refers to the egalitarian social networking that is currently emerging throughout society, enabled by Internet technologies in general.
Architecture of P2P systems
Peer-to-peer networks are typically formed dynamically by ad-hoc additions of nodes. In an 'ad-hoc' network, the removal of nodes has no significant impact on the network. The distributed architecture of an application in a peer-to-peer system provides enhanced scalability and service robustness.
Peer-to-peer systems often implement an Application Layer overlay network on top of the native or physical network topology. Such overlays are used for indexing and peer discovery. Content is typically exchanged directly over the underlying Internet Protocol (IP) network. Anonymous peer-to-peer systems are an exception, and implement extra routing layers to obscure the identity of the source or destination of queries.
In structured peer-to-peer networks, connections in the overlay are fixed. They typically use distributed hash table-based (DHT) indexing, such as in the Chord system (MIT).[citation needed]
Unstructured peer-to-peer networks do not provide any algorithm for organization or optimization of network connections.[citation needed] In particular, three models of unstructured architecture are defined. In pure peer-to-peer systems the entire network consists solely of equipotent peers. There is only one routing layer, as there are no preferred nodes with any special infrastructure function. Hybrid peer-to-peer systems allow such infrastructure nodes to exist, often called supernodes [2]. In centralized peer-to-peer systems, a central server is used for indexing functions and to bootstrap the entire system.[citation needed] Although this has similarities with a structured architecture, the connections between peers are not determined by any algorithm. The first prominent and popular peer-to-peer file sharing system, Napster, was an example of the centralized model. Gnutella and Freenet, on the other hand, are examples of the decentralized model. Kazaa is an example of the hybrid model.
P2P networks are typically used for connecting nodes via largely ad hoc connections.[citation needed] Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and real time data, such as telephony traffic, is also passed using P2P technology.
A pure P2P network does not have the notion of clients or servers but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client-server model where communication is usually to and from a central server. A typical example of a file transfer that is not P2P is an FTP server where the client and server programs are quite distinct: the clients initiate the download/uploads, and the servers react to and satisfy these requests.
The P2P overlay network consists of all the participating peers as network nodes. There are links between any two nodes that know each other: i.e. if a participating peer knows the location of another peer in the P2P network, then there is a directed edge from the former node to the latter in the overlay network. Based on how the nodes in the overlay network are linked to each other, we can classify the P2P networks as unstructured or structured.
[edit] Structured systems
Structured P2P network employ a globally consistent protocol to ensure that any node can efficiently route a search to some peer that has the desired file, even if the file is extremely rare. Such a guarantee necessitates a more structured pattern of overlay links. By far the most common type of structured P2P network is the distributed hash table (DHT), in which a variant of consistent hashing is used to assign ownership of each file to a particular peer, in a way analogous to a traditional hash table's assignment of each key to a particular array slot.
[edit] Distributed hash tables
Distributed hash tables
Distributed hash tables (DHTs) are a class of decentralized distributed systems that provide a lookup service similar to a hash table: (key, value) pairs are stored in the DHT, and any participating node can efficiently retrieve the value associated with a given key. Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption. This allows DHTs to scale to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures.
DHTs form an infrastructure that can be used to build peer-to-peer networks. Notable distributed networks that use DHTs include BitTorrent's distributed tracker, the Kad network, the Storm botnet, YaCy, and the Coral Content Distribution Network.
Some prominent research projects include the Chord project, the PAST storage utility, the P-Grid, a self-organized and emerging overlay network and the CoopNet content distribution system (see below for external links related to these projects).
DHT-based networks have been widely utilized for accomplishing efficient resource discovery[3][4] for grid computing systems, as it aids in resource management and scheduling of applications. Resource discovery activity involve searching for the appropriate resource types that match the user’s application requirements. Recent advances in the domain of decentralized resource discovery have been based on extending the existing DHTs with the capability of multi-dimensional data organization and query routing. Majority of the efforts have looked at embedding spatial database indices such as the Space Filling Curves (SFCs) including the Hilbert curves, Z-curves, k-d tree, MX-CIF Quad tree and R*-tree for managing, routing, and indexing of complex Grid resource query objects over DHT networks. Spatial indices are well suited for handling the complexity of Grid resource queries. Although some spatial indices can have issues as regards to routing load-balance in case of a skewed data set, all the spatial indices are more scalable in terms of the number of hops traversed and messages generated while searching and routing Grid resource queries.
[edit] Unstructured systems
An unstructured P2P network is formed when the overlay links are established arbitrarily. Such networks can be easily constructed as a new peer that wants to join the network can copy existing links of another node and then form its own links over time. In an unstructured P2P network, if a peer wants to find a desired piece of data in the network, the query has to be flooded through the network to find as many peers as possible that share the data. The main disadvantage with such networks is that the queries may not always be resolved. Popular content is likely to be available at several peers and any peer searching for it is likely to find the same thing. But if a peer is looking for rare data shared by only a few other peers, then it is highly unlikely that search will be successful. Since there is no correlation between a peer and the content managed by it, there is no guarantee that flooding will find a peer that has the desired data. Flooding also causes a high amount of signaling traffic in the network and hence such networks typically have very poor search efficiency. Many of the popular P2P networks are unstructured.
In pure P2P networks: Peers act as equals, merging the roles of clients and server. In such networks, there is no central server managing the network, neither is there a central router. Some examples of pure P2P Application Layer networks designed for file sharing are Gnutella (pre v0.4) and Freenet.
There also exist hybrid P2P systems, which distribute their clients into two groups: client nodes and overlay nodes. Typically, each client is able to act according to the momentary need of the network and can become part of the respective overlay network used to coordinate the P2P structure. This division between normal and 'better' nodes is done in order to address the scaling problems on early pure P2P networks. Examples for such networks are for example Gnutella (after v0.4) or G2.
An other type of hybrid P2P network are networks using on the one hand central server(s) or bootstrapping mechanisms, on the other hand P2P for their data transfers. These networks are in general called 'centralized networks' because of their lack of ability to work without their central server(s). An example for such a network is the eDonkey network (eD2k).
[edit] Indexing and resource discovery
Older peer-to-peer networks duplicate resources across each node in the network configured to carry that type of information. This allows local searching, but requires much traffic.
Modern networks use central coordinating servers and directed search requests. Central servers are typically used for listing potential peers (Tor), coordinating their activities (folding@home), and searching (Napster, eMule). Decentralized searching was first done by flooding search requests out across peers. More efficient directed search strategies, including supernodes and distributed hash tables, are now used.
Many P2P systems use stronger peers (super-peers, super-nodes) as servers and client-peers are connected in a star-like fashion to a single super-peer.
[edit] Peer-to-peer-like systems
In modern definitions of peer-to-peer technology, the term implies the general architectural concepts outlined in this article. However, the basic concept of peer-to-peer computing was envisioned in earlier software systems and networking discussions, reaching back to principles stated in the first Request for Comments, RFC 1.[5]
A distributed messaging system that is often likened as an early peer-to-peer architecture is the USENET network news system that is in principle a client-server model from the user or client perspective, when they read or post news articles. However, news servers communicate with one another as peers to propagate Usenet news articles over the entire group of network servers. The same consideration applies to SMTP email in the sense that the core email relaying network of Mail transfer agents has a peer-to-peer character, while the periphery of e-mail clients and their direct connections is strictly a client-server relationship. Tim Berners-Lee's vision for the World Wide Web, as evidenced by his WorldWideWeb editor/browser, was close to a peer-to-peer design in that it assumed each user of the web would be an active editor and contributor creating and linking content to form an interlinked web of links. This contrasts to the broadcasting-like structure of the web as it has developed over the years.
[edit] Advantages and weaknesses
In P2P networks, all clients provide resources, which may include bandwidth, storage space, and computing power. As nodes arrive and demand on the system increases, the total capacity of the system also increases. This is not true of a client-server architecture with a fixed set of servers, in which adding more clients could mean slower data transfer for all users.[citation needed]
The distributed nature of P2P networks also increases robustness,[citation needed] and—in pure P2P systems—by enabling peers to find the data without relying on a centralized index server[citation needed]. In the latter case, there is no single point of failure in the system.[citation needed]
As with most network systems, unsecure and unsigned codes may allow remote access to files on a victim's computer or even compromise the entire network.[citation needed] In the past this has happened for example to the FastTrack network when anti P2P companies managed to introduce faked chunks into downloads and downloaded files (mostly MP3 files) were unusable afterwards or even contained malicious code.[citation needed] Consequently, the P2P networks of today have seen an enormous increase of their security and file verification mechanisms. Modern hashing, chunk verification and different encryption methods have made most networks resistant to almost any type of attack, even when major parts of the respective network have been replaced by faked or nonfunctional hosts.
