Differentials have three jobs:

• To aim the engine power at the wheels
• To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels
• To transmit the power to the wheels while allowing them to rotate at different speeds (This is the one that earned the differential its name.)

The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed.All-wheel-drive vehicles need a differential between each set of drive wheels, and they need one between the front and the back wheels as well, because the front wheels travel a different distance through a turn than the rear wheels.

Viscous Coupling

The viscous coupling is often found in all-wheel-drive vehicles. It is commonly used to link the back wheels to the front wheels so that when one set of wheels starts to slip, torque will be transferred to the other set.The viscous coupling has two sets of plates inside a sealed housing that is filled with a thick fluid. One set of plates is connected to each output shaft. Under normal conditions, both sets of plates and the viscous fluid spin at the same speed. When one set of wheels tries to spin faster, perhaps because it is slipping, the set of plates corresponding to those wheels spins faster than the other. The viscous fluid, stuck between the plates, tries to catch up with the faster disks, dragging the slower disks along. This transfers more torque to the slower moving wheels — the wheels that are not slipping.

When a car is turning, the difference in speed between the wheels is not as large as when one wheel is slipping. The faster the plates are spinning relative to each other, the more torque the viscous coupling transfers. The coupling does not interfere with turns because the amount of torque transferred during a turn is so small. However, this also highlights a disadvantage of the viscous coupling: No torque transfer will occur until a wheel actually starts slipping.

A simple experiment with an egg will help explain the behavior of the viscous coupling. If you set an egg on the kitchen table, the shell and the yolk are both stationary. If you suddenly spin the egg, the shell will be moving at a faster speed than the yolk for a second, but the yolk will quickly catch up. To prove that the yolk is spinning, once you have the egg spinning quickly stop it and then let go — the egg will start to spin again. In this experiment, we used the friction between the shell and the yolk to apply force to the yolk, speeding it up. When we stopped the shell, that friction — between the still-moving yolk and the shell — applied force to the shell, causing it to speed up. In a viscous coupling, the force is applied between the fluid and the sets of plates in the same way as between the yolk and the shell.

Differentials and Traction

There are two factors that determine how much torque can be applied to the wheels: equipment and traction. In dry conditions, when there is plenty of traction, the amount of torque applied to the wheels is limited by the engine and gearing; in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under those conditions. So, even though a car may be able to produce more torque, there needs to be enough traction to transmit that torque to the ground. If you give the car more gas after the wheels start to slip, the wheels will just spin faster.

On Thin Ice
If you’ve ever driven on ice, you may know of a trick that makes acceleration easier: If you start out in second gear, or even third gear, instead of first, because of the gearing in the transmission you will have less torque available to the wheels. This will make it easier to accelerate without spinning the wheels.

Now what happens if one of the drive wheels has good traction, and the other one is on ice? This is where the problem with open differentials comes in.

Open differentials always apply the same torque to both wheels, and the maximum amount of torque is limited to the greatest amount that will not make the wheels slip. It doesn’t take much torque to make a tire slip on ice. And when the wheel with good traction is only getting the very small amount of torque that can be applied to the wheel with less traction, your car isn’t going to move very much.

Off Road
Another time open differentials might get you into trouble is when you are driving off-road. If you have a four-wheel drive truck, or an SUV, with an open differential on both the front and the back, you could get stuck. Open differentials always apply the same torque to both wheels. If one of the front tires and one of the back tires comes off the ground, they will just spin helplessly in the air, and you won’t be able to move at all.

The solution to these problems is the limited slip differential (LSD), sometimes called positraction. Limited slip differentials use various mechanisms to allow normal differential action when going around turns. When a wheel slips, they allow more torque to be transferred to the non-slipping wheel.

There are three basic automobile drivetrain configurations, and each configuration has its own drive characteristics that set it apart from the others.

FRONT-ENGINE/REAR WHEEL DRIVE: The engine is in the front of the vehicle and drives the rear wheels. Rear-wheel drive vehicles tend to oversteer when the rear wheels lose traction – this means the back end of the vehicle may break free and skid under certain conditions, which may cause a spin. Vehicles with this drivetrain configuration don’t have the advantage of having the engine weight over the drive wheels to improve traction.

