David Clark DC Pro-X Headset Review

There’s a brand new aviation headset that’s just recently been released. It’s made by the David Clark company, and it’s called the DC Pro-X. Actually, there are two types of these headsets – an active noise reduction model and a passive noise reduction model. This article will be reviewing the active noise reduction model.

The David Clark DC Pro-X headset is a different type of headset for the company, in that it’s extremely light. Most pilot headsets weigh between 12 and 17 ounces, but this new headset weighs only 7.5 ounces. This can really make a difference in comfort, especially on longer flights.

Another feature that pilots like is the Bluetooth connectivity. A cell phone or an ipod can be connected wirelessly to the headset. This is very convenient for pilots when they need to make a quick call while still on the ground and don’t want to go through the hassle of donning their headset and adjusting it all over again.

It’s also a nice feature to be able to listen to music while flying a long cross country trip. It can help make the time pass more quickly.

The style of the ear cups is known as “rest-on-ear”. The idea is that the ear cups don’t completely envelope the ear and cause discomfort to the pilot’s ears. Sometimes the squeezing effect can cause some real pain after several hours.

The active noise reduction (ANR) technology works well to cancel out surrounding noises in the cockpit. This technology requires batteries, but the DC Pro-X has dual-coil drivers in their mics so communication won’t be lost in the event of battery loss.

Here’s a summary of the pros and cons of the David Clark DC Pro-X:

Pros:

  • Extremely lightweight, good for long flights
  • Easy to use
  • Has Bluetooth connectivity
  • Collapses easily to fit into flight bag
  • Well made – they feel like they’ll last
  • 5 year warranty
  • Excellent customer service
  • Affordable – Priced at $637.00, they’re less than comparable headsets

Cons:

  • Some pilots complain that they don’t block out noise adequately
  • There were also some complaints that the headset didn’t fit over their sunglasses

Because the DC Pro-X was only released a few months ago, it’s difficult to find a lot of reviews, but so far pilots who have purchased them have been quite happy with this newest headset from David Clark. This company has been around a long time and has been producing great aviation products since 1941.

Source by Joseph B Wood

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Radio Broadcasting's Vital Role in Emergencies

Radio broadcasting has a long history; One that goes beyond Tesla, Marconi and Armstrong, and it includes advances in communication and technology, as explained by Radio magazine. Some of the important dates from radio's past are covered on the AmericanRadioHistory.com website. There, one can read about the earliest forms of radiotelegraphy systems.

In fact, early 1920s marks an important date in time of radio telegraph communication: In that time, the basis of public radio network broadcasting and even early TV programming were provided: Scientists were experimenting in 1925 with TVs, to include video content distributed via radio Transmissions on designated channels to a dispensed audience.

Early audio transmission set in motion AM broadcasting on a radio station. To overcome the interference problems of AM radio, stations began to use FM radio in the 1930s as its band provided a more clear-cut audio sound through the air as radio waves from a transmitter to an antenna. It was not until the 2000s that Americans were introduced to digital radio and direct broadcasting by satellite (DBS).

By the 1930s, radio broadcasting and television broadcasting (telecasting) was an integral part of the American way of life.

In the previous decade, the 1920s, early amateur radio transmitted information in the form of Morse code; A series of on-off tones provided communication on telegraph lines, undersea cables and radio circuits for transmitting emergency signals. Radio telegraphy using Morse code proved vital during World War II. Also Mayday calls were made by radio to signal a life-threatening emergency. A fire, an explosion or sinking vessel or aircraft, where announced with a signal transmitted three times in a row ("Mayday Mayday Mayday"); The distress call was broadcasted to reach out for assistance in times of an emergency.

A device dubbed the ham radio was used for amateur radio broadcasting early on; A range of frequencies (set aside for commercial, police and government use only) allowed one-and two-way communication by the 1940s. The ham radio happened to be something of an emergency broadcast system to get the word out to the wider community in the event of an emergency, such as a natural disaster. The SOS (amateur distress call) sent by the Titanic had used a radio ham in April 1912, noted ARRL (American Radio Relay League), the national association for Amateur Radio, on its webpage on "Ham Radio History."

