ComputerHunter.org |
|
|
|||
|
 |
Cisco CCNA Certification: An Illustrated Guide To Ethernet CSMA/CD
When you're studying for your CCNA exams, you're going to study the theory of technologies we basically take for granted in networking. CSMA/CD is one of those technologies. It works beautifully and you don't even have to configure it. But to be an effective network troubleshooter (and to pass the 640-811, 640-801, and 640-821 exams), you have to know Ethernet inside and out, and that means knowing CSMA/CD. The first Ethernet standards were 10Base5 and 10Base2. Network devices such as hubs, repeaters, and switches weren't in the picture yet. The sole physical components were the Ethernet cards in the computers and coaxial cable. The cable made up a bus that all the connected devices would use. (This type of bus is referred to as a shared bus.) If only one of the hosts on this network wanted to send data, there would be no problem. When two hosts would send at the same time, though, a collision would occur. When the signals would collide, both would be rendered unusable. A standard had to be created that would have the hosts follow rules relating to when they could send data and when they could not. This standard is Carrier Sense Multiple Access with Collision Detection, referred to as CSMA/CD. If two of the three computers on this segment send data at the same time, a collision occurs. To avoid this, CSMA/CD forces computers to "listen" to the Ethernet before sending in order to make sure that no other host on the wire is sending. When the Ethernet segment is not busy, the device that wants to send data can do so. The sender will then continue to listen, to make sure that sending the data didn't cause a collision. If a collision is heard, both of the senders will send a jam signal over the Ethernet. This jam signal indicates to all other devices on the Ethernet segment that there has been a collision, and they should not send data onto the wire. (A second indication of a collision is the noise created by the collision itself.) After sending the jam signal, each of the senders will wait a random amount of time before beginning the entire process over. The random time helps to ensure that the two devices don't transmit simultaneously again. In a separate tutorial, we'll discuss more Ethernet fundamentals and values you should know for your CCNA exams and to be a more effective network troubleshooter. To your success, Chris Bryant Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage. The Bryant Advantage offers dozens of FREE CCNA and CCNP tutorials and articles. The Bryant Advantage sells the world's most comprehensive CCNA Study Guide, and my exclusive Binary Math and Subnetting Mastery book. My $299 CCNA Online Fast Track is the world's fastest-growing CCNA course. Visit http://www.thebryantadvantage.com today!
Google News - Top Stories
|
|
|
|
RELATED ARTICLES
Rear Projection TV Facts - Understanding the Pros & Cons of Rear Projection in the Home Theater Rear Projection Television - An Affordable Option 10 Solid Reasons To Make Your Next PC A Notebook Notebook computers are becoming very popular. They seem to be popping up everywhere: on tv shows, on airplanes, in movies, or in your friend's lap. These sleek little machines are invading our daily lives like never before... and the invasion has just started. Find out why they have become so popular with their users and why your next PC should probably be a notebook computer. Trouble-shooting Hard Drive Problems - Part 1 It is extremely important not to make or write any changes to data on the hard drive without first verifying the hard drive configuration. Therefore, the first priority when unable to access information on a hard drive is to verify all of the configuration information dealing with the suspect hard drive. High Definition DVD High definition DVD, also known as HD-DVD (which actually stands for High Density DVD), is one of two competing high definition storage format - the other being Blu-ray. Thin Clients Benefits are Excellent Options for Computer Homeschools... Just a Suggestion Wireless Consulting and Solution Providers have always been important to african american small businesses and now after several years of having the most technologically advanced homes in our neighborhood, we are beginning to realize that our neighbors could benefit from the same technology in educating our children. With the future our african american children are facing being dependent on computers and broadband access it is critical to have the proper tools for our children to have the confidence necessary to face the future. The Importance Of Current Sense Resistor In Switch Mode Power Supply Current sense resistor is usually located in the switch mode power supply section. Newer version of monitor-the b+ (boost) circuit also have this current sense resistor. If you repair electronic equipment especially the switch mode power supplies, the current sensing resistor is connected to the source pin of power FET (field effect transistor) and the other end to HOT GROUND. The value of current sense resistor is in the range of 0.1 ohm to about 1 ohm. The values are depends on the design of each power supply. Laptop Security -Where?d My Laptop Go? Laptops are lovely. They are convenient, mobile, powerful and prestigious. They are also thief magnets. Over 400,000 laptops disappear each year, leaving their owners wondering where they went, what is happening with their data and what to do next. Some of the laptops are just lost ? left in cabs, at hotels, restaurants and at conferences and events. Many of these laptops (but not all) find their way back to their lucky owners. Some are stolen by people ? many of them co-workers, service staff or people taking advantage of a "moment of opportunity" ? who just want to have a laptop. Some are stolen by professional "Laptop Lifters" who may work in teams to steal the laptops for resale. And others are stolen, not for the laptop itself, which may be a bonus, but for the data on the laptop's hard drive ? financial or identity data or business plans or data. For example: QualComm's CEO had his laptop stolen while he was conducting a Press Conference. Reportedly, some of QualComm's most valuable secrets were on that laptop, unencrypted and only protected by an easily bypassed password. A Department of State laptop containing high level information on nuclear proliferation was stolen right from State's headquarters. Two administrators were fired and other personnel were reprimanded. Think about it ? What other piece of equipment or personal possession do we routinely carry around that is worth over a thousand dollars, by itself, and may be worth thousands more in data? Why wouldn't that be attractive to thieves? A large part of the problem is less on the hardware or software end of things, it's in the HUMAN side of things. By raising our