FRONT-ENGINE/FRONT WHEEL DRIVE: The engine is in the front of the vehicle and drives the front wheels. Front-wheel drive vehicles tend to understeer. Under certain conditions, the front wheels may lose traction, forcing the vehicle to want to go straight – or “plow” – to the outside of a curve during hard cornering. In general, front-wheel drive vehicles offer better traction than rear-wheel drive vehicles because the weight of the engine and transmission is directly over the drive wheels.

FRONT-ENGINE/ALL-WHEEL DRIVE: The engine is in the front and drives all four wheels. All-wheel drive helps provide more neutral handling, virtually eliminating unwanted oversteer and understeer. This is the configuration in place in the Subaru model line.

Four-Wheel Drive Defined

Four-wheel drive is not the same as all-wheel drive. There are two basic types of four-wheel systems:

“PART-DRIVE” four-wheel drive systems typically route power to the rear wheels. When the driver goes off-road or encounters slippery conditions, the front wheels have to be manually engaged. Only then is the vehicle powered at all four wheels. These systems can only be utilized properly when driving off-road or in slippery conditions and depend on the driver to engage the system.

“FULL-TIME” four-wheel drive powers all four wheels all of the time. The amount of power is evenly divided among all four wheels.

Subaru All Wheel Drive

The symmetrical All-Wheel Drive (AWD) characteristic, unique to Subaru vehicles, maximises road traction, thus improving control. The transfer of power from the wheels that slip to the wheels that grip provides fundamental driving superiority, particularly in active safety, when compared to two-wheel or 4×4 vehicles.

The AWD in conjunction with the compact, Horizontally Opposed, lightweight Boxer™ engine, which has a low centre of gravity, operates through a perfectly symmetrical drivetrain – a combination that ensures superb balance and handling capabilities.

Many people believe that 4×4 is essentially the preserve of large ‘jeep’ shaped vehicles, even giving them the generic title of ‘four wheel drives’. This is not so with Subaru providing a full-time drive to all wheels in passenger vehicles providing a level of inherent safety, economy, and reassurance not experienced in the larger truck-like 4x4s.

Full-time symmetrical All-Wheel Drive is a standard feature on all Subaru vehicles, and not just an added extra as is the case with some manufacturers. It is important to realise that All-Wheel Drive is not a ‘fad’ or a clever marketing initiative designed to sell cars in greater numbers. It provides a genuine contribution to road safety and will continue to be an integral part of a Subaru vehicle’s make-up. AWD, pioneered by Subaru in 1972, has also been adopted by some luxury vehicle manufacturers such as Volvo, Jaguar and BMW as an add on, and has even been incorporated into the technology of the Formula One racing cars.

The key benefit of All-Wheel Drive is greater traction.
Traction is the force that keeps tyres in stable contact with the road surface during take-off, acceleration, hill climbing, turning and braking. The better a car’s traction, the safer it is. Safe running depends on constant stable traction and traction stability is largely determined by the car’s drive method.

Distributing power to each of the four wheels, All-Wheel Drive achieves much better traction than either of the two-wheel drive methods (Front or Rear Wheel Drive). To understand the reasons for this you have to realise that car tyres lose traction and slip when the maximum value of the frictional force between the tyres and road surface is exceeded.

An AWD vehicle distributes motive power to all four wheels equally, which means the traction limit is approximately twice that of a two-wheel drive.  In the case of a 100kW-engine output to a two-wheel drive, 50kWs would be delivered to each wheel.  But if each wheel only has 30kW traction, 20kWs on each wheel is wasted and normally results in spinning.

With AWD the 100kW will be distributed to four wheels, assuming the weight distribution is symmetrical, resulting in 25kW per wheel … 5kWs below the tyre’s threshold of 30kW.  The result is that the vehicle utilises its maximum power and moves away faster without wheel spin while in full control.