In the 1950s, CONELRAD (Control of Electromagnetic Radiation) was a method of emergency broadcasting to the public; The CONELRAD system (used during the Cold War) was replaced by the Emergency Broadcast System (EBS) in the 60s, which was later replaced with the Emergency Alert System (EAS) in the 90s. Regardless of the name change, each one served as a national warning system for the American public in the event of war or grave national crisis, in addition to local weather emerging. Such broadcasting systems had a vital role in emergencies to quickly provide the necessary alert and message to a community when a catastrophic situation is exposed. In essence, it announced an emergency broadcast response which could potentially save human lives and deliver instructions if an evacuation was required.

To this day, radio broadcasting has been the most utilized media to distribute to the public civil emergency messages.

In history, it has been widely accepted as the mass communication medium for information, especially during times of severe weather and even threats related to wars. In fact, radio communication can be sustained even when other means of communication fail and there is no power. In addition, it is a media everyone has access to. Transmitting real-time warnings to citizens in the event of an emergency proves that communications devices like radios can still be of great importance, today, in emergencies even in the era of computers and mobile devices.

Source by Edward Jules Goodman

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How to Protect Your Passwords Properly

Looking back at last 20 years (I am writing this in 2014), use of systems and passwords has become an unwanted but unavoidable requirement in our daily life. We always require to stay atop of many forms and layers of online protection of our sensitive data. Some examples where we need to use passwords, pass phrases, identifiable pictures etc. Are banks, schools, credit cards, emails, work login, work search, kids account, entertainment, communications, and more and more. As far as the number goes, all these requirements are increasing and as far as complication goes, they are becoming increasingly complicated in nature to use and manage.

20 years back, I had only two account passwords that I had to manage. One email and one bank account. Today I manage over 200 online safety memory chips including for me and for my family! (Wow writing this makes me feel safe! Really ..?)

Again, 20 years back I could put in 6 alphabets or numbers and it was considered a safe, secure password. Today, I have to use alphabets in lower and upper case, numbers and special characters with the strength indicators showing strength of the password as we are typing it to understand how strong and safe the password is (in case case is a cyber crime to crack Down the passwords.) Many companies will not let me use the parts of my name in the password. Then I have to associate my account to an image and keep the image in mind. Further I have to answer some security questions (typically from 3 to 5). To add even more, every now and then I need to associate and confirm my account with a cell phone number! Then there is separate 4 digit pin for bank ATM's etc. Even my voice mail has a 6 digit pass-code!

Talk about complexity! Talk about memorizing!

Is the technology helpful to protect our sensitive data? Yes! Has the technology complicated the issue and pushed us way more to manage in terms of passwords, security etc.? Yes!

So how to manage these complications. Here are some do's and don'ts for it.

Do's

1. Use long complex passwords.

2. Generate and use random passwords yourself.

3. Keep your passwords in an isolated safe file. Write if you want. Even better is to spend a few bucks to have a dedicated drive, USB etc.

4. Use limited login attempts at all the allowed institutions. It basically means after 3 or 2 or 4 (whatever the set number is) unsuccessful log in attempts, your account will be automatically disabled and you will have to go either personally or call to prove your ID and then get your account reinstated. It seems annoying in the beginning but it is a great tool to protect your ID in the long run.

5. Answer security questions in a non traditional manner. Example; Name of the first dog. Traditional answer: whiskey. Non traditional answer: Ihadnodog.

6. Always keep the current back up out of your computer such as in a USB drive.

7. Many experts suggest to use copy + paste rather than typing in the web forms, so follow it when you are logging in.

8. Have a real complex master password for any file that you might be using to store and protect your sensitive information such as passwords, security questions etc.

9. Often change your passwords. Update your record if you are managing it.

10. Always have a working anti-virus program installed. Run the program every few days in manual mode.

11. Delete the accounts you no longer need.

Don'ts

1. Do not use any online system to save and protect your data. It might be chrome or internet explorer provoking you to 'remember' your login information. It may be a service provider tool as Norton protection. I personally call it a third party dependency and it can restrict, corrupt or disintegrate any time. Your passwords and other information is lost without any back up in this case and worst case now all of it can be available to someone else as well ..

2. Never use same password for more than one log-in portfolio ..

3. Do not use easily guessable passwords such as: abc123, 123ABC, 0123456789, XYZ etc. Cyber ​​crime computers attack through the internet and try thousands of password combinations in a minute. They can easily guess the easy passwords and log into your account. The damage can take a-lot to repair in this case !.

4. Do not use a computer to generate random passwords.

5. Do not give access to unknown apps through social media.

6. Avoid using public computers in libraries, schools, restaurants, hotels, etc. If you do have to use it, un-check the "remember me" option before you log-in and clear up everything after use such as cookies, history etc. Make sure you are allowed to clear it and you are not violating any public institution policy.

