Flip-Flop

To prevent any possibility of a "race" condition occurring when both the S and R inputs are at logic 1 when the CLK input falls from logic 1 to logic 0, we must somehow prevent one of those inputs from having an effect on the master latch in the circuit. At the same time, we still want the flip-flop to be able to change state on each falling edge of the CLK input, if the input logic signals call for this. Therefore, the S or R input to be disabled depends on the current state of the slave latch outputs.

If the Q output is a logic 1 (the flip-flop is in the "Set" state), the S input can't make it any more set than it already is. Therefore, we can disable the S input without disabling the flip-flop under these conditions. In the same way, if the Q output is logic 0 (the flip-flop is Reset), the R input can be disabled without causing any harm. If we can accomplish this without too much trouble, we will have solved the problem of the "race" condition.

The circuit below shows the solution. To the RS flip-flop we have added two new connections from the Q and Q' outputs back to the original input gates. Remember that a NAND gate may have any number of inputs, so this causes no trouble. To show that we have done this, we change the designations of the logic inputs and of the flip-flop itself. The inputs are now designated J (instead of S) and K (instead of R). The entire circuit is known as a JK flip-flop.

In most ways, the JK flip-flop behaves just like the RS flip-flop. The Q and Q' outputs will only change state on the falling edge of the CLK signal, and the J and K inputs will control the future output state pretty much as before. However, there are some important differences.

Since one of the two logic inputs is always disabled according to the output state of the overall flip-flop, the master latch cannot change state back and forth while the CLK input is at logic 1. Instead, the enabled input can change the state of the master latch once, after which this latch will not change again. This was not true of the RS flip-flop.

If both the J and K inputs are held at logic 1 and the CLK signal continues to change, the Q and Q' outputs will simply change state with each falling edge of the CLK signal. (The master latch circuit will change state with each rising edge of CLK.) We can use this characteristic to advantage in a number of ways. A flip-flop built specifically to operate this way is typically designated as a T (for Toggle) flip-flop. The lone T input is in fact the CLK input for other types of flip-flops.
The JK flip-flop must be edge triggered in this manner. Any level-triggered JK latch circuit will oscillate rapidly if all three inputs are held at logic 1. This is not very useful. For the same reason, the T flip-flop must also be edge triggered. For both types, this is the only way to ensure that the flip-flop will change state only once on any given clock pulse.

Because the behavior of the JK flip-flop is completely predictable under all conditions, this is the preferred type of flip-flop for most logic circuit designs. The RS flip-flop is only used in applications where it can be guaranteed that both R and S cannot be logic 1 at the same time.

At the same time, there are some additional useful configurations of both latches and flip-flops. In the next pages, we will look first at the major configurations and note their properties. Then we will see how multiple flip-flops or latches can be combined to perform useful functions and operations

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INTEGRATED CIRCUIT SYSTEM

ICS9FG107
7-Output PCI-Express, 3 PCI 33MHz Clock Generator from 14.318MHz or 25MHz XTAL
Features

•Generates common CPU/PCI Express frequencies from 14.318 MHz or 25 MHz
•Crystal or reference input
•7 - 0.7V current-mode differential output pairs
•3 - 33MHz PCI outputs
•1 - REFOUT
•Supports Serial-ATA at 100 MHz
•Two spread spectrum modes: 0 to -0.5 downspread and +/-0.25% centerspread
•Unused inputs may be disabled in either driven or Hi-Z state for power management.

Description

ICS9FG107 is a Frequency Timing Generator that provides 7 differential output pairs that are compliant to the Intel CK409/ CK410 specification. It provides support for PCI-Express, next generation I/O, and SATA. The part synthesizes several output frequencies from either a 14.31818 Mhz crystal or a 25 MHz crystal. The device can also be driven by a reference input clock instead of a crystal. It provides outputs with cycle-to-cycle jitter of less than 85 ps and output-to-output skew of less than 85 ps. ICS9FG107 also provides a copy of the reference clock and 3 33 MHz PCI output clocks. Frequency selection can be accomplished via strap pins or SMBus control.

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Texas Instruments' First Integrated Circuits

1958: Invention of the Integrated Circuit
As with many inventions, two people had the idea for an integrated circuit at almost the same time. Transistors had become commonplace in everything from radios to phones to computers, and now manufacturers wanted something even better. Sure, transistors were smaller than vacuum tubes, but for some of the newest electronics, they weren't small enough.