All-Wheel Drive benefits

• Superior safety
• Superior handling
• Superior comfort
• Low centre of gravity
• Better torque distribution
• Lower fuel consumption
• Permanent AWD
• Lower insurance premiums

4x4s are generally cumbersome, heavy, truck-like vehicles with high fuel consumption and a high centre of gravity that can affect handling and safety.  They have longer stopping distances due to sheer weight.  Smaller 4x4s offer few creature comforts and compromise ride quality on normal roads.

Competing manufacturers incorporating AWD are at a disadvantage when compared to the advanced technology developed by pioneers Fuji Heavy Industries of Japan.  The Horizontally-Opposed Boxer™ engines in Subarus allow a low centre of gravity and a perfectly symmetrical drivetrain that delivers better handling and a smooth, comfortable ride.

Most engines adapted to AWD result in off-centre configurations and imbalances that cause vibrations.  Additional mechanisms to compensate add to vehicle and running costs.

Boxer engines got their name because each pair of pistons moves simultaneously in and out rather than alternately, like boxers showing they’re ready by clashing their gloved fists against each other before a fight.

A boxer, or flat engine, is an internal combustion engine with pistons that are all relatively horizontal. A straight engine canted 90 degrees from straight up is a flat engine, as is one in which the cylinders are arranged in two banks on either side of a single crankshaft. In both configurations, the motion of all the pistons is in the horizontal plane.
Usually, each pair of corresponding pistons from each bank of cylinders share one crank pin on the crankshaft, either by master/slave rods or by two ordinary rods side by side. Some authorities divide flat engines into boxer engines which do not share crank pins in this way, and 180° engines which do.
The boxer engine (also known as a horizontally opposed cylinder engine) in which the corresponding pistons reach top dead centeropposed piston engines, which use a completely different concept. simultaneously.

Flat engines are shorter than in-line engines, and have a lower center of gravity than any other common configuration, giving better stability and control. These engines, however, are also wider than more traditional configurations and are more expensive to build. The extra width may cause problems fitting the engine into the engine bay of a front-engined car owing to the interference with the steering wheels.

One benefit of using a boxer engine versus a V-engine is that the design provides good balance because each piston’s momentum is counterbalanced by the corresponding piston movement of the opposite side.

These engines can run very smoothly and free of unbalanced forces with a four-stroke cycle and do not require a balance shaft or counterweights on the crankshaft to balance the weight of the reciprocating parts, which are required in other engine configurations. Note that this is generally true of boxer engines regardless of the number of cylinders, but not true for all V and straight, or inline engines. However, in the case of boxer engines with fewer than six cylinders, unbalanced moments are unavoidable due to the “opposite” cylinders being not exactly opposite but offset slightly.

Boxer engines tend to produce more noise than inline and V-engines because valve clatter is not so well dampened due to lack of covering by air-filters and other components, and produce a larger torsional vibration than a V-engine, and so tend to require a larger flywheel. They have a characteristic smoothness throughout the rev range and, combined with the mounting position immediately ahead of the rear axle, offer a low center of gravity and more neutral handling.

This is one of those posts where you know that so many will not understand what is being said. My disclaimer to those who view this post as racist: educate yourself on racism, read some books on the subject, I will be happy to recommend some just email me here, open your mind to the idea that you may not understand the many forms of racism, I am not a racist, and I do not tolerate racist ideology.

There are so many Americans that just do not get it. This t-shirt illustrates the fact that so many do not get it. It is unfortunate that a lot of these Obama t-shirts do not have anything to do with our United States, the presidency, or democracy in any way. Is this a display of ignorant black Americans worshiping a man? I certainly hope not, we are in great need in this country now, eight years of a failed presidency, men and women dying for years overseas at war, high unemployment, declining economy, Americans loosing their homes, just to mention a few, not a lot of room to relish in a “not-so-black” man being elected. Barak Obama will be our 44th president, and likely a very good one. It is my hope that Obama helps many black americans in this country get over their race, and the idea that many of the mentioned blacks consider themselves “African-American”. My ancestors immigrated to the United States from Ireland, Scotland, and England, as many other peoples did. I do not refer to myself as Irish-American, or English-American, because I am not, I am American. I have been to Ireland, Scotland, and England, and I am proud of my families heritage. I appreciate the hardships my ancestors  and the determination to leave their countries and ultimately provide a better life for me,  but I know no more of being Irish or English than a hole in the ground. Suffice to say that most black Americans have never been to Africa, nor do they have any clue as to what life is like there any more than an understanding of what it is like to be a slave. If most black Americans went to Africa they would likely not know what to do with themselves after taking in the beauty, and would cherish more their home country, the United States.