Internet service providers (ISPs) have been known to throttle P2P file-sharing traffic due to the high-bandwidth usage [6]. Compared to Web browsing, e-mail or many other uses of the internet, where data is only transferred in short intervals and relative small quantities, P2P file-sharing often consists of relatively heavy bandwidth usage due to ongoing file transfers and swarm/network coordination packets.
A possible solution to this is called P2P caching, where a ISP stores the part of files most accessed by P2P clients in order to save access to the Internet.
[edit] Social and economic impact
Main article: Peer-to-peer (meme)
The concept of P2P is increasingly evolving to an expanded usage as the relational dynamic active in distributed networks, i.e., not just computer to computer, but human to human. Yochai Benkler has coined the term commons-based peer production to denote collaborative projects such as free software. Associated with peer production are the concepts of:
peer governance (referring to the manner in which peer production projects are managed)
peer property (referring to the new type of licenses which recognize individual authorship but not exclusive property rights, such as the GNU General Public License and the Creative Commons licenses)
peer distribution (or the manner in which products, particularly peer-produced products, are distributed)
Some researchers have explored the benefits of enabling virtual communities to self-organize and introduce incentives as a resource sharing and cooperation, arguing that what is missing from today's peer-to-peer systems should be seen both as a goal and a means for self-organized virtual communities to be built and fostered.[7] Ongoing research efforts for designing effective incentive mechanisms in P2P systems, based on principles from game theory are beginning to take on a more psychological and information-processing direction.
[edit] Applications
This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (October 2007)
Active peer-to-peer technologies include:
Many file sharing networks, including Gnutella, G2 and FastTrack. Peer-to-peer file sharing popularized peer-to-peer technologies. As of 2009, it is the largest contributor of network traffic on the Internet.
Completely decentralized networks of peers: Usenet (1979) and WWIVnet (1987).
Free, independ internet in form of a Wireless community network or Netsukuku
Software publication and distribution (Linux, several games); via file sharing networks.
Research like the Chord project, the PAST storage utility, the P-Grid, and the CoopNet content distribution system.
Distributed hash tables
In bioinformatics, drug candidate identification. The first such program was begun in 2001 the Centre for Computational Drug Discovery at the University of Oxford in cooperation with the National Foundation for Cancer Research. There are now several similar programs running under the United Devices Cancer Research Project.
The sciencenet P2P search engine.
Pennsylvania State University, MIT and Simon Fraser University are carrying on a project called LionShare designed for facilitating file sharing among educational institutions globally.
The U.S. Department of Defense has started research on P2P networks as part of its modern network warfare strategy.[8] In May, 2003 Dr. Tether. Director of Defense Advanced Research Project Agency testified that U.S. Military is using P2P networks.
Kato et al.’s studies indicate over 200 companies with approximately $400 million USD are investing in P2P network. Besides File Sharing, companies are also interested in Distributing Computing, Content Distribution.
delivery of TV content over a P2P network (P2PTV)
Skype, one of the most widely used internet phone applications is using P2P technology.
Osiris (Serverless Portal System) allows its users to create anonymous and autonomous web portals distributed via P2P network.
VoIP (using application layer protocols such as SIP)
Streaming media. P2PTV and PDTP. Applications include TVUPlayer, Joost, CoolStreaming, Cybersky-TV, PPLive, LiveStation
Instant messaging and online chat
An earlier generation of peer-to-peer systems were called "metacomputing" or were classed as "middleware". These include: Legion, Globus
Domain Name System, for Internet information retrieval. ee Comparison of DNS server software
JXTA, for Peer applications. See Collanos Workplace (Teamwork software), Sixearch
Peercasting for multicasting streams. See PeerCast, IceShare, FreeCast, Rawflow
Usenet for distributed discussion. See also list of Usenet newsreaders
Windows Peer-to-Peer. Distributed peer application development, collaboration[9] Shipped with Advanced Networking Pack for Windows XP,[10] Windows XP SP2, Windows Vista. This is a Windows component that runs only over IPv6 and provides a 'meta' peer-to-peer network that applications can utilize. It does not have file sharing support but third-parties can develop one.[9] It also includes the Peer Name Resolution Protocol that allows dynamic domain name publication and resolution of names to endpoints. Windows Meeting Space and the People Near Me feature of Windows Vista use this protocol. It can be used to setup a Windows Internet Computer Name (WICN) using netsh p2p.[11] Windows Remote Assistance and HomeGroup features of Windows 7 also use it.[12]
cloud computing
[edit] Examples
Usenet and SMTP servers are connected in a P2P structure, with users connecting to these servers as clients, in the standard client-server arch.
Tim Berners-Lee's vision for the World Wide Web was close to a P2P network in that it assumed each user of the web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links.[citation needed] This contrasts to the current broadcasting-like structure of the web.[citation needed]
Some networks and channels such as Napster, OpenNAP and IRC serving channels use a client-server structure for some tasks (e.g. searching) and a P2P structure for others. Networks such as Gnutella or Freenet use a P2P structure for nearly all tasks, with the exception of finding peers to connect to when first setting up.
P2P architecture embodies one of the key technical concepts of the Internet, described in the first Internet Request for Comments, RFC 1, "Host Software" dated April 7, 1969. More recently, the concept has achieved recognition in the general public in the context of the absence of central indexing servers in architectures used for exchanging multimedia files.
0
comments
read more
Client Server Networking?
Client-server computing or networking is a distributed application architecture that partitions tasks or work loads between service providers (servers) and service requesters, called clients.[1] Often clients and servers operate over a computer network on separate hardware. A server machine is a high-performance host that is running one or more server programs which share its resources with clients. A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await (listen to) incoming requests.
[edit] Description
The client-server characteristic describes the relationship of cooperating programs in an application. The server component provides a function or service to one or many clients, which initiate requests for such services.
Functions such as email exchange, web access and database access, are built on the client-server model. For example, a web browser is a client program running on a user's computer that may access information stored on a web server on the Internet. Users accessing banking services from their computer use a web browser client to send a request to a web server at a bank. That program may in turn forward the request to its own database client program that sends a request to a database server at another bank computer to retrieve the account information. The balance is returned to the bank database client, which in turn serves it back to the web browser client displaying the results to the user.
The client-server model has become one of the central ideas of network computing. Many business applications being written today use the client-server model. So do the Internet's main application protocols, such as HTTP, SMTP, Telnet, DNS. In marketing, the term has been used to distinguish distributed computing by smaller dispersed computers from the "monolithic" centralized computing of mainframe computers. But this distinction has largely disappeared as mainframes and their applications have also turned to the client-server model and become part of network computing.
Each instance of the client software can send data requests to one or more connected servers. In turn, the servers can accept these requests, process them, and return the requested information to the client. Although this concept can be applied for a variety of reasons to many different kinds of applications, the architecture remains fundamentally the same.
The most basic type of client-server architecture employs only two types of hosts: clients and servers. This type of architecture is sometimes referred to as two-tier. It allows devices to share files and resources. The two tier architecture means that the client acts as one tier and application in combination with server acts as another tier.
The interaction between client and server is often described using sequence diagrams. Sequence diagrams are standardized in the Unified Modeling Language.
Specific types of clients include web browsers, email clients, and online chat clients.
Specific types of servers include web servers, ftp servers, application servers, database servers, name servers, mail servers, file servers, print servers, and terminal servers. Most web services are also types of servers.
[edit] Comparison to peer-to-peer architecture
Please help improve this article by expanding it. Further information might be found on the talk page. (September 2009)
In peer-to-peer architectures, each host or instance of the program can simultaneously act as both a client and a server, and each has equivalent responsibilities and status.
Both client-server and peer-to-peer architectures are in wide usage today. Details may be found in Comparison of Centralized (Client-Server) and Decentralized (Peer-to-Peer) Networking.
[edit] Comparison to client-queue-client architecture
While classic client-server architecture requires one of the communication endpoints to act as a server, which is much harder to implement,[citation needed] Client-Queue-Client allows all endpoints to be simple clients, while the server consists of some external software, which also acts as passive queue (one software instance passes its query to another instance to queue, e.g. database, and then this other instance pulls it from a database, makes a response, passes it to database etc.). This architecture allows greatly simplified software implementation. Peer-to-peer architecture was originally based on the Client-Queue-Client concept.