7. Sharing a password is usually prohibited so do not share your passwords.

Creating and managing as per these guidelines will help you protect your accounts and data safety for a long period.

Source by Subodh Sharma

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SMS Daycare & Gaming

Using the Physical World as a Game Board.

This is not Kinky Day Care! SMS stands for Short Message Service.

If your children carry cell phones, or if you have an extra family phone you can let them borrow for the day. This is a good way to get a break and run the kids all over the neighborhood.

The Treasure Hunt. Come up with a few locations around the house or the yard and create hints to explain each location. It's better to have three or four hints for each location. I usually put a card with a number on it at each location. This will help you know if they actually made it to the location. You do not have to use the cards or "PostIt Note" if you do not want to. Once you're setup, get the kids ready.

Page them with the first hint. It's always nice to have your hints as short as possible. You should have at least three hints, from hard to easy. This would also depend on the age groups your working with. Now you get to sit back in the hammock in the backyard while you keep the children busy! It's a great way to take a break.

You can make up as many location as you want, but sometimes they get a little frustrated after about five or so locations.

Always have a prize of some kind at the end. Maybe a candy bar or a trip to the ice cream store.

When they find the first location. They are to page you and give the number you wrote on the card or Post It Note. (The numbers should not be in order, ie 1,2,3 etc. You can use anything you want. Backyard "). At that time, you page them back with a Congratulations and the next hint. If you have more than one cell phone in the group, you will be able to setup teams. You have to be fair as far as which message you send to each group, (hard, medium, or easy hints). If I have more than one group, I'll send them in different directions so they can not cheat off one another. If group number 2 is ahead of group 1, and I give group 2 an easy hint. Be fair, when group 1 gets to that hint; Give them the easy hint first. If they still need help, I'll shoot the others to them also.

I like the easy way to keep kids busy. And it's even fun for you too. If the children are older, you can have them running all over the neighborhood and you can use up to ten or more locations if you like. If they begin to get tired, you can always skip to the last location where the prize might be. So you might be ready with as many locations as you can think of. You can always use them on the next hunt.

It all depends on who you're doing this with. Some kids get bored after 5 locations; Others are still ready to go after 10 locations. The age groups do not matter in this situation. Have fun.

Email me with any new or better ideas on "Creating your own breaks". Thank you.

Source by Robert Lett

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4 Major Questions to Ask While Interviewing a Magento Developer

The key to success of your online store lies on how efficiently you can build it. User-friendliness, functionality, SEO-friendliness and a number of other factors are responsible for the success of your online website. Thus, choosing the eCommerce platform is a critical phase of development. Magento is the most powerful platform and recommended choice of developers for eCommerce development. However, things certainly become more productive when you choose the right Magento developer for your eCommerce website as well.

Skill set and knowledge of a developer greatly affects the efficiency of a website and thus, while interviewing a developer it becomes crucial to check its credibility rightly. Keeping this in mind, here are some of the important questions to know before hiring a developer.

Question 1: Is your company experienced in Magento eCommerce development?
One of the major questions to ask a developer is whether he has a fair experience to work with Magento development projects or not. Magento is typically a complex software which, certainly requires relevant experience to make sure that the project does not get stuck in the middle while addressing the technical challenges. Keep in mind, that the developer has sound experience to work with different types of projects and stay ready to face various technical challenges.

Question 2: Is your work process focussed on quality?
Quality is something of greatest importance while building a Magento online store. Thus, while choosing the right developer for your web development project, it is ideal to keep a note of the QA methods adopted by him to test the process of quality management. Furthermore, you can look for the certificates and accreditation achieved by the developer to know about his level of credibility.

Question 3: How effective is your mode of communication?
Effective communication is a major requisite to carry a smooth relation between the development team and stakeholders. Thus, make sure that they have an effective communication mechanism to connect with their clients. Starting from the first project meeting to its delivery, constant communication with the project managers, development team and account managers is necessary.

Question 4: Do you offer post-development support?
Post-development support is important to deal with the bugs and issues before the eCommerce site goes live. While considering complexities of this platform, it makes the right sense to have extensive support for your post development needs such that you do not need to suffer from and functionality or technical issue in the future course.

Developing an eCommerce store powered by Magento is certainly a daunting task as this platform requires deep technical expertise. Thus, even for making minor changes and improvements, the skill set of a developer is necessary.