It seems that many black Americans need to change the perception they have of their own race. Stop referring to oneself as “African-American”, instead be proud to be an American, because in truth that is what one is. We are all Americans who were born and live in the United States, there is nothing wrong with claiming it, and in fact is a more accurate description of who you are! Don’t believe me? Go to Italy, France, or China and ask some stranger from that country where they think you are from.

“Brotherhood” is another racial divide. Enough with brotherhood already. Many black Americans, will blatantly refer to one another as “brother”, but not refer to another person of a different race as “brother”. This is a display of racism in a true form, and shows a weakness in personal character to attain a false sense of belonging. Do you want to be a “brother”? Go volunteer at the local United Way or Boys and Girls Club and be a true brother or sister to a child of any race in need of a stable, mature figure in their life. This “brotherhood” thing is very selfish, short sighted. To crown thy good with brotherhood, from sea to shining sea, was a phrase intended to encompass a people, not a race.

I do hope Obama can lead the many black Americans in this country who “need” so badly a figure like him. Again, Obama is not even “black”, funny that so many black Americans feel such liberation, I suppose if separation from man is needed the people who should feel true liberation are children from racially mixed parents. Many black Americans are their own hinderance in this society, and perpetuate racism. Obama bringing these types of people to an understanding that he does not stand for “black” or “white” could be this countries greatest gift from him. The real question is this: are these types of people ready to accept his gift? God bless America.

IRAM: Not sure exactly what this test does. It takes several moments to load before running a quick test and rebooting your iPod.

FLASH: This test will do a checksum test of your iPod’s flash memory.

: This option has two tests, Backlight (0 to 255; 128 is the default) and Color. Much like a VRAM test, the Color test will run through a series of colors, patterns and gradients.

HeadphoneDetect: This test checks the Hold Switch and Headphone port.

HardDrive: This option has four tests.

• HDSpecs will tell you everything from hard drive temperature to serial number.
• HDScan scans your iPod’s hard drive. This is a great way to see if you have a healthy iPod and if your hard drive is fragmented. This test will take a few minutes so be patient.
• HDSMARTData returns SMART data for professional repair applications and personnel.
• HDRW tests the ability of your hard drive to RW (read and write data). A FAIL result probably means you need to get your hard drive replaced.

Audio: This option has two tests. Playback plays an audio sample to make sure your iPod can produce sound. MIC tests your iPods ability to record audio.

• PhilipsID checks the power system of your iPod
• A2D lists a series of A2D (analog to digital) tests.

• Sharp: LCD screen
• HP: headphones. Are they connected? [0 = no, 1 = yes]
• FWPWR: FireWire power. Is your FireWire cable charging your iPod?
• USBPWR: USB power. Is your USB cable charging your iPod?

IP Address (Internet Protocol Address): This number is an exclusive number all information technology devices (printers, routers, modems, et al) use which identifies and allows them the ability to communicate with each other on a computer network. There is a standard of communication which is called an Internet Protocol standard (IP). In laymans terms it is the same as your home address. In order for you to receive snail mail at home the sending party must have your correct mailing address (IP address) in your town (network) or you do not receive bills, pizza coupons or your tax refund. The same is true for all equipment on the internet. Without this specific address, information cannot be received. IP addresses may either be assigned permanently for an Email server/Business server or a permanent home resident or temporarily, from a pool of available addresses (first come first serve) from your Internet Service Provider. A permanent number may not be available in all areas and may cost extra so be sure to ask your ISP.

Domain Name Server (DNS): This allows the IP address to be translated to words. It is much easier for us to remember a word than a series of numbers. The same is true for email addresses.

