text:
[...] > > This is using an RDF/N3 presentation syntax > > but the RDF/XML resources are there as well > > (I hope with not too many bugs, as I > > had to do the RDF list stuff by hand > > instead of using CWM's N3-to-RDF) > > Now wait just a minute here. Are you actually suggesting that OWL tests > use N3 or log:entails? If so, I protest in the strongest terms. I am > *not* willing to have any OWL tests be written in a system that has neither > syntax nor semantics, like N3. Neither am i willing to have any OWL tests > written using connectives that do not have a semantics, like log:entails. P log:entails C means that P U ~C is unsatisfiable P is designated as a list of RDF graph URI's and namespace entailment URI's C is designated as a single RDF graph URI N3 syntax is used for those designations IS ALL -- , Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/Received on Sunday, 30 June 2002 01:38:00 UTC
This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 21:56:45 UTC


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1. Types of ovarian fibroma
2. causes of fibroids
3. Clinical manifestations
4. Diagnosis and treatment of ovarian fibroma
Among benign ovarian fibroma formations on the proportion accounted for 10%.This is a relatively rare, non-functioning, malosimptomno tumor, often one-sided.Fibroma is the formation of dense connective tissue clear, round or ovoid shapes, sizes, which range from one to twelve centimeters in diameter.Advantageously, fibroma occurs in old age, but can occur in younger women, starting from the time of puberty.
At small sizes, up to three centimeters in diameter, fibroids do not cause complaints and does not interfere with the normal onset and nurturing pregnancy.Often, such fibroids detected by chance during a routine physical examination.
first complete clinical and pathological and morphological picture of fibroma, described the German gynecologist Kivish RA in 1857Education has a smooth or knobby surface, the presence of tumor pseudofield consisten
Since fibroids generally poor in blood vessels, the tumor on the cut has a white or gray-white color and fibrous structure.If education is developing quite a long time, on a section in the center of the tumor lesions are observed ischemia, hemorrhage, necrosis, or degenerative changes of the brown-red hue.Histologically fibroma is composed of spindle-shaped bundles of connective tissue, which are closely intertwined in different directions.
By macroscopic structure distinguish two separate forms of ovarian fibroma:
diffuse fibroids are much more common.Histologically, these two forms differ in a great variety and do not consist of a fibrous substance and cell components in different proportion.Tissue formation usually swollen and often contain cysts.Fibroma - tumor is slow-growing, but if tissue degenerative changes occur, tumor growth can be accelerated.
There are complications of ovarian fibroma - torsion legs, hemorrhage, necrosis, tumor fester, degenerate into a malignant form.
exact causes of the emergence and development of ovarian fibroids are not installed.It is believed that the formation of developing ovarian stroma, but in some cases the fibroid is formed from a fibrous tissue non-specific.One factor is the risk of tumor development premorbid unfavorable background women, which includes endocrine disorders, decreased immune defenses, chronic inflammation of the ovaries and appendages.Fibroids often observed together with a cyst of the ovary and uterine cancer and may have a similar etiology of development.
a long time, all the symptoms of ovarian fibroma may be missing.Small fibroids, up to three centimeters in diameter, occur completely asymptomatic, with preservation of ovarian function.Symptoms of ovarian fibroids begin to appear when the formation reaches a considerable size and starts to put pressure on adjacent pelvic organs.
Gradually appears anemia develops Meigs' syndrome, which is manifested ascites, abdominal distention, frequent pain, palpitations, fatigue, shortness of breath and general weakness.Clinical symptoms of ovarian fibroids occur more often with symptoms of ascites, and in 40% of cases develop poliserozita - exudative fluid collects in the pleural, peritoneal cavity, pericardium bag.Disease severity is determined by the compression of the liquid bodies.
combination of symptoms of fibroids and ovarian full triad Meigs (ascites, anemia, hydrothorax), in some cases indicate ovarian cancer.
For quite a long period of ovarian fibroma runs completely asymptomatic and can be detected by chance during abdominal surgery or ultrasound examination.One of the most important diagnostic sign of fibroids is greater mobility and density of education that distinguish fibroids from the uterus myoma subzeroznogo node.The main role in the differential diagnosis of Meigs syndrome is the presence of a tumor and one-sidedness.
The diagnosis can be based on the clinical manifestations of disease, examination of the gynecologist, laboratory results (blood tests, tumor markers HE4, CA125), instrumental methods (CT, MRI, pelvic ultrasound) and the data of histological examination of the tumor tissue.
gynecological examination is determined by the presence of the back or the side of the uterus rounded education, painless and mobile.If necessary the pleural puncture or puncture the abdominal cavity for cytology obtained transudate.
Conservative treatment of ovarian fibroma is not carried out, because it does not make sense, medical education is not subject to resorption.Treatment of ovarian fibroma only operative.The nature of the access and the full scope of surgical intervention depends entirely on the size of the tumor, patient age, comorbidities and existing state of the uterus and the other ovary.
removal of the tumor with a small amount, usually performed laparoscopically gentle way.Fibro just husks together with the capsule while keeping the generative and menstrual ovarian function.With a large amount of the tumor, ovarian tissue as a result of the constant squeezing and stretching, most often reshaped into a capsule of ovarian cysts and follicles completely atrophied.In this case, treatment of ovarian fibroma is complete removal of the ovaries.After surgery phenomenon hydrothorax and ascites completely disappear.With bilateral lesions of the ovary, always leave at least part of the affected ovary.
Specific prevention of fibroids does not exist.The prognosis after surgical treatment is favorable, the probability of degeneration of fibroids ovarian malignancy in 1% of all cases.After the restorative treatment course is possible to plan pregnancy.To the disease has been detected in time, it is necessary at least once a year, be inspected by a gynecologist and perform a pelvic ultrasound.
This article is available exclusively in the educational purposes and is not research material or professional medical advice.
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Contents: 1. clinical picture 2. Symptoms of cytomegalovirus 3. disease forms 4. treatment of cytomegalovirus Cytomegalo...
Contents: 1. development of the disease 2. reasons 3. symptoms of cystitis 4. Diagnosis and treatment of cystitis 5. Trea...
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text:
33mm thick toughened, laminated walk on safety glass floor panels - Available to buy online in standard widths or contact us for a bespoke cutting service
This listing is for glass only - Floor support steelwork available by individual quotation.
- Floor glass, suitable for internal or external use
- 33mm thick comprising 3no. 10mm toughened panels with 1.5mm laminate interlayers
- All glass is toughened in accordance with BSEN 12150, BSEN 12600
- All edges are polished
- Corners have 5mm radius unless otherwise specified
- Delivery 2-3 weeks from order
- Delivery nationwide, see our terms for any excluded zones.
- Glass must be supported on all edges by an appropriate base.
- It is the customers responsiblity to ensure the glass suitable for each application, always contact a structural engineer for confirmation if unsure.
Many other toughened glass options are available including :
- Frosted glass
- Tinted glass
- Pattern imprinted glass
- Painted glass
- Please contact us with your enquiries
All you need to know about toughened glass
33mm Walk on Floor Glass
- Inc VAT £31.50


text:
Compact and efficient, the LBP6030w is designed to help save space and perform high-speed print jobs, with low energy consumption. Set up wireless printing effortlessly with the WPS button.
1. On Demand Fixing Technology - Canon's proprietary technology On-Demand Fixing consume less power and warm up quickly compared to the conventional fusing roller designs, enabling a fast warm up time and quick first print.
2. Mobile Printing Enabled - With Canon Mobile Printing app, you can easily print images or documents from your iOS and Android device.
3. Minimal Maintenance - The Canon all-in-one toner cartridge 325 integrates the photosensitive drum, cleaning unit and toner reservoir in one compact package, saving costs and making cartridge replacements easy.
4. Low Energy Consumption - The printer can be configured to enter sleep mode and auto shutdown after it remains idle for a specified length of time, consuming less energy. With a low Energy Star Typical Electricity Consumption value of 0.48 kWh/week, it is easy to be kind to the environment while saving cost.
5. UFR II LT - With Canon UFR II LT print language, the printer takes full advantage of the PC's processing power. UFR II LT effectively removes the need for expensive memory upgrades on the printer.
6. WPS Button - The LBP6030w comes with the WPS button located on the printer. Set up a Wi-Fi connection for wireless printing, with just one-touch of the WPS button on the printer and router.
Effective 1st April 2015, all goods and services may be subjected to GST 6% upon checkout.
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MCIL Multimedia Sdn.Bhd.(515740-D)


text:
One Week Home - It's hard to believe that Emily and I have already been home one week. I'm so thankful to be back. While I love the experience of China, I am always glad w...
11 months ago
...to the city with foundations whose architect and builder is God. Hebrews 11:10
sweet! glad to see your little one here . . .