But there was a limit on how small you could make each transistor, since after it was made it had to be connected to wires and other electronics. The transistors were already at the limit of what steady hands and tiny tweezers could handle. So, scientists wanted to make a whole circuit -- the transistors, the wires, everything else they needed -- in a single blow. If they could create a miniature circuit in just one step, all the parts could be made much smaller.

One day in late July, Jack Kilby was sitting alone at Texas Instruments. He had been hired only a couple of months earlier and so he wasn't able to take vacation time when practically everyone else did. The halls were deserted, and he had lots of time to think. It suddenly occurred to him that all parts of a circuit, not just the transistor, could be made out of silicon. At the time, nobody was making capacitors or resistors out of semiconductors. If it could be done then the entire circuit could be built out of a single crystal -- making it smaller and much easier to produce. Kilby's boss liked the idea, and told him to get to work. By September 12, Kilby had built a working model, and on February 6, Texas Instruments filed a patent. Their first "Solid Circuit" the size of a pencil point, was shown off for the first time in March.

But over in California, another man had similar ideas. In January of 1959, Robert Noyce was working at the small Fairchild Semiconductor startup company. He also realized a whole circuit could be made on a single chip. While Kilby had hammered out the details of making individual components, Noyce thought of a much better way to connect the parts. That spring, Fairchild began a push to build what they called "unitary circuits" and they also applied for a patent on the idea. Knowing that TI had already filed a patent on something similar, Fairchild wrote out a highly detailed application, hoping that it wouldn't infringe on TI 's similar device.

All that detail paid off. On April 25, 1961, the patent office awarded the first patent for an integrated circuit to Robert Noyce while Kilby's application was still being analyzed. Today, both men are acknowledged as having independently conceived of the idea.

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SECAPA AS SPECIAL EDUCATION CENTER OF THE POLICE OF REPUBLIC OF INDONESIA

To urban community and sub-province of Sukabumi have tolerated it, that from since era governance of first president of Soekarno-Hatta, town of Sukabumi this is recognized by there is its place / special school of educationor “penggodokan” all Police enlisted man cadre. Former with the title that police of output of PTIK Sukabumi Before altered to become Secapa ( era governance of belanda " Policie Shcooll").

Special it is of course to urban community citizen of sukabumi, feel proud Academic having / School education of State security government officer of R.I (state police). Popularity of town of sukabumi become " bogey" to metropoliss of diseantero Unity state of R.I this beloved. This matter of other State government officer goodness, and also and especially for all overall itself police government officer.

As real evidence from all police cadres, what have followed maximal and tight “penggodogan” and have passed better. Where they have many tired police government officer of efficacy top and success. They have acted loyal may of devotion to nation society and State of R.I (as according to doctrine of tribrata). Where police member have to ready to place forward service all kind of requirement of society specially security. Hence as according to motto and theme and also police mission and mission, is as “pengayom” of “mengayomi”, service and protector of society, according to also with applicable laws in Indonesia.

But on the otherhand all us realize also, still many all things of insuffiency, weakness both for felt by police institution and also to public society. It is of course this matter is meant by us as ordinary human being and no super human being, it is of course there is limitation of abilitys. Of insuffiency facet, weakness this is us of LSM formation of jawa west of will wishful and good submit suggestion, proposal and opinion which is positive it is of course. This such urge of summery in information ambit and direct aspiration of its source, that is urban community citizen of sukabumi this. After our party/ side of Formation LSM do/conduct monitoring and observation by “silaturahmi”, “anjang sono”, door to door and of man man to, good of society circle / citizen have level to under, middle and also especially chief of RT-RT, RW-RW, and chief of villages of se 7 district of town of sukabumi. Hence is clear is we have earned to accomodate all aspiration and informations. One of the example of of Yani society citizen have highlighted peculiarly to existence all cadres of secapa police, according to them there is no him felt and seen open in general. Especially from all police cadres of propagating / real action and become impressions felt direct by urban community citizen of sukabumi this.

From the mentioned, which/such of execution " Devote special police social from all that cadres ?", more over of is project of that by kontinue to importance of urban community citizen of sukabumi. For example devoting police social (that kader) is majored to be given decent to all orphan pass/through institution which managing in town of sukabumi. To people of jompo, continue age , lessening unemployment which there are in town of sukabumi where them still stand in need of helping. Hopefully with that way will happened a[n good relation/link between police secapa of sukabumi with urban community of sukabumi.

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Titanium dioxide to degrade pentachlorophenol

Pentachlorophenol is a phenolic compound that was chlorinated. Pentachlorophenol very toxic for our breath, cause dermatitis on skin and more toxic than inorganic solvent.