For example, it is much easier for you to remember a web address name such as whatismyip.com than it is to remember 192.168.1.1 or in the case of email it is much easier to remember anonymous@whatismyip.com than anonymous@192.168.1.1

Dynamic IP Address: An IP address that is not static and could change at any time. This IP address is issued to you from a pool of IP addresses allocated by your ISP or DHCP Server. This is for a large number of customers that do not require the same IP Address all the time for a variety of reasons. Your computer will automatically get this number as it logs on to the network and saves you the trouble of having to know details regarding the specific network configurations. This number can be assigned to anyone using a dial-up connection, Wireless and High Speed Internet connections. If you need to run your own email server or web server, it would be best to have a static IP.

Static IP Address: An IP address that is fixed and never changes. This is in contrast to a dynamic IP address which may change at any time. Most ISP’s a single static IP or a block of static IP’s for a few extra bucks a month.

IP version 4: Currently used by most network devices. However, with more and more computers accessing the internet, IPv4 addresses are running out quickly. Just like in a city, addresses have to be created for new neighborhoods but, if your neighborhood gets too large, you will have to come up with an entire new pool of addresses. IPv4 is limited to 4,294,967,296 addresses.

IP version 5: This is an experimental protocol for UNIX based systems. In keeping with standard UNIX (a computer Operating System) release conventions, all odd-numbered versions are considered experimental. It was never intended to be used by the general public.

IP version 6: The replacement for the aging IPv4. The estimated number of unique addresses for IPv6 is 340,282,366,920,938,463,463,374,607,431,768,211,456 or 2^128.

The old and current standard of addresses was this: 192.168.100.100 the new way can be written different ways but means the same and are all valid:

* 1080:0000:0000:0000:0000:0034:0000:417A

* 1080:0:0:0:0:34:0:417A

* 1080::34:0:417A

Helpful commands:

Display Connection Configuration: ipconfig /all

Display DNS Cache Info Configuration: ipconfig /displaydns

Clear DNS Cache: ipconfig /flushdns

Release All IP Address Connections: ipconfig /release

Renew All IP Address Connections: ipconfig /renew

Re-Register the DNS connections: ipconfig /registerdns

Change/Modify DHCP Class ID: ipconfig /setclassid

Network Connections: control netconnections

Network Setup Wizard: netsetup.cpl

Test Connectivity: ping www.whatismyip.com

Trace IP address Route: tracert

Displays the TCP/IP protocol sessions: netstat

Display Local Route: route

Display Resolved MAC Addresses: arp

Display Name of Computer Currently on: hostname

Display DHCP Class Information: ipconfig /showclassid

“Fortunately, all iPod displays already use LEDs for illumination, and therefore contain no mercury,” wrote Jobs. “We plan to introduce our first Macs with LED backlight technology in 2007. Our ability to completely eliminate fluorescent lamps in all of our displays depends on how fast the LCD industry can transition to LED backlighting for larger displays.”

Enter: OLED

The first light-emitting polymer device involved a single layer of poly. Multilayer OLEDs can have more than two layers to improve device efficiency. As well as conductive properties, layers may be chosen to aid charge injection at electrodes by providing a more gradual electronic profile, or block a charge from reaching the opposite electrode and being wasted.

A voltage is applied across the OLED such that the anode is positive with respect to the cathode. This causes a current of electrons to flow through the device from cathode to anode. Thus, the cathode gives electrons to the emissive layer and the anode withdraws electrons from the conductive layer; in other words, the anode gives electron holes to the conductive layer.

Soon, the emissive layer becomes negatively charged, while the conductive layer becomes rich in positively charged holes. Electrostatic forces bring the electrons and the holes towards each other and they recombine. This happens closer to the emissive layer, because in organic semiconductors holes are more mobile than electrons (unlike in inorganic semiconductors). The recombination causes a drop in the energy levels of electrons, accompanied by an emission of radiation whose frequency is in the viable region. That is why this layer is called emissive.

Just like passive-matrix LCD versus active-matrix LCD, OLEDs can be categorized into passive-matrix and active-matrix displays. Active-matrix OLEDs (AMOLED) can make higher resolution and larger size displays possible. For a high resolution display like a TV, a TFT backplane is necessary to drive the pixels correctly.