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June 21st.
Most people enjoy June 21st because it is the longest day of the year. We do too. However, we have another reason to love the longest sunshine day of the year.
June 21st is my husband, Dwight's birthday.
I am not too much of a celebratory kind of person. After working in hospitality for so many years, I lost the notion of having time off on weekends and holidays. Hotels are open 24/7 and as a hotelier, you have to be available to work any day of the year. At first it was hard to accept it but then I got used to it and let holidays go…
But birthdays are different. It is that "one day of the year" that is all about you.
No one, but you…
That is why; I believe that a birthday should be celebrated. It should be a BIG deal.
Our way of birthday celebration is to have a really good birthday cake and eat it with friends. When living on an island, that, pretty much, is the only option because we do not have malls or stores to buy gifts.
Every year, on Dwight's birthday, I try to make a "not so easy to make" cake for his birthday. This year was no different. I have been working on this German Chocolate Cake for a while now. This time, I think, I nailed it.
This is the kind of cake that you make on a day off, for a special occasion.
With its chocolaty and coconuty self, I cannot imagine a better cake for the occasion. He says that it reminds him of his childhood days as his mother used to make it for him when he was a kid. After eating two slices he said that it was just as good.
A sigh of relief…
Most German chocolate cake recipes you find in books use the coconut filling both in between layers and on top. I changed it a little bit. I wanted it to look like a good old chocolate cake with the German chocolate cake hidden inside. Like an unexpected surprise…
Couple of suggestions:
- Make the filling first. When it is cooling in the refrigerator, you can make the cakes.
- It really makes a difference when you toast pecans. It may look like an unnecessary step but toasting them brings out their earthy flavor and develops their sweetness. I would toast pecans even before making the filling so that they will have time to cool before mixing it with the filling, which is at the very end.
- I used a chocolate glaze but you can use the coconut filling to cover the top of the cake.
German Chocolate Cake
- Prep Time: 1 hour
- Cook Time: 30 minutes
- Total Time: 1 hour 30 minutes
- Yield: 8
- Filling
- 4 egg yolks
- 12 oz. evaporated milk
- 1 cup (7 oz.) granulated sugar
- 1/4 cup (1 3/4 oz.) packed light brown sugar
- 6 tablespoons (3/4 stick) unsalted butter, cut in to small pieces
- 1/8 teaspoon table salt
- 2 teaspoons vanilla extract
- 2 1/3 cups (7 oz.) sweetened shredded coconut
- 1 1/2 cups (6 1/2 oz.) finely chopped pecans (or walnuts)
- Cake
- 4 oz. bittersweet chocolate, finely chopped
- 1/4 cup unsweetened cocoa, sifted
- 1/2 cup boiling water
- 2 cups unbleached all-purpose flour (10 oz), plus additional for dusting cake pans
- 3/4 teaspoon baking soda
- 12 tablespoons unsalted butter (1 1/2 sticks), at room temperature
- 1 cup (7 oz.) granulated sugar
- 2/3 cup (4 3/4 oz.) packed light brown sugar
- 3/4 teaspoon table salt
- 4 large eggs, room temperature
- 1 teaspoon vanilla extract
- 3/4 cup sour cream, room temperature
- Chocolate Sauce
- 4 oz. bitter sweet chocolate, finely chopped
- 1 tablespoon good honey
- 1/2 cup heavy cream
- 1 tablespoon granulated sugar
- For the filling: In a small saucepan, whisk yolks; gradually whisk in evaporated milk. Constantly mixing, add sugars, salt, butter and cook over medium- high heat. Mix it until it becomes slightly thickened and is boiling, just about 6 minutes. Let it cool outside first, then cover it with plastic wrap and place it into the fridge. You should keep it in the fridge at least 2 hours. ( I usually make the filling 1 day prior to the occasion. Not only it makes it quicker but also, in time, it turns into the exact consistency that I want for this filling)
- For the cake: Adjust oven rack to the lower middle position and pre-heat it to 350 °F. In a small bowl, combine chocolate, cocoa and boiling water. Let it sit for a couple of minutes and whisk it until smooth. Put it aside for it to come to the room temperature.
- In the mean time, butter and flour (I use baking spray) two 9-inch round cake pans. Line the bottom of each pan with parchment paper. Spray paper rounds with baking spray after placing them in the pan.
- Sift flour and baking soda into a small bowl and set aside.
- Using a standing mixer fitted with paddle attachment, beat butter, sugars and salt at medium-low speed, about 30 seconds. Increase the speed to medium high and beat until the mixture is fluffy for about 4 minutes, scraping down the bottom of the bowl to ensure that no lumps remaining.
- While the mixer is running, add eggs one at a time. Mix for 15 to 20 seconds after each egg to ensure that they are fully incorporated into the butter and sugar mixture. Scrape down the bottom of the bowl again.
- Add the vanilla and mix it for 45 seconds. With mixer running at low speed, add chocolate/cocoa mixture, then increase speed to medium and beat until combined about 30 seconds, scraping down bowl once again. At this point, it may appear like it is curdled or broken.
- With mixer running in low speed, add flour mixture in 3 batches, alternating with sour cream. After the last flour addition, beat until it is fully incorporated, just about 30 more seconds. One last time give it a stir hand. It should look like a homogenous batter.
- Divide the batter equally between two 9-inch pans. Smooth the surface of each batter using a rubber spatula.
- Bake cakes for 30 minutes or until toothpick inserted into the center of cakes comes out clean. Cool cakes in pans for 10 minutes, take them out of the pans and place them onto a greased wire rack. (I use baking spray to grease the wire rack) Cool them for at least an hour.
- For the chocolate sauce/glaze: Place chocolate and honey in a bowl and set aside. Place the heavy cream and sugar in a small saucepan and heat it over medium heat until sugar is fully dissolved. Pour the warm cream and sugar mixture onto the chocolate and honey mixture and stir it until smooth and silky. It may take a couple of minutes for it to thicken. Let it cool at room temperature.
- To assemble: Place the toasted pecans and the shredded coconut into chilled filling and stir. Place the first cake on to a cake stand. Using a serrated knife, holding it parallel to work surface, cut the first cake into two equal layers. Using a spatula, distribute 1 cup filling evenly on the first layer. Place the second layer of the first cake on top and distribute 1 cup of filling once again. Repeat the same process with the second cake. When all layers are completed, coat the outer layer of the cake fully with the chocolate glaze. Let it rest for 1 hour in room temperature and serve. (If you refrigerate it, let it cool at room temperature for 20 minutes before serving.)
This recipe is adapted from America's Test Kitchen.


text:
Having problems with your Dyson DC07 Bagless Upright Cyclonic Vacuum ?
Armature sparking is visable
\015 Sparks/flashes can be see when running - no smoke / fire\015
Answers :
It probably will need a new motor, it maybe safest to take it to a professional.
Repair Help & Product Troubleshooting for Dyson DC07 Bagless Upright Cyclonic Vacuum
Tips for a great answer:- Provide details, support with references or personal experience .
- If you need clarification, ask it in the comment box .
- It's 100% free, no registration required.
Suggested Questions/Answers :
Armature sparking is visable
It probably will need a new motor, it maybe safest to take it to a professional. ... Dyson DC07 Bagless Upright Cyclonic Vacuum
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Good armature maybe needs new brushes
Hello,\015\012Carbon brushes wear over time and may need completely replaced...it doesn't cost a lot and i have guides available for the repair. Try my troubleshooting guide....\015\012\015\012 ... Kirby G4 Bagged Upright Vacuum
Noisy sparking james hoover
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Hello can you help me please? I have a Kirby G4 vacuum cleaner, It did work ok until it started to give off burning smell and lots of sparks from the brushes. I have changed these brushes, the motor still rotates but it still gives off sparks and burning smell. Do i have to change the motor as well? Can you help please? Thankyou Martin
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Not full suction, noisy, sparks at the unit
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Sparking motor on Dyson assume motor brushes at fault?
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text:
The Garrison at Graham, a $22 million condo development in Charlotte's Fourth Ward, has been bought for $8.6 million in a foreclosure sale after failing to make loan payments.
Community One Bank, the project's lender, was the high bidder in the sale Friday.
According to CommunityOne, principal and interest owed on the project totals $11.1 million. The mortgage amount was $13.5 million.
Construction began in 2007 on the 715 N. Graham St. project.
A Dec. 6 letter from CommunityOne's attorney to developer Thomas Barnes says he defaulted on the note and had five days to pay the outstanding balance.
According to the development's website, which was still working today, units range in price from $199,900 for a 1,192-square-foot unit to $650,000 for a 2,470-square-foot unit.
The website advertises the views the project gives of the city's skyline and describes the units as "sleek and edgy bi-level lofts (that) unite tradition and convenience."