[edit] Advantages
In most cases, a client-server architecture enables the roles and responsibilities of a computing system to be distributed among several independent computers that are known to each other only through a network. This creates an additional advantage to this architecture: greater ease of maintenance. For example, it is possible to replace, repair, upgrade, or even relocate a server while its clients remain both unaware and unaffected by that change.
All data is stored on the servers, which generally have far greater security controls than most clients.[citation needed] Servers can better control access and resources, to guarantee that only those clients with the appropriate permissions may access and change data.
Since data storage is centralized, updates to that data are far easier to administer than what would be possible under a P2P paradigm. Under a P2P architecture, data updates may need to be distributed and applied to each peer in the network, which is both time-consuming and error-prone,[citation needed] as there can be thousands or even millions of peers.
Many mature client-server technologies are already available which were designed to ensure security, friendliness of the user interface, and ease of use.[citation needed]
It functions with multiple different clients of different capabilities.
[edit] Disadvantages
Traffic congestion on the network has been an issue since the inception of the client-server paradigm.[citation needed] As the number of simultaneous client requests to a given server increases, the server can become overloaded. Contrast that to a P2P network, where its aggregated bandwidth actually increases as nodes are added, since the P2P network's overall bandwidth can be roughly computed as the sum of the bandwidths of every node in that network.
The client-server paradigm lacks the robustness of a good P2P network.[citation needed] Under client-server, should a critical server fail, clients’ requests cannot be fulfilled. In P2P networks, resources are usually distributed among many nodes. Even if one or more nodes depart and abandon a downloading file, for example, the remaining nodes should still have the data needed to complete the download.
0
comments
What is LAN ,MAN and WAN
Networking methods
One way to categorize computer networks is by their geographic scope, although many real-world networks interconnect Local Area Networks (LAN) via Wide Area Networks (WAN) and wireless networks (WWAN). These three (broad) types are:
[edit] Local area network (LAN)
A local area network is a network that spans a relatively small space and provides services to a small number of people.
A peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities. These can be classified into two types:
1. Single-service servers
2. Print server
The server performs one task such as file server, while other servers can not only perform in the capacity of file servers and print servers, but also can conduct calculations and use them to provide information to clients (Web/Intranet Server). Computers may be connected in many different ways, including Ethernet cables, Wireless networks, or other types of wires such as power lines or phone lines.
The ITU-T G.hn standard is an example of a technology that provides high-speed (up to 1 Gbit/s) local area networking over existing home wiring (power lines, phone lines and coaxial cables).
[edit] Wide area network (WAN)
A wide area network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is a network composed of many smaller networks. The Internet is considered the largest network in the world.[6]. The PSTN (Public Switched Telephone Network) also is an extremely large network that is converging to use Internet technologies, although not necessarily through the public Internet.
A Wide Area Network involves communication through the use of a wide range of different technologies. These technologies include Point-to-Point WANs such as Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.
[edit] Metropolitan area network (MAN)
A metropolitan network is a network that is too large for even the largest of LAN's but is not on the scale of a WAN. It also integrates two or more LAN networks over a specific geographical area ( usually a city ) so as to increase the network and the flow of communications. The LAN's in question would usually be connected via " backbone " lines.
For more information on WANs, see Frame Relay, ATM and Sonet.
[edit] Wireless networks (WLAN, WWAN)
A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network. The media access protocols for LANs come from the IEEE.
The most common IEEE 802.11 WLANs cover, depending on antennas, ranges from hundreds of meters to a few kilometers. For larger areas, either communications satellites of various types, cellular radio, or wireless local loop (IEEE 802.16) all have advantages and disadvantages. Depending on the type of mobility needed, the relevant standards may come from the IETF or the ITU. 8------->
[edit] Network topology
The network topology defines the way in which computers, printers, and other devices are connected, physically and logically. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.
Network topology has two types:
Physical
logical
Commonly used topologies include:
Bus
Star
Tree (hierarchical)
Linear
Ring
Mesh
partially connected
fully connected (sometimes known as fully redundant)
The network topologies mentioned above are only a general representation of the kinds of topologies used in computer network and are considered basic topologies.
As a matter of fact networking is defined by the standard of OSI (Open Systems Interconnection) reference for communications. The OSI model consists of seven layers. Each layer has its own function. The OSI model layers are Application, Presentation, Session, Transport, Network, Data Link, and Physical. The upper layers (Application, Presentation, Session) of the OSI model concentrate on the application while the lower layers (transport, network, data link, and physical) focus on signal flow of data from origin to destination. The Application layer defines the medium that communications software and any applications need to communicate to other computers. Layer 6 which is the presentation layer focuses on defining data formats such as text, jpeg, gif, and binary. An example of this layer would be displaying a picture that was received in an e-mail. The 5th Layer is the session layer which establishes how to start, control, and end links or conversations. The transport layer includes protocols that allow it to provide functions in many different areas such as: error recovery, segmentation, and reassembly. The network layers primary job is the end to end delivery of data packets. To do this, the network layer relies on logical addressing so that the origin and destination point can both be recognized. An example of this would be, ip running in a router’s job is to examine the destination address, compare the address to the ip routing table, separate the packet into smaller chunks for transporting purposes, and then deliver the packet to the correct receiver. Layer 2 is the data link layer, which sets the standards for data being delivered across a link or medium. The 1st layer is the physical layer which deals with the physical characteristics of the transmission of data such as the network card and network cable type. An easy way to remember the layers of OSI is to remember All People Seem To Need Data Processing (Layers 7 to 1). 8----------------------->
read more
One way to categorize computer networks is by their geographic scope, although many real-world networks interconnect Local Area Networks (LAN) via Wide Area Networks (WAN) and wireless networks (WWAN). These three (broad) types are:
[edit] Local area network (LAN)
A local area network is a network that spans a relatively small space and provides services to a small number of people.
A peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities. These can be classified into two types:
1. Single-service servers
2. Print server
The server performs one task such as file server, while other servers can not only perform in the capacity of file servers and print servers, but also can conduct calculations and use them to provide information to clients (Web/Intranet Server). Computers may be connected in many different ways, including Ethernet cables, Wireless networks, or other types of wires such as power lines or phone lines.
The ITU-T G.hn standard is an example of a technology that provides high-speed (up to 1 Gbit/s) local area networking over existing home wiring (power lines, phone lines and coaxial cables).
[edit] Wide area network (WAN)
A wide area network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is a network composed of many smaller networks. The Internet is considered the largest network in the world.[6]. The PSTN (Public Switched Telephone Network) also is an extremely large network that is converging to use Internet technologies, although not necessarily through the public Internet.
A Wide Area Network involves communication through the use of a wide range of different technologies. These technologies include Point-to-Point WANs such as Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.
[edit] Metropolitan area network (MAN)
A metropolitan network is a network that is too large for even the largest of LAN's but is not on the scale of a WAN. It also integrates two or more LAN networks over a specific geographical area ( usually a city ) so as to increase the network and the flow of communications. The LAN's in question would usually be connected via " backbone " lines.
For more information on WANs, see Frame Relay, ATM and Sonet.
[edit] Wireless networks (WLAN, WWAN)
A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network. The media access protocols for LANs come from the IEEE.
The most common IEEE 802.11 WLANs cover, depending on antennas, ranges from hundreds of meters to a few kilometers. For larger areas, either communications satellites of various types, cellular radio, or wireless local loop (IEEE 802.16) all have advantages and disadvantages. Depending on the type of mobility needed, the relevant standards may come from the IETF or the ITU. 8------->
[edit] Network topology
The network topology defines the way in which computers, printers, and other devices are connected, physically and logically. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.
Network topology has two types:
Physical
logical
Commonly used topologies include:
Bus
Star
Tree (hierarchical)
Linear
Ring
Mesh
partially connected
fully connected (sometimes known as fully redundant)
The network topologies mentioned above are only a general representation of the kinds of topologies used in computer network and are considered basic topologies.