Source by Rob Stephen

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PR Crisis Management – Tell It All, Tell It Fast And Tell The Truth

I turned on the television news recently to learn that one of our top football teams may have lost an important match because of illness, the story being brought to us by a reporter stationed outside the hotel where the players enjoyed lunch prior to the game.

In the car, this was the lead story on the radio news with the story read by a reporter, again said to be outside the hotel. He confirmed that the Police had collected samples from the restaurant to pass onto the health authorities.

Guess what? The story was also the lead in the tabloid newspapers sat on my desk when I reached the office. Photographs of the hotel in question usually supported the story.

As a public relations professional, I reflected on what the hotel's PR people are going through this morning. This is a prestigious hotel group with a well-crafted brand image of quality at the premium end of the market. Here they are, in the spotlight for all the wrong sort of reasons!

They will certainly have a documented Crisis Management Plan or, in softer terms, a PR Communications Plan. But it is not only global companies who need to devise a plan in advance. Being in business, or even running a not-for-profit organization, poses everyone to the risk of a PR crisis.

No organization is very far from crises and their resulting media attention. Their reputation can be washed away or seriously damaged in an instant. A crisis is any situation that threaten the integrity or reputation of your company, usually bought on by adverse or negative media attention.

These situations can be any kind of legal dispute, theft, accident, fire, flood or manmade disaster that could be attributed to your company. It can also be a situation where in the eyes of the media or general public your company did not react to one of the above situations in the appropriate manner. This definition is not all encompassing but rather is designed to give you an idea for the types of situations where you may need to follow this plan.

Crisis management is a complex subject, but here are five tips to get you started. And, start, you must.

1. Do not wait. Many organizations only get their crisis plans under once a disaster has stuck. Instead, brainstorm possible scenarios or types of disasters that could happen, and start planning for them. In fact, I have found this to be a positive process as bringing together key executives to share ideas and examine scenarios often bringing out a range of issues that they can take forward.

2. Realize that crises take a wide range of shapes. As I say, this can be anything from the hotel's crisis to a legal dispute getting out of hand to customer dissatisfaction aired on the Internet. I even recall a weekend phone call from a Scout leader who campsite had been washed away in storms with some children being injured; The media were on the telephone badgering her for the story! They will all require slightly different responses. Brainstorm and prepare for as many as you can imagine.

3. Develop a PR communications plan. A barrage of media attention may swamp you within minutes of the news breaking. Also, think about how you will get information out to staff, supporters & investors, and customers – yes, remember to get your side of the story out to customers as soon as you can. Internal communication is as important as communication to the general public.

A physical plan has to do with getting everyone out of the building in case of an earthquake. A communications plan involves identifying a spokesperson, developing press releases, setting up a media hotline, and finding a place where you can have a press conference.

4. Be prepared to speak to the media and to your constituents. Even if you can not say much because your lawyer is concerned about liability, plan to say what you can as soon as you can. Be concerned, show concern, speak concern, and always tell the truth. That does not mean you have to tell everything all at once, but never, never lie.

5. Provide media training for senior management. Do this before a disaster strikes. Make it a regular part of board and senior employee training. Media training need not cost a lot if you have someone on your board working in public relations or someone who is a member of the media. The key is to do it regularly so that new people are always trained and others do not grow stale.

Do not delay your crisis planning. Do not ruin your hard-won reputation by handling situations badly! The directors and PR team of that hotel this morning went to bed last evening little knowing the blast of unwelcome publicity that was facing them this morning. Hopefully, their PR Communications Plan will be a trusted aide today!

Suggested reading

1. "Crisis in Organizations: Managing and Communicating in the Heat of Crisis," by Laurence Barton.

2. "You've Better Have a Hose if You Want to Put Out the Fire: The Complete Guide to Crisis and Risk Communications," by Rene A. Henry.

Source by John Hicks

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Quantum Computing and Healthcare Technology

Imagine conducting an MRI, on a single cell instead of the whole body – taking a picture of the molecule or just a group of molecules within the cell, identifying and examining the problem areas within DNA, and coming up with a more precise diagnosis and patient therapy. This is possible today through the precision of Quantum Computing and Nanotechnology built into an MRI equipment.

In a recent news release IBM declared that they are very close to make a breakthrough in the realms of Quantum computing. As a result of some experimental successes they are closer to build the first Quantum Computer, that can take advantage of the oddities of quantum physics and could solve certain problems in seconds, that would otherwise take present-day computers billions of years to solve.