Pentachlorophenol waste almost dissolvable in water so degradation process is very hard. Some ways have been done to solve biological waste problem, but not efficient enough. For example, active carbon just involve pollutant absorption without decomposition process. Chemical oxidation process can’t decomposition all of organic compound be carbon dioxide and water, and have been used in high concentration waste.

Many century ago, scientist success to describe phenomenon photocatalytic in surface of metal-oxide semiconductor. Firstly, have been issued by Renz in 1921 until 1960, and not responding by scientist. Photocatalytic semiconductor popularity increase since publication Akira Fujishima in Nature magazine was issued in 1972. He was reported decomposition water be oxygen and hydrogen used single crystal TiO2 with input UV light in low energy.

First research, TiO2 have been used as photocatalytic suspension system. Nowadays, the uses TiO2 as photocatalytic is used in thin plate shape, which is immobilization TiO2 to many kinds of supported material like fiber, glass, silica, and titanium plat.

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how to make our body more health and energizer?

This several exercises and meditation help to improve your health, more energizer, more focus and more happy, fell free to do it everyday

Stand erect barefooted, relax your fingers, exhale gently, then bow forward with feet straight, touch your toes with your fingers, maintain this for a few seconds. Then inhale while returning to the standing position with arms raised as high as you can, continue your move until your body is bent backward. Then exhale while returning your fingers to your toes. Maintain this for a few seconds, inhale, and so on .... repeat seven (7) times

Relax your head, neck and shoulder muscles. Slowly rotate your head 360⁰ clockwise while inhaling. Hold your breath for a while, again rotate your head clockwise while exhaling. Repeat twice. Do the whole process but move your head counterclockwise, three times.

Stand straight, arms raised and outstretched to your sides. Rotate your body clockwise 360⁰ with eyes stay open while inhaling. When returning to your starting position, hold your breath, focus your sight forward, then repeat the rotation while exhaling. Do this five times, then repeat the whole process counterclockwise five times.

Stand straight, arms raised and outstretched to your sides. Inhale, hold, then exhale while moving your body so that your right hand is touching your left foot. Hold this position for a while, then return to your starting (standing) position while inhaling, hold, then exhale while moving your body so that your left hand is touching your right foot. Do this seven cycles.

Sit on the floor and cross your legs, spine erect, palms on your lap facing down humbs touching forefingers, eyes closed. breath naturally through your noseThen inhale for five counts, hold for five counts and exhale also for five counts. Then breath normally for a while before repeating the inhale, hold, exhale cycle. Do 25 cycles.

lay on the floor, spine erect, palms on your lap facing down, eyes closed. breath naturally through your nose, attention to the breath, do about 5 minutes

Do meditation, and visualize you are on forest complete with trees, animals and rivers etc, do about 10 minutes

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Homebrew Simple srong 2,4GHz

Antenna on the Cheap (er, Chip)

Like many would-be 802.11b hackers, I'm increasingly obsessed with pushing more bits further and faster for less cost (I believe the unofficial goal of our community wireless project is to provide infinite bandwidth everywhere for free. Of course, there are problems with approaching infinity, but it's still fun to try!)

The work that Andrew Clapp and others have done is helping to demystify the ancient black magick of Resonance (i.e. antenna building). And so, over last weekend, some friends and I decided to give it a go for ourselves.

(standard disclaimer): Anything you do with your gear is YOUR RESPONSIBILITY. This is a stupid idea that will probably ruin your radio, set your house on fire, bring the FCC to your door, ruin your crops, and send famine and pestilence across the land. And as the operator, it is YOUR RESPONSIBILITY to not take the word of some raving lunatic on the web with funny colored hair, and find things out for yourself. Your mileage will vary. I'm probably lying. You have been warned.

Anyway, our first run was a direct rip-off of Andrew Clapp's terrific original design (knowing next to nothing about antenna construction, it's helpful to start off with a working known good.) By using PVC, all-thread, washers, some cheap copper tubing, a Pringles can, and some scrap cardboard, we were able to make a prototype shotgun yagi in a matter of hours. Having a couple of other excited alpha geeks around can help move construction projects along very quickly.

Once this was up and running, we looked at the design, and of course speculated about ways to optimize it. While a directional antenna showing between 12 and 15db gain is impressive, it's also pretty large, physically. We realized that, if we were careful, we could fit a full wavelength inside the Pringles can itself (at a reduced total gain), but make the entire antenna much more compact.

In about 45 minutes, we had the collector rod built, the locknuts on, and the whole thing in place. The result: A Pringles can that pulls about 12db!