As a matter of fact networking is defined by the standard of OSI (Open Systems Interconnection) reference for communications. The OSI model consists of seven layers. Each layer has its own function. The OSI model layers are Application, Presentation, Session, Transport, Network, Data Link, and Physical. The upper layers (Application, Presentation, Session) of the OSI model concentrate on the application while the lower layers (transport, network, data link, and physical) focus on signal flow of data from origin to destination. The Application layer defines the medium that communications software and any applications need to communicate to other computers. Layer 6 which is the presentation layer focuses on defining data formats such as text, jpeg, gif, and binary. An example of this layer would be displaying a picture that was received in an e-mail. The 5th Layer is the session layer which establishes how to start, control, and end links or conversations. The transport layer includes protocols that allow it to provide functions in many different areas such as: error recovery, segmentation, and reassembly. The network layers primary job is the end to end delivery of data packets. To do this, the network layer relies on logical addressing so that the origin and destination point can both be recognized. An example of this would be, ip running in a router’s job is to examine the destination address, compare the address to the ip routing table, separate the packet into smaller chunks for transporting purposes, and then deliver the packet to the correct receiver. Layer 2 is the data link layer, which sets the standards for data being delivered across a link or medium. The 1st layer is the physical layer which deals with the physical characteristics of the transmission of data such as the network card and network cable type. An easy way to remember the layers of OSI is to remember All People Seem To Need Data Processing (Layers 7 to 1). 8----------------------->
0
comments
what computer networking?
Computer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs.[1] Computer networking is sometimes considered a sub-discipline of telecommunications, computer science, information technology and/or computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines. There are three types of networks: 1.Internet. 2.Intranet. 3.Extranet. A computer network is any set of computers or devices connected to each other with the ability to exchange data.[2] Examples of different networks are:
Local area network (LAN), which is usually a small network constrained to a small geographic area. An example of a LAN would be a computer network within a building.
Metropolitan area network (MAN), which is used for medium size area. examples for a city or a state.
Wide area network (WAN) that is usually a larger network that covers a large geographic area.
Wireless LANs and WANs (WLAN & WWAN) are the wireless equivalent of the LAN and WAN.
All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, power lines and various wireless technologies.[3] The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet[4]).
read more
Local area network (LAN), which is usually a small network constrained to a small geographic area. An example of a LAN would be a computer network within a building.
Metropolitan area network (MAN), which is used for medium size area. examples for a city or a state.
Wide area network (WAN) that is usually a larger network that covers a large geographic area.
Wireless LANs and WANs (WLAN & WWAN) are the wireless equivalent of the LAN and WAN.
All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, power lines and various wireless technologies.[3] The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet[4]).
1 comments
Top five tips to protect from virus
Knowing how to prevent getting a computer virus is more important than any anti-virus software you can find. Always remember, knowledge is power. That being said, here are our top 5 tips on how to avoid contracting a computer virus.
1. Never open an attachment in your email if you don't know what it is or who it is from. Most viruses today are spread through email. These can come unknowingly from friends who are innocently passing the virus along as well as from virus writers sending out emails with a short subject line ("check out this attachment") and then, for example, a .exe attachment (click here to see a list of extensions that viruses can hide in). An additional step to take is if you are a Windows user you can set the "hide file extension" option so that it is marked as "not hide" file extension.
2. Include yourself in your own address book. The main reason for this step is so that if your computer becomes infected and sends out duplicates of itself to everyone in your address book then you will receive this email and be alerted to the problem.
3. Set ActiveX and cookies to prompt you before running. This is an important step in preventing virus infections in your computer. When ActiveX shows up in an email it is almost always a virus.
4. Purchase or download a highly recommended and internationally known anti-virus program that puts out frequent updates. We recommend Norton, McAfee, or Kaspersky. If your anti-virus company rarely updates it's programs then it is not doing much to protect your computer.
5. Don't download questionable programs or email attachments... even out of curiosity. That free screensaver that you think you need may be bringing along his computer virus friend for the download.
Nothing, not even the best anti-virus program on the market will protect you 100% from contracting a computer virus. The best defense is to stay up-to-date on the happenings in the computer virus world and pay attention to your computer's performance.
read more
1. Never open an attachment in your email if you don't know what it is or who it is from. Most viruses today are spread through email. These can come unknowingly from friends who are innocently passing the virus along as well as from virus writers sending out emails with a short subject line ("check out this attachment") and then, for example, a .exe attachment (click here to see a list of extensions that viruses can hide in). An additional step to take is if you are a Windows user you can set the "hide file extension" option so that it is marked as "not hide" file extension.
2. Include yourself in your own address book. The main reason for this step is so that if your computer becomes infected and sends out duplicates of itself to everyone in your address book then you will receive this email and be alerted to the problem.
3. Set ActiveX and cookies to prompt you before running. This is an important step in preventing virus infections in your computer. When ActiveX shows up in an email it is almost always a virus.
4. Purchase or download a highly recommended and internationally known anti-virus program that puts out frequent updates. We recommend Norton, McAfee, or Kaspersky. If your anti-virus company rarely updates it's programs then it is not doing much to protect your computer.
5. Don't download questionable programs or email attachments... even out of curiosity. That free screensaver that you think you need may be bringing along his computer virus friend for the download.
Nothing, not even the best anti-virus program on the market will protect you 100% from contracting a computer virus. The best defense is to stay up-to-date on the happenings in the computer virus world and pay attention to your computer's performance.
0
comments
What is a TCP/IP Model?
The TCP/IP model is a description framework for computer network protocols created in the 1970s by DARPA, an agency of the United States Department of Defense. It evolved from ARPANET, which was the world's first wide area network and a predecessor of the Internet. The TCP/IP Model is sometimes called the Internet Model or the DoD Model.
The TCP/IP model, or Internet Protocol Suite, describes a set of general design guidelines and implementations of specific networking protocols to enable computers to communicate over a network. TCP/IP provides end-to-end connectivity specifying how data should be formatted, addressed, transmitted, routed and received at the destination. Protocols exist for a variety of different types of communication services between computers.
TCP/IP is generally described as having four abstraction layers (RFC 1122). This layer architecture is often compared with the seven-layer OSI Reference Model; using terms such as Internet Reference Model in analogy is however incorrect as the Internet Model is descriptive while the OSI Reference Model was intended to be prescriptive, hence Reference Model.
The TCP/IP model and related protocols are maintained by the Internet Engineering Task Force (IETF).
Key architectural principles
An early architectural document, RFC 1122, emphasizes architectural principles over layering[1].
End-to-End Principle: This principle has evolved over time. Its original expression put the maintenance of state and overall intelligence at the edges, and assumed the Internet that connected the edges retained no state and concentrated on speed and simplicity. Real-world needs for firewalls, network address translators, web content caches and the like have forced changes in this principle. [2]
Robustness Principle: "In general, an implementation must be conservative in its sending behavior, and liberal in its receiving behavior. That is, it must be careful to send well-formed datagrams, but must accept any datagram that it can interpret (e.g., not object to technical errors where the meaning is still clear) RFC 791." [3] "The second part of the principle is almost as important: software on other hosts may contain deficiencies that make it unwise to exploit legal but obscure protocol features. RFC 1122" [4]
Even when the layers are examined, the assorted architectural documents—there is no single architectural model such as ISO 7498, the OSI reference model—have fewer and less rigidly-defined layers than the OSI model, and thus provide an easier fit for real-world protocols. In point of fact, one frequently referenced document, RFC 1958 [5], does not contain a stack of layers. The lack of emphasis on layering is a strong difference between the IETF and OSI approaches. It only refers to the existence of the "internetworking layer" and generally to "upper layers"; this document was intended as a 1996 "snapshot" of the architecture: "The Internet and its architecture have grown in evolutionary fashion from modest beginnings, rather than from a Grand Plan. While this process of evolution is one of the main reasons for the technology's success, it nevertheless seems useful to record a snapshot of the current principles of the Internet architecture."
RFC 1122 on Host Requirements is structured in paragraphs referring to layers, but refers to many other architectural principles not emphasizing layering. It loosely defines a four-layer model, with the layers having names, not numbers, as follows:
Application (process-to-process) Layer: This is the scope within which applications create user data and communicate this data to other processes or applications on another or the same host. The communications partners are often called peers. This is where the "higher level" protocols such as SMTP, FTP, SSH, HTTP, etc. operate.
Transport (host-to-host) Layer: The Transport Layer constitutes the networking regime between two network hosts, either on the local network or on remote networks separated by routers. The Transport Layer provides a uniform networking interface that hides the actual topology (layout) of the underlying network connections. This is where flow-control, error-correction, and connection protocols exist, such as TCP. This layer deals with opening and maintaining connections between Internet hosts.