Quantum computing is a computing system based on qubits as opposed to bits; where qubits (Quantum Bits) are basic units of information in a quantum computer. While a bit can represent just one of two possibilities such as 0 or 1, or yes or not, Qubits can represent many more options: 0 or 1, 1 and 0, the occurrence of multiple combinations of Qubits, and that too simultaneously. So, Qubit represents an array of possibilities and all can be calculated simultaneously taking probabilities in account.

The Qubit concept deals with very small particles (subatomic particles). It has been proven that a subatomic particle can have different states simultaneously because the particles are never static. This is evident because they move very fast, close to the speed of light. So, a particle state of the particle (Qubit) looks different to different observers and the particle has several states simultaneously. That is why one subatomic particle can have different states and probabilities, at the same time. We can use it to replace bits and get better performance: Much better performance! And then, when you combine Qubits, that combination holds an exponentially larger amount of information than bits. Subatomic logic is much more powerful than binary logic used in normal computing.

As a result, you can process complicated information faster. Its main applications are encryption, decryption, modeling, databases, voice recognition, structure recognition, simulation and artificial intelligence, plus many others yet non-existent applications.

Imagine its utilization and effect in the realm of Healthcare, specifically e-Health. Volumes of electronically available Patient data, structured, modeled, simulated, and processed in fractions of seconds – artificial intelligence for diagnosis and condition predictability with almost 100% accuracy, will multiply millions of fold, surpassing unthought-of limits.

Quantum Computing has also proved that two entangled particles share its existence. That is when one modifies its state, the other also modifies its own state simultaneously, no matter how far they are in the universe. That means we can “transport” information from one place to another without physical movement, just by modifying one entangled particle state.

In e-Health, this could mean automatic remote and reliable diagnosis, with electronic patient information, through immediate communication with entangled subatomic particles. And, with nano-scale precision applications, this is just the tip of the iceberg.

Source by Dipak Chatterjee

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How to Get Women to Like You – Using Super Powerful Body Language

Listen up – if you do not use body language in any way to get women then you are missing out. The biggest misconception that guys have is that they will need to be smooth talkers to get women to like them. Total nonsense! Up to 93% of all communications is done via non-verbal communications. This explains why the best way to get women to be attracted to you is to use body language! Read on to discover the killer body language tactics to get women to like you…

How To Get Women To Like You – Using Super Powerful Body Language

Technique #1: “Tone of Voice”. This is the easiest thing to do in order to be attractive to women. Guys who speak with a high pitch are perceived to be wimpy. You must speak in a low baritone – and slowly. This conveys heaps of confidence, and gives out masculine signals.

In case you are wondering – ‘voice’ is also considered as part of your body, especially in dating and seducing women.

Technique #2: “Lean Back”. The worst way you can come across is to look super needy and desperate. Therefore, you must lean back and act as if you are just slightly interested in her. Give her the impression that you are going to leave anytime, and she will need to work at it if she wants you to stay.

Once you know of these two powerful body language techniques, then you can supercharge your seduction powers by using hypnosis techniques. One such technique, called fractionation, is known to be able to make women fall in love super quickly – often in 15 minutes or less. Super powerful stuff!

Source by Derek Rake

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Cell Phones – Advantages and Disadvantages

Cell phones are a mind blowing invention of the current century. If you take a look a few years back, a mobile was not measured as a necessity, but it was rather seen as a luxury that was available to a minute group of people. It was not affordable by everyone and only high class or business people actually owned one. But previously, life without mobile looks impossible. No one can imagine a life without a cell phone. Many people do not even leave their home without it. No matter what is the age, people all across the global village are added to cell phone.

There are thousands reasons behind its popularity in such a short span of time but mainly it is because of the fact that mobile phones are no longer considered just as a hand phone but they have transformed into a technological device, offering various technologies such as GPS, Music player, PDA and much more. To stay in competition, almost every week, manufacturers all over the world are introducing a new model with upgraded features that fits best to your lifestyle.

Large number of people find it to be a convenient mean to interact with others. With the blink of an eye you can contact with anyone across the globe. Nowadays, mobile phones are constantly being update which allows you to enjoy a wide range of new features. Based on the mobile model now you can easily watch television on your handset, can play huge number of games, can surf for information from internet, can receive or send electronic mail, can send or take 3D pictures, keep a balance tracks of important meetings And appointment via reminders, store a huge list of contacts with complete description and a lot more.