Parts list:

All-thread, 5 5/8" long, 1/8" OD	$1.00
two nylon lock nuts	$0.10
five 1" washers, 1/8" ID	$0.10
6" aluminum tubing, 1/4" ID	$0.75
A connector to match your radio pigtail (we used a female N connector)	$3.00
1 1/2" piece of 12 gauge solid copper wire (we used ground wire from house electrical wiring)	$0.00
A tall Pringles can (any flavor, Ridges are optional.)	$1.50
Scrap plastic disc, 3" across (like another Pringles can lid)	$0.00
Total:	$6.45

Of course, buying in bulk helps alot. You probably won't be able to find a 6" piece of all-thread; buy the standard size (usually one or two feet) and a 10-pack of washers and nuts while you're at it. Then, you'll have enough for two, for about $10.

Tools required:

Ruler
Scissors
Pipe cutter (or hacksaw or dremel tool, in a pinch)
Heavy duty cutters (or dremel again, to cut the all-thread)
Something sharp to pierce the plastic (like an awl or a drill bit)
Hot glue gun
Soldering Iron

Construction time: about an hour

Front collector construction:

Mark and cut four pieces of tubing, about 1.2" (1 15/64"). Where did I get this number? First figure out the wavelength at the bottom of the frequency range we're using (2.412 GHz, or channel 1). This will be the longest that the pipe should be:

  W = 3.0 * 10^8 * (1 / 2.412) * 10^-9
W = (3.0 / 2.412) * 10^-1
W = 0.124 Meters
W = 4.88 inches 

We'll be cutting the pipe to quarter wavelength, so:

  1/4 W = 4.88 / 4
1/4 W = 1.22" 

Now figure out what the shortest we'll ever use is (2.462 Ghz, or channel 11 in the US):

  W = 3.0 * 10^8 * (1 / 2.462) * 10^-9
W = (3.0 / 2.462) * 10^-1
W = 0.122 Meters
W = 4.80 inches
1/4 W = 1.20" 

Practically speaking, what's the difference between the shortest pipe and the longest pipe length? about 0.02", or less than 1/32". That's probably about the size of the pipe cutter blade you're using. So, just shoot for 1.2", and you'll get it close enough.

Cut the all-thread to exactly 5 5/8". The washers we used are about 1/16" thick, so that should leave just enough room for the pipe, washers, and nuts.

Pierce a hole in the center of the Pringles can lid big enough for the all-thread to pass through. Now is probably a good time to start eating Pringles (we found it better for all concerned to just toss the things; Salt & Vinegar Pringles get to be almost caustic after the first fifteen or so.)

Cut a 3" plastic disc, just big enough to fit snugly inside the can. We found another Pringles lid, with the outer ridge trimmed off, to be ideal. Poke a hole in the center of it, and slip it over one of the lengths of pipe.

Now, assemble the pipe. You might have to use a file or dremel tool to shave the tips of the thread, if you have trouble getting the nuts on. The pipe is a sandwich that goes on the all-thread like this:

Nut Lid Washer Pipe Washer Pipe Washer Pipe-with-Plastic Washer Pipe Washer Nut

Tighten down the nuts to be snug, but don't overtighten (I bent the tubing on our first try; aluminum bends VERY easily.) Just get it snug. Congratulations, you now you have the front collector.

Now for the can:

By now you should have eaten (or tossed) the actual chips. Wipe out the can, and measure 3 3/8" up from the bottom of the can. Cut a hole just big enough for the connector to pass through. We found through trial and error that this seems to be the "sweet spot" of the can.

On the Pringles Salt & Vinegar can, the N connector was directly between Sodium and Protein.

Element construction:

Straighten the heavy copper wire, and solder it to the connector. When inside the can, the wire should be just below the midpoint of the can (ours turned out to be about 1 1/16"). You lose a few db by going longer, so cut it just shy of the middle of the can

We were in a hurry, so we used hot glue to hold the connector in place. If you have a connector that uses a compression nut and washer, and you're really careful about cutting the hole, you could use that instead.

Now, insert the collector assembly into the can, and close the lid. The inside end of the pipe should NOT touch the copper element; it should be just forward of it. If it touches, your all-thread is probably too long.

Now, just read FCC Part 15.247, connect your pigtail, aim carefully, and have fun!

Unfortunately, I don't have access to any of the necessary equipment (spectrum analyzer, power meter, or even an SWR meter) to properly evaluate the characteristics of the antenna. SWR in particular would be a really good idea to measure, as we're not sure how much power is feeding back into the circuit (too much and you can easily blow your transmitter.) With the extremely low power output (15dbm) of the Orinoco cards, I don't think this is too much of a danger, but remember, anything you do with your equipment is your responsibility, and at your own risk!