Internet (internetworking) Layer: The Internet Layer has the task of exchanging datagrams across network boundaries. It is therefore also referred to as the layer that establishes internetworking, indeed, it defines and establishes the Internet. This layer defines the addressing and routing structures used for the TCP/IP protocol suite. The primary protocol in this scope is the Internet Protocol, which defines IP addresses. Its function in routing is to transport datagrams to the next IP router that has the connectivity to a network closer to the final data destination.
Link Layer: This layer defines the networking methods with the scope of the local network link on which hosts communicate without intervening routers. This layer describes the protocols used to describe the local network topology and the interfaces needed to affect transmission of Internet Layer datagrams to next-neighbor hosts. (cf. the OSI Data Link Layer).
The Internet Protocol Suite and the layered protocol stack design were in use before the OSI model was established. Since then, the TCP/IP model has been compared with the OSI model in books and classrooms, which often results in confusion because the two models use different assumptions, including about the relative importance of strict layering.
[edit]
Layers in the TCP/IP model
Two Internet hosts connected via two routers and the corresponding layers used at each hop.
Encapsulation of application data descending through the TCP/IP layers
The layers near the top are logically closer to the user application, while those near the bottom are logically closer to the physical transmission of the data. Viewing layers as providing or consuming a service is a method of abstraction to isolate upper layer protocols from the nitty-gritty detail of transmitting bits over, for example, Ethernet and collision detection, while the lower layers avoid having to know the details of each and every application and its protocol.
This abstraction also allows upper layers to provide services that the lower layers cannot, or choose not to, provide. Again, the original OSI Reference Model was extended to include connectionless services (OSIRM CL).[6] For example, IP is not designed to be reliable and is a best effort delivery protocol. This means that all transport layer implementations must choose whether or not to provide reliability and to what degree. UDP provides data integrity (via a checksum) but does not guarantee delivery; TCP provides both data integrity and delivery guarantee (by retransmitting until the receiver acknowledges the reception of the packet).
This model lacks the formalism of the OSI reference model and associated documents, but the IETF does not use a formal model and does not consider this a limitation, as in the comment by David D. Clark, "We reject: kings, presidents and voting. We believe in: rough consensus and running code." Criticisms of this model, which have been made with respect to the OSI Reference Model, often do not consider ISO's later extensions to that model.
For multiaccess links with their own addressing systems (e.g. Ethernet) an address mapping protocol is needed. Such protocols can be considered to be below IP but above the existing link system. While the IETF does not use the terminology, this is a subnetwork dependent convergence facility according to an extension to the OSI model, the Internal Organization of the Network Layer (IONL) [7].
ICMP & IGMP operate on top of IP but do not transport data like UDP or TCP. Again, this functionality exists as layer management extensions to the OSI model, in its Management Framework (OSIRM MF) [8]
The SSL/TLS library operates above the transport layer (utilizes TCP) but below application protocols. Again, there was no intention, on the part of the designers of these protocols, to comply with OSI architecture.
The link is treated like a black box here. This is fine for discussing IP (since the whole point of IP is it will run over virtually anything). The IETF explicitly does not intend to discuss transmission systems, which is a less academic but practical alternative to the OSI Reference Model.
The following is a description of each layer in the TCP/IP networking model starting from the lowest level.
[edit]
Link Layer
The Link Layer is the networking scope of the local network connection to which a host is attached. This regime is called the link in Internet literature. This is the lowest component layer of the Internet protocols, as TCP/IP is designed to be hardware independent. As a result TCP/IP has been implemented on top of virtually any hardware networking technology in existence.
The Link Layer is used to move packets between the Internet Layer interfaces of two different hosts on the same link. The processes of transmitting and receiving packets on a given link can be controlled both in the software device driver for the network card, as well as on firmware or specialized chipsets. These will perform data link functions such as adding a packet header to prepare it for transmission, then actually transmit the frame over a physical medium. The TCP/IP model includes specifications of translating the network addressing methods used in the Internet Protocol to data link addressing, such as Media Access Control (MAC), however all other aspects below that level are implicitly assumed to exist in the Link Layer, but are not explicitly defined.
The Link Layer is also the layer where packets may be selected to be sent over a virtual private network or other networking tunnel. In this scenario, the Link Layer data may be considered application data which traverses another instantiation of the IP stack for transmission or reception over another IP connection. Such a connection, or virtual link, may be established with a transport protocol or even an application scope protocol that serves as a tunnel in the Link Layer of the protocol stack. Thus, the TCP/IP model does not dictate a strict hierarchical encapsulation sequence.
[edit]
Internet Layer
The Internet Layer solves the problem of sending packets across one or more networks. Internetworking requires sending data from the source network to the destination network. This process is called routing.[9]
In the Internet Protocol Suite, the Internet Protocol performs two basic functions:
Host addressing and identification: This is accomplished with a hierarchical addressing system (see IP address).
Packet routing: This is the basic task of getting packets of data (datagrams) from source to destination by sending them to the next network node (router) closer to the final destination.
IP can carry data for a number of different upper layer protocols. These protocols are each identified by a unique protocol number: for example, Internet Control Message Protocol (ICMP) and Internet Group Management Protocol (IGMP) are protocols 1 and 2, respectively.
Some of the protocols carried by IP, such as ICMP (used to transmit diagnostic information about IP transmission) and IGMP (used to manage IP Multicast data) are layered on top of IP but perform internetworking functions. This illustrates the differences in the architecture of the TCP/IP stack of the Internet and the OSI model.
[edit]
Transport Layer
The Transport Layer's responsibilities include end-to-end message transfer capabilities independent of the underlying network, along with error control, segmentation, flow control, congestion control, and application addressing (port numbers). End to end message transmission or connecting applications at the transport layer can be categorized as either connection-oriented, implemented in Transmission Control Protocol (TCP), or connectionless, implemented in User Datagram Protocol (UDP).
The Transport Layer can be thought of as a transport mechanism, e.g., a vehicle with the responsibility to make sure that its contents (passengers/goods) reach their destination safely and soundly, unless another protocol layer is responsible for safe delivery.
The Transport Layer provides this service of connecting applications through the use of service ports. Since IP provides only a best effort delivery, the Transport Layer is the first layer of the TCP/IP stack to offer reliability. IP can run over a reliable data link protocol such as the High-Level Data Link Control (HDLC). Protocols above transport, such as RPC, also can provide reliability.
For example, the Transmission Control Protocol (TCP) is a connection-oriented protocol that addresses numerous reliability issues to provide a reliable byte stream:
data arrives in-order
data has minimal error (i.e. correctness)
duplicate data is discarded
lost/discarded packets are resent
includes traffic congestion control
The newer Stream Control Transmission Protocol (SCTP) is also a reliable, connection-oriented transport mechanism. It is Message-stream-oriented — not byte-stream-oriented like TCP — and provides multiple streams multiplexed over a single connection. It also provides multi-homing support, in which a connection end can be represented by multiple IP addresses (representing multiple physical interfaces), such that if one fails, the connection is not interrupted. It was developed initially for telephony applications (to transport SS7 over IP), but can also be used for other applications.
User Datagram Protocol is a connectionless datagram protocol. Like IP, it is a best effort, "unreliable" protocol. Reliability is addressed through error detection using a weak checksum algorithm. UDP is typically used for applications such as streaming media (audio, video, Voice over IP etc) where on-time arrival is more important than reliability, or for simple query/response applications like DNS lookups, where the overhead of setting up a reliable connection is disproportionately large. Real-time Transport Protocol (RTP) is a datagram protocol that is designed for real-time data such as streaming audio and video.
TCP and UDP are used to carry an assortment of higher-level applications. The appropriate transport protocol is chosen based on the higher-layer protocol application. For example, the File Transfer Protocol expects a reliable connection, but the Network File System (NFS) assumes that the subordinate Remote Procedure Call protocol, not transport, will guarantee reliable transfer. Other applications, such as VoIP, can tolerate some loss of packets, but not the reordering or delay that could be caused by retransmission.
The applications at any given network address are distinguished by their TCP or UDP port. By convention certain well known ports are associated with specific applications. (See List of TCP and UDP port numbers.)
[edit]
Application Layer
The Application Layer refers to the higher-level protocols used by most applications for network communication. Examples of application layer protocols include the File Transfer Protocol (FTP) and the Simple Mail Transfer Protocol (SMTP)[10]. Data coded according to application layer protocols are then encapsulated into one or (occasionally) more transport layer protocols (such as the Transmission Control Protocol (TCP) or User Datagram Protocol (UDP)), which in turn use lower layer protocols to effect actual data transfer.