Cox & Schepp Construction of Charlotte was the general contractor for the project.
Barnes also redeveloped NoDa@28th Street, a former textile mill converted in 2003 into residential use.


text:
Report NEP-CUL-2006-11-18This is the archive for NEP-CUL, a report on new working papers in the area of Cultural Economics. Roberto Zanola issued this report. It is usually issued weekly.
Subscribe to this report: email, RSS or Twitter.
Other reports in NEP-CUL
The following items were announced in this report:
- J. J. Gabszewicz & Paolo Garella & N. Sonnac, 2005. "Newspapers market shares and the theory of the circulation spiral," Working Papers 0514, University of Crete, Department of Economics.
- Monica Sassatelli (ed.), Raffaele Milani & Kathryn Last & Colin Kaiser & Gian Franco François & Cartei Riccardo & Lafarge Priore, 2006. "Landscape as Heritage: Negotiating European Cultural Identity," EUI-RSCAS Working Papers 5, European University Institute (EUI), Robert Schuman Centre of Advanced Studies (RSCAS).


text:
Meet the Biggest Unknown Factor in LA Lakers Season TurnaroundMarch 30, 2013
The Los Angeles Lakers' season has been tumultuous, but they've shown improvement since starting 19-25.
While many will point to Steve Nash's fractured fibula as the primary reason for the Lakers' early-season struggles, an injury to the team's backup point guard, Steve Blake, didn't help matters either.
Blake saw action in the team's first few games, but an abdominal tear that required surgery sidelined him for nearly two months.
After missing 37 games, Blake returned on January 29 against the New Orleans Hornets, a game the Lakers won 111-106.
Since Blake's return, the Lakers have gone 18-11 (through Saturday afternoon) and currently find themselves tied for the eighth seed in the Western Conference.
Blake's return has been a welcome one and not just because it gave the Lakers improved depth at point guard. His steady perimeter shooting has helped the Lakers' floor spacing and bolstered the team's rather pedestrian second unit.
Shooting 41.6 percent from three and 43 percent from the field since returning (per NBA.com's stats database) from abdominal surgery, Blake has added another dimension to the Lakers' perimeter attack.
And now that Metta World Peace has been lost (via Los Angeles Times) for what appears to be the remainder of the regular season, Blake will be relied upon to produce more for the depleted Lakers.
While Blake's 41.5 percent shooting from the field isn't mind-blowing, it's much improved over his averages (35.9 percent in 2010-11 and 37.7 percent in 2011-12) during his first two seasons in L.A. In fact, the 41.5 percent Blake is shooting from the floor this season will be the fourth-best mark of his career, if he can sustain his current pace.
Examining Blake's shot chart (via NBA.com), it's clear that he's become more comfortable knocking down threes from the wings. Blake has converted on 50 percent of his three-point attempts from the left wing and nearly 53 percent from the right wing.
For comparison's sake, let's examine the point guard's shooting from those spots over the last two seasons. Blake shot 38.46 percent from the left wing and 25.64 percent from the right win in 2011-12, according to NBA.com's stats database, while he hit on 28 and 48.65 percent from the left and right wings respectively in 2010-11.
On a team that ranks 14th in three-point percentage (35.8 percent), Blake's consistent shooting from beyond the arc has been a welcome sight. Nash is the only other Laker shooting better than 40 percent from deep, with reserve marksman Jodie Meeks hovering below the 37 percent mark.
It would be easy to look at Blake's 5.9 point per game average and dismiss him as a non-factor, but the fact remains that the Lakers' second unit is aided by his presence.
According to Basketball-Reference, the five-man unit consisting of Blake, Meeks, World Peace, Earl Clark and Antawn Jamison is the unit Blake has posted the second-most minutes with.
While World Peace's minutes will need to be replaced, that lineup has posted a net three-point percentage of plus-.278, the highest mark of any five-man unit the Lakers have trotted out this season.
That grouping has also posted the highest net effective field-goal percentage (plus-.155) of any Laker lineup this season, according to Basketball-Reference.
With relatively fresh legs, Blake's presence has helped take some of the onus off of the 39-year-old Nash, who's spent the better part of his first season in Los Angeles adjusting to life surrounded by superstars.
Now, Nash is hurting once again (via Mike Trudell on Twitter), evident by his inability to finish Thursday night's game against the Milwaukee Bucks.
Mike Trudell @LakersReporter
D'Antoni said Nash tweaked his back/hamstring/hip last night. Tried to tough it out tonight, but he was really struggling physically.
As Nash and the Lakers limp toward the finish line, Blake's ability to guide the team's second unit will be key. The Lakers have been decimated by injuries all season long, and with Blake as one of the team's few healthy bodies, he could have an impact on the team's standing in the playoff race in the weeks ahead.


text:
Rangel Could Join Martinez At Wigan Athletic
Full back Angel Rangel could follow Martinez to Wigan Athletic, the Daily Mirror reports.
The defender has caught the eye of a number of clubs who have shown a keen interest in the Spaniard.
Roberto Martinez will soon complete his move to Wigan Athletic and he is believed to be interested in taking Angel Rangel with him.
Also likely to depart the club are his assistant Graeme Jones and chief scout Kevin Reeves.
Martinez said last month that 'his players' would cost 'millions' and I'm sure Huw Jenkins would hold out for £2-3million for Rangel.
Roberto is also likely to make a move for Espanyol midfielder Jordi Gomez, who impressed during his season-long loan with us last season.


text:
Title: "Royal Sympathy for Flood Victims. Belgium's King and Queen tour the streets of Namur in an Army Pontoon".
M/S of a flooded town street, a man in uniform - King Albert - walks along a raised pathway made of planks, soldiers and onlookers stand on every available bit of dry land to greet him, the Queen and several dignitaries follow him along the pathway and get into a rowing boat.
Various point of view shot from a moving vessel following the Royal party in their pontoon travelling down badly flooded streets, more rowing boats follow behind. People wave at the King and Queen from upper-storey windows of flooded buildings, one man even tips his hat whilst clinging onto a lamp post. C/U of the King, Queen and Royal entourage in the pontoon.
After a few seconds of spacing, story resumes at 01:11:09, looks like cuts. More shots of the King and Queen getting into the army pontoon. More shots of the flotilla of boats following the Royal pontoon. Various shots of chaotic scenes as soldiers try to manoeuvre the pontoon around. Brief shot of rowing crew - from another story in this Gazette issue, INTERVARSITY BOAT RACE.
Various high angled L/Ss of the burst river and flooded city of Namur. Various shots of ordinary people in boats and walking along the raised pathways. Various shots showing soldiers / policemen delivering bread and post to flood victims by boat, horse and cart or by wading through the water. M/S of two men walking through the water, one carrying the other on his back.
More shots of the King and Queen's visit to the flood area, shots are the same or similar to former part of item.
- Archive
- British Pathé
- Issue Date:
- 14/01/1926
- Sound:
- Silent
- Media URN:
- 25461
- HD Format:
- Available on request
- Film ID:
- 446.04
- Stock:
- Black & White
- Duration
- 00:08:22:00
- Time in/Out:
- 01:09:05:00 / 01:17:27:00
- Canister:
- Sort Number:
Appears in...


text:
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COMMENTS (16 to date)
Daniel Kuehn writes:
RE: "I think that this is a misleading way to look at productivity. Remember Garett Jones' point that workers are building organizational capital, not producing widgets. We can get increased output without much increase in labor input."
But isn't this an empirical question? Some of the productivity growth surely comes from the fact that you fire the unproductive workers first. Some of it surely comes from "true" productivity gains. I'm not sure you can just declare that one story is right and one is wrong. They're both right - the question is how do you parse the productivity growth between these two interpretations.
Posted November 16, 2009 1:25 PM
Marc D writes:
I think the ECRI comment on jobs and productivity is a cyclical one, i.e., fairly short term in nature. Other commentors seem to be talking over the longer term, i.e., many years.
Posted November 16, 2009 1:33 PM
Gary Rogers writes:
Here is my take:
We have an economy that is supported by interest rates that are near zero. With these low interest rates, the dollar is falling and who wants to hold assets that are falling in value. That means money will be invested somewhere, which makes all the Keynesians happy. So, where is all the money going? The amount of money injected over the last year makes inflation almost inevitable so bonds are a dangerous proposition. This forces the investment into gold and equities. We have a new bubble financed by our treasury and the more it grows, the more everyone wants to buy into the promise that good times are here again.
Unfortunately, we are doing this at the expense of our currency and increased debt. Eventually (within the next three years) interest rates must increase and our fragile economy, unable to support the higher rates, will collapse again. I guess that makes me one of the pessimists.
If only we had someone in charge that understands economics.
Posted November 16, 2009 2:02 PM
How is this any different than the Hayekan trade cycle?