Without the proper (multi-thousand dollar) tools, how were we able to estimate antenna performance?

Using the Link Test software that comes with the Orinoco silver cards, you can see the signal and noise readings (in db) of a received signal, and your test partner's reception of your signal. As I happen to be 0.6 mile LOS from ORA headquarters, with very little noise on the channel between, we had a fairly controlled testbed to experiment with. We shot at the omni on the roof, and used the access point at ORA as our link test partner.

To estimate antenna performance, we started by connecting commercial antennas of known gain, and taking readings. Then, we connected our test antennas and compared the results. We had the following at our disposal:

two 10db, 180 degree sector panel antennas
one 11db, 120 degree sector panel antenna
one 24db parabolic dish
a couple of Pringles cans and some tin foil

Here were the average received signal and noise readings from each, in roughly the same position:

Antenna	Signal	Noise
10db A:	-83db	-92db
10db B:	-83db	-92db
11db:	-82db	-95db
24db:	-67db	-102db
Pringles can (shotgun):	-78db	-99db
Pringles can (internal):	-81db	-98db

The test partner (AP side) signal results were virtually the same. Interestingly, even at only 0.6 mile, we saw some thermal fade effect; as the evening turned into night, we saw about 3db gain across the board (it had been a particularly hot day: almost 100 degrees. I don't know what the relative humidity was, but it felt fairly dry.)

Yagis and dishes are much more directional than sectors and omnis. This bore out in the numbers, as the perceived noise level was consistently lower with the more directional antennas. This can help alot on long distance shots, as not only will your perceived signal be greater, the competing noise will seem to be less. More directional antennas also help keep noise down for your neighbors trying to share the spectrum as well. Be a good neighbor and use the most directional antennas that will work for your application (yes, noise is everybody's problem.)

When trying to aim a yagi (like our little can), keep in mind that they have large side lobes that extend up to 45 degrees from the center of the can. Don't point directly at where you're trying to go, aim slightly to the left or the right. We also found that elevating the antenna helped a bit as well. When aiming the antenna, hold it behind the connector, and SLOWLY sweep from left to right, with the Link Test program running. When you get the maximum signal, slowly raise the end of the can to see if it makes a difference. Go slowly, changing only one variable at a time.

Remember that the can is polarized, so match the phase of the antenna you're talking to (for example, if shooting at an omni, be sure the element is on the bottom or the top of the can, or you won't be able to see it!) You can use this to your advantage to try to eliminate some noise on a long distance link: slowly turn both ends of the link from vertical through horizontal, and stop at the point that you see the most gain (and lowest noise.)

We haven't looked into weatherproof housing for the can; sinking the whole thing into some 3" PVC should do the trick. Of course, at $10 for two, it might just be more economical to replace them when they fail.

Apparently, antennas of comparable gain cost upwards of $150. Over a clear line of sight, with short antenna cable runs, a 12db to 12db can-to-can shot should be able to carry an 11Mbps link well over ten miles.

Have fun!

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Nokia 770 Internet Tablet

Nokia 770 Internet Tablet
Manufacturer	Nokia
Type	Internet appliance
Connectivity	IEEE 802.11, Bluetooth
Retail availability	2005-11-03
Media	RS-MMC or MMCmobile
Operating system	Internet Tablet OS 2006, (Debian GNU/Linux - based Maemo)
Input	Touchscreen
Camera	N/A
Power	BP-5L Li-Polymer 1500 mAh Battery
CPU	252 MHz Texas Instruments OMAP 1710
Memory	64MB Random Access Memory, 128MB Flash
Display	800 × 480 resolution, 4.13 in diagonal, widescreen
Successor	Nokia N800

The Nokia 770 Internet Tablet is a wireless Internet appliance from Nokia, originally announced at the LinuxWorld Summit in New York City on May 25, 2005.^[1] It is designed for wireless Internet browsing and e-mail functions and includes software such as Internet radio, an RSS news reader, image viewer and media players for selected types of media.

The device went on sale in Europe on November 3, 2005, at a suggested retail price of €349 to €369 (£245 in the United Kingdom).^[2] In the United States, the device became available for purchase through Nokia USA's web site on November 14, 2005 for $359.99. On January 8, 2007, Nokia announced the Nokia N800, the successor to the 770.^[3] In the summer of 2007, the price for the Nokia 770 fell to under USD 150 / EUR 150 / GBP 100. ^[4][5][6]

Contents 1 Specifications 2 Software 2.1 Internet Tablet OS 2006 edition 3 Accessories 4 Versatility 5 Criticism 6 References 7 See also 8 External links

Specifications

• Dimensions: 141×79×19 mm (5.5×3.1×0.7 in)
• Weight: 230 g (8.1 oz) with protective cover or 185 g (6.5 oz) without.