In simple words, a mobile phone is a need of every individual. Nowadays, the need has also transformed into a fashion. People opt for expensive mobile devices to impress others. Every phone has an option of 'customize your phone' through which users can easily adjust the phone according to the environment or taste.

You will come across with many such parents who gift their children with a cell phone. This is not because they want to provide their children with a new technology but the major reason behind it is their safety. Mobile phone can proof to be the best source of protection in case of emergency.

Everything has pro and cons, and cell phone has its drawbacks as well. Following are some drawbacks of cell phone:

1. Health issues: Recent research says that radiations emitted by the cell phone results in blurring of eye sight, earaches, and headache and can even lead to cancer.

2. No privacy: If somehow your cell is misplaced, it will lead you to a couple of difficulties; Unless you have put on strong passwords which are not easily breakable with software.

3. Cell phone and driving: Mostly, accident occurs because of carelessness and the major reason behind it is the use of mobile while driving.

No matter what are the disadvantages of using cell phone, its pros are simply uncountable. These advantages have made people an addict of the cell phone.

Source by Carlyn McKinley

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Vlans

In order to implement VLANs in a network environment, you'll need a Layer 2 switch that supports them. Almost all switches sold today that are described as "managed" switches provide the ability to make ports members of different VLANs. However, switches that do not provide any configuration function (such as many basic, lower-end switches) do not provide the ability to configure VLANs. Almost any Cisco Catalyst switch that you'll come across today provides the ability to make ports part of different VLANs.

Before getting into the details of how a VLAN functions, it's worth exploring some of the advantages that a VLAN provides. First and foremost, VLANs provide the ability to define broadcast domains without the constraint of physical location. For example, instead of making all of the users on the third floor part of the same broadcast domain, you may use VLANs to make all of the users in the HR department part of the same broadcast domain. The benefits of doing this are many. Firstly, these users might be spread through different floors on a building, so a VLAN would allow you to make all of these users part of the same broadcast domain. To that end, this can also be viewed as a security feature – since all HR users are part of the same broadcast domain, you could later use policies such as access lists to control which areas of the network these users have access to, or which Users have access to the HR broadcast domain. Furthermore, if the HR department's server were placed on the same VLAN, HR users would be able to access their server without the need for traffic to cross routers and potentially impact other parts of the network.

VLANs are defined on a switch on a port-by-port basis. That is, you may choose to make ports 1-6 part of VLAN 1, and ports 7-12 part of VLAN 2. There's no need for ports in the same VLAN to be contiguous at all – you could make ports 1, 3 and 5 on a switch part of VLAN 1, for example. On almost all switches today, all ports are part of VLAN 1 by default. If you want to implement additional VLANs, these must first be defined in the switch's software (such as the IOS on a Cisco switch), and then ports must be made members of that VLAN. A VLAN is not limited to a single switch, either. If trunk links are used to interconnect switches, a VLAN might have 3 ports on one switch, and 7 ports on another, as shown below. The logical nature of a VLAN makes it a very effective tool, especially in larger networking environments.

Inter-VLAN Communication

I mentioned a few times already that a VLAN is simply a special type of broadcast domain, in that it is defined on a switch port basis rather than traditional physical boundaries. Recall from the earlier articles in this series that when a host in one broadcast domain wishes to communicate with another, a router must be involved. This same holds true for VLANs. For example, imagine that port 1 on a switch is part of VLAN 1, and port 2 part of VLAN 99. If all of the switch's ports were part of VLAN 1, the hosts connected to these ports could communicate without issue. However, once the ports are made part of different VLANs, this is no longer true. In order for a host connected to port 1 to communicate with another connected to port 2, a router must be involved.

You may already be familiar with the concept of a Layer 3 switch. A Layer 3 switch is generally a Layer 2 switching device that also includes the ability to act as a router, typically through the use of additional hardware and software features. If a switch includes Layer 3 capabilities, it can be configured to route traffic between VLANs defined in the switch, without the need for packets to ever leave the switch. However, if a switch only includes Layer 2 functionaility, an external router must be configured to route traffic between the VLANs. In some cases, it's entirely possible that a packet will leave switch port 1, be forwarded to an external router, and then be routed right back to port 2 on the originating switch. For this reason, many companies have decided to implement Layer 3 switches strategically through their network. Regardless of the method chosen, it's most important for you to recognize that when a host on one VLAN wants to communicate with a host on another, a router must somehow be involved.