Since the IP stack defines no layers between the application and transport layers, the application layer must include any protocols that act like the OSI's presentation and session layer protocols. This is usually done through libraries.
Application Layer protocols generally treat the transport layer (and lower) protocols as "black boxes" which provide a stable network connection across which to communicate, although the applications are usually aware of key qualities of the transport layer connection such as the end point IP addresses and port numbers. As noted above, layers are not necessarily clearly defined in the Internet protocol suite. Application layer protocols are most often associated with client-server applications, and the commoner servers have specific ports assigned to them by the IANA: HTTP has port 80; Telnet has port 23; etc. Clients, on the other hand, tend to use ephemeral ports, i.e. port numbers assigned at random from a range set aside for the purpose.
Transport and lower level layers are largely unconcerned with the specifics of application layer protocols. Routers and switches do not typically "look inside" the encapsulated traffic to see what kind of application protocol it represents, rather they just provide a conduit for it. However, some firewall and bandwidth throttling applications do try to determine what's inside, as with the Resource Reservation Protocol (RSVP). It's also sometimes necessary for Network Address Translation (NAT) facilities to take account of the needs of particular application layer protocols. (NAT allows hosts on private networks to communicate with the outside world via a single visible IP address using port forwarding, and is an almost ubiquitous feature of modern domestic broadband routers).
[edit]
Hardware and software implementation
Normally, application programmers are concerned only with interfaces in the Application Layer and often also in the Transport Layer, while the layers below are services provided by the TCP/IP stack in the operating system. Microcontroller firmware in the network adapter typically handles link issues, supported by driver software in the operational system. Non-programmable analog and digital electronics are normally in charge of the physical components in the Link Layer, typically using an application-specific integrated circuit (ASIC) chipset for each network interface or other physical standard.
However, hardware or software implementation is not stated in the protocols or the layered reference model. High-performance routers are to a large extent based on fast non-programmable digital electronics, carrying out link level switching.
[edit]
OSI and TCP/IP layering differences
The three top layers in the OSI model—the Application Layer, the Presentation Layer and the Session Layer—are not distinguished separately in the TCP/IP model where it is just the Application Layer. While some pure OSI protocol applications, such as X.400, also combined them, there is no requirement that a TCP/IP protocol stack needs to impose monolithic architecture above the Transport Layer. For example, the Network File System (NFS) application protocol runs over the eXternal Data Representation (XDR) presentation protocol, which, in turn, runs over a protocol with Session Layer functionality, Remote Procedure Call (RPC). RPC provides reliable record transmission, so it can run safely over the best-effort User Datagram Protocol (UDP) transport.
The Session Layer roughly corresponds to the Telnet virtual terminal functionality[citation needed], which is part of text based protocols such as the HTTP and SMTP TCP/IP model Application Layer protocols. It also corresponds to TCP and UDP port numbering, which is considered as part of the transport layer in the TCP/IP model. Some functions that would have been performed by an OSI presentation layer are realized at the Internet application layer using the MIME standard, which is used in application layer protocols such as HTTP and SMTP.
Since the IETF protocol development effort is not concerned with strict layering, some of its protocols may not appear to fit cleanly into the OSI model. These conflicts, however, are more frequent when one only looks at the original OSI model, ISO 7498, without looking at the annexes to this model (e.g., ISO 7498/4 Management Framework), or the ISO 8648 Internal Organization of the Network Layer (IONL). When the IONL and Management Framework documents are considered, the ICMP and IGMP are neatly defined as layer management protocols for the network layer. In like manner, the IONL provides a structure for "subnetwork dependent convergence facilities" such as ARP and RARP.
IETF protocols can be encapsulated recursively, as demonstrated by tunneling protocols such as Generic Routing Encapsulation (GRE). While basic OSI documents do not consider tunneling, there is some concept of tunneling in yet another extension to the OSI architecture, specifically the transport layer gateways within the International Standardized Profile framework [11]. The associated OSI development effort, however, has been abandoned given the overwhelming adoption of TCP/IP protocols.
[edit]
Layer names and number of layers in the literature
The following table shows the layer names and the number of layers of networking models presented in RFCs and textbooks in widespread use in today's university computer networking courses.Kurose[12], Forouzan [13] Comer[14], Kozierok[15] Stallings[16] Tanenbaum[17] RFC 1122, Internet STD 3 (1989) Cisco Academy[18] Mike Padlipsky's 1982 "Arpanet Reference Model" (RFC 871)
Five layers Four+one layers Five layers Four layers Four layers Four layers Three layers
"Five-layer Internet model" or "TCP/IP protocol suite" "TCP/IP 5-layer reference model" "TCP/IP model" "TCP/IP reference model" "Internet model" "Internet model" "Arpanet reference model"
Application Application Application Application Application Application Application/Process
Transport Transport Host-to-host or transport Transport Transport Transport Host-to-host
Network Internet Internet Internet Internet Internetwork
Data link Data link (Network interface) Network access Host-to-network Link Network interface Network interface
Physical (Hardware) Physical
These textbooks are secondary sources that may contravene the intent of RFC 1122 and other IETF primary sources such as RFC 3439[19].
Different authors have interpreted the RFCs differently regarding the question whether the Link Layer (and the TCP/IP model) covers Physical Layer issues, or if a hardware layer is assumed below the Link Layer. Some authors have tried to use other names for the Link Layer, such as network interface layer, in view to avoid confusion with the Data Link Layer of the seven layer OSI model. Others have attempted to map the Internet Protocol model onto the OSI Model. The mapping often results in a model with five layers where the Link Layer is split into a Data Link Layer on top of a Physical Layer. In literature with a bottom-up approach to Internet communication[13][14][16], in which hardware issues are emphasized, those are often discussed in terms of physical layer and data link layer.
The Internet Layer is usually directly mapped into the OSI Model's Network Layer, a more general concept of network functionality. The Transport Layer of the TCP/IP model, sometimes also described as the host-to-host layer, is mapped to OSI Layer 4 (Transport Layer), sometimes also including aspects of OSI Layer 5 (Session Layer) functionality. OSI's Application Layer, Presentation Layer, and the remaining functionality of the Session Layer are collapsed into TCP/IP's Application Layer. The argument is that these OSI layers do usually not exist as separate processes and protocols in Internet applications.[citation needed]
However, the Internet protocol stack has never been altered by the Internet Engineering Task Force from the four layers defined in RFC 1122. The IETF makes no effort to follow the OSI model although RFCs sometimes refer to it and often use the old OSI layer numbers. The IETF has repeatedly stated[citation needed] that Internet protocol and architecture development is not intended to be OSI-compliant. RFC 3439, addressing Internet architecture, contains a section entitled: "Layering Considered Harmful".[19]
read more
The TCP/IP model, or Internet Protocol Suite, describes a set of general design guidelines and implementations of specific networking protocols to enable computers to communicate over a network. TCP/IP provides end-to-end connectivity specifying how data should be formatted, addressed, transmitted, routed and received at the destination. Protocols exist for a variety of different types of communication services between computers.
TCP/IP is generally described as having four abstraction layers (RFC 1122). This layer architecture is often compared with the seven-layer OSI Reference Model; using terms such as Internet Reference Model in analogy is however incorrect as the Internet Model is descriptive while the OSI Reference Model was intended to be prescriptive, hence Reference Model.
The TCP/IP model and related protocols are maintained by the Internet Engineering Task Force (IETF).
Key architectural principles
An early architectural document, RFC 1122, emphasizes architectural principles over layering[1].
End-to-End Principle: This principle has evolved over time. Its original expression put the maintenance of state and overall intelligence at the edges, and assumed the Internet that connected the edges retained no state and concentrated on speed and simplicity. Real-world needs for firewalls, network address translators, web content caches and the like have forced changes in this principle. [2]
Robustness Principle: "In general, an implementation must be conservative in its sending behavior, and liberal in its receiving behavior. That is, it must be careful to send well-formed datagrams, but must accept any datagram that it can interpret (e.g., not object to technical errors where the meaning is still clear) RFC 791." [3] "The second part of the principle is almost as important: software on other hosts may contain deficiencies that make it unwise to exploit legal but obscure protocol features. RFC 1122" [4]
Even when the layers are examined, the assorted architectural documents—there is no single architectural model such as ISO 7498, the OSI reference model—have fewer and less rigidly-defined layers than the OSI model, and thus provide an easier fit for real-world protocols. In point of fact, one frequently referenced document, RFC 1958 [5], does not contain a stack of layers. The lack of emphasis on layering is a strong difference between the IETF and OSI approaches. It only refers to the existence of the "internetworking layer" and generally to "upper layers"; this document was intended as a 1996 "snapshot" of the architecture: "The Internet and its architecture have grown in evolutionary fashion from modest beginnings, rather than from a Grand Plan. While this process of evolution is one of the main reasons for the technology's success, it nevertheless seems useful to record a snapshot of the current principles of the Internet architecture."