• Processor: Texas Instruments OMAP 1710 CPU running at 252 MHz. It combines the ARM architecture of the ARM926TEJ core subsystem with a Texas Instruments TMS320C55x digital signal processor.
• Memory: 64MB of DDR RAM, and 128MB of internal FLASH memory, of which about 64MB should be available to the user. Option for extended virtual memory (RS-MMC up to 1 GB (2GB after flash upgrade))

• Display and resolution: 4.1 inches, 800×480 pixels at 225 pixels per inch with up to 65,536 colors
• Connectivity: WLAN (IEEE 802.11b/g), Bluetooth 1.2, dial-up access, USB (both user-mode, and non powered host-mode)
• Expansion: RS-MMC (both RS-MMC and DV-RS-MMC cards are supported).
• Audio: speaker and a microphone

This device is manufactured in Estonia and in Germany.

Software

The operating system is a modified version of Debian GNU/Linux (running Linux 2.6.12), including an X Window System-based graphical user interface in the form of a window manager incorporating the GTK+ toolkit and Hildon user interface widgets. BusyBox replaces many common Linux system utilities. The device includes a PDF viewer and the Opera Web browser, along with a media player application. These allow it to process the following media file formats:

• Audio: MP3, RealAudio, MPEG-4, AAC, WAV, AMP, MP2
• Image: JPEG, GIF, BMP, TIFF, PNG, Animated GIF, SVG Tiny, ICO
• Video: MPEG-1, MPEG-4, RealVideo, H.263, AVI, 3GP

The development platform for the Nokia 770 is known as Maemo.

Internet Tablet OS 2006 edition

On May 16, 2006 Nokia announced a new version of the Internet Tablet operating system which includes major improvements in response to user requests.^[7]

Most notable of these improvements include a thumb-driven on-screen keyboard for fast text input and Jabber-based Voice over IP and instant messaging software. The VoIP software is compatible with Google Talk. Also included was the ability to support 2Gb RS-MMC cards (formatted FAT). This upgrade is the default OS shipped on new 770 Internet Tablets and became available as a downloadable upgrade for existing users on June 30, 2006. The Linux kernel was upgraded to 2.6.16 with the associated patches for the OMAP platform. This new version uses kernel preemption for improved interactivity.

On June 9, 2006 Nokia released a beta version of the development platform aimed at developers porting their programs to Internet Tablet 2006 Edition (shortened to IT2006). End users were advised to remain with the April IT2005 edition until IT2006 was officially released. Some of the final features in IT2006 were not yet present in the beta, such as multi-protocol messaging.^[8]

The full release version of the Internet Tablet OS 2006 edition was posted by Nokia on June 30, 2006.^[9]

An update to IT 2006 came out in November 2006. This adds support for 2 GB RS-MMC cards and also adds Wikipedia as a searchable resource on the Home Page Search Applet and many more enhancements.^[10]

Accessories

In October 2006, Nokia released the Navigation Kit for Nokia 770 Internet Tablet. It includes a Bluetooth-based Nokia LD-3W GPS receiver, navigation software from Navicore with maps of Europe, a memory card, a car holder and a car charger.

Versatility

Because of the Linux based operating system and the open-source contributions from Nokia, the Nokia 770 Internet Tablet has a great appeal to the hacker and DIY markets. Programmers are porting applications to the Maemo platform allowing a much more rapidly growing application catalog than other mobile platforms would enjoy.^[11] The inclusion of WiFi, Bluetooth, and USB host functionality (through a hack) permits enthusiasts to expand their tablets to include USB mass storage, Bluetooth GPS receivers, a normal USB keyboard, or other devices.

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COMPUTER NETWORK

A computer network is an interconnection of a group of computers. Networks may be classified by what is called the network layer at which they operate according to basic reference models considered as standards in the industry such as the four-layer Internet Protocol Suite model. While the seven-layer Open Systems Interconnection (OSI) reference model is better known in academia, the majority of networks use the Internet Protocol Suite (IP) as their network model.

By connection method

Computer networks may be classified according to the hardware technology that is used to connect the individual devices in the network such as Ethernet, Wireless LAN, HomePNA, or Power line communication.

Ethernets use physical wiring to connect devices. Often, they employ the use of hubs, switches, bridges, and routers.