Extended VLANs Between Switches

In order to extend VLANs across different switches, a trunk link must connect the switches. Think of a trunk link as being similar to an uplink between hubs – typically a trunk link is implemented between fast switch ports on two different switches using a crossover cable. For example, you may interconnect two Gigabit Ethernet ports on different switches using fiber optics, or two 100 Mbps switch ports using a traditional Cat5 crossover cable. In most cases it is generally recommended that you use the fastest port available for trunk connections, since this link will often carry a great deal of traffic, possibly for multiple VLANs.

To begin, let's assume that you have connected a link between the 100 Mbps ports of two switches, as shown below. Notice that each of these ports are members of VLAN 1 on each switch. By default, without any additional configuration, these ports will act as a trunk link, but will only pass traffic for the VLAN associated with their port connections – VLAN 1. This type of link, where only traffic for a single VLAN is passed, is Referred to as an "Access Link". While an access link does the job for a single VLAN environment, multiple access links would be required if you wanted traffic from multiple VLANs to be passed between switches. Having multiple access links between the same pair of switches would be a big waste of switch ports. Obviously another solution is required when traffic for multiple VLANs needs to be transferred across a single trunk link. The solution for this comes through the use of VLAN tagging.

VLAN Tagging

When you want traffic from multiple VLANs to be able to traverse a link that interconnects two switches, you need to configure a VLAN tagging method on the ports that supply the link. Although there are a number of tagging methods in use for different technologies, the two that you need to be aware of for the purpose of the CCNA exam are known as InterSwitch Link (ISL) and 802.1q. ISL is a Cisco proprietary VLAN tagging methods, while 802.1q is a open standard. When connecting two Cisco switches, ISL is usually the best choice, but if you need to connect switches of different types (a Cisco switch and an Avaya switch, for example), then you'll need to use IETF.

For the CCNA exam, the only thing that you really need to know about 802.1q is that it is the open standard for VLAN tagging, and should be used in mixed environments. The exam expects you to have a certain deeper understanding of ISL, including how it works, when it can be used, and quite, its purpose.

First and foremost, you need to be aware that ISL will only function on ports with a speed of 100 Mbps or greater. That is, you can not use ISL in conjunction with a 10 Mbps port. That should not be an issue, since most Cisco Catalyst switches provide at least one or two Fast Ethernet ports, even on lower-end models like the 1912. Secondly, the ports on either end of the link need to support and be configured for ISL.

ISL is referred to as a VLAN tagging method. Essentially, what ISL does is tag a frame as it leaves a switch with information about the VLAN that the frame belongs to. For example, if a frame from VLAN 99 is leaving a switch, the ISL port will add information to the frame header, designating that the frame is part of VLAN 99. When this ISL frame reaches the port at the other end of the switch, It will look at the ISL header, determine that the frame is meant for VLAN 99, will strip off the ISL information, and will forward it into VLAN 99. One of the issues with VLAN tagging is that by adding information to an Ethernet frame, The size of the frame can move beyond the Ethernet maximum of 1518 bytes, to 1522 bytes. Because of this, all non-ISL ports will see frames larger than 1518 bytes as giants, and as such, invalid. This is the reason why a port needs to be configured for ISL in order for it to understand this different frame format.

One VLAN tagging is configured on the ports associated with the link connecting switches, the link is known as a "Trunk Link". A trunk link is capable of transferring frames from many different VLANs through the use of technologies like ISL or 802.1q.

A better strategy here would be to configure ISL tagging on one of the router's Fast Ethernet interfaces, and then configure ISL on the connected switch port. This configuration, also known as a "router on a stick", would allow the router to process the traffic of multiple VLANs, and route traffic between them. We'll get into the details of routing within the next few articles.

Beyond its intended purpose of configuring trunk links between switches, ISL is often used in other ways. For example, it is possible to purchase network interface cards that support ISL. If a server were configured with an ISL-capable network card, it could be connected to an ISL port on a switch.

This would allow a server to be made part of multiple VLANs simultaniously, the benefit being that hosts from different broadcast domains could then access the server without the need for their packets to be routed. While this may seem like a perfect solution, you need to remember than the server would now see all traffic from these VLANs, which could negatively impact performance.

I hope this article has provided you the good information about the Vlans.

Source by Kashif Raza

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