OLEDs enable a greater range of colors, brightness, and viewing angle than LCDs, because OLED pixels directly emit light. OLED pixel colors appear correct and unshifted, even as the viewing angle approaches 90 degrees from normal. LCDs use a backlight and cannot show true black, while an “off” OLED element produces no light and consumes no power. Energy is also wasted in LCDs because they require polarizers which filter out about half of the light emitted by the backlight. Additionally, color filters in color LCDs filter out two-thirds of the light.

OLEDs also have a faster response time than standard LCD screens. Whereas a standard LCD currently has an average of 4-8 millisecond response time, an OLED can have less than 0.01ms response time. 

The biggest technical problem for OLEDs is the limited lifetime of the organic materials. In particular, blue OLEDs historically have had a lifetime of around 14,000 hours (5 years at 8 hours a day) when used for flat-panel displays, which is lower than typical lifetime of LCD, LED or PDP technology—each currently rated for about 60,000 hours, depending on manufacturer and model. Toshiba and Panasonic have come up with a way to solve this problem with a new technology that can double the lifespan of OLED displays, pushing its expected life past that of LCD displays. A metal membrane helps deliver light from polymers in the substrate throughout the glass surface more efficiently than current OLED’s. The result is the same picture quality with half the brightness and a doubling of the screens expected life.

In 2007, experimental PLEDs were created which can sustain 400 cd/m² of luminance for over 198,000 hours for green OLEDs and 62,000 hours for blue OLEDs.

The intrusion of water into displays can damage or destroy the organic materials. Therefore, improved sealing processes are important for practical manufacturing and may limit the longevity of more flexible displays.

• George Washington began commercial distilling in 1797 at the urging of his Scottish farm manager, James Anderson, who had experience distilling grain in Scotland and Virginia. He successfully petitioned George Washington that Mount Vernon’s crops, combined with the large merchant gristmill and the abundant water supply, would make the distillery a profitable venture. 
• In February 1797, the cooperage at the mill was converted for distilling and two stills began operating.
• By the following summer, the makeshift distillery was so successful that Anderson lobbied George Washington to increase the number of stills. 
• Construction began in October of 1797 of a stone still house large enough for five stills. The foundation was large river rocks brought from the Falls of the Potomac and the walls of the distillery were made of sandstone quarried from Mount Vernon. 
• Anderson’s son, John, managed the production assisted by six enslaved African-Americans named Hanson, Peter, Nat, Daniel, James, and Timothy. The enlarged distillery was working by the spring of 1798. 
• That George Washington was willing to commit to distilling by building such a large structure is evidence of his desire to pursue the most innovative and creative farming practices of the day. Despite having no prior experience in distilling, he quickly became acquainted with the process. 
• The finished product was contained in barrels manufactured at the site and marketed to local farmers in Alexandria, and supplied the needs of the Mount Vernon plantation as well. The distillery produced a great quantity of waste and this slop was fed to over 150 hogs and cattle penned at the site.
• George Washington’s death in 1799 halted the brief success of the distillery and within a decade the building fell into disrepair and many of the stones were taken away to use in local construction projects. 
• In George Washington’s will the Gristmill, distillery and all associated buildings are left to Lawrence and Eleanor Parke Custis Lewis (Washington’s step-granddaughter and her husband). 
• In 1932, the property was purchased by the Commonwealth of Virginia. The Gristmill and miller’s cottage were reconstructed and the distillery outlined. Both were opened as a state park. 
• 1995 – The Mount Vernon Ladies’ Association enters agreement to restore the mill and research the property.
• 1997 – An archaeological survey of the area uncovered the “footprint” of the distillery, revealing an unusually large structure and a well-preserved site. 
• 1999 – Mount Vernon began an archaeological and documentary research program to find out as much historical data about the building as possible. 
• 2001 – The Distilled Spirits Council of the United States (DISCUS) provided a generous donation that allowed Mount Vernon to begin a five-year program of archaeological and documentary research, with the goal of reconstructing and interpreting George Washington’s distillery. 
• 2002 – Restoration completed at George Washington’s Gristmill and the site is dedicated April 12. Archaeology work continues at the distillery. 
• 2003 – Investigation continues as archaeologists dig down to the eighteenth-century construction layer.