Wireless LAN technology is built to connect devices without wiring. These devices use a radio frequency to connect.

By functional relationship (Network Architectures)

Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example Active Networking, Client-server and Peer-to-peer (workgroup) architectures.

By network topology

Computer networks may be classified according to the network topology upon which the network is based, such as Bus network, Star network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical topology network, etc.

Network Topology signifies the way in which intelligent devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a Bus Topology. In this regard the visual and operational characteristics of a network are distinct.

By protocol

Computer networks may be classified according to the communications protocol that is being used on the network. See the articles on List of network protocol stacks and List of network protocols for more information.

Types of networks:

Below is a list of the most common types of computer networks in order of scale.

Personal Area Network (PAN)

A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that may be used in a PAN are printers, fax machines, telephones, PDAs, or scanners. The reach of a PAN is typically within about 20-30 feet (approximately 4-6 Meters). PANs can be used for communication among the individual devices (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).

Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.

Local Area Network (LAN)

A network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. For example, a library will have a LAN for users to connect to the internet. All of the computers in the library are connected through a system of hubs and eventually connect to the internet. The hub is just like what it sounds. A bicycle wheel uses a hub and spokes - all the spokes connect to a central point - the hub.

LANs use different technologies to link computers together. Depending on the circumstance, the computers in the network might be connected using cables and hubs. Other networks might be connected strictly wirelessly. It depends on the number of PCs that you are trying to connect, the physical layout of your workspace, and the various needs that you have as you develop your network.

The defining characteristics of LANs, in contrast to WANs (wide area networks), include their much higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s. Inverse multiplexing is commonly used to build a faster aggregate from slower physical streams, such as bringing 4 Gbit/s aggregate stream into a computer or network element with four 1 Gbit/s interfaces.

Campus Area Network (CAN)

A network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, or a military base. A CAN, may be considered a type of MAN (metropolitan area network), but is generally limited to an area that is smaller than a typical MAN.

This term is most often used to discuss the implementation of networks for a contiguous area. For Ethernet based networks in the past, when layer 2 switching (i.e., bridging (networking) was cheaper than routing, campuses were good candidates for layer 2 networks, until they grew to very large size. Today, a campus may use a mixture of routing and bridging. The network elements used, called "campus switches", tend to be optimized to have many Ethernet-family (i.e., IEEE 802.3) interfaces rather than an arbitrary mixture of Ethernet and WAN interfaces.

Metropolitan Area Network (MAN)

A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN.

Wide Area Network (WAN)

A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

The highest data rate commercially available, as a single bitstream, on WANs is 40 Gbit/s, principally used between large service providers. Wavelength Division Multiplexing, however, can put multiple 10 or 40 Gbyte/s streams onto the same optical fiber.

Global Area Network (GAN)

Global area networks (GAN) specifications are in development by several groups, and there is no common definition. In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is "handing off" the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial Wireless local area networks (WLAN) ^[1]. INMARSAT has defined a satellite-based Broadband Global Area Network (BGAN).

IEEE mobility efforts focus on the data link layer and make assumptions about the media. Mobile IP is a network layer technique, developed by the IETF, which is independent of the media type and can run over different media while still keeping the connection.

Internetwork

Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them:

• Intranet
• Extranet
• "The" Internet

Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.

Intranet

An intranet is a set of interconnected networks, using the Internet Protocol and uses IP-based tools such as web browsers, that is under the control of a single administrative entity. That administrative entity closes the intranet to the rest of the world, and allows only specific users. Most commonly, an intranet is the internal network of a company or other enterprise.

Extranet

An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g. a company's customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered 'trusted' from a security standpoint). Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Internet

A specific internetwork, consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the Advanced Research Projects Agency Network (ARPANET) developed by ARPA of the U.S. Department of Defense – also home to the World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks.

Participants in the Internet, or their service providers, use IP Addresses obtained from address registries that control assignments. Service providers and large enterprises also exchange information on the reachability of their address ranges through the BGP Border Gateway Protocol.

Basic Hardware Components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").

Network Interface Cards

A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.

Repeaters

A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.

Because repeaters work with the actual physical signal, and do not attempt to interpret the data being transmitted, they operate on the Physical layer, the first layer of the OSI model.

Hubs

A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub. ^[2]

Bridges

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do. but learns which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types:

1. Local bridges: Directly connect local area networks (LANs)
2. Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
3. Wireless bridges: Can be used to join LANs or connect remote stations to LANs

Switches

Switches are a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.

Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.