RFC 1122 on Host Requirements is structured in paragraphs referring to layers, but refers to many other architectural principles not emphasizing layering. It loosely defines a four-layer model, with the layers having names, not numbers, as follows:
Application (process-to-process) Layer: This is the scope within which applications create user data and communicate this data to other processes or applications on another or the same host. The communications partners are often called peers. This is where the "higher level" protocols such as SMTP, FTP, SSH, HTTP, etc. operate.
Transport (host-to-host) Layer: The Transport Layer constitutes the networking regime between two network hosts, either on the local network or on remote networks separated by routers. The Transport Layer provides a uniform networking interface that hides the actual topology (layout) of the underlying network connections. This is where flow-control, error-correction, and connection protocols exist, such as TCP. This layer deals with opening and maintaining connections between Internet hosts.
Internet (internetworking) Layer: The Internet Layer has the task of exchanging datagrams across network boundaries. It is therefore also referred to as the layer that establishes internetworking, indeed, it defines and establishes the Internet. This layer defines the addressing and routing structures used for the TCP/IP protocol suite. The primary protocol in this scope is the Internet Protocol, which defines IP addresses. Its function in routing is to transport datagrams to the next IP router that has the connectivity to a network closer to the final data destination.
Link Layer: This layer defines the networking methods with the scope of the local network link on which hosts communicate without intervening routers. This layer describes the protocols used to describe the local network topology and the interfaces needed to affect transmission of Internet Layer datagrams to next-neighbor hosts. (cf. the OSI Data Link Layer).
The Internet Protocol Suite and the layered protocol stack design were in use before the OSI model was established. Since then, the TCP/IP model has been compared with the OSI model in books and classrooms, which often results in confusion because the two models use different assumptions, including about the relative importance of strict layering.
[edit]
Layers in the TCP/IP model
Two Internet hosts connected via two routers and the corresponding layers used at each hop.
Encapsulation of application data descending through the TCP/IP layers
The layers near the top are logically closer to the user application, while those near the bottom are logically closer to the physical transmission of the data. Viewing layers as providing or consuming a service is a method of abstraction to isolate upper layer protocols from the nitty-gritty detail of transmitting bits over, for example, Ethernet and collision detection, while the lower layers avoid having to know the details of each and every application and its protocol.
This abstraction also allows upper layers to provide services that the lower layers cannot, or choose not to, provide. Again, the original OSI Reference Model was extended to include connectionless services (OSIRM CL).[6] For example, IP is not designed to be reliable and is a best effort delivery protocol. This means that all transport layer implementations must choose whether or not to provide reliability and to what degree. UDP provides data integrity (via a checksum) but does not guarantee delivery; TCP provides both data integrity and delivery guarantee (by retransmitting until the receiver acknowledges the reception of the packet).
This model lacks the formalism of the OSI reference model and associated documents, but the IETF does not use a formal model and does not consider this a limitation, as in the comment by David D. Clark, "We reject: kings, presidents and voting. We believe in: rough consensus and running code." Criticisms of this model, which have been made with respect to the OSI Reference Model, often do not consider ISO's later extensions to that model.
For multiaccess links with their own addressing systems (e.g. Ethernet) an address mapping protocol is needed. Such protocols can be considered to be below IP but above the existing link system. While the IETF does not use the terminology, this is a subnetwork dependent convergence facility according to an extension to the OSI model, the Internal Organization of the Network Layer (IONL) [7].
ICMP & IGMP operate on top of IP but do not transport data like UDP or TCP. Again, this functionality exists as layer management extensions to the OSI model, in its Management Framework (OSIRM MF) [8]
The SSL/TLS library operates above the transport layer (utilizes TCP) but below application protocols. Again, there was no intention, on the part of the designers of these protocols, to comply with OSI architecture.
The link is treated like a black box here. This is fine for discussing IP (since the whole point of IP is it will run over virtually anything). The IETF explicitly does not intend to discuss transmission systems, which is a less academic but practical alternative to the OSI Reference Model.
The following is a description of each layer in the TCP/IP networking model starting from the lowest level.
[edit]
Link Layer
The Link Layer is the networking scope of the local network connection to which a host is attached. This regime is called the link in Internet literature. This is the lowest component layer of the Internet protocols, as TCP/IP is designed to be hardware independent. As a result TCP/IP has been implemented on top of virtually any hardware networking technology in existence.
The Link Layer is used to move packets between the Internet Layer interfaces of two different hosts on the same link. The processes of transmitting and receiving packets on a given link can be controlled both in the software device driver for the network card, as well as on firmware or specialized chipsets. These will perform data link functions such as adding a packet header to prepare it for transmission, then actually transmit the frame over a physical medium. The TCP/IP model includes specifications of translating the network addressing methods used in the Internet Protocol to data link addressing, such as Media Access Control (MAC), however all other aspects below that level are implicitly assumed to exist in the Link Layer, but are not explicitly defined.
The Link Layer is also the layer where packets may be selected to be sent over a virtual private network or other networking tunnel. In this scenario, the Link Layer data may be considered application data which traverses another instantiation of the IP stack for transmission or reception over another IP connection. Such a connection, or virtual link, may be established with a transport protocol or even an application scope protocol that serves as a tunnel in the Link Layer of the protocol stack. Thus, the TCP/IP model does not dictate a strict hierarchical encapsulation sequence.
[edit]
Internet Layer
The Internet Layer solves the problem of sending packets across one or more networks. Internetworking requires sending data from the source network to the destination network. This process is called routing.[9]
In the Internet Protocol Suite, the Internet Protocol performs two basic functions:
Host addressing and identification: This is accomplished with a hierarchical addressing system (see IP address).
Packet routing: This is the basic task of getting packets of data (datagrams) from source to destination by sending them to the next network node (router) closer to the final destination.
IP can carry data for a number of different upper layer protocols. These protocols are each identified by a unique protocol number: for example, Internet Control Message Protocol (ICMP) and Internet Group Management Protocol (IGMP) are protocols 1 and 2, respectively.
Some of the protocols carried by IP, such as ICMP (used to transmit diagnostic information about IP transmission) and IGMP (used to manage IP Multicast data) are layered on top of IP but perform internetworking functions. This illustrates the differences in the architecture of the TCP/IP stack of the Internet and the OSI model.
[edit]
Transport Layer
The Transport Layer's responsibilities include end-to-end message transfer capabilities independent of the underlying network, along with error control, segmentation, flow control, congestion control, and application addressing (port numbers). End to end message transmission or connecting applications at the transport layer can be categorized as either connection-oriented, implemented in Transmission Control Protocol (TCP), or connectionless, implemented in User Datagram Protocol (UDP).
The Transport Layer can be thought of as a transport mechanism, e.g., a vehicle with the responsibility to make sure that its contents (passengers/goods) reach their destination safely and soundly, unless another protocol layer is responsible for safe delivery.
The Transport Layer provides this service of connecting applications through the use of service ports. Since IP provides only a best effort delivery, the Transport Layer is the first layer of the TCP/IP stack to offer reliability. IP can run over a reliable data link protocol such as the High-Level Data Link Control (HDLC). Protocols above transport, such as RPC, also can provide reliability.
For example, the Transmission Control Protocol (TCP) is a connection-oriented protocol that addresses numerous reliability issues to provide a reliable byte stream:
data arrives in-order
data has minimal error (i.e. correctness)
duplicate data is discarded
lost/discarded packets are resent
includes traffic congestion control
The newer Stream Control Transmission Protocol (SCTP) is also a reliable, connection-oriented transport mechanism. It is Message-stream-oriented — not byte-stream-oriented like TCP — and provides multiple streams multiplexed over a single connection. It also provides multi-homing support, in which a connection end can be represented by multiple IP addresses (representing multiple physical interfaces), such that if one fails, the connection is not interrupted. It was developed initially for telephony applications (to transport SS7 over IP), but can also be used for other applications.