Posted November 16, 2009 2:39 PM
What would the effect of a crash in commercial property right now be? Would it cause a double dip, would it help us out of recession by reducing prices, what would the effect be?
I mean, would it speed up the recalculation or cause the need for more recalc.
Posted November 16, 2009 2:45 PM
q writes:
Dr Kling -- can you state a testable hypothesis re: the Recalculation theory?
Posted November 16, 2009 4:11 PM
Ryan Vann writes:
"How is this any different than the Hayekan trade cycle?"
I don't think it is.
Posted November 16, 2009 5:35 PM
Dirtyrottenvarmint writes:
Productivity may be econospeak for doing more work with the same amount of labor, but I suspect many economists don't know what they are talking about.
In this case, I do not see how what is being called productivity matches that definition. The statistic being measured as productivity can be increased, while holding hours worked and hourly wages (Labor) constant, by
A) Increasing the number of units produced
This can be accomplished, ceteris paribus, by
A) Decreasing unit quality (assuming this also decreases production times/increases production output) while holding prices constant
When the price of a good increases for no competitive reason, we might call this price inflation. Most economists would probably agree that it may be possible to cause price inflation by massively increasing the money supply.
Interestingly, a massive increase in the money supply is exactly what occurred in the third quarter. Also vaguely of interest is that the largest increase in "productivity" occurred in the manufacturing sector. I believe automobile manufacturers are considered part of the manufacturing sector. I recall that the Car Allowance Rebate System was active in the third quarter.
Just off the top of my head, given the massive, ground-shaking, record-breaking amounts of new government spending that was thrown against the wall in Q3, I would be Extremely Surprised were the statistic being called "productivity" not to have shown a significant increase.
I am interested in Arnold's interest in profits. Arnold has written and spoken many times (and, dare I say, wisely) about the importance of profits. However, I cannot find a Kling Definition of "profit" beyond the simplistic "revenue minus costs", which as discussed above is clearly lacking in sophistication. I am interested in why Arnold thinks these third quarter "profits" are at all economically meaningful, given that a company can apparently increase "profits" simply by sending a couple high-class hookers to the right politician.
Posted November 16, 2009 7:36 PM
Dr. T writes:
"We can get increased output without much increase in labor input."
Bullcrap. I've run businesses (clinical laboratories). Three of the labs I directed were very high productivity (using industry norms as comparisons). Getting substantially increased productivity out of such labs without adding personnel requires one or both of the following: purchase of expensive new instruments that are much more automated than existing instruments or firing back room staff and hiring more lab techs. However, in a well-run lab, the back room staff (personnel, billing, computer support, HR, pay & benefits, general admin, etc.) already is lean. That leaves only option 1 which requires substantial capital expenditures and probably will not be economical.
Increased productivity is never free, and I cannot imagine why any economists would believe otherwise.
Posted November 16, 2009 8:54 PM
Scott Sumner writes:
June sounds about right to me---but I consider my self a pessimist.
Posted November 16, 2009 9:41 PM
another bob writes:
I am a management consultant with four customer companies. During 2008 and 2009, each postponed new product development, new marketing and new systems and capital acquisition to support same. Each laid-off a significant percentage of their workforce. Most of the lay-offs were over 40 years of age and over $100k/year salary. These were the folks who planned and designed the next generation of products, introduced those products to new or existing customers and implemented new systems and infrastructure.
Without these folks, the existing capabilities hum along just fine, for a while. In the aggregate, to economists, this looks like much lower cost and no reduction in current capacity so, big productivity gains as long as demand is adequate.
More and more, US job growth depends on the first derivative of the demand curve not it's absolute value. Offshore, lower cost labor, depends on the absolute level of output.
That makes me an optimist.
Posted November 17, 2009 12:01 AM
Alan Harvey writes:
Productivity in the current quarter is dramatically out of scale. Absurd, I think is the word. It involves production from a larger workforce ascribed to a reduced workforce.
It happens every time jobs are cut, and people always say it is because the current workforce is being worked harder. In fact, plant capacity is lower. People have more tools. Plus, other people no longer on the payroll contributed time and talent to the plant, systems and products that are credited to the cut-down work force.
The proof is that the longer term action is in exactly the opposite direction. Productivity goes up in the medium and long term when the unemployment rate goes down.
I don't know if this comment function takes links, but here is the chart: http://2.bp.blogspot.com/_PusdiXNNmgs/StgX-pGtnZI/AAAAAAAAAXs/FLI76dFAyjA/s1600-h/Prod+v+Unemployment+Web+Site.jpg
Posted November 17, 2009 12:49 PM
Brick writes:
On productivity there is no one answer fits all businesses.For some businesses as was pointed out in comments above the only option to increase productivity is to invest in people and machinery. For many businesses you can increase productivity by adjusting costs, reorganising work flow, investing in software and machinery and effects started now tend to have lasting effects for about a 3 year timeline. More worrying is the fact that future product development may have taken a hit over the last year, reducing the competativeness of businesses over a 5 year timeline.
Posted November 18, 2009 4:06 AM
Kenny Evitt writes:
I have a good example of 'organizational capital' that came to mind as I was reading this post. {Sorry for not using the trackback – Blogger doesn't support them (yet?).}
My (short) career has been mostly focused on supporting line-of-business applications with mostly small-businesses as customers. I can attest that there is a huge amount of productivity growth waiting be unleashed through better business software. I predict that at some point (next 50 years?), nearly every business will have at least one internal programmer.
Posted November 21, 2009 9:14 AM
Arnold, you keep using that one-line Garett Jones tweet as the foundational basis of arguments. But you've never discussed the statement, or the evidence (preferably empirical) for and against its accuracy.
Solid discussion would be much appreciated by those of us who don't have the wherewithal to dig through it ourselves.
Posted November 21, 2009 11:48 AM
For instance, this seems a propos:
Posted November 21, 2009 7:55 PM
Comments for this entry have been closed


text:
Networking Primer
Important LAN and WAN High-Speed Technologies
In today's business environment, among the most widely discussed networking topics are the technologies that make networks faster, such as Fast Ethernet and Gigabit Ethernet, as well as the technologies that connect geographically distant networks, such as frame relay, ATM, and SONET. As networks grow, so does the amount of information sent across these networks. For this reason, transmission speed is of utmost importance. This section will provide brief descriptions of the following technologies that are dramatically improving the transmission speed on computer networks.
- Fast Ethernet
- Gigabit Ethernet and 10 Gigabit Ethernet
- Firewire and USB
- Fiber Channel
- Bluetooth
- 802.11
- Fiber Distributed Data Interface (FDDI)
- Frame Relay
- Asynchronous Transfer Mode (ATM)
- xDSL and Cable
- Synchronous Optical Network (SONET)
- Wireless Packet-Switched Networks
- Circuit-Switched Cellular (CSC)
The first seven items—Fast Ethernet, Gigabit Ethernet and 10 Gigabit Ethernet, Firewire and USB, Fibre Channel, Bluetooth, 802.11, and HIPERLAN/1—apply primarily to LANs. The other technologies in this list are reserved almost exclusively for WANs.
Fast Ethernet
100Base-T—also known as Fast Ethernet—is a high-speed LAN technology. It has been designated as the IEEE 802.3u standard and functions at the data-link (OSI Layer 2) layer's MAC sublayer, providing data transfer rates as high as 100 megabits per second (Mbps). Three kinds of wiring carry Fast Ethernet: 100Base-T4, which is four pairs of twisted-pair wires; 100Base-TX, which is two pairs of data-grade twisted pair wires; and 100Base-FX, which is two strands of fiber optic cable.
Distinguishing Characteristics
Like 10Base-T Ethernet, 100Base-T uses CSMA/CD as the MAC method. 100Base-T is based on the scalability of CSMA/CD. Scalability means that you can easily enlarge or downsize your network without degrading network performance, reliability, and manageability.
CSMA/CD was known to be scalable before the 100Base-T standard was created: a scaled-down version of Ethernet (1Base-5) uses CSMA/CD, provides data transfer rates of 1 Mbps, and enables longer transmission distances between repeaters. Because CSMA/CD could be scaled down, people reasoned that it could be scaled up. Specifying changes such as decreased transmission distances between repeaters produced a reliable data transfer rate of 100 Mbps, 10 times faster than traditional 10Base-T Ethernet.
Figure 37: On 100Base-T networks, the physical topology is a star and the logical topology is a bus. A broadcast signal travels to all parts of the cable
100Base-T adapter cards and compatible cable are currently available from various vendors.