awareness many of the vulnerabilities can be greatly lessened. There are 3 areas of vulnerability: 1) Securing the actual laptop, 2) Securing the Data, 3) Getting the laptop back. Ink Cartridges - A Humble Beginning Computers and their accompanying printers were huge years ago. In the past toner reservoirs and toner cartridges were used instead of ink cartridges like those used now. It was difficult to fill a toner cartridge and it was very messy. What You Should Know Before You Buy Computer Equipment You will have many factors to consider when deciding on which computer equipment to buy. The bewildering amount of choices can seem overwhelming. This guide will help you compare computer equipment features, and help you to examine and sift through many of the basic items before you buy a new computer. If it be a desktop PC, laptop, discount/surplus computer, a refurbished computer or a computer accessory, this quick guide will help you to get the most for your money. Batteries for Your Laptop With technology advancing more every day, electronics have become smaller and more mobile. This includes computers. The laptop, or notebook computer is extremely popular these days and many people have them as backup or secondary computers or even as their main computers. The great thing about a laptop is that it uses a battery to power the unti when you are away from a power source so you can literally take your computer anywhere. But in addition to the batteries, there are other parts of the laptop computer that make it work. The Importance of Ergonomic Products Interestingly, ergonomics though sounds to be a modern and trendy phenomenon, its principles are based on primitive life style. It is a known fact that earlier generations did not have to face a whole lot of medical complications that our generation is facing. Some of the factors that contribute to these medical complications are associated with our poor work conditions and our unhealthy life style which our forefathers and mothers instinctively avoided. We are running short of that life saving instinct. They knew how and how not an action is to be performed, when and when not something can be done easily. They were attuned to nature and to their own bodily nature. They were sensitive to the bodily cues and were able to modify their actions and hence lead a healthy life. Three Must Have Accessories For Notebook Computers An Optical Mouse How to Add or Remove an IDE ROM drive CD ROMS - If you're adding or removing an internal cd-rom, dvd-rom, or just about any internal ROM that has an opening CD door, read on. Almost all IDE devices such as CD-ROM, DVD-ROM, etc. including burners and dvd burners are all installed or removed in the same fashion. If you're removing your rom, first remove the scrues from both sides of the rom. Make sure both sides are removed or you won't be able to get the device out. Once the scrues are off, unplug the drive; both the IDE ribbon cable that goes to your mainboard and your power cable. You may also have another wire running from your cd-rom to your sound card. This wire enables sound to play from your rom drive to your sound card, so when you play a cd on your drive you can hear it. Yank all cables running to the drive, then remove it. Simple. Buying Cheap Refurbished Laptops When comparing refurbished laptop models, ask about these specifications: Drop On Demand Printers Most HP and Epson printers are drop on demand printers. They use electrical pulses to fulfill requests for ink. The ink is expelled out of the print head by a bubble which forms as a reaction to being heated. Once the ink is propelled out of the cartridge, the bubble cools, contracts, and forms a vacuum of sorts, which pulls more ink into the nozzle. Alternatives to Tape Backup You may ask, isn't tape an anachronism in the age of optical disks, removable hard drives and a plethora of whiz-bang, random-access storage media? In many ways it is, but because of the nature of backup it doesn't really matter that tape is slow and sequential-access. Remember, tape is cheap. Businesses use tape because they find it to be a cost-effective backup solution. What is Blu-Ray DVD Video technology has increased significantly over the past years, and is continuing to grow at an incredible rate. Digital Video Disc's aka DVD's are the most likely the last big jump in consumer video technology that everyone is familiar with. To keep up with the ever advancing world of electronics a new format of video storage will be released soon called Blu-ray. Coping with a Serious Data Loss from your Computer Hard Drive Data loss is an expensive reality. It's a hard fact that it happens more often then users like to admit. A recent study by the accounting firm McGladrey and Pullen estimates that one out of every 500 data centers will experience a severe computer disaster this year. As a result, almost half of those companies will go out of business. At the very least, a data loss disaster can mean lost income and missed business opportunities. What is ESR Meter? All capacitors have a certain amount of resistance to the passage of AC current. ESR (Equivalent Series Resistance) is the sum of all internal resistances of a capacitor measured in Ohms. An ideal capacitor has ZERO ohms ESR. From the diagram below you can see a resistor in series with a "PERFECT CAPACITOR". The value of the resistor is called ESR. Electrolytic Capacitors have a tendency to increase its ESR overtime due to drying or corrosion. High ESR is a frequent problem in today's electronic circuit. Even a 1 or 2 ohms rise in ESR can cause complicated problems. Under normal conditions the ESR has a very low value, which stays that way for many years unless the rubber seal is defective, in which case the electrolyte's water component gradually dries out and the ESR creeps up with time. The increase in ESR increases both voltage drops within the capacitor and the heat, produced in the capacitors due to resistive heating. If you don't check for ESR, you may be in for a "TOUGH DOG" repair. High ESR is the first sign of a capacitor failure. High ESR will cause complete circuit failure, over heating of capacitor, loading of the circuit, overstressing of other circuit components and other undesirable effects. Testing Flyback Transformer - How to Test and When to Replace It Nowadays, more and more monitor comes in with flyback transformers problems. Testing flyback transformers arenot difficult if you carefully follow the instruction. In many cases, the flyback transformer can become short circuit after using not more than 2 years. This is partly due to bad design and low quality materials used during manufactures flyback transformer. The question is what kind of problems can be found in a flyback transformer and how to test and when to replace it. Here is an explanation that will help you to identify many flyback transformer problems.
|
|
|
|
|