In general traceroute and ping have the lowest priority of all packets. E-mail, web browsing, ftp, etc. data take precedence over traceroute data.

For example if a router is passing secure web data to a customer and another customer starts to ping that router. The router will put a ‘hold’ on the ping packets until it is ready. Because of situations like this, most traceroute programs send 3 different requests. Since one of the requests may be put on ‘hold’ due to higher priority data being sent, the program tests the path 3 times.

Over the past several years network devices have been electronically attacked via the use of ICMP. These attacks have proved to be very effective in the past, and in some situations they still are. Network device (routers, switches, etc) vendors have taken steps to lessen the impact of these attacks destined to their devices. They have done this by limiting the number of ping and traceroute messages received/processed per unit of time. In any given service providing network, multiple devices send/receive ping and traceroute messages on a perpetual basis. Add to this, the number of user/gamer/student/entrepreneurs who continuously run traceroute programs like ping plotter, and the ping and traceroute limits to the devices will be reached very quickly.

How to read traceroute data:

Let us do a traceroute to a site we know responds to ICMP packets.

Tracing route to cnn.com [64.236.16.20] over a maximum of 30 hops:

1 57 ms 28 ms 50 ms ip68-100-1-97.dc.dc.cox.net

2 341 ms 74 ms 156 ms ip68-100-0-1.dc.dc.cox.net [68.100.0.1]

3 28 ms 207 ms 52 ms mrfddsrj01gex070004.rd.dc.cox.net

4 * ms 274 ms 235 ms mrfdbbrj01-ge020.rd.dc.cox.net

5 73 ms 12 ms 84 ms mrfdbbrj02-ge030.rd.dc.cox.net

6 107 ms 38 ms 47 ms ashbbrj02-so000.r2.as.cox.net

7 35 ms 39 ms 54 ms ashbbbrj01-ae0.0.r2.as.cox.net

8 100 ms 38 ms 51 ms pop1-ash-S0-3-2.atdn.net

9 65 ms 40 ms 20 ms bb1-ash-P0-0.atdn.net [66.185.144.192]

10 40 ms 37 ms 51 ms bb2-vie-P11-0.atdn.net [66.185.152.101]

11 36 ms 35 ms 64 ms bb2-atm-P3-0.atdn.net [66.185.152.33]

12 51 ms 70 ms 45 ms bb2 [66.185.152.3]

Looking at this traceroute, one can see that roundtrip times to the site are very good (12 51 ms 70 ms 45

ms bb2 [66.185.152.3]) However looking at #4, one may determine that there is a problem at that device when there is not. When an actual problem occurs with a device that causes latency, that latency is carried on through the other hops.

If the router at #4 was causing latency to the connection at www.cnn.com, one would see increasing times at hop #5, #6, #7 and so on. Since all packets have to traverse the router at #4, any latency created by that device would carry on to the end of the traceroute.

Vendors sometimes limit the amount of ICMP packets that their equipment will respond to. This can produce confusing results. When reading a traceroute, look for latency (high return times) to carry though to the final destination.

Here is an example of a traceroute when there is a problem inside a network:

1 31 ms 27 ms 28 ms core1-loopback-0.Brisbane.netspace.net.au [203.17.101.6]

2 33 ms 30 ms 28 ms AS7496.brisbane.pipenetworks.com [218.100.0.20]

3 228 ms 329 ms 228 ms fa1-0-6.xr2.wic.server-web.com [203.147.255.118]

4 215 ms 232 ms 228 ms gi2-0.xr2.bne.server-web.com [203.147.255.237]

5 233 ms 229 ms 233 ms core.mls1.bne.server-web.com [203.147.255.246]

6 232 ms 232 ms 233 ms bne606d.server-web.com [202.139.232.71]

As one can see, between hop #2 and #3, the time jumps from 33 ms to 228 ms and the latency continues through to its final destination at #6.