In addition, it is easy to upgrade from 10Base-T Ethernet to 100Base-T Ethernet. Both use CSMA/CD, and most network cards now support both 10 Mbps and 100 Mbps Ethernet. The adapter cards automatically sense whether it is a 10 Mbps or 100 Mbps environment and adjust their speed accordingly. Because 10Base-T and 100Base-T Ethernet can coexist, network supervisors can upgrade network stations from 10Base-T to 100Base-T one at a time, as needed. Moreover, most network supervisors are already familiar with CSMA/CD, so there is no need for expensive retraining.
100Base-T can be an inexpensive way to make your network faster. Adapter cards are not significantly more expensive than 10Base-T cards. In addition, Category 5 UTP cable (also called "CAT 5") is relatively inexpensive.
100Base-T reduces the maximum network size compared to 10Base-T because the standard specifies shorter transmission distances between repeaters. Compared to 10Base-T, 100Base-T reduces the maximum network diameter from 500 to 205 meters. For existing networks that exceed 205 meters, routers must be installed between 100Base-T network segments.
Gigabit Ethernet and 10 Gigabit Ethernet
Faster standards are always being developed and established and those for Ethernet are no exception. One standard is Gigabit Ethernet, also known as 1000Base-T or 802.3z. Gigabit Ethernet increases transmission speed on a standard Ethernet network to 1000 Mbps, or ten times that of 100Base-T. It was designed to function on the same cabling as 100Base-T so that upgrades would be inexpensive and straightforward. Right now, the primary focus for Gigabit Ethernet is as a backbone service for 100Base-T networks. As the hardware becomes more prevalent, however, 1000Base-T subnetworks and workstations should become more common.
In addition to Gigabit Ethernet, there is also an emerging standard known as 10 Gigabit Ethernet or 802.3ae. 10 Gigabit Ethernet will support data transmission speeds of 10,000 Mbps. Analysts predict that in some cases it could replace high-speed WAN technologies such as ATM and SONET.
Although Gigabit Ethernet is enjoying widespread adoption, 10 Gigabit Ethernet has not yet reached wide-scale acceptance in the world of computer networking. Part of the problem is that details of the standard, such as the medium over which it will be propagated, are not yet defined. Also, because Ethernet has not been a long-range standard in the past, it does not include management-control capabilities to alert network administrators when something goes wrong. However, Gigabit and 10 Gigabit Ethernet are gaining popularity as a solution for the thin-client application-on-demand model.
IEEE 1394 (Firewire) and USB
The IEEE 1394 standard (also known as Firewire) and the Universal Serial Bus (USB) standard are two standards that apply to data transmission between computers and peripheral hardware. Although these two standards are different, their application is fundamentally related and therefore they are covered in the same section here.
Distinguishing Characteristics
The IEEE 1394 standard is a high-speed standard developed for processing-intensive peripherals such as scanners, digital cameras, and removable storage devices. As a complementary standard, USB is more suitable for peripherals that do not require as much speed, such as mice and keyboards. Both standards use a simple cable with jacks similar to telephone jacks or Ethernet RJ-45 jacks. Most newer computers include USB ports; IEEE 1394 ports are integrated into higher-end computers.
The most obvious advantage of both IEEE 1394 and USB is the ease of use. Both standards support "hot swapping" of peripheral components. This means that one device can be unplugged from the computer and another plugged in (and recognized by the computer) without having to reboot the system. This is not possible with standard parallel port or serial port connections. In addition, both 1394 and USB standards allow you to connect peripherals according to a tree topology or as a "daisy chain" (linked in a straight line) and then attach them to a single port on the computer—each peripheral does not require its own port. The IEEE 1394 standard allows for 63 devices per port, whereas USB will support more than one hundred. In addition, both standards support data transfer speeds higher than conventional ports. USB supports 12 Mbps data transfer, USB 2.0 supports 36–48 Mbps, and IEEE 1394 supports up to 400 Mbps (with several faster versions currently under development). USB is expected to replace serial and parallel ports for most simple peripherals such as mice and keyboards, and 1394 will meet the high-throughput requirements of video and real-time equipment.
Although USB has gained widespread acceptance—USB-compatible peripherals are readily available—IEEE 1394-compatible hardware is harder to find. Part of the reason is that 1394 is the intellectual property of Apple Computer, which tightly controls the dissemination of the standard. In addition, 1394-compatible peripherals tend to be on the high end of the technological spectrum and therefore are much more expensive than their USB counterparts. Firewire and USB are also not compatible, so hardware manufacturers either have to install both ports or choose between the two: given the popularity of USB, Firewire often loses.
Fiber Channel
Fiber channel refers to a relatively new application for optical fiber components. The most common usage of fiber channel is in storage area networks (SANs), where it is used to connect clustered servers to storage systems. This technology is also being considered as an internal drive interface (between the hard drive and the processor within a computer) and as a high-speed switching service to connect several server clusters and SANs into a large interconnected network.
Distinguishing Characteristics
Fiber channel technology consists of optical fiber cables, specialized hubs, and Gigabit interface converters (GBICs). The GBICs are used to convert electrical signals into optical signals and vice versa. The cabling is divided into two categories: multimode and single-mode fiber. Multimode fiber has a larger diameter core and allows multiple transmissions to travel simultaneously. Single-mode fiber allows only one transmission path.
Fiber channel technology has several advantages over other transmission media, but the most important is the speed of data transmission. Fiber channel supports data-transmission speeds of 100 Mbps. In addition, since the data is transmitted as a pulse of light rather than an electronic signal, it can travel much greater distances (up to 10 kilometers) before suffering any signal degradation. Likewise, the data is immune to electromagnetic interference and radiates no energy (no heat-shielding required).
The main disadvantage of fiber channel is the cost: optical fiber is much more costly than conventional copper cable and more expensive to install. The advantages of fiber channel, however, greatly outweigh the cost in many applications.
Bluetooth, a wireless standard developed by Ericsson, IBM, Intel, Nokia and Toshiba, is named after a Danish king who united Denmark and Norway in the 10th century. It is designed for short-range radio transmissions between devices no more than 10 meters apart. Bluetooth operates at a frequency of 2.4GHz and transmits at speeds up to 1 Mbps. (A next generation of Bluetooth will transmit at 2 Mbps.) Bluetooth is primarily for use in mobile devices to provide connectivity and synchronization; for example, two Bluetooth-enabled handheld devices a few meters apart can synchronize phone lists or schedules. The devices can connect on a one-to-one or one-to-many basis so that when near each other, Bluetooth devices create a "piconet": an ad-hoc, peer-to-peer network of up to 10 nodes. For example, if all the participants at a meeting have Bluetooth-enabled laptops, they can create a piconet for sharing documents and messages. A Bluetooth-enabled printer in the room could be used by all without the need for cabling.
Bluetooth is already a de facto standard that has garnered widespread interest and support among vendors. It supports both data and voice transmissions and does not require a line of sight.
Bluetooth's limited range makes it useful only for instances when the device is near another Bluetooth transmitter. Its data transmission rates are not nearly as fast as those of 802.11. It has so far been prohibitively expensive to implement, but it is predicted that the price will go down as vendor interest increases.
IEEE 802.11 is an extension of the Ethernet standard, adapted for wireless LANs. It consists of one MAC-layer standard and three physical-layer standards: two for radio transmissions (DSSS and FHSS) and one for infrared. 802.11 operates at 2.4GHz and can transmit at speeds up to 2 Mbps at a range of 30–100 meters. IEEE 802.11b, ratified in 1999, boasts transmission rates of up to 11 Mbps, but only over the DSSS physical layer.
Distinguishing Characteristics
Similar to its wired Ethernet counterpart, the 802.11 MAC layer uses a variation of CSMA/CD called carrier sense multiple access with collision avoidance (CSMA/CA). Unlike wired devices, a wireless device is unable to "listen" and transmit at the same time because the noise from transmission drowns out incoming signals; therefore, if there is a collision during transmission the device will not detect it. To solve the problem CSMA/CA provides for explicit packet acknowledgement. After each packet is sent, the receiver sends an acknowledge (ACK) packet to confirm that the packet arrived intact. If the ACK packet does not arrive, the sender assumes the original packet did not arrive, probably because of a collision, and sends the packet again.
Wireless environments are also susceptible to the "hidden node" issue in which a wireless node can hear traffic from the AP but not from another wireless node, due to distance or an obstruction. To prevent a collision between hidden nodes, 802.11 specifies an optional Request to Send/Clear to Send (RTS/CTS) protocol, also at the MAC layer. When this protocol is engaged, a sending device sends an RTS packet to the AP and waits for the CTS packet before transmitting. Because all other devices interfacing with that AP receive the same CTS packet, they delay any intended transmissions until the medium is free.
Because 802.11 is a true Ethernet specification, 802.11 devices can be integrated seamlessly into conventional Ethernet LANs. With a laptop and an 802.11 network adapter card, an employee can roam throughout a building, go from building to building, or even go to a remote office and always be connected to the network.