Routers

Routers are the networking device that forward data packets along networks by using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. Routers also provide interconnectivity between like and unlike media (RFC 1812) This is accomplished by examining the Header of a data packet, and making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols to select the best route between any two subnets. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home use, have been integrated with routers to allow multiple home computers to access the Internet.

Building a simple computer network

A simple computer network may be constructed from two computers by adding a network adapter (Network Interface Controller (NIC)) to each computer and then connecting them together with a special cable called a crossover cable. This type of network is useful for transferring information between two computers that are not normally connected to each other by a permanent network connection or for basic home networking applications. Alternatively, a network between two computers can be established without dedicated extra hardware by using a standard connection such as the RS-232 serial port on both computers, connecting them to each other via a special crosslinked null modem cable.

Practical networks generally consist of more than two interconnected computers and generally require special devices in addition to the Network Interface Controller that each computer needs to be equipped with. Examples of some of these special devices are hubs, switches and routers.

Ancillary equipment used by networks

To keep a network operating, to diagnose failures or degradation, and to circumvent problems, networks may have a wide-ranging amount of ancillary equipment.

Providing Electrical Power

Individual network components may have surge protectors - an appliance designed to protect electrical devices from voltage spikes. Surge protectors attempt to regulate the voltage supplied to an electric device by either blocking or shorting to ground voltage above a safe threshold.^[3]

Beyond the surge protector, network elements may have uninterruptible power supplies (UPS), which can be anywhere from a line-charged battery to take the element through a brief power dropout, to an extensive network of generators and large battery banks that can protect the network for hours or days of commercial power outages.

A network as simple as two computers linked with a crossover cable has several points at which the network could fail: either network interface, and the cable. Large networks, without careful design, can have many points at which a single failure could disable the network.

When networks are critical the general rule is that they should have no single point of failure. The broad factors that can bring down networks, according to the Software Engineering Institute ^[4] at Carnegie-Mellon University:

1. Attacks: these include software attacks by various miscreants (e.g., malicious hackers, computer criminals) as well as physical destruction of facilities.
2. Failures: these are in no way deliberate, but range from human error in entering commands, bugs in network element executable code, failures of electronic components, and other things that involve deliberate human action or system design.
3. Accidents: Ranging from spilling coffee into a network element to a natural disaster or war that destroys a data center, these are largely unpredictable events. Survivability from severe accidents will require physically diverse, redundant facilities. Among the extreme protections against both accidents and attacks are airborne command posts and communications relays^[5], which either are continuously in the air, or take off on warning. In like manner, systems of communications satellites may have standby spares in space, which can be activated and brought into the constellation.

Dealing with Power Failures

One obvious form of failure is the loss of electrical power. Depending on the criticality and budget of the network, protection from power failures can range from simple filters against excessive voltage spikes, to consumer-grade Uninterruptible Power Supplies(UPS) that can protect against loss of commercial power for a few minutes, to independent generators with large battery banks. Critical installations may switch from commercial to internal power in the event of a brownout,where the voltage level is below the normal minimum level specified for the system. Systems supplied with three-phase electric power also suffer brownouts if one or more phases are absent, at reduced voltage, or incorrectly phased. Such malfunctions are particularly damaging to electric motors. Some brownouts, called voltage reductions, are made intentionally to prevent a full power outage.

Some network elements operate in a manner to protect themselves and shut down gracefully in the event of a loss of power. These might include noncritical application and network management servers, but not true network elements such as routers. UPS may provide a signal called the "Power-Good" signal. Its purpose is to tell the computer all is well with the power supply and that the computer can continue to operate normally. If the Power-Good signal is not present, the computer shuts down. The Power-Good signal prevents the computer from attempting to operate on improper voltages and damaging itself

To help standardize approaches to power failures, the Advanced Configuration and Power Interface (ACPI) specification is an open industry standard first released in December 1996 developed by HP, Intel, Microsoft, Phoenix and Toshiba that defines common interfaces for hardware recognition, motherboard and device configuration and power management.

Monitoring and Diagnostic Equipment

Networks, depending on their criticality and the skill set available among the operators, may have a variety of temporarily or permanently connected performance measurement and diagnostic equipment. Routers and bridges intended more for the enterprise or ISP market than home use, for example, usually record the amount of traffic and errors experienced on their interfaces.

Diagnostic equipment, to isolate failures, may be nothing more complicated than a spare piece of equipment. If the problem disappears when the spare is manually replaced, the problem has been diagnosed. More sophisticated and expensive installations will have spare elements that can automatically replace a failed unit. Failures can be made transparent to user computers with techniques such as the Virtual Router Redundancy Protocol (VRRP), as specified in RFC 3768.

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