User Datagram Protocol is a connectionless datagram protocol. Like IP, it is a best effort, "unreliable" protocol. Reliability is addressed through error detection using a weak checksum algorithm. UDP is typically used for applications such as streaming media (audio, video, Voice over IP etc) where on-time arrival is more important than reliability, or for simple query/response applications like DNS lookups, where the overhead of setting up a reliable connection is disproportionately large. Real-time Transport Protocol (RTP) is a datagram protocol that is designed for real-time data such as streaming audio and video.
TCP and UDP are used to carry an assortment of higher-level applications. The appropriate transport protocol is chosen based on the higher-layer protocol application. For example, the File Transfer Protocol expects a reliable connection, but the Network File System (NFS) assumes that the subordinate Remote Procedure Call protocol, not transport, will guarantee reliable transfer. Other applications, such as VoIP, can tolerate some loss of packets, but not the reordering or delay that could be caused by retransmission.
The applications at any given network address are distinguished by their TCP or UDP port. By convention certain well known ports are associated with specific applications. (See List of TCP and UDP port numbers.)
[edit]
Application Layer
The Application Layer refers to the higher-level protocols used by most applications for network communication. Examples of application layer protocols include the File Transfer Protocol (FTP) and the Simple Mail Transfer Protocol (SMTP)[10]. Data coded according to application layer protocols are then encapsulated into one or (occasionally) more transport layer protocols (such as the Transmission Control Protocol (TCP) or User Datagram Protocol (UDP)), which in turn use lower layer protocols to effect actual data transfer.
Since the IP stack defines no layers between the application and transport layers, the application layer must include any protocols that act like the OSI's presentation and session layer protocols. This is usually done through libraries.
Application Layer protocols generally treat the transport layer (and lower) protocols as "black boxes" which provide a stable network connection across which to communicate, although the applications are usually aware of key qualities of the transport layer connection such as the end point IP addresses and port numbers. As noted above, layers are not necessarily clearly defined in the Internet protocol suite. Application layer protocols are most often associated with client-server applications, and the commoner servers have specific ports assigned to them by the IANA: HTTP has port 80; Telnet has port 23; etc. Clients, on the other hand, tend to use ephemeral ports, i.e. port numbers assigned at random from a range set aside for the purpose.
Transport and lower level layers are largely unconcerned with the specifics of application layer protocols. Routers and switches do not typically "look inside" the encapsulated traffic to see what kind of application protocol it represents, rather they just provide a conduit for it. However, some firewall and bandwidth throttling applications do try to determine what's inside, as with the Resource Reservation Protocol (RSVP). It's also sometimes necessary for Network Address Translation (NAT) facilities to take account of the needs of particular application layer protocols. (NAT allows hosts on private networks to communicate with the outside world via a single visible IP address using port forwarding, and is an almost ubiquitous feature of modern domestic broadband routers).
[edit]
Hardware and software implementation
Normally, application programmers are concerned only with interfaces in the Application Layer and often also in the Transport Layer, while the layers below are services provided by the TCP/IP stack in the operating system. Microcontroller firmware in the network adapter typically handles link issues, supported by driver software in the operational system. Non-programmable analog and digital electronics are normally in charge of the physical components in the Link Layer, typically using an application-specific integrated circuit (ASIC) chipset for each network interface or other physical standard.
However, hardware or software implementation is not stated in the protocols or the layered reference model. High-performance routers are to a large extent based on fast non-programmable digital electronics, carrying out link level switching.
[edit]
OSI and TCP/IP layering differences
The three top layers in the OSI model—the Application Layer, the Presentation Layer and the Session Layer—are not distinguished separately in the TCP/IP model where it is just the Application Layer. While some pure OSI protocol applications, such as X.400, also combined them, there is no requirement that a TCP/IP protocol stack needs to impose monolithic architecture above the Transport Layer. For example, the Network File System (NFS) application protocol runs over the eXternal Data Representation (XDR) presentation protocol, which, in turn, runs over a protocol with Session Layer functionality, Remote Procedure Call (RPC). RPC provides reliable record transmission, so it can run safely over the best-effort User Datagram Protocol (UDP) transport.
The Session Layer roughly corresponds to the Telnet virtual terminal functionality[citation needed], which is part of text based protocols such as the HTTP and SMTP TCP/IP model Application Layer protocols. It also corresponds to TCP and UDP port numbering, which is considered as part of the transport layer in the TCP/IP model. Some functions that would have been performed by an OSI presentation layer are realized at the Internet application layer using the MIME standard, which is used in application layer protocols such as HTTP and SMTP.
Since the IETF protocol development effort is not concerned with strict layering, some of its protocols may not appear to fit cleanly into the OSI model. These conflicts, however, are more frequent when one only looks at the original OSI model, ISO 7498, without looking at the annexes to this model (e.g., ISO 7498/4 Management Framework), or the ISO 8648 Internal Organization of the Network Layer (IONL). When the IONL and Management Framework documents are considered, the ICMP and IGMP are neatly defined as layer management protocols for the network layer. In like manner, the IONL provides a structure for "subnetwork dependent convergence facilities" such as ARP and RARP.
IETF protocols can be encapsulated recursively, as demonstrated by tunneling protocols such as Generic Routing Encapsulation (GRE). While basic OSI documents do not consider tunneling, there is some concept of tunneling in yet another extension to the OSI architecture, specifically the transport layer gateways within the International Standardized Profile framework [11]. The associated OSI development effort, however, has been abandoned given the overwhelming adoption of TCP/IP protocols.
[edit]
Layer names and number of layers in the literature
The following table shows the layer names and the number of layers of networking models presented in RFCs and textbooks in widespread use in today's university computer networking courses.Kurose[12], Forouzan [13] Comer[14], Kozierok[15] Stallings[16] Tanenbaum[17] RFC 1122, Internet STD 3 (1989) Cisco Academy[18] Mike Padlipsky's 1982 "Arpanet Reference Model" (RFC 871)
Five layers Four+one layers Five layers Four layers Four layers Four layers Three layers
"Five-layer Internet model" or "TCP/IP protocol suite" "TCP/IP 5-layer reference model" "TCP/IP model" "TCP/IP reference model" "Internet model" "Internet model" "Arpanet reference model"
Application Application Application Application Application Application Application/Process
Transport Transport Host-to-host or transport Transport Transport Transport Host-to-host
Network Internet Internet Internet Internet Internetwork
Data link Data link (Network interface) Network access Host-to-network Link Network interface Network interface
Physical (Hardware) Physical
These textbooks are secondary sources that may contravene the intent of RFC 1122 and other IETF primary sources such as RFC 3439[19].
Different authors have interpreted the RFCs differently regarding the question whether the Link Layer (and the TCP/IP model) covers Physical Layer issues, or if a hardware layer is assumed below the Link Layer. Some authors have tried to use other names for the Link Layer, such as network interface layer, in view to avoid confusion with the Data Link Layer of the seven layer OSI model. Others have attempted to map the Internet Protocol model onto the OSI Model. The mapping often results in a model with five layers where the Link Layer is split into a Data Link Layer on top of a Physical Layer. In literature with a bottom-up approach to Internet communication[13][14][16], in which hardware issues are emphasized, those are often discussed in terms of physical layer and data link layer.
The Internet Layer is usually directly mapped into the OSI Model's Network Layer, a more general concept of network functionality. The Transport Layer of the TCP/IP model, sometimes also described as the host-to-host layer, is mapped to OSI Layer 4 (Transport Layer), sometimes also including aspects of OSI Layer 5 (Session Layer) functionality. OSI's Application Layer, Presentation Layer, and the remaining functionality of the Session Layer are collapsed into TCP/IP's Application Layer. The argument is that these OSI layers do usually not exist as separate processes and protocols in Internet applications.[citation needed]
However, the Internet protocol stack has never been altered by the Internet Engineering Task Force from the four layers defined in RFC 1122. The IETF makes no effort to follow the OSI model although RFCs sometimes refer to it and often use the old OSI layer numbers. The IETF has repeatedly stated[citation needed] that Internet protocol and architecture development is not intended to be OSI-compliant. RFC 3439, addressing Internet architecture, contains a section entitled: "Layering Considered Harmful".[19]
Subscribe to:
Posts (Atom)