Unlike Bluetooth, 802.11 does not support voice transmissions, and the additional overhead from the ACK and RTS/CTS packets means 802.11 transmissions will always be slower than wired Ethernet. It is also feared that 802.11 transmissions can inadvertently disrupt critical Bluetooth transmissions, such as wireless medical or manufacturing monitoring devices.
High-Performance Radio LAN, Type 1 (HIPERLAN/1) is a standard developed by the European Telecommunications Standards Institute (ETSI) to improve on the data throughput rates of 802.11. It is the first in a suite of HIPERLAN standards that operate in the 5GHz range: HIPERLAN/2 is Wireless ATM, HIPERLAN/3 (renamed HIPERAccess) is for wireless local loop (the last segment between a home and the telephone system), and HIPERLAN/4 (renamed HIPERLink) is for wireless point-to-point connections. Of the four standards, only HIPERLAN/1 has been approved; the others are still in development.
Distinguishing Characteristics
The HIPERLAN/1 transmission scheme is the same as that for GSM, which means it uses TDMA as its air interface and Gaussian Minimum Shift Keying (GMSK) as its modulation scheme. HIPERLAN/1 can achieve data transfer rates up to 23.5 Mbps.
With HIPERLAN the MAC layer is subdivided into the Channel Access Control (CAC) layer, and the MAC layer. The CAC layer defines how a given channel access attempt will be made, depending on whether the channel is busy or idle and at what priority level the attempt will be made, if contention is necessary. Packets receive higher priority as they age.
Multi-hop routing support (not included in 802.11) is part of the HIPERLAN/1 specification. HIPERLAN-enabled devices choose a nearby "controller" and forward all outgoing traffic to that controller. The controller will then route the packet toward its destination. HIPERLAN-enabled devices also employ "hello" packets to announce their presence to other devices. In this sense, HIPERLAN-enabled devices behave similarly to conventional routers and are therefore able to structure their own network.
HIPERLAN/1 is compatible with wired and wireless Ethernet. It is very stable and flexible.
HIPERLAN is an emerging technology, so only a few HIPERLAN/1-compatible devices exist.
Fiber Distributed Data Interface (FDDI)
FDDI is also a high-speed LAN technology. It is not generally used for direct connection to desktop computers, but rather as a network backbone connecting two or more LAN segments to provide a path for data transmission between them. A simple backbone might connect two servers through a high-speed link consisting of network adapter cards and cable. An example of such a backbone is illustrated in Figure 38.
FDDI has been designated ANSI X3T9.5 and operates at the physical and data-link layers (Layers 1 and 2) of the OSI model. Like 100Base-T, FDDI provides data transfer rates as high as 100 Mbps.
Figure 38: A simple server-based backbone connecting two LAN segments
Distinguishing Characteristics
FDDI networks have a dual, counter-rotating ring topology. This topology consists of two logical closed signal paths called "rings." Signals on the rings travel in opposite directions from each other. Although both rings can carry data, the primary ring usually carries the data while the secondary ring serves as a backup.
On FDDI networks every node acts as a repeater. FDDI supports four kinds of nodes: dual-attached stations (DASs), single-attached stations (SASs), single-attached concentrators (SACs), and dual-attached concentrators (DACs). DASs and DACs attach to both rings, while SASs and SACs attach only to the primary ring. Several SASs often attach to the primary ring through a concentrator, so that an SAS failure will not bring down the entire network. If the cable is cut or a link between nodes fails, DASs or DACs on either side of the failure route signals around the failed segment, using the secondary ring to keep the network functioning.
FDDI uses token passing for its MAC method and is implemented using fiber-optic cable.
Figure 39: If a cable section on an FDDI network goes down, DASs on either side of the failed section automatically reconnect the primary and secondary rings. Also note that the server has a redundant connection to improve reliability.
FDDI is a fast, reliable standard. The dual, counter-rotating ring topology increases the network's reliability by keeping it functioning even if a cable is damaged. FDDI also offers network management support, which was designed directly into the standard. In addition, the standard includes the Copper Distributed Data Interface (CDDI) specification for building a network using UTP cable (which is less expensive than fiber-optic cable).
FDDI's main disadvantages are availability and price. Because FDDI is not useful for transmitting large graphic and sound files (such as video), it is being replaced by Gigabit Ethernet. And because most fiber backbones are now running SONET, FDDI hardware is difficult to find. Furthermore, FDDI adapter cards and fiber-optic cable are both expensive compared to other technologies offering the same speed. Fiber-optic cable installation also requires technicians trained specifically for this purpose. Even CDDI adapters (for copper wire), which are less expensive than FDDI adapters, are more costly than 100Base-T adapters. It is expected that FDDI will soon be replaced by other technologies.
X.25 is an ITU standard and includes data-link and physical-layer protocols (Link Access Procedure Balanced [LAPB] and X.21). X.25 provides data transfer rates of 9.6 Kbps to 256 Kbps, depending on the connection method.
Distinguishing Characteristics
X.25 specifies the interface for connecting computers on different networks with an intermediate connection through a packet-switched network. X.25 was defined when the quality of transmission media was relatively poor. As a result, the standard specifies that each node in the packet-switched network must receive each packet completely and check it for errors before forwarding it.
Figure 40: X.25 networks are often provided by telecommunication carriers.
X.25 is well understood and reliable. Connections to X.25 networks can be made through the existing telephone system, Integrated Services Digital Network (ISDN), and leased lines. Because access is simple, it is comparatively inexpensive. X.25 is available worldwide, although its market share in the United States is rapidly decreasing. In countries with little digital telecommunications infrastructure, X.25 is the best WAN technology available.
X.25 is slow compared to newer technologies. The process of checking each packet for errors at each node limits data transfer rates. X.25 also uses variable-size packets, which can cause transmission delays at intermediate nodes. In addition, many people connect to X.25 networks through modems, which limit data transfer rates to between 9.6 Kbps and 56 Kbps. Although X.25 is still in use in some areas, newer, faster standards such as ATM and frame relay have largely replaced it.
Frame Relay
Frame relay is a WAN technology. Approved by ANSI and the ITU, frame relay works at the data-link layer (OSI Layer 2) of the OSI model and provides data transfer rates from 56 Kbps to 1.544 Mbps.
Distinguishing Characteristics
Frame relay is an interface specification for connecting LANs over public packet-switched networks. This standard can be thought of as a simplified version of X.25 designed to take advantage of digital transmission media.
Frame relay services are typically provided by telecommunications carriers. Customers install a router and lease a line (often a T1 or fractional T1 line) to provide a permanent connection from the customer's site to the telecommunications carrier's network. This connection enables frame relay to use "permanent virtual circuits" (PVCs), which are predefined network paths between two locations.
With frame relay the router encapsulates (or frames) network-layer packets, such as IP and IPX packets, directly into a data-link-level protocol and sends them on to the packet-switched network. Like X.25, frame relay uses variable-size frames but it eliminates the error checking required on X.25 networks. A frame relay switch simply reads the header and forwards the packet, sometimes without first receiving the frame completely. Intelligent end stations must identify missing or corrupted frames and request retransmission.
Figure 41: Frame relay is a WAN technology that enables companies to connect LANs through a telecommunications carrierÂ's network.
Frame relay uses PVCs over leased lines rather than a modem connection. PVCs transmit and receive data immediately, eliminating the call setup and handshaking that modems must perform. In addition, frame relay does not require error checking and flow control at the switches, thereby reducing overhead and leaving more bandwidth for data transmission. Frame relay is also a common standard in many countries. Finally, frame relay is less expensive than other WAN technologies because it provides bandwidth on demand rather than dedicating bandwidth regardless of whether data is being transmitted.
Although frame relay is fairly complex to implement, value-added resellers and most telephone companies will assist customers in determining their needs and will help install the technology.
Frame relay's speed is limited because it uses variable-size frames, which can cause delays at switches along the frame's path. As a result, frame relay cannot support applications that require low latency (delayed response time) such as real-time video.
Asynchronous Transfer Mode (ATM)
ATM is a WAN technology that is generally implemented as a backbone technology. The exact relationship of the ATM layers to the OSI model is currently undefined, although ATM LAN emulation works at the data-link layer (OSI Layer 2).
ATM provides data transfer rates of 100 Mbps and 155 Mbps. At the high end, WAN implementations using ATM and SONET together have achieved data transfer rates of 2.4 Gbps.
Distinguishing Characteristics
ATM is a cell-relay technology, meaning that it uses standard-sized packets called "cells." The size of an ATM cell is 53 bytes.
In a LAN implementation ATM functions at the data-link layer's MAC sublayer. It further divides the MAC sublayer into three layers: LAN Emulation, ATM Adaptation Layer (AAL), and ATM. LAN Emulation enables you to integrate ATM with Ethernet and token-ring networks without modifying existing Ethernet or token-ring protocols.
On a mixed network, LAN Emulation hardware sits between the Ethernet or token-ring segment and the ATM part of the network. It uses the three layers mentioned above to convert packets moving toward the ATM segment into cells, and to assemble cells moving toward the Ethernet or token-ring segment into packets. AAL and ATM put data into standard-sized cells. In most network computing situations, an ATM adaptation layer breaks packets into 48-byte blocks that are then passed to the ATM layer, where the five-byte header is attached to form a complete 53-byte cell.
ATM offers high data-transfer rates, which have climbed into the gigabit range and are still increasing. One reason that ATM is so fast is its use of cells: because they are a standard size, ATM networks handle data in a predictable, efficient manner at the switches. Standard-sized cells and high-bandwidth media like fiber-optic cable also enable ATM to support real-time voice, video, and data traffic.
ATM also offers flexibility in its transmission media. As many as 27 ATM specifications exist for media like UTP, shielded twisted-pair (STP), and fiber-optic cable. (ATM is generally implemented with fiber-optic cable.)
Ethernet and token-ring networks can be integrated with ATM through use of LAN Emulation. The ATM network can emulate (or imitate) enough of the MAC layer of Ethernet and token-ring technologies so that higher-layer protocols can be used without modification. This allows existing network applications and network protocols to run over ATM networks, resulting in great cost savings.
ATM is more expensive than the other high-speed LAN technologies and is extremely complex to set up and maintain; the expense is preventing many companies from implementing ATM.
ISDN is a set of protocols defined by the ITU to integrate data, voice, and video signals into digital telephone lines. It functions at the physical, data-link, network, and transport layers (Layers 1 through 4) of the OSI model. ISDN offers data transfer rates between 56 Kbps and either 1.544 Mbps or 2.048 Mbps, depending on the country where it is implemented.
Distinguishing Characteristics
ISDN makes end-to-end digital connections over telephone lines. Although many telephone networks are almost completely digital, the local loop that connects a home or office to the telephone company's network usually is not. Most local loops send analog rather than digital signals. ISDN replaces local analog signaling with digital signaling, enabling end-to-end digital communications.
ISDN offers Basic Rate Interface (BRI) for individuals or small branch offices and Primary Rate Interface (PRI) for larger companies.
BRI uses two bearer, or B, channels (providing 64 Kbps each) to transmit and receive data, and one delta, or D, channel for call setup and management.
PRI is a T1 line. A T1 line in the United States consists of 23 B channels and one D channel, providing a total data transfer rate of 1.544 Mbps. A T1 line in Europe, known as an E1 line, consists of 30 B channels and one D channel, providing a total data transfer rate of 2.048 Mbps. A fractional T1 uses only some of the B channels in a T1 line (and thus offers some fraction of the total T1 data transfer rate).
ISDN requires special equipment at the customer's site, including a digital phone line and a network termination unit (NT-1). An NT-1 converts the bandwidth coming over the line into the B and D channels, and aids the phone company in diagnostic testing. The NT-1 also provides a connection for terminal equipment, such as ISDN telephones and computers that have an ISDN interface. In addition, the NT-1 provides terminal adapter (TA) equipment to connect equipment that is not compatible with ISDN. TA equipment provides an intermediary connection point: such equipment has an ISDN interface for connection to the NT-1, and a non-ISDN interface for connection to non-ISDN equipment.
ISDN increases speed and broadens data transmission capabilities, especially for those currently using analog modems to remotely connect to an office or to access the Internet. It offers faster call setup and data transfer rates. The transfer rates are acceptable for transmitting voice, data, limited video, fax, and images. ISDN can also be used for limited LAN-to-LAN communications.
With ISDN you can transmit voice and data traffic simultaneously: over the same telephone line you can concurrently talk on the phone and download a data file to your computer. For example, one BRI ISDN configuration enables you to use the two B channels (128 Kbps) for data and part of the D channel for a telephone conversation.
To understand ISDN well enough to simply order services requires considerable effort. Furthermore, configuration can be difficult. ISDN speeds are faster than those of a conventional modem (56 Kbps), but they are not as fast as ADSL or other emerging technologies.
xDSL and Cable
xDSL refers to the various types of Digital Subscriber Line (DSL), a relatively new, high-speed Internet access technology. With the explosive growth in computer networking, business networks, and the use of the Internet, the demand for fast and cost-effective access has also been growing steadily. Although there are many technologies available to provide high-speed Internet access—such as leased lines, wireless connections, and ISDN—most are expensive to install and costly to maintain. xDSL was developed as a low-cost alternative to these technologies. xDSL is a technology that uses the existing standard telephone cable (twisted pair) to provide data transmission speeds rivaling and often exceeding those of much more expensive solutions. Cable modems, which connect to the Internet via cable TV hookups, provide speeds and service options similar to xDSL. Many modems available on the market support both xDSL and cable.
Distinguishing Characteristics
xDSL lines are always "on," which means that you do not have to establish a modem connection to use the Internet and then disconnect when you are finished—you are always connected. And unlike most dial-up Internet connections, xDSL can transmit both voice (or fax) and data signals over the same line at the same time. Conventional phone lines are capable of transmitting signals up to 1MHz, but voice transmissions only use the range between 1kHz and 4kHz. xDSL, on the other hand, transmits digital signals between 26kHz and 1.1MHz. A "splitter," installed at the user site, divides the signal into digital and analog signals for data and voice, respectively. For this reason, xDSL is especially attractive to home and small-business users who do not want to install separate lines for voice and data transmissions.
DSL comes in a variety of "flavors," the most common of which are listed below:
The most popular kind of consumer xDSL is Asymmetric DSL (ADSL), also called G.dmt and Full-rate ADSL (ITU-T G.992.1). By asymmetrically dividing the available bandwidth, ADSL allows you to receive data much faster than you send it. With respect to an Internet connection, this is the optimal configuration: you send out much less data (about five percent of total transmission) than you download. Standard ADSL provides for downstream (data received) speeds of 8 Mbps and upstream (data sent) speeds of 1.5 Mbps.
ADSL Lite
A variant of ADSL is G.Lite, also ADSL Lite, splitterless DSL, and Universal DSL (ITU-T G.992.2). ADSL Lite provides a data transmission rate of 1.5 Mbps downstream and 512 Kbps upstream. ADSL Lite does not require a visit from the phone company because the splitting is managed at a central location, an arrangement which sacrifices some speed to save cost. It is expected to become the most widely installed form of DSL in private residences even though it does not handle voice and entertainment applications well.
Rate Adaptive Asymmetric Digital Subscriber Line (RADSL) is similar to ADSL but it "listens" to see how much traffic is on the wire and adjusts its speed accordingly. Depending on the distance from the telephone company's central office, RADSL can transmit at speeds up to 7 Mbps downstream and 1.5 Mbps upstream (10,000 feet for the highest speed, 17,000 feet for the lowest).
High bit-rate DSL (HDSL) is symmetric, meaning that it provides an equal amount of bandwidth upstream and downstream. Generally used for wideband connections within a corporation and between telephone companies and their customers, HDSL is often used in lieu of a T-1 connection. The data transmission rate varies depending on how many twisted-pair wires are used. Two wires provide 1.5 Mbps; three carry 2 Mbps. HDSL II, a variant of HDSL, provides the same speeds as HDSL but over a single wire.
Symmetric DSL (SDSL) also provides the same speeds as HDSL but differs in two important ways: it is limited to 10,000 feet and it uses only one wire. It also uses the same modulation technique as ISDN. SDSL is a forerunner to HDSL II.
ISDN DSL (IDSL) is a hybrid between ISDN and DSL. Using the same modulation technology as IDSN, IDSL bypasses voice lines and uses the less-busy data network instead. Transmission speeds are slightly higher than those of ISDN.
Very high bit-rate DSL (VDSL) is a developing technology that will provide higher transmission rates over shorter distances. At 1,500 feet the speeds may be as high as 13 Mbps and at 1,000 feet an amazing 52 Mbps. High-definition television signals are one proposed use for VDSL.
|8.0 Mbps
|1.5 Mbps
|18,000 ft
|single twisted pair
|ADSL Lite
|1.5 Mbps
|512 Kbps
|18,000 ft
|single twisted pair
|7.0 Mbps
|1.5 Mbps
|17,000 ft
|single twisted pair
|1.5 Mbps
|1.5 Mbps
|15,000 ft
|2 twisted-pair wires
|2.0 Mbps
|2.0 Mbps
|15,000 ft
|3 twisted-pair wires
|1.5 Mbps
|1.5 Mbps
|10,000 ft
|single twisted pair
|144 Kbps
|144 Kbps
|18,000 ft
|single twisted pair
|13–52 Mbps
|1.5–3.2 Mbps
|1,000 ft – 4,500 ft
|fiber-optic cable
The most obvious advantage of xDSL is the low cost. Although the modems are fairly expensive, the price is still less than that of leased lines and ISDN. Also, many phone companies and ISPs are offering G.Lite service for a monthly fee with low or no installation charges. And because xDSL uses existing telephone wiring, you do not need to have new lines installed. The next most important advantage is the data transmission speed: ASDL offers 8 Mbps downstream as opposed to 128 Kbps with ISDN.
The primary disadvantage of xDSL is security. Because the connection is always on, it is easier for "crackers" (unscrupulous users who break in to others' computers) to find your computer on the Internet. Those who subscribe to xDSL will need to ensure they have sufficient security in place to prevent identity theft or other mischief. Some solutions are security software, firewalls, switches, and modifying OS settings to reduce the chance of a security breach.
Another disadvantage may be availability. Because of the nature of the technology there is a limit placed on how far a subscriber can be from a major telephone line switching hub. For that reason, xDSL may not be available in your area; however, most phone companies and many ISPs are rapidly increasing the scope of xDSL availability.
Synchronous Optical Network (SONET)
SONET, also known in some countries as Synchronous Digital Hierarchy (SDH), is a WAN technology that functions at the physical layer (OSI Layer 1) of the OSI model. SONET has been accepted by ANSI and recommended by the ITU. It specifies a number of data transfer rates from 51.8 Mbps to 13.21 Gbps.
Distinguishing Characteristics
SONET defines a fiber-optic standard for high-speed digital traffic. This standard provides the flexibility to transport many digital signals with different capacities.
Data communications sometimes prove difficult because digital signaling rates can vary. For example, as stated in the above section on ISDN, in the United States a T1 line provides 1.544 Mbps, while in Europe an E1 line provides 2.048 Mbps. SONET resolves such problems by defining how switches and multiplexers coordinate communications over lines with different speeds, including defining data transfer rates and frame format.
SONET defines a number of Optical Carrier (OC) levels. Each level defines an optical signal and a corresponding electrical signal called Synchronous Transport Signal (STS). The base level is OC-1/STS-1 or 51.84 Mbps. Each level's rate is a multiple of 51.84 Mbps. The table below shows the OC levels and the corresponding data transfer rates that SONET defines.
|OC Level
|Data Rate
|51.8 Mbps
|155.5 Mbps
|466.5 Mbps
|622.0 Mbps
|933.1 Mbps
|1.24 Gbps
|1.86 Gbps
|2.48 Gbps
|4.976 Gbps
|10 Gbps
|13.21 Gbps
SONET also provides easy access for low-speed signals such as DS-0 (64 Kbps) and DS-1 (1.544 Mbps) by assigning them to sub-STS-1 signals called "Virtual Tributaries."
The SONET standard defines data transfer rates and a frame format that all vendors and telephone companies throughout the world can use, creating a framework for global networking. SONET also includes management capabilities for telephone company equipment. Cell relay technologies such as Switched Multimegabit Data Services (SMDS) and ATM operate above SONET, making SONET the foundation for many broadband services. And because SONET uses a ring topology, line breaks and equipment failures barely affect service.
SONET is primarily a technology for voice transfer. Developments in optic fiber and data-transfer technologies such as in ultra long-haul dense wavelength division multiplexing (DWDM) may make SONET obsolete.
Wireless Packet-Switched Networks
To accommodate the demand for data transmission capabilities in mobile devices, many service providers offer access to wireless packet-switched networks. A packet-switched network does not require a continuous connection the way circuit-switched networks do (the telephone system is circuit switched). In the United States, the principal wireless packet-switched networks use one of the following technologies: DataTAC, Mobitex, Cellular Digital Packet Data (CDPD) and microcellular data network (MCDN). DataTAC was created by Motorola and IBM, Mobitex was developed in Sweden by Eritel, CDPD by the Wireless Data Forum, and MCDN by Mobitel.
Distinguishing Characteristics
DataTAC networks use one of two protocols: MDC4800 and Radio Data Link Access Procedure (RD-LAP), the former providing raw throughput rates up to 4.8 Kbps and the latter up to 19.2 Kbps (actual data rates are about half that after factoring out overhead). DataTAC networks are hierarchical networks wherein base stations connect to area communications controllers that connect to message switches. Customers' fixed-end systems connect to message switches. Depending on the area, DataTAC networks use between one and ten 25 kHz channels in the 800 MHz range. Connection to wired networks is through X.25 or TCP/IP protocols.
Mobitex, on the other hand, operates on the 400MHz or 900MHz frequency with an 8 Kbps data rate on 12.5 kHz channels. Each Mobitex packet, called an MPAK, can be no more than 512 bytes long. The Mobitex system is also hierarchical, consisting of network management centers, switches, and base stations that cover up to 30 km per cell. The standard Mobitex configuration connects via the X.25 protocol to wired networks, but IP connectivity is available as well.
CDPD differs from the other two in that it transmits over the existing analog cellular infrastructure rather than radio transmission towers. CDPD is non-proprietary, which means that you can use the same software to access any CDPD network. A faster alternative than DataTAC or Mobitex, CDPD also supports more operating systems than the other two. CDPD also uses RD-LAP and is based on TCP/IP.
MCDN, called Ricochet by Metricom, is a high-speed, "desktop quality" wireless packet-switched network designed for laptop computers. It operates at speeds of 28.8 Kbps, and a 128 Kbps implementation is now under way. MCDN uses FHSS and operates at the 900MHz, 2.3GHz, and 2.4GHz frequencies. MCDN employs microcell radio transceivers and a wired access point. The wired access point cell covers about 20 square miles, and within that cell the microcell radios are positioned in a checkerboard pattern (approximately 100 per cell), connected according to a wireless mesh topology. These radios are about as big as a shoe box and are installed on streetlight and utility poles. An MCDN user has a special modem connected to the laptop that connects with the closest microcell radio. The radio then sends the signal to the next radio and the next until it reaches the wired access point. From there, the signal is carried to the Internet or a corporate LAN via a T1 or fiber optic line. MCDN is based on IP protocols.
Devices for all four technologies operate in an "always on" mode; that is, they do not require dedicated connections that need to be established every time they are used. Because the networks are packet switched (as opposed to circuit switched, like the conventional telephone system) the devices send data in small bursts, allowing several devices to use the same frequency at the same time. The technologies also employ store-and-forward techniques to ensure that packets are delivered even when the remote device is temporarily unavailable.
Except for MCDN, the technologies are not capable of transmitting large files: video conferencing, Web browsing, file transfer, and high-speed multimedia cannot be accommodated. And although MCDN can provide these services, the network is available only in a handful of cities.
Circuit-Switched Cellular (CSC)
Circuit-Switched Cellular (CSC) technology, like CDPD, runs on the existing analog cellular infrastructure; however, it is capable of handling larger file transfers, albeit at a slower rate than CDPD.
Distinguishing Characteristics
CSC uses the established analog frequencies and infrastructure the same way a conventional modem uses land-based telephone lines: with a cellular phone and a CSC-enabled modem, you call another modem to establish a connection with it. Because many wired modems do not accept wireless protocols, many providers have set up modem pools that receive the cellular modem signals and translate them into the standard voice frequencies of the conventional modem before sending the signals to the intended modem. CSC operates at air frequencies between 824MHz and 894MHz and offers transmission rates between 14.4 Kbps and 20 Kbps.
CSC technology has the same coverage area as standard analog cellular; in other words, it is nearly ubiquitous.
Because it uses a continuous connection on the same frequencies as analog voice cellular, providers often charge the same rate for CSC as for voice. For infrequent data transfers this may not be expensive, but for lengthy Internet connections it can become so.
General Packet Radio Service (GPRS)
General Packet Radio Service (GPRS) is a connection-oriented technology that runs on top of the existing GSM and TDMA infrastructure to provide a wireless packet-switched network similar to the Internet.
Distinguishing Characteristics
GPRS has been developed as an intermediary step between second- and third-generation cellular systems. Unlike CSC, GPRS traffic does not actually go through the GSM network but only uses the GSM network to look up user profile data. It employs between one and eight channels that can be used by several devices at once and offers transmission rates between 14.4 Kbps and 115 Kbps. GPRS supports Quality of Service (QoS), and because connection setup is fast, it appears to users that their connection is always on.
GPRS can provide most of the functionality of the current wired Internet, with services such as chat, textual and visual information, still and moving images, document sharing and collaborative work, audio, e-mail, remote LAN access, and file transfer.
Voice and GPRS calls occupy the same resources, which means that if there is heavy voice traffic on the GSM or TDMA network, fewer resources will be available for GPRS links and vice versa. GPRS also does not have store-and-forward capabilities.Return to Primer Index | Next Section